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Discernibly Turgid
Mar 30, 2010

This was not the improvement I was asking for!
Within a schematic it’ll look like this:



On a PCB:




The idea (on paper) is that polarized caps can only take on a charge in one polarity, so putting two in series in this fashion allows one cap to act on the upper half of the wave form and the other cap to handle the lower half. This was a common practice on a lot of vintage gear from an era that didn’t have reliable, low ESR non-polarized capacitors, so it was a necessity. The board from that Sansui 919 (I’ve got one here but wasn’t digging it out for a quick picture) is experienced but the user as the “pre out/power in” section on the rear panel where you could replace the pre-or power amp portion of the unit with a separate external pre- or power amp (usually if you were testing something) or (infinitely more likely) you were inserting a crossover for incorporating a subwoofer or biamping. “I hear you, but those amps have all kinds of stickers and adverts touting that they’re DC-coupled with no capacitors in the signal path, so who’s full of poo poo?” In addition to the jacks, there’s a switch that connects the pre- and power amps (for normal listening or disconnects them (for the use cases above.) The capacitors in that case are inserted into the input circuit of the power amp when you separate the two sections because DC-coupling your amp to an external preamp with its own ground is going to put DC on your amplifier’s outputs (and, by extension, you’re speakers.) It’s one thing to account for offset in your own chassis (and why there are SO many offset controls stage to stage within a given unit, so you can dial out the DC.) The only way to reliably get ultra-low DC offset from a direct coupled preamp is to include servo correction via an op amp, but constant correction (like any feedback system) has a price.)

In reality, this “works” but is far from what it looks like on paper. The small signals in line level audio (even smaller before you get into the actual amplification stage) are <1V in amplitude with very little current and are constantly crossing the zero line, and at those levels the capacitors are not staying strictly on their respective halves of the waveform. The stage outputting through that circuit has very weak control over what comes out the other side, which manifests as loose, tubby bass and, at the upper end of the spectrum, a poor spatial image (because that essential phase information gets muddled in the process as well.)



$.30 is not an exorbitant price for a solution. In the original picture I sent, this is the cap that would replace a series pair in each channel. If you look at the first I ages, you see the “+” are connected together. These capacitors (near as makes no difference) have no polarity (though it’s a good idea to observe a practice of going short leg first both for matching side to side performance and noise rejection) and just “jump” over the shared “+” solder pad.

Nowadays it’s pretty easy to find a very good quality non-polar cap, and even a mediocre one will produce infinitely better results than the old series-cap-bandage solution.

The above is why DC-coupled audio gear became such a “thing,” since that way of dealing with the challenge extracted a terrible cost performance wise.

DC-coupling an entire unit has its own unfortunate cost (current across volume and balance controls creates a ton of noise on devices that are best off doing their original job as voltage dividers, not to mention that the more current you run through a volume control, the quicker you degrade the contact surfaces, so the sooner you get noise and cut-outs) but there’s a happy, easily implemented way around that. Next time.

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Keret
Aug 26, 2012




Soiled Meat
Anyone know of a good EQ, preferably 16 band x2, that would fit into a space 12" wide? That's the width of my receiver and it'd be nice to fit them together into a space I have that is that size.

GnarlyCharlie4u
Sep 23, 2007

I have an unhealthy obsession with motorcycles.

Proof

Keret posted:

Anyone know of a good EQ, preferably 16 band x2, that would fit into a space 12" wide? That's the width of my receiver and it'd be nice to fit them together into a space I have that is that size.

oof that's a tough one. I can list off rack sized gear for days but you're asking for a unicorn. I don't even think you can fit 16 sliders in a 12" space.

Keret
Aug 26, 2012




Soiled Meat

GnarlyCharlie4u posted:

oof that's a tough one. I can list off rack sized gear for days but you're asking for a unicorn. I don't even think you can fit 16 sliders in a 12" space.

Yeah, that's a fair point. I may just have to resign myself to having it live separate since most are rack-mount sized.

GnarlyCharlie4u
Sep 23, 2007

I have an unhealthy obsession with motorcycles.

Proof

Keret posted:

Yeah, that's a fair point. I may just have to resign myself to having it live separate since most are rack-mount sized.

Alternatively you could go with a really cool project.
Old iPad + MiniDSP
https://www.minidsp.com/applications/acoustic-measurements/using-the-umik-1-with-signalpro-on-ipad

Discernibly Turgid
Mar 30, 2010

This was not the improvement I was asking for!

GnarlyCharlie4u posted:

oof that's a tough one. I can list off rack sized gear for days but you're asking for a unicorn. I don't even think you can fit 16 sliders in a 12" space.

