Krell KSA 50 PCB

[still4given]

OK, I'm confused. Did the original have one or two transformers?

Also, where do you find a 26-0-26vac 800VA transformer? That's like 30A isn't it?

Thanks, Terry

 

[K-amps]

IIRC the KSA-50 had one, the KSA-100 had two of the same....

Don't worry about the Amps, any 800VA 26-0-26 or 28-0-28 will do. Toroids can deliver multiples of their rated current for brief periods unlike BJT's ;-)

 

[still4given]

OK that answered how many, but where does one buy such a transformer. So far I have purchased my transformers off of ebay. Who sells transformers in the range we need for these amps?

Thanks, Terry

 

[apassgear]

"It is better to ask and bear the shame than not to ask and bear the pain"


While we are on subject,

I’m planning to dismantle my Aleph 4 (clone) and build the Baby Krell (50W) and use the box plus PSU as is.

The single PSU has around +- 40/42 V rails in a LC filter configuration supplied by two 750 VA EI trafos connected to a single diode bridge. Configuration of the intended amp is a stereo version (single supply).

Power requirement are very low (max 10W) for my actual speakers which are 6/8 Ohms. But want to retain the 50 W basic capability of this amp to use different speakers in the future.

Does this rail voltage and general configuration seems adequate for this project?

 

[jacco vermeulen]

Terry,

my thoughts:

for push-pull class A amplifiers 1.2 times the continuous dissipation was enough for a number of amplifier builders.

e.g. ,
the 100 watt class A French Audio Analyse ran on a 300VA toroid per channel.
(that one was elected for permanent exhibition at the museum of modern art in New York, btw)(around $5000 in the high 80s)
But it had huge powersupply capacitor capacity.

A nominal 50 watt amplifier can theoretically do a little over 400 watts in 1 Ohm, but in practice only for a very short period.
A toroid can easilly deliver twice the rating for brief moments, so a 200va model can push out 400 watts if necessary.
If you like to go overkill you better do the same for the output stage, otherwise no go.

More important, imo, is the voltage ripple of the PS.
If you go deep in class A you need much electrolytic capacity to keep the ripple low.
Or, as on the Pass front, CLC/CRC powersupplies.
With a choke powersupply much energy is stored in the coil and caps, little need for a huge transformer.

Given the choice, i'd go for:
1, a toroid per channel and a separate ps for the front end
2, one toroid for both channels and separate ps for the front end.
3, one toroid with separate windings for both channels, and for the front.
4 One really big monster with only the regular number of windings.

If you desire a S/N ratio of 90 dB at 1 watt, or higher, a large part will come from noise rejection by the amplifier circuit, the rest is coming from the ripple reduction of the capacitors in the powersupply.
Twice the power in class A, means twice the capacity number.
Minimum will be 1000uF in the ps for every watt of class A.
(= just a rule of thumb)

(thank you for the very kind words, Terry)

 

[Coulomb]

OK that answered how many, but where does one buy such a transformer. So far I have purchased my transformers off of ebay. Who sells transformers in the range we need for these amps?

Thanks, Terry

Well Terry to address your question about where to buy, there are several purveyors of good toroids.
Hammond
Plitron
Amveco
Victoria Magnetics
Avel Lindburgh

Just to name a few.

Here is where you can find them
www.partsexpress.com
www.digikey.com
www.partsconnextion.com
www.mouser.com
www.Newark.com
www.plitron.com
www.victoriamagnetics.com



Regards

Anthony

 

[still4given]

Thanks jacco,

I have maybe 18 each, 80V, 15000uf filter caps. I thinks I can cover the capacitance alright. I still need to know where I can purchase a toroid of the proper size. Does anyone have some suggestons where I can find one or two?

Thanks, Terry

 

[Coulomb]

Thanks jacco,

I have maybe 18 each, 80V, 15000uf filter caps. I thinks I can cover the capacitance alright. I still need to know where I can purchase a toroid of the proper size. Does anyone have some suggestons where I can find one or two?

Thanks, Terry

uummmm Terry did you read my note?

Regards

Anthony

 

[still4given]

Hi Anthony,

Seems we were typing at the same time.

Thanks, I'll check into those.

Blessings, Terry

 

[K-amps]

Hi Anthony,

Seems we were typing at the same time.

Thanks, I'll check into those.

Blessings, Terry

Terry,

For excellent prices, As Tony said, parts express has 800VA Avels for less than $70 each. For 1000VA you need to go to Avel directly.

 

[K-amps]

"It is better to ask and bear the shame than not to ask and bear the pain"


While we are on subject,

I’m planning to dismantle my Aleph 4 (clone) and build the Baby Krell (50W) and use the box plus PSU as is.

The single PSU has around +- 40/42 V rails in a LC filter configuration supplied by two 750 VA EI trafos connected to a single diode bridge. Configuration of the intended amp is a stereo version (single supply).

Power requirement are very low (max 10W) for my actual speakers which are 6/8 Ohms. But want to retain the 50 W basic capability of this amp to use different speakers in the future.

Does this rail voltage and general configuration seems adequate for this project?

Tony, Never built an Aleph so don't know much about them,

but the PSU specs you mention are just right for a baby Krell. You might get 60-70 watts from that rig.

K-

 

[VT67]

Whilst we're talking power supply section.
Any advantage in using exotic fast recovery diodes over a die cast rectifier bridge? I believe this was asked before but with a thread that's a mile long......

Regards

 

[K-amps]

In NP's opinion, it affected sound in the Pass amps.... if so, you would not have the original Krell sound, is that what you want?

 

[still4given]

Terry,

For excellent prices, As Tony said, parts express has 800VA Avels for less than $70 each. For 1000VA you need to go to Avel directly.

Hi K-amps,

At Parts-express, the lowest VAC they list at 800va is 40v+40v.
They have the 30x+30v at 500va. Would that work?

Thanks, Terry

 

[Upupa Epops]

For cca 50 W in class A, by efficiency cca 30 %, you will need teoreticaly transformer up to 200 VA. Do you mean, that by using 800 VA transformer, will be sound four times better ? Take eis on you head, guys. 😎

 

[K-amps]

If you plan to run 8 ohm loads, yes it will work. But I'd rather go here:

http://avellindberg.com/transformers/y23_range_specs.htm

and order Part number: Y236900 (25-0-25) or Y236901 (30-0-30); The 800VA parts are not too much more pricey than the smaller ones and have better regulation. Smaller will work, but Krell used a 800VA model from Avel or Hammond. The 900 will get you a 55 watt Amplifier and the 901 will get you an 80 watt amplifier. Even if you bias both at 50w pure class-A, the latter will get much hotter than the first.

If you have large heatsinks and want more power get the latter.

K-

PS: To order, call (860) 355 4711 and ask for sales, order via either Melanie or Patty.

Tip: Ask for extra foam insulators ;-)

 

[pinkmouse]

Terry, 500 VA will be fine.

 

[VT67]

In NP's opinion, it affected sound in the Pass amps.... if so, you would not have the original Krell sound, is that what you want?

It depends on how the sound was affected!
But O.K. I'll stick to a run of the mill standard bridge rectifier. My friend who owns a KSA100 loves that thing, and that also has a simple rectifier bridge.

Regards

 

[K-amps]

I delibrately used the word "affected" and not "improved". 😎

 

[Nexus]

schematic Krell ksa50

Hello All,

I am intersted too in building this Krell clone, but can anybody link me to the last schematic of this krell (ksa50)?

because searching in 198 pages in this thread is quite a lot of work..

Thank you in advance!

Best Regards:
Nexus

🙂