[BUILD] New FET/RACK Official Help Thread - Please read first post!

[Echo North]

The collector of Q4 is where 62Hz is getting crazy amplified (and everywhere after). I have double checked values around that area and everything checks out. I replaced one by one, Q4, C8, R24, R25, R26, and C10. In the process, I discovered that my output pot's middle pin had continuity with the right pin, so I grabbed a spare I had, which also had the same problem. I had one left and thankfully that one is good. I thought that would be the answer, but nope. DC voltages are good.

You're getting GAIN @ 60Hz or you have a LPF causing everything above it to be attenuated?

 

[Deejsirois]

Edit: Ok DC voltages are NOT good. Specifically, at R34 I am getting 31.07 VDC on one side and 7.88 VDC on the other. On a working unit, I get 30.59 VAC on one side and 26.26VDC on the other. What is pulling my voltage down so much? I even replaced R34 for good measure. Both R34 resistors (old and new) tested at 8.2k.

Q14: B=12.47 VDC, C= 30.92 VDC, E= 11.87 VDC (normal)
Q4: B= 0.579 VDC, C= 2.482 VDC, E= 0.112 VDC (off)

"You're getting GAIN @ 60Hz or you have a LPF causing everything above it to be attenuated?"

From what I am seeing, yes, it is a GAIN @ 60Hz.

 

[Echo North]

What is pulling my voltage down so much?

Too much current across that resistor.

Can be a bunch of things all sitting on that current path.  Another branch of that path has a wrong/damaged resistor/transistor/cap or bad solder joint. Anything attached to that path that's off will change all of the current/ohms law conditions.

Though the amplification is way weird. 

 

[Deejsirois]

Too much current across that resistor.

Can be a bunch of things all sitting on that current path.  Another branch of that path has a wrong/damaged resistor/transistor/cap or bad solder joint. Anything attached to that path that's off will change all of the current/ohms law conditions.

Though the amplification is way weird.

Well, let the surgery begin! I will replace the whole path (a number already done) and hope for the best. Ya the Gain was tripping me out too. The voltage goes up by 2 volts at BRN on output transformer when feeding signal @ 62Hz vs 1kHz

 

[Deejsirois]

I sure wish I had gone with my instincts...would have saved me a boat load of time and parts. The issue was the output transformer. It is not working properly. Swapped it out and everything was fine. Put it back in and the problem came back.

I will send you an email for replacement output pot (x2) and an output transformer. What an annoying process that was, but sure glad I discovered the problem.

 

[Purplenoise]

Hi guys, I need some help installing a utc o-12 in my revD unit. I have gathered as much info as I could but I would greatly appreciate it if someone could double check my findings and tell me if I am on the right track. Here it goes:

Utc pin 1  to  pcb pad 1
Utc pin 5 to pcb pad 4
Utc pin 6 to pcb pad 5
Utc pin 8 to pcb pad 8
Utc pin 3 to pcb pad 6

Thank you so much in advance. Any help would be greatly appreciated

 

[Echo North]

Hi guys, I need some help installing a utc o-12 in my revD unit. I have gathered as much info as I could but I would greatly appreciate it if someone could double check my findings and tell me if I am on the right track. Here it goes:

Utc pin 1  to  pcb pad 1
Utc pin 5 to pcb pad 4
Utc pin 6 to pcb pad 5
Utc pin 8 to pcb pad 8
Utc pin 3 to pcb pad 6

Thank you so much in advance. Any help would be greatly appreciated

The UTC gets installed backwards, so flip it around and make the secondary the primary.

 

[Purplenoise]

The UTC gets installed backwards, so flip it around and make the secondary the primary.

Thanks, yes I figured that part out. I am just not sure yet about the pcb pads and ground (metal can)pin of utc.
Which  pin of utc is ground 3 or 7? And that should go to pcb pad 6 right? Thank you so much again.

