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Old 22nd February 2009, 08:45 PM   #1
kaybe is offline kaybe  United Kingdom
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Location: Malvern
Default 40w Class A Circuit

Hi-Fi World Solid State Pure class A monoblocks

Hi this is the first post i have made on this forum or any forum.
I built this amplifier in 1996 to replace a JLL Hood 80w mosfet amp.
The Design was by Andy Grove and they sold a complete kit or as I purchaced 2 x pcb's and 8 power transistors they are as follows
4xSM7401
4xSM0718
These transistors were only available from the magazine at the time,and,I can find no info on them anywhere Hi-Fi World know nothing about them all diffrent staff now.
Could anybody sugest an alternative set of power transistors if anything goes wrong during the rebuild all the caps need replacing and i dont want to touch these fine amps wit no hope of repai if somthing goes wrong during the rebuild.I have posted the circuit diagram below.
these monoblocks sound fantastic loads better bass smoother treble than the JLLHood and very powerfull for their 40watts I used a 250va transformer in each rather than the 160va sugested. I would be gratefull for adviceon the power transistors or any sugestions on other improvements
cheers kaybe
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Old 22nd February 2009, 09:27 PM   #2
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Default Re: 40w Class A Circuit

Quote:
Originally posted by kaybe
Hi-Fi World Solid State Pure class A monoblocks

I would be gratefull for adviceon the power transistors or any sugestions on other improvements
cheers kaybe
Cannot see the circuit, the image is too small.

Nico
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Nico
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Old 23rd February 2009, 02:20 PM   #3
kaybe is offline kaybe  United Kingdom
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Default circuit diagram

sorry couldnt get picture the right size see new one below
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Old 23rd February 2009, 09:47 PM   #4
AndrewT is offline AndrewT  Scotland
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I followed that article and the follow up.
Nearly bought the kit.

The output devices are likely to be low droop, fast similar to 1302/3281 that had become the rage at that time.
ONsemi or Sanken or Toshiba will probably replace those, but you will need to check stability if you change the outputs.
Some of the Zetex were/are difficult to source.
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