Amp Camp Amp - ACA

I'll answer but take this with a pinch of salt... my Whammy is 2 days old!!

Fast answer: Perfect Match!

For my setup, just exactly what I wanted. Built mostly with the kit parts and exactly as per the recommended BOM, the Whammy has 14dB of gain. For my setup, this yields perfect volume at 12 o'clock, and nice margin up and and down for whatever needs.

Sound is superb!

Now... after I finished my cable soldering, Wayne has gone on record saying he would put 20 to 100 Ohm resistors in series with the pre output to prevent oscillation.

I have not done that, have no way to measure if that oscillation is present (nor would I know how to 'detect it'), and I don't know if that would change the gain with the pre output.

So, still a bit early to give a final 'green light' all the way... but it is working beautifully!!!

I did use a different OpAmp and I am planning on doing some tests with other OpAmps, but I'll record all this in the Whammy thread.

So, for about $200, I couldn't be happier. And since I had all from the ACA chassis, the chassis cost me $10 of cutting and folding the pieces. :)

I'll post pictures on he Whammy soon.

Best regards,
Rafa.

Rafa

Congratulations on another successful build!! :) I would put those resistors in there now rather than risk oscillations happening. Depending on the frequency and amplitude, an oscillation could cause serious problems. Even at low levels they can cause strange sounds and odd listening impressions which is not what you want when testing your new diy creation.
This is especially relevant given that the very experienced designer of the Whammy is recommending the resistors.
 
Max PSU voltage ACA 1.6

Hi All!

First of all, thanx for this brilliant little piece of fun! I'm having a great time buildig this gem :)

I just have this one question that bothers me... If we went from a 19V laptop PSU to a 24V lighting PSU, that's 25% increase. Apperently there is quite some range. What would be the optimum voltage performance-wise?

It must be written somewhere in this massive thread, but I cannot find it by just using the search function... :eek:
 

6L6

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24V is better for performance.

More voltage in the PSU is more power on the output, giving more headroom and swing before clipping. It's also makes everything hotter. :)

The originals were 19v as the surplus store Nelson bought much of the materials from for the original ACA had them. (The actual "camp" event in the hills of California in 2012) A reliable source of suitable quiet 24v bricks had not yet been found. They exist now, and are highly recommended. You could also build a linear 24v supply of you like, but honestly the modern bricks are very nice.
 
24V is better for performance.

More voltage in the PSU is more power on the output, giving more headroom and swing before clipping. It's also makes everything hotter. :)

The originals were 19v as the surplus store Nelson bought much of the materials from for the original ACA had them. (The actual "camp" event in the hills of California in 2012) A reliable source of suitable quiet 24v bricks had not yet been found. They exist now, and are highly recommended. You could also build a linear 24v supply of you like, but honestly the modern bricks are very nice.

Ahh, I guessed the optimum would be somewhere in between 19V and 24V, but if 24V ís the optimum, I won't be bothering with a lineair supply :)

Thanks all!
 
I really don't understand terms like '12 o'clock' or '2 o'clock'. Surely, not all potentiometer knobs are set equally. Or should it be?

Wouldn't percentage of travel, like 50% or 75% be more logical?
You are correct, of course! Still, most volume pots have a 7ish to 4ish travel. So 9 is relatively low, 12 is dead center and 3 would be really loud.

But I agree if you have those non-mechanical ones you have several turns of travel to change from 0 to 100, so percentage is more universal.

I meant 50%.

Rafa... I would put those resistors in there now rather than risk oscillations happening... This is especially relevant given that the very experienced designer of the Whammy is recommending the resistors.
Oh, absolutely! I was just finished with it when I read his post. So I haven't done that yet!

Sad thing is that I don't have nice non-magnetic resistors here, I'm going to have to put the 1 cent 5% tolerance in, and am I kind of OCD about those things, so I wish I could have ordered those parts with the others.

I'll post all that over at the Whammy to prevent polluting the ACA with that!

Thanks,
Rafa.
 
Completed my ACA 1.6 build about 4 months ago and am enjoying it immensely. It's (temporarily?) replaced my naim NAP250, driving a pair of Spendors, and it's really let me know the magic that can be done with just 8 watts.


Question: I'm getting the occasional "pip fzzzz" from the right speaker in silent or quiet moments (could also be occurring during music with the music masking it). Would the source of this be one of caps? I suspect this, as I learned how to solder on one of the boards and I had trouble with the big pins on the 3300uF cap.


If I want to replace one of the caps, where can I get a replacement?


Thanks to DIYAudio for putting this kit out. It's my first electronics build ever and a total gateway drug; I'm getting the parts ready to build an F5 and am combing the forums to learn about PSUs.


