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Old 11th May 2013, 03:31 AM   #101
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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 18th May 2013, 08:29 AM   #102
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Quote:
Originally Posted by PMik View Post
Wynand

Are you still interested to get the original article ?

I can send it for your email

Ps. I have today bought a "functional" Cresendo 180W for a symbolic amount of cash compared to the real cost of the parts/project, the owner informed me was not up to the task of getting the project finalized to perfection
The issues he had incounted was the ones bjornagain has posted the solution of in this tread ...
Thx bjornagain
dear PMik, if you still have this article, please email me a copy to nkanil.klm@gmail.com
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Old 26th June 2013, 10:34 AM   #103
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Hey!
Make a crescendo amp.
Question: R23-24, R25-26 does not get put on the PCB?
THX!
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Old 9th August 2013, 02:00 PM   #104
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Quote:
Originally Posted by farkincza74 View Post
Hey!
Make a crescendo amp.
Question: R23-24, R25-26 does not get put on the PCB?
THX!
(Late answer)
Yes they are. Depending of the radiator you use, you can solder them track side of the Printed board.
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Old 1st November 2013, 06:37 PM   #105
Haerter is offline Haerter  Germany
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I had the same problem, and how in real life, the solution was easy.
150pF between gate and source of J50 an the oscillation has gone.
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Old 7th January 2014, 06:47 PM   #106
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Default Update and new build

Hi guys.

I am starting a new project based on Esperado's design: Update for Elektor Crescendo Power Amplifier 1982

I am an electronics engineer and built the original (also created a whole made by hand plans and drawings, no computers for me in 85!) as a school project when I was studying, the job which was part digital electronics & part mechanical construction.

This amplifier is very good but very unstable as many of you have noticed/said.

I also still got the original Elektor mag. featuring the Crescendo, in French, as you will see also on the pics.

I subsequently worked as a PCB designer ranging from PSU to RF devices in Switzerland and then the UK where I currently live.

I am planning to redo a brand new PCB based on the original with Esperado's mods and re-use some of the original parts I still have (Huge toric transformer output 2x 75V and heat sinks with "L's" attached to it) all dressed into a very modern hand crafted case.

I have a fondness for this Amp as it was rated 7.5 out of 10 when compared to a 10/10 McIntosh amp tested on JM's speakers in a auditorium environment back in Switzerland where I used to live.

Given that the McIntosh was about $8000 I think that it is worth re-building one!

I measured an RMS output of 138W on one channel whereas the other threw 217W before clipping.

It also had a nasty bout of oscillation in the MHz's and this was more or less sorted by shielding/shorting the P fetmos TO3's cases with a piece of aluminium(!). But it fried a few T's in my time.

Well the new system will be designed with the experience I gained over the last 30years in the business (I since changed career, but it is like swimming, you never forget)

So I will try to post some updates from time to time, what I will also likely do is post on my blog: sxg.com | The personal site of Gilbert Serex – Linux enthusiast & Internet entrepreneur with a background in Electronic Engineering

which might move here: welcome to serex.me

Cheerio.
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Old 10th January 2014, 02:25 PM   #107
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Hi,

unfortunately I don't speak French. But solely by the look at the schematics shown by Esperado I can't follow why his mods convert the Crescendo from voltage controlled to current controlled NFB. Do you manage to follow him?

Best regards!
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Old 10th January 2014, 04:02 PM   #108
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Quote:
Originally Posted by trilbies View Post
I am starting a new project based on Esperado's design: Update for Elektor Crescendo Power Amplifier 1982
Nice idea, but i still have few questions:
The power Fets used on this amplifier are no longer available. What is you position on this point ?
The original printed board was far to be optimal and participate to instability by their surface, tracks lengths and some other points. Did-you project to redesign-them from scratch ?
I believe we can improve this amp by adding a CCS to the input stage and add some cap multiplier to the input+VAS rails. What do-you think ?
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Old 14th January 2014, 10:48 AM   #109
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They're available still... Not by Hitachi mind you.

2SJ50
2SK135

With regards to PCB, yes, I am going to redo the whole layout. Bit of trial and error but I think I might put the design on this Forum for scrutiny and then I can always rework it. I am using an open source program called Fritzing to do the PCB. looks good and they also provide etching service!

I'll keep you posted.

P.S. good to hear from you Esperado! I emailed you via your Form recently did you not get it? Might want to check your Form.

My question to you was about the image on your page which links to this image, I reckon your latter schematic is the right one, right?

Kay Pirinha
Sorry you don't read French it could be useful sometimes. Frankly I haven't really though about the ins and outs of Esperado's schematics, apart that any improvements is a good idea, removing the counter reaction circuit made of the BC546 and BC556 chain is definitely a good idea as they tended to go up in smoke in a wink whenever there were interferences.

I also did add some safety barriers in the original design at the time, like head butted Zeners between the input/ground to clip any massive glitches one can introduce when plugging or unplugging the audio cables. As one knows the Crescendo being such a sensitive and gigantic OP AMP was quite happy spewing whatever you fed it. Limiting the input is recommended.
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Old 17th January 2014, 01:12 AM   #110
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Quote:
Originally Posted by trilbies View Post
Hi guys.

This amplifier is very good but very unstable as many of you have noticed/said.

It also had a nasty bout of oscillation in the MHz's and this was more or less sorted by shielding/shorting the P fetmos TO3's cases with a piece of aluminium(!). But it fried a few T's in my time.
Cheerio.
I have seen oscillation in a few amps including some of my early designs.
This is due to the signal getting to the output transistors before it gets to the return path in the LTP. The result is oscillation to some degree at the output.
I usually fix it with 100pf at the VAS stage across CB.

I recently updated and fixed a couple of Maplin 150WRMS amps that had the same problem. Fitting brand new transistors which were faster and had more gain set off oscillation. The 100pf trick fixed both of these too.
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