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Old 28th February 2012, 12:39 PM   #151
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The Elector Crescendo was my first DIY amp that wasn't a kit.

I borrowed the Elector magasins at our local library and had some 'amateur' make the PCBs, which turned out having lanes that didn't connect properly.

I am far from being an expert in electronics, but I think maybe ocsillation was never a problem in my project because I put some very small caps close the the FETs. I think this was recommended because I had to move the FETs away from the PCB on to a cooling tunnel. And then all the old tricks like, one ground in the cabinet. No hum at all.

It had dual Toroids with 'cumputer graded' Caps that was speeded up with some small poly caps? Wow.. It's all coming back to me know. It was good fun to build and the amp proved to be stable and lived for some years being mistreated in a Disco -often driving speaker configurations in 2 ohms. Then I sold it for good money. This was back when DIY could actually save you or make you some money.

What is not good about this design? - except for the tendency to oscillate?

/ Andy
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Old 28th February 2012, 01:01 PM   #152
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Quote:
Originally Posted by Andy1967 View Post
What is not good about this design? - except for the tendency to oscillate?
I was referring to the circuit linked by wengtech some post above.
Drawing errors in the schematic and a mismatch between schematic and layout...enough reasons to avoid it!
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Old 28th February 2012, 01:25 PM   #153
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Yes I know Juergen, but someone said earlier in the thred that the Crescendo design was old and that newer amp designs were better.
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Old 13th April 2012, 07:03 PM   #154
JohanB is offline JohanB  Sweden
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Quote:
Originally Posted by wengtech View Post
Hi im newbie here...
need to ask the expert, is this audio circuit worth to be build?
http://www.tasel.net/images/200W-MOS...58-diagram.jpg
are there any suggestion from you guys...
some said this is a pure class A and better than crescendo, what do you think.?
This is not a non-feedback (NFB) design. The feedback goes to the input in an normal inverting amplifier mode.

This is not a class A amp. Ordinary class AB output stage.

There are some capital flaws in the schematic.

The "miller" capacitors C6, C7 are in phase in the loop that will oscillate the VAS.

Also the circuit board contans the same fault as the schematic, wich guaranteed will burn the driver transistors & the output FETīs (ie the whole amp) if the ouput is shorted to ground.

F.ex. diodes D5, D6 & D7, D8 should be connectet to the VAS output, not the emitter follower drivers. The VAS transistors must then also have some current limiting.
Otherwise the VAS transistors will still go into unsafe operating area and burn (etc), if theirs collectors are shorted to the output......

When there are so sewere faults in a design, you should know that the designer has never built it to funktion. He has probably just borrowed some schematics and modified, without knowing much of amp design or actually building it.

I really advise NOT TO BUILD this amp.

Johan

Last edited by JohanB; 13th April 2012 at 07:20 PM.
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Old 11th May 2013, 03:36 AM   #155
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I have had 20 years and 3 months cressedno as the used preamp tube amplifier and the result was incredible and I found the atmosphere and warmth of the sound produced. Currently I'm stringing SK135 and J50 mosfet in the circuit that uses a buffer of LME 49830 from National Semiconductor, does anyone of you have tried it? and what were the results?
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Old 17th May 2013, 06:35 AM   #156
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Default it is better then crescendo

Quote:
Originally Posted by wengtech View Post
Hi im newbie here...
need to ask the expert, is this audio circuit worth to be build?
http://www.tasel.net/images/200W-MOS...58-diagram.jpg
are there any suggestion from you guys...
some said this is a pure class A and better than crescendo, what do you think.?
It is better than crescendo,but without reversing transistor polarity or some other catastrofic mistakes.I put this amp in another thread named AXL.
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Old 17th May 2013, 06:43 AM   #157
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Default it is better then crescendo

Quote:
Originally Posted by wengtech View Post
Hi im newbie here...
need to ask the expert, is this audio circuit worth to be build?
http://www.tasel.net/images/200W-MOS...58-diagram.jpg
are there any suggestion from you guys...
some said this is a pure class A and better than crescendo, what do you think.?
It is better than crescendo,but without reversing transistor polarity or some other catastrofic mistakes.I put this amp in another thread named AXL.
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