• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Kondo KSL-M77 phone preamp clone project

And what about the sound quality? What advantages or disadvantages has a phono M77 clone compared to EAR834 clone?

I can't really say yet. The 834 has been my phono preamp for more than a year, and it does sound excellent. I've only listened to the M77 once. It sounds great, but it's to early to tell. I'll try to do some more comparisons the coming weeks. Also impossible to do proper blind tests at home, unfortunately.

The chassis I put the M77 in came with some really poor RCA-connectors. The cables are simply falling of because the diameter of the connectors are too small. Ordered new Neutrik connectors, so it will take a week before the M77 is up and running again.
 

hesener

Member
Paid Member
2005-03-11 11:09 am
Munich, Germany
Here is my biased and subjective opinion, after having my M77 burned in for two months now, and comparing it to some other phono preamps, it does sound very nice! And, it does benefit from better components in the phono section in particular, I used Dale RN65 resistors and Silver Mica caps, as well as silver coupling caps, and the preamp does make the difference audible.

I much appreciate the midrange, very detailed and nice warmth but not too much. In comparison, many (semiconductor) preamps sound clearer but more cold and sterile. Highs are very good and clear. Bass is fine albeit a little weak, probably need to increase the coupling caps a little bit. No lack of fine details.

Many reviews of the original M77 have talked about the "added golden shine" or similar wording, I will admit that I really do not like this kind of review language. But my clone does something to the music, that makes me understand why people would say so. I don't want to say it "adds" to the music, it rather "presents" it in a slightly different way, which is probably due to the subtle but present 2nd and 3rd harmonics.

(Now I sound like a hifi reviewer :D)

As for music, I really enjoy it with chamber music, vocal jazz, and similar. Not sure it is the best choice for hardrock, it lacks a little punch - the presentation is never forward or edgy, always on the lean-back side of things.

(The rest of the chain was a Dynavector XX-2 with Lundahl step-ups, power amp is a modified Quad 405, and Quad ESL63 speakers.)
 
Nice review!

I didn't replace the resistors in mine (apart from the 33k). At least I think all the resistors in the phono section measured within 1%. I did replace the 1nF and 10nF capacitors with 1% polystyrene and also the coupling capacitors (found some impressive looking Soviet capacitors on eBay).

Still waiting for some parts (knobs, etc) before I put the preamp to service.
 
Just to follow myself up. I just realised that there is something called a balance potentiometer (MN-taper), and that I had bought one some time ago without realising what it was. With some experimentation and measurement with my multimeter I managed to wire it to the M77 pcb. It seems to function properly. I think. It attenuates 3.5 dB maximum, which should be enough to to adjust for a slight asymmetric listening position or some imbalance in the sound.
 

Attachments

  • alps.jpg
    alps.jpg
    493 KB · Views: 286
In old commercial gear I found that the stereo volume imbalance was usually worse at low volume so you just have to play loud :D. I often wondered if all it needed was a fixed value resistor on the one channel. I guess youll find out if you need to adjust the balance once its been set.

I'm more thinking about any imbalance in the source (real or perceived). The preamp channels are very equal (which might be luck?).
 
The imbalance I’ve noticed in the past with commercial amps is not the electronics because they are feedback designs which have gain match guaranteed by resistor tolerances, but rather in the stereo volume pots which often struggle to match an audio taper. The expensive one’s are usually tested and selected out at the factory, e.g. TDK pots are very well matched. I recently bought a stereo audio pot 500k Ohm from ebay, which looks like blue Alps but
I’m not holding my breath.
 

tomashans

Member
2020-04-26 2:04 pm
Changhe

Hi, also in the process of building this clone, and I came across this 10M resistor for the upper triode in the input stage. Simulation shows strong increase in the higher frequencies, that disappears when the resistor is reduced to ~200k.

Scratched my head but couldnt come up with an explanation..... Is this on purpose? Kondo magic?

:D


you mean if replace 10m resistor against 200k resistor is that better??

Thanks