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Old 10th October 2004, 01:19 AM   #1
SRMcGee is offline SRMcGee  United States
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Default Gain Adjustment Advice Requested for Brian's PCBs

Folks:

Now that I have reinstalled the resistors in the PCBs supplied by BrianGT, I find that there is an abundance of gain -- far too much, in fact. Before I start tearing out the R3 (680 ohm) resistors and replacing them with something else to lower the gain, can anyone suggest a good starting point? How much gain do I need when using 88db-efficient speakers, the AVEL 330V 25/25 transformer, a 20k impedence attenuator and a standard CD player as a source, all located in a moderately-sized (22' x 15' x 8') room? Right now, the volume is LOUD when the attenuator is at the lowest settings -- can anyone suggest a good starting value for the replacement R3s?

Also, is there a better way to reduce the gain, such as with a T-pad or L-pad?

Thanks to all for your advice!

Regards,
Scott
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Old 10th October 2004, 01:59 AM   #2
BrianGT is offline BrianGT  United States
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Default Re: Gain Adjustment Advice Requested for Brian's PCBs

Quote:
Originally posted by SRMcGee
Folks:

Now that I have reinstalled the resistors in the PCBs supplied by BrianGT, I find that there is an abundance of gain -- far too much, in fact. Before I start tearing out the R3 (680 ohm) resistors and replacing them with something else to lower the gain, can anyone suggest a good starting point? How much gain do I need when using 88db-efficient speakers, the AVEL 330V 25/25 transformer, a 20k impedence attenuator and a standard CD player as a source, all located in a moderately-sized (22' x 15' x 8') room? Right now, the volume is LOUD when the attenuator is at the lowest settings -- can anyone suggest a good starting value for the replacement R3s?

Also, is there a better way to reduce the gain, such as with a T-pad or L-pad?

Thanks to all for your advice!

Regards,
Scott
The gain is specified by 1+Rf/R3. You can choose a gain, and calculate the required R3 resistor.

As for a recommended starting value, you could try 1k to see how it works out for you.

I would also make sure your attenuator is setup properly. Is it a audio taper?

--
Brian
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Old 10th October 2004, 03:49 AM   #3
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I agree with Brian. - check your attenuator.

My setup is almost identical to yours, except my speakers are MORE sensitive, and I don't have this problem.

Steve
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Old 10th October 2004, 12:25 PM   #4
SRMcGee is offline SRMcGee  United States
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I'm using a DACT CT-2 20k attenuator. I'll double-check the wiring, but I'm pretty sure I got it right. Thanks for the responses!

Regards,
Scott
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Old 10th October 2004, 05:50 PM   #5
KT is offline KT  United States
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Is there concern that lowering the gain may result in lower sound reproduction quality? I ask because I recall a thread that suggested the optimal gain for achieving the best sound quality was around 33 or so.

If I remember properly, this was around the gain setting 47 Labs used in the original Gaincard, and I think Peter Daniel experimented with these values and found this value to sound best. I could be remebering incorrectly, but this is the impression I came away with.

If anyone could elaborate on this, it would be most instructive.

Best,
KT
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