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My Krell:        

Got it cased.  Pretty standard.  I apologize for the power switch--I couldn't resist.  

I completed the full modification (output stage and front end) on both channels and listened to the amp briefly. The headphones were Grado GS1000 and Sennheiser HD595, the 8ohm speaker were B&W 60

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I'm no expert, but I'd just use the suggested parts. You're thinking of using these instead of LSK389 or 2N5564? I know this is generally not advised, but I got the 2N5564 on eBay from seller Top Chips. I've recently fully powered up and tested the amp prior to casing things up and the amp plays music. So the parts are legit? I have no way of telling. My guess is the amp wouldn't work at all if the parts were fake.

On another note, you do have to watch out with eBay - I tried to skimp on paying $12 x4 for the OPA445 and bought them on eBay. When trying them out in the PSU no voltage or close to none. I ended up having to go to Mouser with my tail between my legs and bought 'em there. Boom success!

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Please give a link to a good seller for 2n5564-5566 on ebay. Input assemblies affect the constant voltage at the output, the less it is without an integrator, the more likely it is that transistors are not fake. I have a lot of original BF256C, so I asked about the possibility of using them.

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Do you mean that the voltage across the test points will constantly change? In my case I set the voltage to 125mV via pot after the amp has been warmed up. It drifts a little but doesn't stay exactly at 125mV. Or do you mean the dc offset with OPA445 removed?

This is who I bought 2n5564 from...

https://www.ebay.com/itm/1PCS-New-2N5564-CAN-6-Matched-N-Channel-JFET-Pairs/392370230460?hash=item5b5b1694bc:g:wDEAAOSwvFNdSPV7

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Not sure, they might work.

I took a look on diyaudio. Not much discussion or mention of the BF256C. I did find this:

alternative transistors, not as costly as the Toshibas SK170 and much easier to source could be the BF256C and the BF246A/247A. The former is a bit higher in noise (still sufficient for highlevel circuits), the latter features much higher Idss which allows for larger source resistor values and for higher bias currents, which could be advantageous in output buffers and buffers that need to drive capacitive loads -which is a very common case with filters.

https://www.diyaudio.com/forums/analog-line-level/169005-jfet-active-crossover-3.html#post2227453

EDIT: and from earlier in that thread from the same poster:

well regarding soundjudgements aren´t easy, because everybody has a different taste. To me all OP-Amp filters I built sounded artficial to a certain degree. I never doubted to listen to a reproduction of music. The first discrete JFET-filter changed that. Now there was music a lifelike quality which sounded authentic. Music instead of HiFi. I know that distortion-wise the simple Buffer is very good, but dosen´t reach a OP´s low values. But the...who cares about distortion figures, which -as we know for 30 years now- don´t correlate at all with the sonic impression? Noisewise even the BF256C settles around -100dB, the BF246A, 2SK373, 2SK170 beeing even better. So noise should be no big issue. Hum can be an issue in every circuit and typically it depends alot more on the circuits surroundings than on the circuit itself.

A different thread, but doesn't sound promising:

https://www.diyaudio.com/forums/pass-labs/145201-building-symmetrical-psu-b1-buffer-230.html#post2794067

I'd probably just go ahead and try them, observing pinout, but without the correct part or know equivalent, it might be hard to tell.

 

Edited by Pars
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  • 1 month later...

I recently finished my Krell KSA-5 Klone. I'm having something weird that I can't quite wrap my head around. When listening to music there is a lack of bass. It just seems to be sucked out. I swap the same HD800S headphones into another amp and voila bass is there on any given track. I don't hear any distortion or a buzz or anything that would be akin to a ground loop. Anyone ever heard of this kind of phenomenon with this amp?

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Definitely not the case with the one I built, so something is off. Could be many things though :) 

Aside from out of phase driven cancellation, I wonder if this is unique to your HD800 or does the same thing happen with lower ohm headphones?  

