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donovas 1st September 2020 08:31 PM

hi ive built this circuit following the layout that was posted by a member and the thing works, and offset is almost zero when the input is shorted. however when its not, the offset is 3.8v both at the output and the input. what could be the cause of this? oscillation?

it seems to play fine, and the sound is marvelously clear. however im missing a lot of drive i am used to and thinking its related to the misbehavior that is the offset.

i should add i did not use bc560C but instead used B... whereas bc550 is C

keantoken 3rd September 2020 12:14 AM

It sounds like your DC trimmer may be open or has a bad connection.

donovas 3rd September 2020 08:49 AM

Thank you, Keantoken. Yes, I fixed it by omitting the dc trimmer R9 altogether. I neglected to read the whole thread and chose a 5k pot based on the schematic alone.

As for the sound- this is by far the most delicate mid and high freq ive ever heard from a buffer. It seems to add that special something to the sound which makes yoh want to listen more and more, while being so much more transparent than most of my builds in the past that im hearing things ive never heard before.

That being said, id like to try the push pull 8 transistor version you mentioned earlier. I believe it will help with the bass because the current transfer is bipolar. I can always tell the leaning of the bass with single ended circuits and the k buffer is sadly not an exception.

If you could tell me how to go about doing the push pull version id muxh appreciate it.

Do i just mirror the circuit and tie the input and output?

keantoken 3rd September 2020 10:58 AM

Glad you like it!

One half probably wouldn't perform as well and one would always dominate over the other. In which case you would get better performance by just omitting the worse half. This is why I didn't go that route. The Kuartlotron is not like an EF stage where both halves need each other in order to approach linearity. You would not get a symmetrical output behavior, but rather something in between a good performing Kuartlotron and a worse performing one.

One thing you could try is to use the BC337-40/327-40. These are slower but more robust transistors. I decided the BC550C/560C were best overall, but the others are also interesting.

donovas 6th November 2020 06:13 AM

If i change the 10k ohm input to gnd to 100k ohm, will it affect the performance much, and what other values should be changed?

Also instead of 22pf of lpf, id like to use the 100pf wima caps i have. Once again what other values should be changed?

keantoken 6th November 2020 07:36 PM

Those will both be fine. 100k input resistance will be more sensitive to the input offset trim, but it is a common input resistance chosen for the Kuartlotron.

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