Amp Camp Amp - ACA

[Lemonss]

Hi all, posted in the build guide thread, but this looks way more active. Running into some weird issues with my 4th build of the 1.6.

Running into some strange voltage readings. These readings are consistent across both pcbs. This would mark the 4th ACA I have built with the exact same resistors and capacitors and the same rear panel layout ( 2 sets of monoblocks). Since getting these readings all solder joints have been reflowed, all resistors and capacitors replaced and new pcbs. The only thing consistent and not replaced are the LS JFETs.

Anyway, the readings on Q1 are pin 1: 0v, pin 2: 173mv, pin 3: 24v. I am also getting low readings or 24v readings across many other resistors. Everything measured to spec prior to stuffing. Any thoughts? Attached are some pics.

 

[Mooly]

I've deleted your posts in the build thread as it would get confusing for those replying

 

[Mooly]

There are several possibilities for the 24v you are seeing.

First thing to do would be to record all the voltages on all the transistors. Copy and past this with the results and lets see if anything stands out.

Q1
D=
G=
S

Q2
D=
G=
S=

Q3
C=
B=
E=

Q4
D=
G=
S=

 

[exw9]

to follow up, here is what my ACA looks like. I did a little poking around for dry solder joints and didn't see anything right away but also not super sure what i am looking for. I will continue to look and take measurements.

 

[semmyroundel]

to follow up, here is what my ACA looks like. I did a little poking around for dry solder joints and didn't see anything right away but also not super sure what i am looking for. I will continue to look and take measurements.

ecxw9, just an observation: I normally see some bleed through of solder to top side of the board, and I don't see much of it at all looking at those resistors on the bottom photo, besides, I think that the knowledegable chaps here (not me) would be able to tell from a photo of the bottom where the soldered connections are if there was a potential problem.

 

[semmyroundel]

Semiroundel, the Objective 2 was on my short list of preamps last year for use with the ACA, but then I decided to build the B1. Thus, I wouldn't know how it compares with the AKSA Lender pre.

What I can tell you is that I was pretty happy with the B1 until now with most of my music, except for the older Pink Floyd stuff (recorded at lower level than is done currently) and classical music. The B1 doesn't have gain (arguably needed for the ACA), but the sound quality is very good, being a Pass design.

Now, if you'd ask me how the AKSA Lender is shaping up against the B1, I'd have to tell you that I prefer the AKSA Lender for it's better soundstage imaging and layering. The AKSA Lender is quite new and wasn't available when I started my preamp short list in July 2017. I believe the PCB's became available around Nov/Dec 2017.

Thanks for that input Skylar88, I think I'll keep an eye out for the AKSA in case a group buy appears, just to compare up against the Objective 2.
I don't know if it makes any difference, but I decided to upgrade the pot to an Alps blue 10k, the kit one I'm sure is good but I had an alps blue left over from another job, also my selector switch is an Elma 04-1264 (hopefully a good one)

 

[Alan4411]

to follow up, here is what my ACA looks like. I did a little poking around for dry solder joints and didn't see anything right away but also not super sure what i am looking for. I will continue to look and take measurements.

OK, please report back on the voltages, but the first thing I notice is there is very little solder 'flow through' on the component side of the board. Normally on 'good joints' capillary action brings a small amount of solder round the component leads - see the example from the build guide.

If you are brave, do the tap and poke test with power on speakers connected and with a low level input. If you find a component that reacts you might be able to re solder it from the top of the board. In the end though, I think you will need to remove the board and re-flow all the solder joints...
Alan

 

[semmyroundel]

Thanks Alan4411, what I mistakenly called bleed through is actually called flow-through? Good to get the terminology right! I did say I'm a bit of a novice.

 

[Skylar88]

Thanks for that input Skylar88, I think I'll keep an eye out for the AKSA in case a group buy appears, just to compare up against the Objective 2.

If you do, please post your findings on the Objective 2 vs AKSA Lender Pre.

And you don't have to wait for a group buy. I'm pretty sure xrk971 keeps stock of the boards.

 

[Lemonss]

There are several possibilities for the 24v you are seeing.

First thing to do would be to record all the voltages on all the transistors. Copy and past this with the results and lets see if anything stands out.

