krell ksa5 klone

[jack]

Good morning

Can I change the voltage of the version 2 PSU. from 22 to 21 or 20V? Could somone please tell me how this change could be made?

Kind regards

Jack

[Pars]

Why? 1 to 2 volts is a pretty minimal change.


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[jack]

my quiescent current is a bit too high, and the potentiomere are at minimum, therefore lowering the voltage might help.

[Pars]

It appears that the 750R / 511R voltage divider feeding the opamp is what sets the gain, but I didn’t find a formula for calculating the output voltage. One guy dropped his to 19V by paralleling a 2k resistor with the 511R.

https://www.diyaudio.com/forums/headphone-systems/109618-krell-ksa5-10.html#post5190186

 

 

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[alexcp]

FIf you are working with the "new" power supply, the one with opamps, then each opamp compares the reference 12V voltage (supplied by D1 or D2) with the portion of the output voltage from the R8/R7 or R9/R10 voltage divider. If the voltages differ, the opamp drives the pass transistor so that the voltages become equal.

With the 511/750 ohm divider, V(out) = 12V * (511+750) / 750 = approx. 21.2V.

If you want a lower output voltage, you can reduce the value of the top resistor in each divider (R8 and R9). For example, 499ohm instead of 511ohm would give you 12V * (499+750) / 750 = approx. 20V, 475ohm would give you 19.6V, and so on. Paralleling 2kohm with the 511ohm gives you 1/(1/511+1/2000) = 407ohm and approx 18.5V.

However, if you bias is too high, a better thing to do may be to carefully tweak resistors around V(be) multiplier (Q14) in the amp itself. Reducing R19 from 825ohm and/or increasing R18 from 221ohm would decrease bias. Be careful though - should R19 be missing, your bias current would be very high.

[jack]

Thank you, this helped me a lot!

on DIY forum, that Pars mentioned, Algar added a CRC filer:

"Then on the supply added an input CRC filter (4R resistor and second 4700uF cap) to reduced a little the regulator input voltage from 32V to 30V, since I increased the bias current.
That will reduces the pass regulator power dissipation.

That also reduce the amp already low noise floor. Regulator input ripple went from 300mVac to 100mVac..."

How was this connected? is it between the leads of the existing 4700 uF caps?

[alexcp]

A CRC filter is something along these lines:

In that diyAudio post, both capacitors were 4700uF and the resistor was 4ohm.

Have a look e.g. here: http://www.learnabout-electronics.org/PSU/psu12.php for the theory behind it.

[jack]

Thank you Alexcp and Pars. This should solve all my troubles with this great amp, that I'm using as a stage pre-amp. Have a great x-mas and a happy new year

[jack]

with CRC filer i still get a temperarure of 50c on the PSU radiator...

[alexcp]

50C is normal for power semiconductors, you don’t need to make it cooler. 

[Rael]

Does any of you kind folks have an up to date BOM for Kevin's boards and PSU.

Apologies if I have missed it....

[jack]

53 minutes ago, Rael said:

Does any of you kind folks have an up to date BOM for Kevin's boards and PSU.

Apologies if I have missed it....

I do have both. PM me if still interested.

[seroxatmad]

Hi

I have sent you a  PM also as I need them also.

Finally going to start my boards.

Thanks

John

 

[Pars]

Maybe just post them to the thread...
Still not sure what all the interest is in this, but I confess to not having built one. The SS Dynalo is a better amp from what I understand. Or the CFP2...


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[jack]

Here is the my BOM

fell free to use it

BOM_KSA5 (version 1).xlsb.xlsx

[jose]

I guess this is because the pcb can be easily obtained on eBay ...

 

[belt250]

Hi everyone, I'm a newbie here 

Thank you all for this great project, I just finish my first KSA5 amp, The sound is absolutely crazy good. 

I use a small chassis for my ksa5 mainboard. 10k pot.

To reduce power chassis depth, I raise the power board and let the transformer under the power board.

 

 

[ang728]

 

2 hours ago, belt250 said:

Hi everyone, I'm a newbie here 

Thank you all for this great project, I just finish my first KSA5 amp, The sound is absolutely crazy good. 

I use a small case for my ksa5 mainboard. 10k pot.

To reduce power case depth, I raise the power board and let the transformer under the power board.

 

 

nice.

恭喜台灣 DIYer 再+1名

[belt250]

3 hours ago, ang728 said:

 

nice.

恭喜台灣 DIYer 再+1名

Thank u, ang728. I have seen your other DIY build, then I found these chassis.

Try to build my 2nd KSA5 amp.

[kudrik]

14 hours ago, belt250 said:

I use a small chassis for my ksa5 mainboard. 

 

 

 

 

Case from Aliexpress ? Please link.

[belt250]

6 hours ago, kudrik said:

Case from Aliexpress ? Please link.

I bought the chassis here Model ID #2806
I also found #2806 in AliExpress here.

My chassis for power here Model ID#BZ1409P

Knob and foot.

[Southman]

Dear all,

I did my first KSA5 Clone and tested everything are normal. The sound is good but i heard some Hummmmm sound when i turn the volume to highly and the sound is not clear compare with my  Audioquest dragonfly and Denon DA-300. I don't know the reason, maybe i have not mounted it in chassis.

I can't order 5N5564 because this transistor was stop manufacturer, so i use two 2sk366-BL to instead it (2 N channel).

And PSU are sigma22 and use 100W 27-0-27 VAC transformer(E type) to provide +/- 22VDC. (i want to change to 100W R type transformer).

The below shown the board photos and some waveform about the it.    

More details will updated future. 

 

 

 

[Pars]

A 27V transformer is awfully high for generating 22V DC (raw dc after the rectifiers would be ~36.7V). That has to run hot!

 

I don’t know that this would be causing your problem however. I’m also not sure how good of substitute your input FETs are. The BOM I have calls for 2SK389/LSK389 or 2x2SK170BL.

 

Are the other semis per the BOM (MPSA06/56, MJF15030/31? Are they genuine?

 

 

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[jose]

Yes, Input FETs LSK389* (or 2x2SK170BL)

 

*B grade I think 

Edited August 9, 2019 by jose

[Southman]

Dear Pars,

Thank you for your quick reply, and constructive comments. As i have not look all of the post before i do, so i don't know the 2SK389/LSK389 or 2x2SK170BL can instead of it.

The 2SK389/LSK389 or 2x2SK170BL are very difficult to order from RS, Digikey etc, i can find some of its in Tabao, but i can't sure that they are genuine.

I know the 2sk366-BL gm is not same as 2N5546 or 389/170, but the value are nearly,  and i had done the 1% device matching of it, so maybe it is OK but not sure.

The MPSA06/56, MJF15030/31 are genuine and the MPSA06/56 had done the 1% device matching. so i have not worries .

The machine run is not hot when i use sigma22 PSU, just can said warm.  I don't know why, it is out of my expectation (i think it run hot so).

I will try KG PSU with 22VAC after i finish sigma22 and KSA5 chassis mounting.

 

Dear Jose,

Thx for your reminder.

_________________________________________________________________________________________________________________________

I will mount the sigma22 on chassis  the coming few day.

This is sony R type transformer(from Sony audio machine).27-0-27

 

This is customer make E type transformer. 28-0-28