Cheers
 
Unbalanced Stereo to Mono Conversion

I just completed my V1.6 ACA build and am impressed with the result. The family resemblance to my Pass Labs Aleph 3 is remarkable. It may be even more transparent. I’m thinking about buying another kit in order to run the amps in unbalanced mono mode. Is the toggle switch on the rear only applicable to the XLR and balanced mode? The way I understand it I would have to apply Step 46 in the build guide to run the amp in bridged mode? If so, can I just implement this jumper inside the amp using the unused half of the toggle switch? Then it would be switched in the circuit when the toggle is in the lower position. Will this work? Thanks for your help!
 
... Question: I'm getting the occasional "pip fzzzz" from the right speaker in silent or quiet moments (could also be occurring during music with the music masking it). Would the source of this be one of caps? I suspect this, as I learned how to solder on one of the boards and I had trouble with the big pins on the 3300uF cap.

If I want to replace one of the caps, where can I get a replacement?

It should be silent after the initial fizzzz at switch on.
I suspect you have a dry or 'cold' solder joint somewhere. (The big capacitor would be a good candidate too.) 8 out of 10 faults turn out to be poor solder joints... First thing to do is re-flow all the solder connections on the noisy board. Then check the wire connections.

Very unlikely that the big cap is faulty, but it is a common part. (Spec is 3300uF, 35 volt, 105 degree C, 10mm lead spacing snap in.) Mouser, Digikey or local parts store will have a range.

Alan
 
I just completed my V1.6 ACA build and am impressed with the result. The family resemblance to my Pass Labs Aleph 3 is remarkable. It may be even more transparent. I’m thinking about buying another kit in order to run the amps in unbalanced mono mode. Is the toggle switch on the rear only applicable to the XLR and balanced mode? The way I understand it I would have to apply Step 46 in the build guide to run the amp in bridged mode? If so, can I just implement this jumper inside the amp using the unused half of the toggle switch? Then it would be switched in the circuit when the toggle is in the lower position. Will this work? Thanks for your help!

Hi Franksr, I am confused by your question?
Which version of the Build Guide are you using V1.5 or V1.6?
Step 46 of V1.5 is the link plug. This has been updated in the V1.6 guide and may answer your question perhaps. See steps 34 and 55 for instance.
Alan
 
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I was looking for some nice heatsinks for my ACA build, and came across these which appear to be similar to some Pass heat sinks that are horizontal. Would a pair of these work for a pass amp, or would I need to cut them in half and run multiples vertical? Or should I pass on them?

1 unids negro oxidacion amplificador disipador grande Clase A pasar amplificador disipador radiador en Amplificador de Electronica en AliExpress.com | Alibaba Group
As someone living in very similar conditions to yours in terms of availability, I can certainly relate to your problem!

Actually those look very good (perhaps too big even?), at 26 x 15cm, they are more than enough (if they are quality heatsinks). Still, some more info on the dissipation characteristics, rather than max wattage, would have been nice.

I have some questions / concerns. Attaching those to a case is not easy! How are you planning on doing that?

As a side issue: are you sure you are going to get what is pictured? I find it suspicious that they don't list the manufacturer (and that GZbotolave 'brand' is their own shop, not the manufacturer, apparently).

My concern is that you would get different distributions, sizes, taps, or other complications. I am a bit overly paranoid about this things, but I have never been ripped off with on line shopping. That means I probably missed some really good deals, but I prefer to stay on the other side of the sidewalk.

Best regards,
Rafa.
 
Greetings,
I just ordered a complete ACA Kit. I plan on using it to drive my Klipsch Cornwalls 102db/w they are Crites modified series 2. I will also be using my Carver C1 preamp to start with, I modified years ago, very clean. I'm NASA Certified solder tech. I have built speakers for decades. I just wanted to say Hi.

NASA certified sounds impressive. Looking forward to seeing your solder joints!
 

sov

Member
Joined 2016
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I was looking for some nice heatsinks for my ACA build, and came across these which appear to be similar to some Pass heat sinks that are horizontal. Would a pair of these work for a pass amp, or would I need to cut them in half and run multiples vertical? Or should I pass on them?
I read somewhere that ACA is OK with heatsinks temperature coefficient 0,6 C°/W or below depending on bias I think. Is the kit sinks temperature coefficient 0,5 C°/W (200x4x120)?
 
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I've been using the Rod Elliott p88 pre for a few days now and really like what I'm hearing. I only just now noticed, that the original p88 article says the following: "The paralleled caps at the output are designed to ensure that the preamp can drive a power amp impedance as low as 22k with an overall response that is about 1dB down at 10Hz"

Now the input impedance of the ACA seems to be 10k while the p88 can "drive as low as 22k". I guess at least on paper this combination would not be ideal. How can I find out what the output impedance of p88 really is? Can anyone comment on the problems that this impedance combination might cause? Can I lower the impedance of the p88?
 
I raised the two ACA feedback resistors to about 121k and 33k. So 33k in input impedance for my ACAs.......reason was that I wanted to startup using a passive preamp. It works very well also using an active preamp. So this could be a solution......in fact ACAs works better using an active preamp.......