I’m with Charlie on this. Short of running a mobile unit off of a sturdy 12V supply, you’re in a tough spot. I don’t explicitly recall one existing, but there were some micro component systems (like the slick Toshiba Aurex separates, although that particular set didn’t include one) that may have something comparable in form factor to an autosound device.

Happy hunting

GnarlyCharlie4u
Sep 23, 2007

I have an unhealthy obsession with motorcycles.

Proof
I deeply searched my knowledge of mini component stereos and I couldn't come up with an eq that was even "good" let alone had more than a few sliders. I think you're likely to max out at 5-6 and it'll probably cost you an arm and a leg if you can even find one.
You're mostly just going to find preamps with "Bass" and "Treble" knobs.

trilobite terror
Oct 20, 2007
BUT MY LIVELIHOOD DEPENDS ON THE FORUMS!

GnarlyCharlie4u posted:

I deeply searched my knowledge of mini component stereos and I couldn't come up with an eq that was even "good" let alone had more than a few sliders. I think you're likely to max out at 5-6 and it'll probably cost you an arm and a leg if you can even find one.
You're mostly just going to find preamps with "Bass" and "Treble" knobs.

Yeah, I’d honestly just get a Schiit Loki or something of that ilk if I really wanted an EQ

Discernibly Turgid
Mar 30, 2010

This was not the improvement I was asking for!
For speakers hampered by (almost) purely amplitude troubles (instead of phase issues), the Audio Control C-101 Series II is pretty incredible. Genuine high fidelity, practical and usable features, and frequently available at the kind of prices that remind you to be happy you listen with your ears and not your wallet. Great aesthetic, too.



I found a nicer picture, but the “smile” positioning of the sliders made me a little more upset than is really reasonable.

actionjackson
Jan 12, 2003

Hello, I have an old technics turntable with a phono pre-amp connected to some KRK monitors through the JDS labs atom amp. I also have my computer audio go through an audio interface, which connects to that same amp. This way I can control the volume of, and switch between, the two sources using the amp. It works great, but I'm wondering about possible ways to place the speakers elsewhere in the room, for example on top of the tv stand on the other side. I suppose I could run a super long cable underneath my rug? But I also wondering if there's someway the atom amp can interact with some sort of bluetooth device so then I could use wireless speakers and not have to deal with running a cable to the other side of the room.

If there's some other way to get these speakers off my desk to make things a bit cleaner that would be fine also.

GnarlyCharlie4u
Sep 23, 2007

I have an unhealthy obsession with motorcycles.

Proof

actionjackson posted:

Hello, I have an old technics turntable with a phono pre-amp connected to some KRK monitors through the JDS labs atom amp. I also have my computer audio go through an audio interface, which connects to that same amp. This way I can control the volume of, and switch between, the two sources using the amp. It works great, but I'm wondering about possible ways to place the speakers elsewhere in the room, for example on top of the tv stand on the other side. I suppose I could run a super long cable underneath my rug? But I also wondering if there's someway the atom amp can interact with some sort of bluetooth device so then I could use wireless speakers and not have to deal with running a cable to the other side of the room.

If there's some other way to get these speakers off my desk to make things a bit cleaner that would be fine also.

The cheapest thing you can do is just try longer RCA cables and see if it works without introducing noise.
Otherwise get a preamp and/or dac that has balanced outputs like the Emotiva XDA-2 or TEAC UD-501 or an interface like the Focusrite Scarlett something or other. There are cheaper options than what I just mentioned but all of what I just suggested is the best for the money in it's own way. If you do get an XDA-2 then you can sell the Atom because the headphone amp is FANTASTIC (but mutes the other outputs.) The headphone amp on the Scarlett is serviceable but not amazing. The headphone amp on the Teac is on par with the Atom but not quite as good.

large hands
Jan 24, 2006
Hey electronics guys, maybe you can point me in the right direction, the other night my amp blew the tweeters on my towers while nothing was playing.

During the day we'd heard a couple of loud zap sounds coming through the speakers. I should have unplugged them then but foolishly didn't. Later that night my wife heard a louder zap and the next morning the tweeters were out.

The amp is the Sony ES power/pre combo I posted about buying a few pages back. The speakers were my old set of Energy 5.1e's. The pre was plugged into our turntable which was off and PC which was on and the input for the PC was selected on the pre. Pre was plugged into a Costco power bar and the power amp plugged into the outlet on the preamp.

Luckily I don't really care about the speakers but I need to figure out what happened before I plug in a new pair, obviously.

GnarlyCharlie4u
Sep 23, 2007

I have an unhealthy obsession with motorcycles.

Proof

large hands posted:

Hey electronics guys, maybe you can point me in the right direction, the other night my amp blew the tweeters on my towers while nothing was playing.

