Guys is there any good audio electricians in auckland that specialize in power amps, Im looking at replacing the transistors on my Krell KSA poweramp and as she is my baby I need someone that has expertise and that comes highly recommended,

Cheers

Deano

Manager & Product specialist at Rapallo AV & HI-FI

Just some general thoughts....
This would be a specialist exercise, possibly needing access to Krell service data - my guess is that there will be such considerations as selection of the devices, appropriate heatsink interfacing, biasing, for example.

So, first stop may be the Krell NZ Distributor (Audio Reference?), for their service technician contact.

Secondly, shipping around the country, if necess, may be worthwhile to get the right person.

Keep us posted.

PS. Why the need to replace transistors?

DarkLantern blog - darklanternforowen.wordpress.com

Hi Deano,

I had the thought that if it were me and it's going to be a keeper then why not investigate sending it back to the US. From memory the Krell service dept is excellent, its going to cost you, for freight as much as anything else I suspect, but at least then it can be given a good going over by Krell, everything as per their specifications and maybe even a new warranty.

what model ksa ?

Thanks guys appreciate your thoughts will speak to Terry at audio reference and go from there

Cheers

Manager & Product specialist at Rapallo AV & HI-FI

Feb 20, 2017 14:01:29 GMT 12 michaelw said:

what model ksa ?

Its the KSA50S

Manager & Product specialist at Rapallo AV & HI-FI

Feb 20, 2017 10:14:14 GMT 12 Owen Y said:

Just some general thoughts....
This would be a specialist exercise, possibly needing access to Krell service data - my guess is that there will be such considerations as selection of the devices, appropriate heatsink interfacing, biasing, for example.

So, first stop may be the Krell NZ Distributor (Audio Reference?), for their service technician contact.

Secondly, shipping around the country, if necess, may be worthwhile to get the right person.

Keep us posted.

PS. Why the need to replace transistors?

I had a general recap done when i lived in Malaysia by the Krell technician and the only parts not changed was the transistors, and i have noticed that the left side of the amp seems to be running a little hotter than the right and from experience this could be caused by the transistors, im no electrical electrician but generally people say on the forums that these can cause the issue if they are on their way out

Maybe im wrong but thought an experienced EE could take a look and go from there

Cheers

Manager & Product specialist at Rapallo AV & HI-FI

Modern SS devices should last a very long time, decades - transistors, diodes, regulators, op amps, etc.
Modern passive parts also - resistors.
Capacitors can tend to deteriorate, but again, modern ones have v long life - the killer for many parts is heat - keep the device cool, well ventilated.

If something is running hot, it's as likely to be passive parts associated with the heatsinked devices (transistors), not necessarily the device itself.

So yes, I'd go to an experienced tech - who has access to the Krell service data (as said, to check biasing etc.).

DarkLantern blog - darklanternforowen.wordpress.com

Feb 20, 2017 15:18:30 GMT 12 deano1974 said:

Feb 20, 2017 14:01:29 GMT 12 michaelw said:

what model ksa ?

Its the KSA50S

quite different sounding to the original ksa50 but still a nice amp with fancy multi-level biasing.

Feb 20, 2017 17:06:03 GMT 12 Owen Y said:

Modern SS devices should last a very long time, decades - transistors, diodes, regulators, op amps, etc.
Modern passive parts also - resistors.
Capacitors can tend to deteriorate, but again, modern ones have v long life - the killer for many parts is heat - keep the device cool, well ventilated.

If something is running hot, it's as likely to be passive parts associated with the heatsinked devices (transistors), not necessarily the device itself.

So yes, I'd go to an experienced tech - who has access to the Krell service data (as said, to check biasing etc.).

Its well ventilated and i have fans cooling it also, but definitely will get a tech to take a look

Thanks

Manager & Product specialist at Rapallo AV & HI-FI

Hi Deano
Have you a multimeter ? If so first thing to check is DC offset at the speaker terminals
Red probe to positive , Black Probe to negative There should be very close to 0.00- 0.10
for each channel but if its showing more than that, its DC offset referring to the KSA50
schematic R19 is a 20k trim and very easy to adjust. I presently do not have the KSA50S schematic
but ...

I would email Krell and ask them what DC offset range they expect, but generally close to
0.00 as possible is desirable. And if they can email a schematic well and good,
but otherwise what schematic differences the S model had.

I am happy to look at it & Do you have another amp in the meantime to use.I have a Quad 405 with Net Audio Mk3 boards.
Email me, we can chat, and sort it out

Cheers / Chris

Feb 21, 2017 21:27:42 GMT 12 attenuator said:

Hi Deano
Have you a multimeter ? If so first thing to check is DC offset at the speaker terminals
Red probe to positive , Black Probe to negative There should be very close to 0.00- 0.10
for each channel but if its showing more than that, its DC offset referring to the KSA50
schematic R19 is a 20k trim and very easy to adjust. I presently do not have the KSA50S schematic
but ...

I would email Krell and ask them what DC offset range they expect, but generally close to
0.00 as possible is desirable. And if they can email a schematic well and good,
but otherwise what schematic differences the S model had.

I am happy to look at it & Do you have another amp in the meantime to use.I have a Quad 405 with Net Audio Mk3 boards.
Email me, we can chat, and sort it out

Cheers / Chris

Chris thank you so much can you pm me your email address please

Manager & Product specialist at Rapallo AV & HI-FI

How did you go with this - I had a KSA 200 which proved almost impossible to recap?