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Best way to reduce gain in this circuit?
Best way to reduce gain in this circuit?
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Old 28th October 2019, 09:07 PM   #1
kodabmx is offline kodabmx  Canada
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Best way to reduce gain in this circuit?
Default Best way to reduce gain in this circuit?

The input is capacitor coupled (not shown).

I'm thinking NFB, but I'm used to driving NFB into a cathode, and this circuit inverts... What about using the unused grid or the cathode of the same triode?

Any idea are appreciated. And yes, I know 2 cents for a 2 resistor divider is also a solution...
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Old 28th October 2019, 09:19 PM   #2
deafbykhorns is offline deafbykhorns  United States
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Take out a gain stage?
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Old 28th October 2019, 09:20 PM   #3
kodabmx is offline kodabmx  Canada
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Best way to reduce gain in this circuit?
There is only one, without it it would be a buffer... The gain is about 10 now. 5-8 would be better.
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Old 28th October 2019, 10:01 PM   #4
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Introduce negative feedback between the anode of the 6N6P pin 6 and the cathode of the 6N14P pin 8.Try 4k7 resistor in series with a 470n capacitor.
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Old 28th October 2019, 10:05 PM   #5
kodabmx is offline kodabmx  Canada
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Best way to reduce gain in this circuit?
Thank you, Jon. 470n == 0.047u I think? 0.1u good enough? Also, the cap and resistor values are dependant on each other? I couldn't use a 10k pot instead to "dial-a-gain" could I?
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Old 28th October 2019, 10:14 PM   #6
Tjj226 is offline Tjj226
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I wouldn't use NFB on a preamp. It just seems like an unnecessary complication when all you really need to do is tweak the circuit to accept an input tube with a lower amplification factor. 5687s for instance are cheap and have an amplification factor of 15 compared to 22 on the 6N14P.
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Old 28th October 2019, 10:20 PM   #7
kodabmx is offline kodabmx  Canada
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Best way to reduce gain in this circuit?
Different pinout though... And they weren't cheap the last time I bought them (which is why I switched to 6N6P)

I'd rather use a 2 resistor divider on the input that rewire the sockets.

Last edited by kodabmx; 28th October 2019 at 10:22 PM.
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Old 28th October 2019, 10:31 PM   #8
rayma is offline rayma  United States
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For this circuit the gain is mu/2, and the tubes tend to cancel their distortion.
Any change of topology (other than an input or output attenutator) would degrade
the operation of the circuit.
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Old 28th October 2019, 11:01 PM   #9
RajkoM is offline RajkoM  Bosnia and Herzegovina
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I second for input attenuator (L or T type)
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Old 28th October 2019, 11:04 PM   #10
Ketje is offline Ketje  Belgium
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Before you make a nice oscillator with Jon's proposal , try it this way.
Mona
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