During the day we'd heard a couple of loud zap sounds coming through the speakers. I should have unplugged them then but foolishly didn't. Later that night my wife heard a louder zap and the next morning the tweeters were out.

The amp is the Sony ES power/pre combo I posted about buying a few pages back. The speakers were my old set of Energy 5.1e's. The pre was plugged into our turntable which was off and PC which was on and the input for the PC was selected on the pre. Pre was plugged into a Costco power bar and the power amp plugged into the outlet on the preamp.

Luckily I don't really care about the speakers but I need to figure out what happened before I plug in a new pair, obviously.

Do you have a multimeter?
If so, then start by turning the amp on (with nothing plugged into the inputs) and measuring the DC output voltage across the + and - terminals of each of the two speaker outputs and see if you get a reading.
Do the same thing to the Preamp line outputs. It's probably easier to test the center pins of the RCA cables rather then try to hold the probes in the RCA jacks.
Also, watch this:
https://www.youtube.com/watch?v=M6cDAlRXOL0
Then read up on DC output bias and come join us in the Learning electronics thread. Be prepared to spend a SHITLOAD of time learning about electronics.

If you don't have a multimeter then that's an easy fix; just take to your local electronics repair guy.

large hands
Jan 24, 2006
I have a multimeter and will watch that video and see if I can narrow it down before I take it to the local hifi shop. Thanks!

actionjackson
Jan 12, 2003

GnarlyCharlie4u posted:

The cheapest thing you can do is just try longer RCA cables and see if it works without introducing noise.
Otherwise get a preamp and/or dac that has balanced outputs like the Emotiva XDA-2 or TEAC UD-501 or an interface like the Focusrite Scarlett something or other. There are cheaper options than what I just mentioned but all of what I just suggested is the best for the money in it's own way. If you do get an XDA-2 then you can sell the Atom because the headphone amp is FANTASTIC (but mutes the other outputs.) The headphone amp on the Scarlett is serviceable but not amazing. The headphone amp on the Teac is on par with the Atom but not quite as good.

Sorry I'm a little confused. I can definitely try the long cables but I didn't understand the rest of what you said. I have a focus rite Scarlett already. I just want to move the monitors elsewhere and I'm wondering if this can be done wirelessly at all. I'll post a pic of my setup a bit later.

GnarlyCharlie4u
Sep 23, 2007

I have an unhealthy obsession with motorcycles.

Proof

actionjackson posted:

Sorry I'm a little confused. I can definitely try the long cables but I didn't understand the rest of what you said. I have a focus rite Scarlett already. I just want to move the monitors elsewhere and I'm wondering if this can be done wirelessly at all. I'll post a pic of my setup a bit later.
Short answer; no.
Long answer; no, because...
There's not a good wireless solution for what you are trying to achieve. There are RF solutions but they're not great, so don't bother.
There's no bluetooth solution that currently exists where you could place a single receiver at each speaker and move them around wherever you want. That only exists in something like a Sonos system and I think Google Chromecast? But I'm not sure if either of those are true stereo or just dual mono.
You could get away with using a single stereo bluetooth receiver and then running cables from it to each of the speakers but that's going to be a messy solution and sounds like it's going to defeat the purpose of what you are trying to achieve from what I understand.

You can mount your monitors wherever you want and connect them back to the Focusrite using a long balanced cable (XLR male to TRS male OR TRS male to male) and you will be fine, but you'll have a cable running to each of the monitors from the Focusrite.

Why is the JDS Atom even involved in any of this? Which Model Focusrite do you have?
If you have spare inputs on the Focusrite, why not just plug the phono preamp (using RCA to TS cables OR TS cables* + an RCA adapter) into the focusrite and use that as the volume control for your KRK's? That way everything connects to your Focusrite, and then there's only a pair of long cables going to your speakers.
*Note: TS and TRS cables are not the same thing. You should not use a TRS cable where you need a TS cable.

actionjackson
Jan 12, 2003

GnarlyCharlie4u posted:

Short answer; no.
Long answer; no, because...
There's not a good wireless solution for what you are trying to achieve. There are RF solutions but they're not great, so don't bother.
There's no bluetooth solution that currently exists where you could place a single receiver at each speaker and move them around wherever you want. That only exists in something like a Sonos system and I think Google Chromecast? But I'm not sure if either of those are true stereo or just dual mono.
You could get away with using a single stereo bluetooth receiver and then running cables from it to each of the speakers but that's going to be a messy solution and sounds like it's going to defeat the purpose of what you are trying to achieve from what I understand.

You can mount your monitors wherever you want and connect them back to the Focusrite using a long balanced cable (XLR male to TRS male OR TRS male to male) and you will be fine, but you'll have a cable running to each of the monitors from the Focusrite.

