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Old 30th November 2003, 08:26 PM   #1
Bricolo is offline Bricolo  France
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Default Reducing the gain with an inverting gainclone

I'm using Peter Daniel's IGC schematic, with the 10k input resistor and the 220k feedback resistor.

But when I use it with my CD player (Marantz CD62), I don't even turn the volume pot more than 5%. 10% is real loud. (I've got 92dB/w/m speakers)

Could I simply lower the gain by increasing the input resistance's value?

I think that could be a good think, since it would also result to a higher input impedance.
Is there no problem in doing it?
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Old 30th November 2003, 08:30 PM   #2
Pedja is offline Pedja  Serbia
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Bricolo, what's the volume control you are using?

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Old 30th November 2003, 08:38 PM   #3
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Is it log, linear and what value?
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Old 30th November 2003, 08:46 PM   #4
Bricolo is offline Bricolo  France
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It's a cheap Pihier stareo linear 50k pot.


Do you think a log would give me more sensitivity at low volumes?
In fact, I think it's true. But lowering the gain, and this way, rising the input impedance, looked nice to me.

But I can do both...
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Old 30th November 2003, 08:56 PM   #5
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I found that 50k log pot works much better than linear pot and gives better control over the usable range.

If you really insist on using linear pot in this application, the value should be higher (at least 100k) although I'm not sure it would give as good control range (as log pot).

I wouldn't lower the amp's gain, as supposedly, GC works better with higher gain.
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Old 30th November 2003, 09:06 PM   #6
Bricolo is offline Bricolo  France
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I'll change it.

I already wanted to do this, since the two channels aren't very well matched at low volume
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Old 30th November 2003, 09:53 PM   #7
Pedja is offline Pedja  Serbia
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Quote:
Originally posted by Bricolo
It's a cheap Pihier stareo linear 50k pot.
Then yes, a logarithmic pot will solve the problem. That 10% of the linear pot will appear as the center position of the logarithmic one. Bad channel tracking you mentioned is the feature of all Piher pots which is a pity since these pots sound pretty dynamical (though not as clean and open as, say, ALPS, but the difference in cost is obvious). You should be really lucky to get the Piher with good channel tracking (or you should try at least a couple of them).

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Old 30th November 2003, 09:59 PM   #8
Bricolo is offline Bricolo  France
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Quote:
Originally posted by Pedja

Then yes, a logarithmic pot will solve the problem. That 10% of the linear pot will appear as the center position of the logarithmic one. Bad channel tracking you mentioned is the feature of all Piher pots which is a pity since these pots sound pretty dynamical (though not as clean and open as, say, ALPS, but the difference in cost is obvious). You should be really lucky to get the Piher with good channel tracking (or you should try at least a couple of them).

Pedja
I've got a 100K log stereo Pihier with a good channel tracking.
But 100K could be too much for a gainclone.

I could also go the the local store with my dmm and ask to test a few 50K ones, the guy will certainly be ok
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Old 30th November 2003, 10:31 PM   #9
Pedja is offline Pedja  Serbia
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The 100k log will be fine considering the attenuating curve. However, the total gain with thus formed feedback will be likely too low - I liked better the sound of 50k pot with 220k/10k feedback network. The best for you - try both, especially because you already have one and you have a possibility to measure before you buy. Btw be careful (nothing special, a bit of care will be enough), Piher is fragile and might not be happy because of too many/long soldering and/or too hot soldering iron.

Pedja
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Old 1st December 2003, 09:05 AM   #10
Nuuk is offline Nuuk  United Kingdom
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...or build the stepped attenuator described on my Gainclone FAQ page which is designed for the IGC.

Cost is about 15-20 euros depending on what type of resiistors you use.
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