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Shearne Audio Phase 2 Anniversary

chartz

chartz

If it’s broke fix it!
Hi everyone,

I’m not really holding my breath, but I’m looking for the schematics of this John Shearne amp. It’s the one with the alu fascia.

There is a really complex volume control PCB, and most of it is burnt, not looking good.

A long shot, perhaps. Is the amp even worth bothering anyway?

Ta!
 
How the hell do you get a burnt vol control board? :eek:

I think it could be a long shot on a schematic... We used to make some of them at Alchemist actually but I have no info I'm afraid.
 
I know. I’ll try to post a picture in a minute Jez.

Shearne.jpg
 
Somebody had a shot at fixing it, possibly making things worse... sometimes...:mad:
 
Yes. Volume, remote.
The circuit doesn’t look as if it was made in-house. OEM module perhaps?
 
chartz said:
Yes. Volume, remote.
The circuit doesn’t look as if it was made in-house. OEM module perhaps?
Click to expand...

Possibly. I reckon you'll have to reverse engineer the good channel of the headphone amp and make a schematic from that. Probable collateral damage to PSU/regulators.
 
chartz said:
Used to that. Thanks for the moral support!
John Shearne still with us?
Click to expand...

I don't know... As I said we used to assemble some of the Shearne gear at Alchemist at one time but I only briefly met him once. He used the same metalwork supplier and, IIIRC, PCB supplier as us.
 
Was still around a few years back, used to drink at the same pub as my stepson!

Apparently had stories about the murky downsides of Chinese manufacturing such as dealing with the local mafia!
 
chartz said:
Did you design the Kraken?
Click to expand...

No. Only the Axiom/Maxim, parts of "The Alchemist" pre amp and several items which never went into production including an FM tuner and a very nice sounding class A power amp. I did quite a few updates to various items we made to reduce manufacturing difficulties and to further reduce mains hum etc... we had a big following in the far east and many would use 100dB/W efficient speakers in tiny rooms which would expose hum we hadn't even noticed so that had to be dealt with. The main range of products was designed by Glen Gayle who was one of the 3 partners in Alchemist.
 
A guy called Michael Merry used to build them up for him at one time in premises in Surrey, if you can find him he may be able to help.
 
Hi,
So far: a burnt negative rail regulator, BD140 and its BC212 driver shot (top left). I didn't find the cause.
Also, I can't explain the head amp burnt channel. I tested the jack and it is fine, no short after insertion. Perhaps someone left it half way in...
Same as below pic in silver. Found on a Vietnamese audio forum.

img_8163-jpg.207734
 
Last edited:
Okay, let’s try FB, I see John has an account. Perhaps one of his relatives?
Waiting for replies...
 
Yes, I think problem solved, many components were also burnt on the V+ PSU, including driver transistor, zener, cap, well the usual...
But schematics would be really nice for the community, and I have no time for redrawing it.
 
Jez, what would you put before the 7812 regulator to lower voltage from 37 V? The photos I find show a 560 ohms 3W and a Zener but the Zener value is hidden. Would a 22 V zener do?

Shearne%20preamp%20unpopulated%20pcb.jpg


Shearne%20preamp%20psu.jpg
 
Not sure I'm with you here... there's already Zeners fitted and you are asking if you should fit Zeners? All looks well to me and those 560R's will be an effective current limiter. The fact that the 560R's and board around them are not charred suggests all is well... Lift up one end of Zeners to find voltage... 22v should be fine.
 
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