Jump to content
kevin gilmore

krell ksa5 klone

Recommended Posts

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

Share this post


Link to post
Share on other sites

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).

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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

 

  • Like 1

Share this post


Link to post
Share on other sites

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.

  • Like 1

Share this post


Link to post
Share on other sites

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?

Share this post


Link to post
Share on other sites

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 :)

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites

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...


Sent from my iPhone using Tapatalk

Share this post


Link to post
Share on other sites

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

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×