 

[Purplenoise]

So for those interested here is the correct way to connect a utc o-12.
Let’s say the pad numbers on the pcb start from 1 where the dot is and then going up counter clockwise ( so 5 is above 4)

Utc pin1 to pcb1
Utc pin5 to pcb4
Utc pin6 to pcb5
Utc pin8 to pcb8
Utc can you pcb7 ( I just wired from one of the screws that hold the metal shield)
I also installed a UA 5002 ( same color wiring as EA) and some nos ERO caps.

The interesting thing is that after those “mods” there is very small difference with the stock kit. That shows what a great job hairball did to recreate this unit. My stock build sounds a lot closer to our vintage urei unit than the UA reissue we also have. Just a tiny bit cleaner...younger. Cheers.

 

[Deejsirois]

So for those interested here is the correct way to connect a utc o-12.
Let’s say the pad numbers on the pcb start from 1 where the dot is and then going up counter clockwise ( so 5 is above 4)

Utc pin1 to pcb1
Utc pin5 to pcb4
Utc pin6 to pcb5
Utc pin8 to pcb8
Utc can you pcb7 ( I just wired from one of the screws that hold the metal shield)
I also installed a UA 5002 ( same color wiring as EA) and some nos ERO caps.

The interesting thing is that after those “mods” there is very small difference with the stock kit. That shows what a great job hairball did to recreate this unit. My stock build sounds a lot closer to our vintage urei unit than the UA reissue we also have. Just a tiny bit cleaner...younger. Cheers.

I did very similar mods and found the same thing...better than UA revision and damn close to the vintage unit. After screwing around with a bunch of different things, I now have "my mod" that I absolutely love. None of that would have been possible without the top notch work of Hairball Audio. I second the much deserved kudos to Mike, mnats, and Ed Anderson!

 

[Purplenoise]

I did very similar mods and found the same thing...better than UA revision and damn close to the vintage unit. After screwing around with a bunch of different things, I now have "my mod" that I absolutely love. None of that would have been possible without the top notch work of Hairball Audio. I second the much deserved kudos to Mike, mnats, and Ed Anderson!

Absolutely. After a few sessions I switched the EA 5002  back and took the UA 5002 out. The EA sounds better and more balanced actually with less mid emphasis. Also the vintage caps were replaced back by the stock caps. The only mod now is the original utc input. Very similar to EA. The EA is a touch cleaner with a touch more energy at 4/5k but we are talking subtle differences here.

 

[completelytorqued]

Hey ya'll! I've built and have been using two Hairball Rev A's day in day out for about 1.5 years now. I love them! However...

Yesterday, one my units stopped passing signal and the meter pinned hard right. I popped the lid and started probing voltages, and realized the 30v rail is at 18v! After much troubleshooting, I happened to bend the heat sink on Q6, and suddenly my voltage returns to 30v and I get signal! Wild! It's fidgety (moving the heatsink would cause the 30v to drop down to 18v and back up to 30v), but it appeared to working. Seems like either a short to the transistor can or an intermittent fault.

I then begin recalibration, and realize there's some weirdness; the gain reduction meter isn't correctly responding (no movement, or wildly bouncing and then resetting back to zero) AND I can't get more 1.2v output while feeding in 0.775 (even with the output pot fully clockwise with the attack pot ON).

Could I have a blown Q6? Could another component have been damaged with the voltage swinging between 30v and 18v? I ordered some extra 2n3053's and 2n3707's just in case!

 

[YoDudeRock]

Hey ya'll! I've built and have been using two Hairball Rev A's day in day out for about 1.5 years now. I love them! However...

Yesterday, one my units stopped passing signal and the meter pinned hard right. I popped the lid and started probing voltages, and realized the 30v rail is at 18v! After much troubleshooting, I happened to bend the heat sink on Q6, and suddenly my voltage returns to 30v and I get signal! Wild! It's fidgety (moving the heatsink would cause the 30v to drop down to 18v and back up to 30v), but it appeared to working. Seems like either a short to the transistor can or an intermittent fault.

I then begin recalibration, and realize there's some weirdness; the gain reduction meter isn't correctly responding (no movement, or wildly bouncing and then resetting back to zero) AND I can't get more 1.2v output while feeding in 0.775 (even with the output pot fully clockwise with the attack pot ON).

