krell ksa5 klone

[jack]

On 3/2/2017 at 5:24 PM, Pars said:

Linear Systems makes one now. Trendsetter has them, and they also have the LSK389.


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Trendsetter want to charge me like hell for shipping. Found some on ebay. hope they are not fake ;-)

I am looking for a transformer, I read in this forum, that 2x27V 50VA should be used. my question is 27 V with or without load.

Is my understanding correct that the board will draw less than 400mA (0.4 A x 21 V= 8.4 VA)so should not make a difference for a 50VA transformer?

[luvdunhill]

Transformer voltages are always stated under load.

[Pars]

http://www.antekinc.com/as-0528-50va-28v-transformer/

Earlier in the thread (had you read it) KG said you need ~35V raw dc, so 27 * 1.414 will get you ~38V minus the diode drops for the rectifier(s). I haven't looked at the schematic, but assume a bridge, so -1.4V, so you are at about 32.6V raw DC. Might work. 27-28V transformer will get you closer. 28V Antek above would put you at (28 * 1.414) - 1.4 = 38.2V. It appears some have built this with a 25V transformer.

Edited March 9, 2017 by Pars

[jack]

I will be using the power supply as in the picture bellow (the PCB arrived today )



So happy


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[jack]

http://www.antekinc.com/as-0528-50va-28v-transformer/ Earlier in the thread (had you read it) KG said you need ~35V raw dc, so 27 * 1.414 will get you ~38V minus the diode drops for the rectifier(s). I haven't looked at the schematic, but assume a bridge, so -1.4V, so you are at about 32.6V raw DC. Might work. 27-28V transformer will get you closer. 28V Antek above would put you at (28 * 1.414) - 1.4 = 38.2V. It appears some have built this with a 25V transformer.

 

Thank you for explaining. I have read this thread several times, nevertheless it happens to me to ask silly questions as I know less than a little about electronics ;-)

Am I correct ?The best would be to have a transformer maid with a voltage between 27 and 28 V so that DC right after the rectifier (bridge) is 35 V. I think this can be done since my toroids are custom made.

I have also read in this thread that some pushed PSU voltage higher and changed opamps. Could someone tell me if this is worth it? What are the benefits? I can still return my ops. So why not benefit from a good advise.

 

 

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[cwucnspt]

Does anybody has the PCBs?  Or should I get those at Ebay?

[jack]

Could someone please confirm that a dual 28V 50W toroidal transformer with the alternate psu version  (to-3) will be ok to use the amp a a line preamp?

[Thai Tao]

Hi Kelvin! After some time, i have discovered that my amp have some serious problem: when i turn the volume up, after half volume the noise is increased to very audible level, so i measure the output with nothing connected, maximum volume and got this:

Some serious 50hz harmonic at -55dbv lvl !

At min volume, it's fine:

I thought it could be the power supply problem but i measure the PS and it's fine:

So the problem must come from amp board, do you think what can cause this? Thanks!

[kevin gilmore]

very noisy input fets or fakes, and volume pot of too high impedance. original was 10k pot.

[spritzer]

yup, pretty much the only logical cause

[Thai Tao]

I don't think the input jfet (2sk170bl) is fake as i buy it from a very high reputation local shop, the volume is 50k type, i will try it with 10k. Thanks for your suggestion. 

[RudeWolf]

Shouldn't be bad input devices, if you're getting noise variation with potentiometer. Even more - 50Hz should be a grounding problem, check the grounding scheme of your amp.

[kevin gilmore]

I have seen ground loops do the 50(60) and 100(120) bumps, but never that amount of wideband noise.

a missing ground wire between the pot and board ground could do it.

[museguy]

Dear Dr. Gilmore,

  Thank you !!  I am a total nOOb with electronics, trying to teach myself.  Have purchased the ebay amp and power supply.

Just wanted to thank you for sharing your knowledge !

All the best,

-Mark 

Hi All so far I can only find one of the two power supplies (ZeroZone): 

Is the other power supply also available? Can someone help me with specifying an Antek transformer ? Thank you !  

[Pars]

I haven't built one of these and am not familiar with that particular PSU, but don't you just need a single PSU (dual, which that one appears to be)? Not sure what the other one you refer to is?
As for transformer, see the rest of the thread. A dual secondary in the range of 25-27Vac seems to be what is recommended. I posted an Antec AS-0528 above, but an AS-0525 50VA 2x25V might work as well.
I'm not sure, but I might be inclined to use a GRLV PSU set for +/-22Vdc for this, with a 2x18Vac transformer. Of course that moves away from a strict clone however.
Someone who has built one of these might comment...


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[kevin gilmore]

I did both ksa5 power supplies. The original is triple pass transistor/zener regulated

[cwucnspt]

I am having a bit of problem with the PSU (re-testing and substituting components after an accidental short between +22 and gnd).  Does the components in it get warmish after 15 min without load.  On PSU, I noticed that PNP and NPN and lm4040 diodes can get warm or slightly hot (how high?).  Second, the short happened  when amp was connected.  Do you think I damaged any component on amp.  Thanks.

[dabore84]

On 2017-3-13 at 1:30 PM, cwucnspt said:

Does anybody has the PCBs?  Or should I get those at Ebay?

I'm also interested where to get the pcb. Only managed to find them on eBay, mostly 'zero zone' brand. Anyone have suggestion? 

[cwucnspt]

I got the ones at Ebay.  They are OK.  3-4 weeks to arrive thru USPO.

On 4/24/2017 at 5:20 PM, kevin gilmore said:

I did both ksa5 power supplies. The original is triple pass transistor/zener regulated

 

I am having a bit of problem with the MJ15025/15024 version of PSU (re-testing and substituting components after an accidental short between +22 and gnd).  Does the components without heatsink get warmish after 15 min without load.  On PSU, I noticed that PNP and NPN and lm4040 diodes can get warm/slightly hot (how high?).  Second, the short happened  when amp was connected.  Do you think I damaged any component on amp.  Thanks.

[mypasswordis]

Just finished building up the Krell power supply at 300V rails. Took me a really long time to figure out what was wrong, I was swapping parts and messing with traces like crazy, and of course it was the one thing I didn't expect. The pre-reg caps aren't connected to ground. I did already drill out a cap hole that wasn't supposed to be connected to ground. Probably should have read this thread first...

[Pars]

These Krell Klones run at 300V?


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[mypasswordis]

It will power the modded SRM212 but I just took a look at the KSA5 schematic and now know exactly what Dynahi HV v3 will be: diamond differential. v2 still needs some tweaking/figuring stuff out in LTspice.

[jack]

I am done with the boards. now wornikng on the case, and some setup. Could you please help me with the bias? what are the optimal values, and what are the measeure points?

Many thanks

[MLA]

It's in the thread.

 

 

[jack]

On 7/1/2017 at 4:26 PM, MLA said:

It's in the thread.

 

 

Thank you, i can see, 125mV cold 100 mV warm. In another post i read that the test points are between any of the 2 ohm resistor. is that correct?