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Old 28th November 2005, 10:18 AM   #11
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Just for general info, I have a mono 3875 running on a 20VA 15-0-15 that I use for speaker testing. It easily drives any driver to reasonable listening levels.
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Old 28th November 2005, 11:31 AM   #12
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Hi Katapum,

12V secondary (AC) will give you about 16V rail (DC). Check the chip documentation (rail voltage vs power), I think 12VAC will give you at least 12W, and with your sensitive speaker this may be enough. You can improve a bit tho by using pre-amp.

But you can also get 24V secondary by connecting two 12V secondaries together. So, two 12V secondaries become one 24V secondary. Simply connect the 2 centermost cables of the 0-12V-0-12V to get 0-24V (Then you can connect the 2 transformers to get for example 24V-CT-24V). If you cannot locate the centermost cables, make sure you can locate each secondary of 0-12V (different secondaries have no interconnection so no voltage between them) and then simply try any connection between 2 secondaries and measure the output. If you get 24V, you don't have phase problem.
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Old 28th November 2005, 09:24 PM   #13
Katapum is offline Katapum  Europe
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Hi all,

I measured V+ and V- at 1000uF caps and I found:
+16,4V
-16,3V

+15,7V
-15,5V

PSU is ok.

I also measured 100K pot (connected) I found: 82K.

I don’t know what’s happen with my GC. I think it has less then 5W.


Katapum
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Old 29th November 2005, 04:27 AM   #14
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Have you got all three wires of the pot hooked up correctly?
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Old 29th November 2005, 07:48 AM   #15
Katapum is offline Katapum  Europe
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Hi,

Quote:
Have you got all three wires of the pot hooked up correctly?
Big question could you check it for me?


PS: It´s a linear 100k pot.

Katapum
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Old 29th November 2005, 09:12 AM   #16
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i could not but notice you used pieces of perf board for the chip amps.

I'd check if you did not switch input and feedback resistor.
If you did, max output voltage would not be 16 volts but 1/16th.
If your loudspeakers are really that sensitive you'd still have them produce sound with such extreme feedback.

At first i used 300VA toroids for the GC kits i got from BrianGT.
Then switched to 225VA, 160VA and 80VA per channel.
imo, can't say that using bigger toroids is worth it.
Tried the GCs on junk speakers first, then big 90 dB/W vifa's, then 86 dB/W ELS63s.
Plenty power on 25Vac, 22Vac and 18Vac.
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Old 29th November 2005, 01:36 PM   #17
Jay is offline Jay  Indonesia
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Hi katapum, I cannot see why there could be a problem with potensio. I don't remember the concept of this inverted topology, it's just that the circuit looks strange to me. But if there is something wrong with the circuit, jacco must have noticed that. So the possibility is you put wrong resistor at wrong position, like jacco would like you to check.
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Old 29th November 2005, 10:15 PM   #18
Katapum is offline Katapum  Europe
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Hi,

I checked the entire amplifier and I think everything’s ok except the ground speakers wire. I have connected speakers ground to signal ground. So I fixed it.

Next I made two tests.

First test system:
Cdplayer
Dac (diy)
Gainclone
Speakers

It sounds very low (no power), big hum, bzzzz, ….., many noise, …...

Second test system:
Cdplayer
Dac (diy)
TVC (transformer volume control, gain=+6db)
Gainclone
Speakers

It sounds very good, a lot of power, almost no noise.

So I think gainclone has a ground problem. What do you think?

How can I fix it? (I´m a newbie).

Katapum
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Old 29th November 2005, 11:22 PM   #19
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Might be an impedance mismatch between your DAC and gainclone, what design is it, ( the DAC)?
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Old 30th November 2005, 07:23 AM   #20
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Hi,

dac

Katapum
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