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krell ksa5 klone


kevin gilmore
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Hi AlSp

I built KG's device as a pre. There is not much information in this thread about how this amp. reproduces sound.
IMHO there is no need to use a thicker layer of copper, bearing in mind that you will be using a maximum of 30 Watts.

 

I believe we could use better capacitors and resistors.

 

Cheers

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2 Oz boards tend to be a little more tolerant if you need to replace components because the traces will take a bit more heat. Thick 3 Oz traces may actually require more heat than you usually need to get good joints and make the boards seem difficult to solder, so if you don't need the high current I wouldn't bother with that (they also tend to be much more expensive).

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  • 2 months later...

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

 

 

Sent from my iPhone using Tapatalk

 

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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.

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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?

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  • 2 weeks later...
  • 6 months later...

Hi everyone, I'm a newbie here :D

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.

cch0gqI.jpg

ZTgXHoK.jpg

hReqRZ8.jpg

fVaP1FG.jpg

 

 

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2 hours ago, belt250 said:

Hi everyone, I'm a newbie here :D

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.

cch0gqI.jpg

ZTgXHoK.jpg

hReqRZ8.jpg

fVaP1FG.jpg

 

 

nice.

恭喜台灣 DIYer 再+1名

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  • 3 weeks later...

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. 

 

07689009e62100161841cd7b5e8c40d67533db371941476272e1c9e416a1a5d017acde34a4a46a15
 

 

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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?

 

 

Sent from my iPhone using Tapatalk

 

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