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Old 4th September 2008, 10:45 AM   #1
rabbitz is offline rabbitz  Australia
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Question NAD 106 pre gain changes

I've picked up a nice old NAD 106 pre and would like to drop the gain from around 16dB to 6dB or less.... unity would even be better but I don't know if it's possible?

I've attached the schematic of the pre amp section and think the gain is set via R314 and R322.... but I'm probably wrong.

I thought I would ask before I play.

TIA
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Old 4th September 2008, 10:53 AM   #2
h_a is offline h_a  Europe
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Depends on the stability of the amp; stability is reduced by increasing feedback. However the load is not really reactive (power amp), so it might be possible.

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Old 4th September 2008, 11:22 AM   #3
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lowering the value of R314 to about 3k (actually 2.7k would bring it down to unity gain. R314 and R322 are part of your feedback divider, the other part is the tone control circuit (with tone defeat off) and R326 and R328 (when the tone defeat is on).
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Old 4th June 2009, 11:58 AM   #4
joe is offline joe  Germany
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Default Success?

Hi Rabbitz,
have you been successful by reducing R314? Any stability problems? I am trying to do the same.

Thx
Joe
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Old 4th June 2009, 01:02 PM   #5
rabbitz is offline rabbitz  Australia
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Hey Joe..... hang on, that's got a nice ring to it. Maybe someone should use it in a song.

I tried different values of R314 down to 8R2 and with each step it lost sonics. I also tried a dividing network before the pot and it lost dynamics.

I did consider changing the circuit to an op amp buffer or a B1 buffer but more trouble than what is was worth.

In the end the clue came from Goldpoint to pad down the power amp.
http://www.goldpt.com/bal_amps.html

My power amp has an input impedance of 47K so used a 22K / 22K dividing network between the power amp input pin and input cap. Worked a treat and in addition I reduced the gain in the power amp by around 3.4dB which was the maximum recommended so gave me 9.4dB total.

I've chased high gain problems for years and even used Rothwell attenuators as well as dividing networks at the power amp RCA but still had dynamic losses as well as bass issues. For some reason doing it at the start of the power amp circuit on the PCB worked.

I now have a C162 which has a variable pre output with a 1K pot which gives up to 12dB reduction but that caused loss in dynamics and bass. So I only use the fixed output with the changes to the power amp as described above. Now the pot works between 11 to 1 for my normal listening levels and have finally fine adjustment.

I hate high gain in pre amps.
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