Amp Camp Amp - ACA

[jfuquay]

Well, I saw that all the values were within range, so hooked up the amp, and it’s making music just fine. So either I’ve got an intermittent problem or there was a poor connection someplace. Sorry to waste your time.

 

[Ben Mah]

Looking at the voltages, I would say that both channels seem to be working properly and should produce sound.

The only adjustment I would suggest is to adjust the pot of Board 2 in order to have the voltage at Q1 drain match that of Board 1.

 

[Mooly]

Pleased to hear its working 🙂

If it happens again:

i do not know how to take the measurement at the 5W resistors or Between Q1D and Q2S.

You got most of the way there... taking one channel you measured Q1 Drain at 11.5 and Q2 Source at 12.5 volts. If you look at the circuit you will see that equates to 1 volt across the resistors. Measuring between the resistors can be a bit more accurate as it removes errors due to long term temperature drift.

All good 🙂

 

[jfuquay]

I see that now. Thanks for the explanation. One question: looking at the top surface of the PCB, I’m going to guess “between the 5W resistors“ starts at the right pin of R1 and ends at the left pin of R4. I’m just going by the traces and the schematic.

I'm going to experiment with turning off the amps at night to see if it’s an intermittent temperature related issue. I sure hope not. I generally leave them on.

 

[Mooly]

One question:................

Well I've never built an ACA or seen the real PCB's but looking at a picture what you describe sounds correct.

You measure between any points on these traces. One lead on one trace and the other lead on the other. Depending which around you connect the leads one reading will be negative (ignore the - sign) So on this board you could measure between R15 and R8 and get the same result... just don't short anything 🙂

 

[Watts-Up]

Can't recommend speakers, but just thought I'll make you aware that the preamp you use should have some gain otherwise you'll be disappointed in the ACA's - even if you use quite sensitive speakers. And while I'm mentioning speaker sensitivity, you want at least 94dB, preferably 100dB or thereabouts.

Hi Skylar88, please forgive my ignorance. My basic knowledge of electricity is from grade 9 Industrial Ed in the late 60s. My old Adcom GFP-750 is still operating. The specs from Stereophile mag shows the following. Just wonder if the Adcom pre can work with the ACA. Thanks in advance!

Adcom GFP-750 preamplifier Sidebar 1: Specifications

Description: Solid-state, remote-control preamplifier switchable to passive attenuator/switcher. Rated main output level: 1V. Frequency response: 5Hz-85kHz, ±0.5dB. S/N ratio: >102dB, A-weighted. Input sensitivity: 183mV balanced, 365mV unbalanced. Input impedance: 94k ohms balanced, 47k ohms unbalanced. Output impedance: 1200 ohms balanced, 600 ohms unbalanced.

 

[Skylar88]

Just wonder if the Adcom pre can work with the ACA.

"The maximum gain in active mode was 8.33dB unbalanced and 14.33dB balanced."
Source: www.stereophile.com/content/adcom-gfp-750-preamplifier

Going by those numbers, it should work just fine with the ACA, provided you set the preamp to active mode.

 

[Watts-Up]

@Skylar88 Thank you kindly for taking the time to look into my question, much appreciated! I went to the link you've provided and read the piece a few times. Unfortunately, it was in Martian. Thank you for helping out the lay people.

 

[AudioFanMan]

Just gotta say... 2 pass ACA monoblocks driving Elsinore's, fed by the color preamp with a dash of picore lms dishing out Lenny Kravits is 100% scookum!

 

[smype]

I have a basic question. What are the advantages of the 1.8 wiring over the 1.6 wiring other than the mono block options? If I don't care about those additional choices, can I just use the 1.6 wiring and get all the sonic benefits of the ACA amp? Thanks.

 

[Loudthud]

If the speakers you are using are happy with the slightly lower power and don't require the ability to drive low impedance loads or impedance dips, then v1.6 will work fine for you.

 

[ItsAllInMyHead]

And the great news is that the wiring changes shown in the build guides between batches 1 and 2 for V1.6 and V1.8 have absolutely nothing to do with the ability to drive lower impedance loads or the output power availability. 🙂

@smype - you are correct. Below is the list of all differences between V1.6 and V1.8:

1. Rear switch is a 3 position DPDT instead of 2 position, necessitating a change in wiring
2. Rear panel is printed with a connection diagram
3. Chassis rails are improved using weld nuts and secured by bolts
4. Blade terminals are included for the front power switch
5. Longer wire
6. LED resistors have been changed from 10k to 33.2k to reduce LED brightness

Edited to add - and you still do have all the same options. Forgot to include link below.

ACA V1.6 Operating Modes

 

[smype]

Thanks guys for your responses.

 

[CWelsh52]

I have a basic question. What are the advantages of the 1.8 wiring over the 1.6 wiring other than the mono block options? If I don't care about those additional choices, can I just use the 1.6 wiring and get all the sonic benefits of the ACA amp? Thanks.

Just curious, is there a reason you do not want to use the 1.8 wiring?

 

[smype]

I have a friend who purchased 2 unfinished 1.6 kits. He has a 3-way switch that he could uses but wanted to know if the 1.6 wiring would work for him. I think he is going to use the 1.8 wiring.

 

[ItsAllInMyHead]

^ If he really wants... he can get 1.8 back panels separately to match. They're truly not necessary, particularly if they remember the switch positions and/or mark them some other way.

 

[Watts-Up]

Hi all. Looking at maybe putting two ACA kits into one case. I have a power amp by Adcom, GFA-8520 that has one dead channel. The heat sink area is quite large (350 x 200 x 50 mm). The amp is A/B and IMO, ran hot when it was working. Just wondering if this is a wise idea if I were to gut the interior and put these little guys in it. The case is in excellent shape, and quite beautiful to my eyes. Love to not see it in the dumps.

 

[Zen Mod]

that one also looks as from Papa's shop

pity to gut it

sell it as is, if nothing else, someone will be happy to repair and use it

then buy new case

 

[Mooly]

I agree with ZM, it would be a real pity to cannibalise that. Those boards would clean and wash and come up like new... yes it needs repair but that is half the fun 🙂

 

[6L6]

Yes, the chassis of your Adcom would be more than sufficient for a pair of ACA, much like a hangar for a 747 would be able to park a couple of cars.

I agree with the rest, repair the Adcom, it’s worth the trouble.