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!