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In Reply to: RE: Listening to my New Korneff Clone 45 SET Amps ................. posted by Tre' on March 27, 2021 at 07:41:54
I needed a high pass filter at 70Hz, so I added a .0022uF mylar cap to the input stage grids my of SE DC breadboard amp.
The circuit uses a 6SN7 with a 1Meg grid leak resistor.
THD @ 1W/1KHz increased by .3%
The caps are cheap and outer foil orientation was easy to determine, not sure if that is the reason why or not.
DT 667
Follow Ups:
And His response was the following:
"Yes, true but ...
Depending on the used amplifier you can or you shouldn't. If your main amp is capable to give good bass signals without noise (without the need for much power) then your present connections are optimal.
This way you keep the harmonic signature of the sound fed into the bass system the same for optimal sounding integration.
***************************************************************************************
If your main amp is not capable (makes too much noise or uses relative small output transformers then it can be beter to use a pre-amplifier or split the signal on the input of your main amplifer and connect from there to your bass amplifier. Make sure that the input impedance of both amps are not too low, your source might not be able to drive this load if it has a relative high output impedance (TVC's do not like this at all!).
As long as the output impedance is roughly 10 times lower then the combined input impedance then you're good to go. A pre-amplifier with output a buffer or 2 buffered outputs work best."
********************************************************************************
Upon further discussion with him and sending him the Schematics of My Amplifier, His recommendation was to feed the Full Signal to amp.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
I removed some carbon comp grid stoppers from the 6SN7 driver stage relay sockets on my breadboard.My ARTA test setup uses a 100K pot to trim voltage coming out of the sound card. It is housed in a plastic box with rca jacks for in/out.
For some reason, I am getting odd THD readings from on the left channel, so I think the grid might be going into oscillation as I turn the pot.
A test signal directly from the soundcard into the amp causes no problems.
I will have to investigate further and try to input cap mod again.
DT 667Edit : found an issue related to power supply returns.
Once corrected, ARTA measurements seemed to normalize.
I will need to re-test the input cap mod again.
Edits: 04/01/21 04/01/21 04/07/21
Yes, but did it sound any different?
Yes, but did it sound any different?No, I did not listen.
I might reinvestigate with some different film caps to see if the distortion issue happens again or not.
FWIW, I also noted an small increase in THD at 100Hz as well.
Not what I was hoping to see.
I would leave the TAL SE 45's unmodified.
Don't void the warranty.
DT 667
Edits: 03/29/21
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