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I initially noticed issue when both channels were out of balance. I first looked at the hp jack because I noticed it wasn't isolated from chassis ground. I've since fixed that issue. Then the sound got better. Both channels balanced with same apparent level, but with the lack of bass and what seems like a really wide stereo image. Wider than expected. It could be a phase issue. Would a grounding issue show up as phase problems? What's interesting is that it's only in the bass region.

Connectivity looks correct. I've toned everything out with a DMM. So I don't think I have anything backwards. IN1 is my left channel and IN2 is my right channel. Same goes for outputs.

Other things to note: I did have signal ground connected to the chassis then through a ground loop breaker. I haven't been getting hum so I've removed the GLB. Same issue. Using the GLB, It made the chassis share the same ground as signal ground. Not sure I'd want this... maybe I do?

I also originally only had OUT1, OUT2, and one of the GND paths going to my HP jack. I've since added the the 2nd GND path. No dice. Sounds the same.

I did buy 2N5564 on eBay. I know I prolly shouldn't have. Could poorly spec'd or fake 2N5564 create a situation where the bass is so rolled off?

FInally, trying different headphones didn't make much of a difference. I mean they sound different, but don't have bass.

I'm going to try a full rewire on the outputs to see if that makes a difference, but may look at replacing the 2N5564 next.

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Ok... I think I figured it out. I used Belden cable for my hookup wiring and it looks like ground and left channel were touching because a dodgy stripping job. So chalk it up to faulty cabling. Phew!

Edited by Mullet
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  • 1 month later...

Привет всем, пожалуйста, скажите мне, какие пары выходного каскада лучше выбрать, если это возможно по схеме.

Hello everyone, please tell me which pairs of the output stage are better to choose, if possible according to the scheme.

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I matched the quad of Q23-Q26 by hFE, and separately matched the octet Q15-Q22. However, my main reason for matching was because I could. You cannot get perfect symmetry between NPN and PNP transistors no matter what. In my case, I could not match MJE15030 with MJE15031 from the batch I had, so I replaced them with D44H and D45H, respectively - these matched much better.

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  • 6 months later...

I built my KSA-5 clone back in 2013 (see my post dated August 9, 2013 in this thread on page 8) but was never quite satisfied with it. I made every effort to make it look good and perform well, and it was well within the original KSA-5's specs. Yet, although it worked well with my 32ohm Grado headphones, it could not compete, in my subjective opinion, with Musical Fidelity's X-CANv8. Connected to a pair of 8ohm speakers, the clone would become rather confused with anything but simplest music. Because of this, the amplifier fell into disuse and was gathering dust on my rack.

Until this weekend.

This weekend, I finally got around to make KSA-5 work for me. I kept the overall topology and the PCB, only changing some passive parts. The results are quite remarkable:

  • The original KSA-5 was rated for 5W into 8ohm with THD<0.5%. Before modification, my clone gave 5W into 8ohm with THD @1kHz of 0.18%, well within the specs. The revised clone delivers 5W into 8ohm with 0.0015% THD, an improvement of more than two orders of magnitude.
  • The original KSA-5 was advertised to deliver THD<0.03% into 100ohm load, although the brochure did not give the signal level for this performance. Assuming the same output voltage as for 5W into 8ohm, about 6.3Vrms @ 1kHz, my unmodified clone demonstrated THD of 0.02%, again within the specs. The revised clone drives a 100ohm load to the same level with 0.0017% THD, an improvement of more than an order of magnitude.
  • The modified channel sounds very well, clear and transparent. I still need to complete the second channel and do some real listening.

I will post the revised schematic with some explanations, as well as additional measurements, in this thread.

converted-2.gif

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Let me start with a few measurements of the unmodified KSA-5. They seem to confirm the listening experience described above.

With a 100 ohm load, KSA-5 never leaves Class A, and the performance is decent, with 0.02% THD and dominant 2nd and 3rd harmonics:

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