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-   -   Aleph-2 50W@8ohm 20KHz (http://www.diyaudio.com/forums/pass-labs/85741-aleph-2-50w-8ohm-20khz.html)

emb51 1st September 2006 08:31 PM

Aleph-2 50W@8ohm 20KHz
 
Hi all,

My Aleph-2 amplifier can deliver 50W@8ohm laod at 20KHz , if I increase the input signal frequency, the output power will drop, what problem occus? refer to spec. Aleph-2 can deliver 70W@8ohm(-2db) at 100KHz. any suggest???

MikeW 1st September 2006 08:37 PM

Could be the cap in the feedback. Could it be what you are using to test it ?

emb51 2nd September 2006 10:35 AM

I use 10pF of C8 & 680pF of C6

Nelson Pass 5th September 2006 07:19 PM

The Alephs are not what we would call fast amplifiers, but using
minimal feedback I haven't found much reason for emphasis
on speed aboce 20 KHz.

The Alephs generally slew at 15 V/uS, and if you have a power
bandwidth issue, it may relate to the slew rate, which is easily
checked with a square wave.

:cool:

emb51 6th September 2006 04:02 PM

2 Attachment(s)
Dear Sir,

Very happy for your reply, attach is the 20KHz Sin-wave, What I can do? thanks you very much.

B.R.
Edwin

Nelson Pass 6th September 2006 05:45 PM

Assuming that it does not do this at lower frequencies, then
I think the current source is being overcompensated, or you
might have a wrong resistor value in the current source. Check
the capacitor next to the npn transistor, perhaps removing it
altogether.

emb51 6th September 2006 08:38 PM

Dear Sir,

Thanks your suggestion, I try to increase the Bias current to 4Amp, the output power can be increase to around 60W@8ohm, for low frequency eg. 1KHz it is not problem occus. it can deliver 100@8ohm & 196W@4 ohm. that mean the bias level can affect the high frequency response.

Anyway could you point out which component you suggect I can check first? the schematic was attached, thank you very much

B.R.
Edwin

RoboMan 8th September 2006 05:27 AM

It looks like the constant current source cannot supply enough current at the peak fast enough. Increasing bias provides higher power indicates this too.

Mr. Pass has already suggested to remove the .001 cap (C7 in the original circuit. It seems you did attach your schematic successfully.) That may help. If not, try to adjust 681 resistor (R21) and see.

emb51 8th September 2006 04:10 PM

Dear Sir,

Thanks for your help, my Aleph-2 is back to normal, I set to 3A bias current, input a 20KHz signal it can deliver 66W@8ohm load.
because I remove the 0.01uF cap. thanks a lot.

otherwise due to Nelson Pas not given permission to post the A-2 schematic, the Diyaudio webmaster already delete the schematic.

B.R.
Edwin


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