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Amp Camp Amp Kit V1.6
Amp Camp Amp Kit V1.6
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Old 16th August 2018, 07:21 PM   #111
fred0 is offline fred0  Portugal
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Default Another EU nuts glad

Hello everyone.



Just to thank all involved in getting my 1.6 kit here.
Arrived today, diyaudio store perfect follow up and now i can finally try to make my dream come true, build my 1st class A power amp.


You ROCK!
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Old 17th August 2018, 04:49 AM   #112
rossinsd is offline rossinsd  United States
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I've taken the amp apart and I am once again going over each and every resistor. I know for a fact that all the transistors and capacitors are installed correctly and have good solder joints. The other obvious connections such as the input, LED, output and power are all connected correctly. For anyone interested in the characteristics of the amp before I disassembled it, here is an FRA plot of gain and phase shift.
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Old 17th August 2018, 08:39 AM   #113
eddyvb is offline eddyvb  Belgium
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Phase shift should be 180 deg between in and out.
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Old 17th August 2018, 05:00 PM   #114
rossinsd is offline rossinsd  United States
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OK, I could shift the input or output polarity and make that happen but why the low gain and the poor frequency response curve? That is what I wonder. Last night I took it all out of the chassis and went over the color code on each and every resistor 2x. I also looked at the solder joints under a magnifier. Caps and transistors are in the proper direction. Bias current is 1.45 A / channel at 12 VDC (I am using the higher voltage Meanwell SMPS). My load is a 100W capable 8 ohm "non-inductive" power resistor. It does measure as being a ~20 microH inductor but it is a pretty pure load.

It seems to me that I've assembled and biased this correctly. The only conclusion I can draw is that while some may like the sound of a Class A due to the harmonics, the ACA V1.6 is a pretty low gain amp with some phase shift and frequency response limitations at very high frequencies. Most likely will those limitations will not change the sound for most people and maybe I should put the instruments away.
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Old 17th August 2018, 05:04 PM   #115
jaaptina is offline jaaptina
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Has the August 14th batch of the ACA 1.6 been shipped on schedule?
I haven't received a shipping notification yet...
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Old 17th August 2018, 05:04 PM   #116
poseidonsvoice is offline poseidonsvoice  United States
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Amp Camp Amp Kit V1.6
Rossinsd,

Did you read post #106?: Amp Camp Amp Kit V1.6

Is it low gain? Yes, +10dB. But not negative gain. That you will have to explain. Are the 100 ohm, 1K, 10K resistors measured with a DVM and in the right places? I almost goofed on my build actually.

Best,
Anand.
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Last edited by poseidonsvoice; 17th August 2018 at 05:09 PM.
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Old 17th August 2018, 05:26 PM   #117
rossinsd is offline rossinsd  United States
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Thanks for the reply. Yes, I read the post but I fail to appreciate how a non-polar device (the power resistor) polarity should matter. I also understand that the red output binding post is actually at ground potential because of the amp design. I have checked the component placement so many times now that I am 100% convinced that no br-bl-bl-bl has been put where a br-bl-bl-br should be.

The amp does play. If I use my phone as a source and connect to some NHT speakers it is somewhat louder than the phone can play. It can obviously provide more current into a speaker than the crappy amp in the headphone circuit of the phone. I started this whole FRA testing stuff because it seemed like this was a pretty weak 6-8 watts with the NHT speakers.

Negative gain is how the data is presented in the FRA plot I showed in the message attachment. That is the voltage output is lower than the input. However the output impedance is much lower and so the output current can be higher. The - 10 dB is based on voltage, not on power.

Thanks for the response and suggestions.
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Old 17th August 2018, 05:45 PM   #118
poseidonsvoice is offline poseidonsvoice  United States
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Amp Camp Amp Kit V1.6
Rossinsd,

Personally I think your amp probably works fine. I do believe that it has to do with your measurement setup as was shown on post 106. I donít think it has anything to with the 8 ohm power resistor you are using, although I generally donít place a load on most of my solid state builds to just test gain. The polarity reversal has to do with the configuration of the gain stage which is a common source design which intrinsically reverses polarity, period. Math is math and 1V P-P input should be 3V P-P output on this amplifier.

That being said, if you are satisfied that the amp is working, enjoy the music

Kind regards,
Anand.
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Old 17th August 2018, 06:27 PM   #119
eddyvb is offline eddyvb  Belgium
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As stated above, you are sure that you don’t short circuit the output as explaned in #106?
If you connect channel A probe ground clip to ground of signal generator, and connect the generator to input and ground of aca, and channel B ground probe clip to the hot output (black connector), then your ls output is shorted to ground. Use only the groundclip of channel A to be sure.
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Old 18th August 2018, 03:51 AM   #120
6L6 is offline 6L6  United States
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Amp Camp Amp Kit V1.6
rossinsd - Please post some well-lit, in-focus photos of your amp. From what you are describing, you've got something wired wrong. Let some other eyes look at it.
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