Why is the JDS Atom even involved in any of this? Which Model Focusrite do you have?
If you have spare inputs on the Focusrite, why not just plug the phono preamp (using RCA to TS cables OR TS cables* + an RCA adapter) into the focusrite and use that as the volume control for your KRK's? That way everything connects to your Focusrite, and then there's only a pair of long cables going to your speakers.
*Note: TS and TRS cables are not the same thing. You should not use a TRS cable where you need a TS cable.

The JDS atom amp is used primarily to control the volume of the turntable audio (I can also use it to listen to turntable audio through headphones of course). Now that I have this, I also use it to control the audio from my computer which first runs through the focusrite. It's the base focusrite model, so I don't think I'm able to only use that. If I'm wrong though please let me know! A while back someone in this thread told me that I should get this atom amp so I can control both sources through that.

So here's how the connections are working

turntable -> phono pre-amp

phono pre-amp -> 3.5 in connection on back of atom amp

computer -> focusrite via usb

focusrite -> input on back of atom amp

monitors -> output on back of atom amp

all the connections on the atom amp are used, as are all the connections on the back of the focusrite.

I even made a video, hope it helps!

https://twitter.com/fuck_it_all___/status/1279496143429394437

RIP Paul Walker
Feb 26, 2004

You can buy Bluetooth transmitter/receiver things on amazon and eBay (most are switchable), they’re pretty cheap.

Just an example: https://www.amazon.com/ZIIDOO-Bluet...ooth+tra&sr=8-4

Downside is quality will suck.

You can also get rca over Ethernet bridges, running cat5 is cheap and easy (I like the flat cables for this stuff) and they’re fairly resistant to interference.

Example: https://www.amazon.com/LINESO-2Pack-Stereo-Extender-Female/dp/B01IXYSE2A/ref=mp_s_a_1_3?dchild=1&keywords=cat+5+rca&qid=1593890861&sr=8-3

actionjackson
Jan 12, 2003

RIP Paul Walker posted:

You can buy Bluetooth transmitter/receiver things on amazon and eBay (most are switchable), they’re pretty cheap.

Just an example: https://www.amazon.com/ZIIDOO-Bluet...ooth+tra&sr=8-4

Downside is quality will suck.

You can also get rca over Ethernet bridges, running cat5 is cheap and easy (I like the flat cables for this stuff) and they’re fairly resistant to interference.

Example: https://www.amazon.com/LINESO-2Pack-Stereo-Extender-Female/dp/B01IXYSE2A/ref=mp_s_a_1_3?dchild=1&keywords=cat+5+rca&qid=1593890861&sr=8-3

Thank you.

Maybe I should just start with a more simple question - I am using the focusrite because my laptop sound card is a piece of crap, and it allows me to then connect to in my case powered monitors. If I wanted to play my computer audio (forget about the turntables for now) through bluetooth speakers, I would not use the focusrite at all, correct? I would just place the bluetooth speakers wherever and then set them up using my macbook audio settings?

Also with the video I posted, I do actually need both the focusrite and atom amp if I want to control the audio level of both the computer audio and turntable from one device correct? I just had the focusrite before getting the turntable. I'm pretty sure that if I had a fancier model of the focus rite with more than one pair of outputs on the back, then I would not need the atom amp as I could just connect the turntable to the other pair.

actionjackson fucked around with this message at 20:51 on Jul 4, 2020

actionjackson
Jan 12, 2003

btw if I wanted to move the monitors, I'd probably get actual speakers since they would be farther away, and then set them up with my turntable on top of my tv table. I think this would be a grea option because I can use it with the turntable and it even has a built in phono pre-amp, but it also has bluetooth for playing computer audio from the other side of the room.

https://www.kantoaudio.com/powered-speakers/yu6/

Discernibly Turgid
Mar 30, 2010

This was not the improvement I was asking for!

large hands posted:

Hey electronics guys, maybe you can point me in the right direction, the other night my amp blew the tweeters on my towers while nothing was playing.

During the day we'd heard a couple of loud zap sounds coming through the speakers. I should have unplugged them then but foolishly didn't. Later that night my wife heard a louder zap and the next morning the tweeters were out.

The amp is the Sony ES power/pre combo I posted about buying a few pages back. The speakers were my old set of Energy 5.1e's. The pre was plugged into our turntable which was off and PC which was on and the input for the PC was selected on the pre. Pre was plugged into a Costco power bar and the power amp plugged into the outlet on the preamp.

Luckily I don't really care about the speakers but I need to figure out what happened before I plug in a new pair, obviously.

Have to finish taxes now, but if yours is the Sony 77ES, I can give you a hand.

Is the amp in protection? Does it still power on? If the answer to those is yes, proceed.

