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Old 23rd April 2008, 11:37 AM   #1
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Default stan curtis 60w class a

Hello

I am going to make the Stan curtis 60w class a amplifier. I tried this amp many years ago when in my early twenties and the project failed. Now I have more experience I wold like to try again. I have all the parts but need the PCB artwork. I thing the original project was published in ETI winter audio edition in the mod 1980's.
I have just heard this amp made with the original PCBS and I was very impressed with the sound. Does any one out there have the mag for sale or a copy of the pcb artwork so I can get some PCBs made. I would like to keep to the original artwork

regards

Nick
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Old 23rd April 2008, 12:37 PM   #2
AMV8 is offline AMV8  United Kingdom
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Nick

I have the original magazine with the full article for the pre and power amps including the pcb artwork. I will also add the updates that Stan Curtis published a year later.

I made the pre and power amps and they do sound very good. I like the design. Not unlike the Krell in sound. I have swapped out the output devices for later faster ones and that helped. I built the amps as monoblocks and added a 4" fan to each monoblock to keep them running at reasonable temperatures. The amps do run at 60 watt class A and give off a lot of heat. The pre amp also sounds good.

The overall article plus pcb plus updates is very long and I only have hard copies. If you give me your address I will post you a photo copy.


Don
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Old 23rd April 2008, 12:43 PM   #3
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Many thanks for the quick reply

My address is 18

the chase rayleigh Essex

SS6 8QL

Can I purchase the originals? if yes I can purchase through ebay as a buy it now item?

regards

Nick
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Old 23rd April 2008, 12:51 PM   #4
AMV8 is offline AMV8  United Kingdom
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Nick

I will send you copies. I intend to kep the originals.

Don
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Old 23rd April 2008, 12:53 PM   #5
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Ok

Thanks again for your help, are you still using you amps today? and what output transistors did you use?

best regards

Nick
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Old 23rd April 2008, 04:12 PM   #6
paulf is offline paulf  United Kingdom
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Default Stan Curtis 60W class A

Nick,

The article and schematics can be found at the excellent class A amplifier site, run by Geooff Moss:

http://www.tcaas.btinternet.co.uk/curtis60w.pdf
http://www.tcaas.btinternet.co.uk/curtis60w.gif

Not 100% sure about the update article, as I don't recall seeing this, but there is an "update" section at the end of the article, so I assume this is the same thing.

PaulF
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Old 23rd April 2008, 04:39 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
is this a ClassA push pull amp?
If so, then why is the output bias set to 3A, when the specification claims 60W of ClassA into 8r0?
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Old 23rd April 2008, 06:11 PM   #8
Shaun is offline Shaun  South Africa
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Quote:
Originally posted by AMV8

I have the original magazine with the full article for the pre and power amps including the pcb artwork. I will also add the updates that Stan Curtis published a year later.

Don
Hi Don/Nick

Could I beg a favour and ask that you share the preamp article with me? I built it years ago, and remember it being very good.
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Old 23rd April 2008, 06:19 PM   #9
djk is offline djk
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If this amp had an active current source for half the output, you would be correct.

3A bias is higher than need be for push-pull class A.

Only enough bias to keep the un-driven half of the output stage from cutting off when the oher half is driven to peak is required. This is typically one half of the peak current required. 2A is probably all that is needed.
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Old 23rd April 2008, 06:52 PM   #10
AndrewT is offline AndrewT  Scotland
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That's the problem.
It either needs 4A bias for a single ended ClassA or 2A bias for push pull.
Stan Curtiss would not have got it wrong so why 3A of bias?
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