I have a Nikko Beta II preamp (the D-TYPE) that has too much gain for modern sources.
Is there any way to decrease its gain by some 15dB?
Service manual attached.
Any input is appreciated!
Is there any way to decrease its gain by some 15dB?
Service manual attached.
Any input is appreciated!
Altering the feedback factor might have a couple of drawbacks. One is that you will reduce the phono stage volume as well because the phono amp feeds into this line stage. Secondly altering the gain by 15db is 'a lot' and you might alter the sonic character of the line stage. It would also certainly alter the gain/bandwidth of the amp. You would need to explore the result of that. Worst case could lead to instability.
I'm going to suggest something different. Just nick the PCB with a sharp knife to break the input traces and add a suitable resistor value. Change the 2.2 meg resistors to say 6.8k and have the series resistor at 30k. That would get you -15dB (which is a heck of a lot... are you certain you need that much?)
Doing it like this also lets you set the gain for each input individually which is nice as you can set all sources to sound subjectively the same.
I'm going to suggest something different. Just nick the PCB with a sharp knife to break the input traces and add a suitable resistor value. Change the 2.2 meg resistors to say 6.8k and have the series resistor at 30k. That would get you -15dB (which is a heck of a lot... are you certain you need that much?)
Doing it like this also lets you set the gain for each input individually which is nice as you can set all sources to sound subjectively the same.
What is important it's ratio. Current gain set to 6.8k / 1k = 6.8. To lower by 15 dB ratio need to be changed to 6.8 / 5.62 = 1.2.
So ether replace R527 by 1.2 k or R525 by 5.6 k. Of course, both resistors may be altered, just keep ratio.
Thanks everyone for your suggestions!
I have tried a ratio R527/ R525 = 5.6K / 3.3K to go somewhere close and i do feel that this somehow altered the sonic character of the line stage. This makes me wonder why the other versions of the preamp have R527/ R525 = 10K / 1.2K instead of the D-type that has R527/ R525 = 6.8K / 1K
In addition after the mod, i hear some pops from the speakers when traveling through the first and last steps of the volume pot, i don't know why.
Before any mod, i was using the preamp with the 20dB muting switch on , but this also altered the sonic character somehow. That's why i have started this thread.
15db sounds actually 'a lot' but my speakers have also a lot of sensitivity and this makes things worse.
I have tried a ratio R527/ R525 = 5.6K / 3.3K to go somewhere close and i do feel that this somehow altered the sonic character of the line stage. This makes me wonder why the other versions of the preamp have R527/ R525 = 10K / 1.2K instead of the D-type that has R527/ R525 = 6.8K / 1K
In addition after the mod, i hear some pops from the speakers when traveling through the first and last steps of the volume pot, i don't know why.
Before any mod, i was using the preamp with the 20dB muting switch on , but this also altered the sonic character somehow. That's why i have started this thread.
15db sounds actually 'a lot' but my speakers have also a lot of sensitivity and this makes things worse.