For starters, put a scope on the output of the amp (with your damaged speakers still hooked up) and see if you can spot runaway HF going on. You will want to look at any pF value caps that are positioned to stop individual transistors from going into oscillation.

I’ll dig up a manual, but I did a complete rebuild on one of those a few years back (and if I’ve confused your amp with a different one it’d be a waste of time to keep going with this response.)

large hands
Jan 24, 2006
It's this pair:



Not in protection, except for the normal 5 second startup

GnarlyCharlie4u
Sep 23, 2007

I have an unhealthy obsession with motorcycles.

Proof

actionjackson posted:

Thank you.

Maybe I should just start with a more simple question - I am using the focusrite because my laptop sound card is a piece of crap, and it allows me to then connect to in my case powered monitors. If I wanted to play my computer audio (forget about the turntables for now) through bluetooth speakers, I would not use the focusrite at all, correct? I would just place the bluetooth speakers wherever and then set them up using my macbook audio settings?

Also with the video I posted, I do actually need both the focusrite and atom amp if I want to control the audio level of both the computer audio and turntable from one device correct? I just had the focusrite before getting the turntable. I'm pretty sure that if I had a fancier model of the focus rite with more than one pair of outputs on the back, then I would not need the atom amp as I could just connect the turntable to the other pair.

Yes, your computer audio would go straight to the bluetooth speakers with no wires. But you could also use your Focusrite to take inputs (like your turntable), send it to your computer, and then send that audio over Bluetooth to the speakers. However it looks like you have a Focusrite 2i2 (it's hard to tell in the video) so you've only got 2 mono inputs, meaning the Turntable Left and Right would take both of your inputs leaving you with no ability to connect anything else.
You do not need the Atom. Your Focusrite outputs are controlled with the "Monitor" knob. BUT you'll have to plug the red wire from the phono pre into one input of the Focusrite and the white wire into the other using an RCA cable and a couple of RCA to TS adapters. This is not ideal because you'll have to manually level match the left and right channels using the gain knobs on the front.
If you had a 4i4 this wouldn't be an issue because you could just use the line in jacks in the back.

actionjackson
Jan 12, 2003

GnarlyCharlie4u posted:

Yes, your computer audio would go straight to the bluetooth speakers with no wires. But you could also use your Focusrite to take inputs (like your turntable), send it to your computer, and then send that audio over Bluetooth to the speakers. However it looks like you have a Focusrite 2i2 (it's hard to tell in the video) so you've only got 2 mono inputs, meaning the Turntable Left and Right would take both of your inputs leaving you with no ability to connect anything else.
You do not need the Atom. Your Focusrite outputs are controlled with the "Monitor" knob. BUT you'll have to plug the red wire from the phono pre into one input of the Focusrite and the white wire into the other using an RCA cable and a couple of RCA to TS adapters. This is not ideal because you'll have to manually level match the left and right channels using the gain knobs on the front.
If you had a 4i4 this wouldn't be an issue because you could just use the line in jacks in the back.

ok, thank you. I got the focus rite (and yes it's the 2i2) before the turntable so at that point I was fine just getting the basic model.

If on the other hand I just want to keep the monitors I have but get a subwoofer, is there any brand(s) you would recommend? So this would just be for computer and turntable audio, nothing related to tvs or home theater.

I was looking at the ones from Jamo as they are in my budget and tend to be pretty sleek looking.

https://www.crutchfield.com/p_701S808WWN/Jamo-S-808-SUB-Walnut.html

Discernibly Turgid
Mar 30, 2010

This was not the improvement I was asking for!
TA-N55ES stuff

Still powers up and doesn’t go into protection.

Do you know if it still produces any sound through your now-messed-up speakers? Have you confirmed it’s only the tweeters that went out?

If the amp has any DC offset beyond 100-200mV, the protection engages because of excessive DC, and even if it could stay on with more, that wouldn’t have any effect on your tweeters, as the crossover has a cap blocking DC.

If the thing was making noises throughout the day and eventually ate your tweeters (while still turning on in the condition above), you’re looking at a high-frequency oscillation (higher than what you can hear and what the tweeter can safely reproduce, especially with the kind of runaway that can ensue.)

I’ve got 4 of those in different conditions (I don’t know why the guy had four to sell, but he gave me a nice price (around $75/ amp IIRC) while I was picking up some other stuff, so I’ve got the service manual.