Q1
D=172.3 MV
G= 23.1 V
S= 26.8 MV

Q2
D= 23.75 V
G= 5.64 V
S= 1.098 V

Q3
C= 5.61 V
B= .809 V
E= 198.1 MV

Q4
D= 23.76 V
G= 23.1 V
S= 23.1 V

I added them above. Thanks for the help, like I said, Odd voltages.

 

[chrisb]

Lender pre-amp

And you don't have to wait for a group buy. I'm pretty sure xrk971 keeps stock of the boards.

Yes, I see that now on his Etsy store page.

 

[exw9]

ecxw9, just an observation: I normally see some bleed through of solder to top side of the board, and I don't see much of it at all looking at those resistors on the bottom photo, besides, I think that the knowledegable chaps here (not me) would be able to tell from a photo of the bottom where the soldered connections are if there was a potential problem.

OK, please report back on the voltages, but the first thing I notice is there is very little solder 'flow through' on the component side of the board. Normally on 'good joints' capillary action brings a small amount of solder round the component leads - see the example from the build guide.

If you are brave, do the tap and poke test with power on speakers connected and with a low level input. If you find a component that reacts you might be able to re solder it from the top of the board. In the end though, I think you will need to remove the board and re-flow all the solder joints...
Alan

Thanks so much for the observation. The flow through makes sense. Can i just add solder to all of them from the top?


I assume the tap and poke test is to use something non-conductive to nudge each component while listening for changes in the audio output from the amp? it seems like at low levels that could work, i can give it a try.


I started with the Resistance checks but was having trouble getting the readings even after waiting several minutes for the caps to charge as instructed. I will try again tomorrow and post my results.

 

[Dennis Hui]

Don't forget to check the soldering on the input RCA connectors and output
binding posts. I had a distortion show up on one channel of an F6 build and
it was cured when the soldering at the binding post was reflowed.

 

[Jason]

Amp Camp Amp Batch 3 is now open for pre-order. Shipping end of this month, Nov 30th. We are making various small improvements based on feedback (more wire!), thanks to everyone who all the customers who participated in the feedback survey.

 

[Alan4411]

The flow through makes sense. Can i just add solder to all of them from the top?

You could for the resistors, though it is not easy for the transistors and impossible for the capacitors.

I assume the tap and poke test is to use something non-conductive to nudge each component while listening for changes in the audio output from the amp? it seems like at low levels that could work, i can give it a try.

Correct.

I started with the Resistance checks but was having trouble getting the readings even after waiting several minutes for the caps to charge as instructed. I will try again tomorrow and post my results.

That is a fair indication a cap or associated component is not connected...

On a second look at your pictures, I would take it out and re-do all the joints...

 

[Mooly]

I added them above. Thanks for the help, like I said, Odd voltages.

Very odd. At face value it looks like Q4 is duff or not what its supposed to be. Q3 is working fine and limiting the current correctly. Its almost as if Q4 is near short or its not a FET but an NPN transistor with the base where the drain should be. That would give near identical voltage readings to what you are getting.

 

[exw9]

Don't forget to check the soldering on the input RCA connectors and output
binding posts. I had a distortion show up on one channel of an F6 build and
it was cured when the soldering at the binding post was reflowed.

That is a fair indication a cap or associated component is not connected...

On a second look at your pictures, I would take it out and re-do all the joints...

Thanks guys. I am going to roll up my sleeves and get into this.

 

[astromo]

Amp Camp Amp Batch 3 is now open for pre-order. Shipping end of this month, Nov 30th. We are making various small improvements based on feedback (more wire!), thanks to everyone who all the customers who participated in the feedback survey.

Good work on the order capacity indicator - nice touch.

 

[Lemonss]

Very odd. At face value it looks like Q4 is duff or not what its supposed to be. Q3 is working fine and limiting the current correctly. Its almost as if Q4 is near short or its not a FET but an NPN transistor with the base where the drain should be. That would give near identical voltage readings to what you are getting.

Yep, that was my thought too. I have two replacements on the way which I assume will fix the issue. Thanks for the help!

 

[bloozestringer]

This is a stupid question, but what’s a single stereo ACA set at 24V pulling from the mains? I’ve found out the home we just bought has 1/2 our basement (lights and outlets) on a single 15A breaker. Just trying to add up everything and figure it’s about 1.2-1.5A. Is that correct?