Could I have a blown Q6? Could another component have been damaged with the voltage swinging between 30v and 18v? I ordered some extra 2n3053's and 2n3707's just in case!

I've built about 65 units and just had this exact thing happen to me 2 days ago.    When I powered my Rev D up, my voltage at the big ole CR8 diode(1N2989B) was a normal 30vDC, but after the unit warmed up a bit, it would drop down to 24vDC.  It would act right for awhile, then the audio started dramatically dropping out and crackling.    I couldn't even get the calibration process done before it started freaking out.    I noticed the voltages were way off on Q6 (2N3053).    I think it was grounding out slightly.
Once I changed it out Q6, everything fixed and 100% normal from then on.

-Chris

 

[Echo North]

Hey ya'll! I've built and have been using two Hairball Rev A's day in day out for about 1.5 years now. I love them! However...

Yesterday, one my units stopped passing signal and the meter pinned hard right. I popped the lid and started probing voltages, and realized the 30v rail is at 18v! After much troubleshooting, I happened to bend the heat sink on Q6, and suddenly my voltage returns to 30v and I get signal! Wild! It's fidgety (moving the heatsink would cause the 30v to drop down to 18v and back up to 30v), but it appeared to working. Seems like either a short to the transistor can or an intermittent fault.

I then begin recalibration, and realize there's some weirdness; the gain reduction meter isn't correctly responding (no movement, or wildly bouncing and then resetting back to zero) AND I can't get more 1.2v output while feeding in 0.775 (even with the output pot fully clockwise with the attack pot ON).

Could I have a blown Q6? Could another component have been damaged with the voltage swinging between 30v and 18v? I ordered some extra 2n3053's and 2n3707's just in case!

Could start with switching out Q6.  Yes it can easily be damaged.

Mike

 

[Ricardus]

Greetings. I found other people with this issue, but mine seems to be a little more out of spec than the other person's.

So I started the PSU on my 2nd Rev D, and I get -9.6 volts at CR9, which is in spec, but at CR8, when I first turned it on, it was at 31.8, just slightly out of the 5% tolerance, but then over the next five minutes the voltage rose steadily to 32.4, which is almost a full volt out of spec.

I just turned it off for a few mins, and turned it back on and I was getting 31.7, and it's climbing again, 1/100th of a volt at a time. I just had lunch. It's been on 20 minutes or so and it seems to have leveled off at 32.44 volts.

Bad diode?

 

[Echo North]

Greetings. I found other people with this issue, but mine seems to be a little more out of spec than the other person's.

So I started the PSU on my 2nd Rev D, and I get -9.6 volts at CR9, which is in spec, but at CR8, when I first turned it on, it was at 31.8, just slightly out of the 5% tolerance, but then over the next five minutes the voltage rose steadily to 32.4, which is almost a full volt out of spec.

I just turned it off for a few mins, and turned it back on and I was getting 31.7, and it's climbing again, 1/100th of a volt at a time. I just had lunch. It's been on 20 minutes or so and it seems to have leveled off at 32.44 volts.

Bad diode?

Maybe.  Could be a weird ground, or something in your meter too.

I probably wouldn't worry, but I'm happy to send you a new stud diode as well.

Mike

 

[Ricardus]

Maybe.  Could be a weird ground, or something in your meter too.

I probably wouldn't worry, but I'm happy to send you a new stud diode as well.

Mike

I feel confident my ground and meter are fine. I'll reach out and have you send me another diode. Thank you. 

 

[Ricardus]

I have some nice NOS 2N3819s. Would they be a suitable sub for the 2N5457's in this application?

 

[Echo North]

I have some nice NOS 2N3819s. Would they be a suitable sub for the 2N5457's in this application?

Never heard of them as an option.  Some reading if you want to play around with it.

https://stompville.co.uk/?p=763

 

[andow]

I was just about to pull the trigger on a stereo set and at the checkout I saw that there's no shipping to Europe at the moment.
Damn you, Corona!!