Once we know the casualties we will have an idea of where to look (faulty STK, individual styrene caps.) The description of the failure (intermittent hellsounds followed by loudest hellsound, failed tweeter (quite possibly singular) but still turning on and appearing normal, it leans toward a styrene pF value cap giving out, starting to short intermittently, and then giving up altogether, which would leave it open and that circuit element free to oscillate. Best place to look is C310,311,360, and C361 (if it’s a single tweeter, this is a great place to start) which are 33pF and span the B-C on the driver transistors.) Other likely culprit would be a failed STK (again, if it’s a single dead tweeter), as a failure of any of the transistors outside there would prevent the bias from being set.

To check:

Remove the bottom service panel before turning it on. This gives you easier access to the STK pins if memory serves. Also, before checking the following you’ll want to disconnect speakers and set the selector to “OFF.”

1- turn it on and give it 1-2 minutes before checking the binding posts (with no input, volume set to max, and the speaker selector set to A+B (so it doesn’t master which set of posts you check) for any kind of DC offset (or, better yet, high-frequency action if you’re also wielding a scope) as proof of life for both channels. Something other than “0.00mV” and probably below 100mV or so.

2- bias adjust (page 5 of the service manual) - does it end up where it needs to be, is it 0mV, or does it start climbing after being on with no input for an extended period? Check both channels every 15 minutes or so for about 2 hours and answer the above for both channels.

3 - while it’s warming up, check pins 5,6,10, and 11 of the STK for the requisite +/- 1.2V.

Report back.

If you end up having a bad STK I’m happy to send you a spare (I gutted one of the amps so I could use the transformer and “Gibraltar” platform for a non-amp DIY project I’m currently prototyping.)

GnarlyCharlie4u
Sep 23, 2007

I have an unhealthy obsession with motorcycles.

Proof

actionjackson posted:

ok, thank you. I got the focus rite (and yes it's the 2i2) before the turntable so at that point I was fine just getting the basic model.

If on the other hand I just want to keep the monitors I have but get a subwoofer, is there any brand(s) you would recommend? So this would just be for computer and turntable audio, nothing related to tvs or home theater.

I was looking at the ones from Jamo as they are in my budget and tend to be pretty sleek looking.

https://www.crutchfield.com/p_701S808WWN/Jamo-S-808-SUB-Walnut.html

I can't really speak to small subwoofers, sorry. Rel makes some nice ones, but I'm firmly in the "big subs are best subs" camp.
Maybe get a KRK sub to match your monitors?


Discernibly Turgid posted:

TA-N55ES stuff

Still powers up and doesn’t go into protection.

Do you know if it still produces any sound through your now-messed-up speakers? Have you confirmed it’s only the tweeters that went out?

If the amp has any DC offset beyond 100-200mV, the protection engages because of excessive DC, and even if it could stay on with more, that wouldn’t have any effect on your tweeters, as the crossover has a cap blocking DC.

If the thing was making noises throughout the day and eventually ate your tweeters (while still turning on in the condition above), you’re looking at a high-frequency oscillation (higher than what you can hear and what the tweeter can safely reproduce, especially with the kind of runaway that can ensue.)

I’ve got 4 of those in different conditions (I don’t know why the guy had four to sell, but he gave me a nice price (around $75/ amp IIRC) while I was picking up some other stuff, so I’ve got the service manual.

Once we know the casualties we will have an idea of where to look (faulty STK, individual styrene caps.) The description of the failure (intermittent hellsounds followed by loudest hellsound, failed tweeter (quite possibly singular) but still turning on and appearing normal, it leans toward a styrene pF value cap giving out, starting to short intermittently, and then giving up altogether, which would leave it open and that circuit element free to oscillate. Best place to look is C310,311,360, and C361 (if it’s a single tweeter, this is a great place to start) which are 33pF and span the B-C on the driver transistors.) Other likely culprit would be a failed STK (again, if it’s a single dead tweeter), as a failure of any of the transistors outside there would prevent the bias from being set.

To check:

Remove the bottom service panel before turning it on. This gives you easier access to the STK pins if memory serves. Also, before checking the following you’ll want to disconnect speakers and set the selector to “OFF.”

1- turn it on and give it 1-2 minutes before checking the binding posts (with no input, volume set to max, and the speaker selector set to A+B (so it doesn’t master which set of posts you check) for any kind of DC offset (or, better yet, high-frequency action if you’re also wielding a scope) as proof of life for both channels. Something other than “0.00mV” and probably below 100mV or so.

2- bias adjust (page 5 of the service manual) - does it end up where it needs to be, is it 0mV, or does it start climbing after being on with no input for an extended period? Check both channels every 15 minutes or so for about 2 hours and answer the above for both channels.

3 - while it’s warming up, check pins 5,6,10, and 11 of the STK for the requisite +/- 1.2V.

Report back.

