crescendo amp

[neeraj]

Hi, guys,😀
i have build a Crescendo millenium amp publishrd in Electors mag.But it dosent work. while teasting supply & out putis shorted & the pair of 2sj 201 /2sk1530.
now the set is dead. I have purchased 2 new pairs Can any budy
guide that from where to start re cheacking the cercuit.
neeraj

 

[lineup]

Crescendo ME can be a little tricky.
Hard to say what you should change.

There has been a number of topics about Crescendo ME before.
So there are several members here that have also built this amplifier.

goto search http://www.diyaudio.com/forums/search.php
and search for

Threads with 'Crescendo' in title only.

 

[peranders]

Were the output transistors insulated properly? Did you have the bias turned down?

Are you aware of that you can test the amp _without_ the mosfet's soldered? Is driver OK? Just the mosfet's went

 

[neeraj]

Dear all ,
thanks for your reply.i will be back on 17.2.05

 

[neeraj]

Hi PA ,
Sorry for delay.no i am not aware of testing amp without power transister. Any link or idea?

 

[neeraj]

Were the output transistors insulated properly? Did you have the bias turned down?

Are you aware of that you can test the amp _without_ the mosfet's soldered? Is driver OK? Just the mosfet's went

Hi PA
Transisters are properly insulated, Bias was turned down, But while checking out put voltage onput & out put get Shorted

 

[peranders]

Hi PA ,
Sorry for delay.no i am not aware of testing amp without power transister. Any link or idea?

Move the feedback resistor 22k or 33k (if I remember correctly) to the gates instead from the output. It doesn't matter which gate you take. By this you'll take the feedback from the VAS stage (BF470/471 or whatever you have there).

Of course you have fuses on both rails and you have also chosen low values when you test, like 315 mA or so.

You don't have fuses

 

[jacco vermeulen]

You don't have fuses

P-A,

thanks for the laugh, i needed that.

 

[masood]

dear neeraj,
i am also reluctant to know/construct cres, ampli.do you make that ampli.what was the fault plz give me also falt by which i can built this thank u.

 

[Tekko]

This amplifier topology was notorious for oscillating and beeing hard to get working. It's a overall not so very good design, as far as i know, noone have managed to make it work on the first try.

 

[Bonsai]

Yes, this amplifer has a name for either working, or giving lots of problems. I took a close look at the circuit, and the compensation really needs some work. This is another design where in the all out pursuit for low distortion, the designer has played it too close to the edge and ended up with something with very marginal stability. A pity, because it has all the ingredients that could have made it solid, classic design. You are not the first one to be burnt neeraj, and you will not be the last. If you are looking for a good design, try one of Apex's circuits, or an Ostripper bipolar output one.