If you end up having a bad STK I’m happy to send you a spare (I gutted one of the amps so I could use the transformer and “Gibraltar” platform for a non-amp DIY project I’m currently prototyping.)
This is a very good post.

large hands
Jan 24, 2006
Turgid, thanks so much! I'll go through it step by step as soon as i have time and let you know what i find.

actionjackson
Jan 12, 2003

GnarlyCharlie4u posted:

I can't really speak to small subwoofers, sorry. Rel makes some nice ones, but I'm firmly in the "big subs are best subs" camp.
Maybe get a KRK sub to match your monitors?


yep KRK does have one though it's kind of unsightly. By big how big are you talking? Is 10" enough for a desktop setup?

I'm also realizing that that one I linked to requires a receiver or something similar to connect through first. I would just be going directly from an unbalanced RCA.

here's the 10" KRK one https://www.krkmusic.com/Powered-Subwoofer/10s

actionjackson fucked around with this message at 18:39 on Jul 5, 2020

GnarlyCharlie4u
Sep 23, 2007

I have an unhealthy obsession with motorcycles.

Proof

actionjackson posted:

yep KRK does have one though it's kind of unsightly. By big how big are you talking? Is 10" enough for a desktop setup?

I'm also realizing that that one I linked to requires a receiver or something similar to connect through first. I would just be going directly from an unbalanced RCA.

here's the 10" KRK one https://www.krkmusic.com/Powered-Subwoofer/10s

I would say it depends on what you want the sub to do. If it's just making music thumps to piss off the neighbors then whatever is fine and you can stick it anywhere.
If you want it to sound good, you're going to have to do a subwoofer crawl and place it wherever the bass sounds cleanest and then gently caress around with dialing in the crossover.

I'm assuming that since you're looking at not using a receiver with LFE channel you're going to feed your line out from the Focusrite to the sub and then the sub to the monitors? Meaning a bunch of cables, so it's probably just going to wind up under/next to your desk. In my opinion, I'd pass on that in favor of upgrading to some 8" monitors. You'll get all the thump you want without too much complication and none of the home theater sub-bass you're not looking for anyway. You could get a pair of Adam T7V or Mackie MR824's for about what you're gonna spend on just a subwoofer alone.

A proper sub is something like an HSU VTF-2 or SVS PB2000. REL also makes some very nice subs but none of those are going to integrate well into your KRK setup without getting a receiver that has an LFE channel.

actionjackson
Jan 12, 2003

GnarlyCharlie4u posted:

I would say it depends on what you want the sub to do. If it's just making music thumps to piss off the neighbors then whatever is fine and you can stick it anywhere.
If you want it to sound good, you're going to have to do a subwoofer crawl and place it wherever the bass sounds cleanest and then gently caress around with dialing in the crossover.

I'm assuming that since you're looking at not using a receiver with LFE channel you're going to feed your line out from the Focusrite to the sub and then the sub to the monitors? Meaning a bunch of cables, so it's probably just going to wind up under/next to your desk. In my opinion, I'd pass on that in favor of upgrading to some 8" monitors. You'll get all the thump you want without too much complication and none of the home theater sub-bass you're not looking for anyway. You could get a pair of Adam T7V or Mackie MR824's for about what you're gonna spend on just a subwoofer alone.

A proper sub is something like an HSU VTF-2 or SVS PB2000. REL also makes some very nice subs but none of those are going to integrate well into your KRK setup without getting a receiver that has an LFE channel.

Okay thanks for the advice! The cable thing actually really isn't an issue because I'm going to get some cable management stuff - basically you get a basket that you can attach to the underside of the desk, or use some velcro cable ties.

I will look at those monitors you mentioned - I'm not really doing any music production, but the "monitor" part is more because they are meant to be listened to up close right?

bradburypancakes
Sep 9, 2014

hmm. hmmmmmmmm
Has anyone seen motor mounts like these before, or know how to remove them? I’m trying to replace the motor on my philips 212 and I can’t figure out how to get it out of these rubber grommet things. It looks like maybe I have to push down on the rubber while at the same time levering the washer out, but I wanted to get some advice before I go this route and end up putting too much force where it doesn’t belong
and the underside


edit: For clarification the top side is layered like so: top of motor mount -> semi-circular washer -> full circle washer -> rubber grommet -> table body -> rubber grommet -> bottom of motor mount

bradburypancakes fucked around with this message at 19:46 on Jul 5, 2020

Flipperwaldt
Nov 11, 2011

Won't somebody think of the starving hamsters in China?



I would for sure start with taking those semi circular washers off. I think they're called e-clips? I expect they are pretty much what is holding the whole sandwich together.

Discernibly Turgid
Mar 30, 2010

This was not the improvement I was asking for!

Flipperwaldt posted:

I would for sure start with taking those semi circular washers off. I think they're called e-clips? I expect they are pretty much what is holding the whole sandwich together.

Flipoerwaldt is exactly right. You CAN improvise a tool for removing them (as I assume you don’t have one since you haven’t already removed them,) but you’ll want to put new ones on if you bend those prying them off.

Additionally, you’re going to want to either replace the rubber OR get a rubber renewal product (like Gummi Pflege from nextzett via Amazon, which is great) and then clean the rubber and rub that in a few times. It’ll get supple again and will be a good deal talker than now, meaning you’ll get better motor alignment and, with that, less wandering on the belt so more consistent speed.

bradburypancakes
Sep 9, 2014

hmm. hmmmmmmmm

Flipperwaldt posted:

I would for sure start with taking those semi circular washers off. I think they're called e-clips? I expect they are pretty much what is holding the whole sandwich together.

Bingo! I never noticed the notches on the closed side, so using a pair of pliers I was able to just pop 'em away from the open side and off. That name was just what I needed to Google to figure out what these were, thanks!

spookygonk
Apr 3, 2005
Does not give a damn

Flipperwaldt posted:

I would for sure start with taking those semi circular washers off. I think they're called e-clips? I expect they are pretty much what is holding the whole sandwich together.

https://www.wikihow.com/Remove-E-Clips

GnarlyCharlie4u
Sep 23, 2007

I have an unhealthy obsession with motorcycles.

Proof

actionjackson posted:

Okay thanks for the advice! The cable thing actually really isn't an issue because I'm going to get some cable management stuff - basically you get a basket that you can attach to the underside of the desk, or use some velcro cable ties.

I will look at those monitors you mentioned - I'm not really doing any music production, but the "monitor" part is more because they are meant to be listened to up close right?

The nearfield part is more that they're meant to be listened to up close. The monitor part refers more to the fact that they're meant to have a more neutral and flat frequency response curve, which is helpful for mixing if you're into music production.
And I mentioned cabling because it could very well be that the placement where your sub sounds best is like in the middle of the room behind you or something ridiculous, which I assume is a deal-breaker for you.

actionjackson
Jan 12, 2003

GnarlyCharlie4u posted:

The nearfield part is more that they're meant to be listened to up close. The monitor part refers more to the fact that they're meant to have a more neutral and flat frequency response curve, which is helpful for mixing if you're into music production.
And I mentioned cabling because it could very well be that the placement where your sub sounds best is like in the middle of the room behind you or something ridiculous, which I assume is a deal-breaker for you.

So my plan is to have a sideboard or something with the turntable and the two bluetooth speakers on top, and then connect the speakers to my new subwoofer. I'd be fine with the subwoofer going underneath or to the side of the sideboard. In this case there would no longer be a phono pre-amp, focusrite, or atom amp at all. Does that make sense?

With my current setup I'll just connect the monitors to the subwoofer and see how it sounds on the floor below or to the side of my desk.

Sorry if I asked this before but are there other bluetooth speakers you'd recommend above the Kantos? The most common brand I saw otherwise was audio engine. I would want enough to fill a 15x20 room.

e.g. https://www.crutchfield.com/p_772A5PBTB/Audioengine-A5-Wireless-Satin-Black.html

actionjackson fucked around with this message at 03:52 on Jul 6, 2020

actionjackson
Jan 12, 2003

btw do you guys have any suggestions for minimalistic furniture for a turntable, speakers, record storage and subwoofer? ideally something around 30-35" in height

Here are some ideas I found:

ikea kallax https://www.ikea.com/us/en/p/kallax-shelf-unit-black-brown-20275885/

ikea stockholm sideboard https://www.ikea.com/us/en/p/stockholm-sideboard-walnut-veneer-40239721/

taller ikea besta unit with legs https://www.ikea.com/us/en/p/besta-tv-unit-black-brown-80299874/

cb2 sideboard on sale https://www.cb2.com/inez-wood-credenza/s644651

LooksLikeABabyRat
Jun 26, 2008

Oh dang, I'd nibble that cheese

Kallax on its side is about as simple and cheap as it gets. If you get the 4x2 you can put a receiver and turntable on it side by side with enough room to put a little stand to display what you're currently playing on it.

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actionjackson
Jan 12, 2003

LooksLikeABabyRat posted:

Kallax on its side is about as simple and cheap as it gets. If you get the 4x2 you can put a receiver and turntable on it side by side with enough room to put a little stand to display what you're currently playing on it.

yeah that's what I figured, though the CB2 thing looks really nice (though I'd really need to see it in person to judge).

I'm someone that likes to have things stowed away and hidden as much as possible, which is why I asked about that and the sideboard. I don't have that many records, so with the kallax most of those cubes would just sit empty.

Can you put the speakers in the cubes or is that not a good idea?

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