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EAR 834P mod - help identifying components
EAR 834P mod - help identifying components
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Old 8th July 2018, 01:28 PM   #1
Herr Grau is offline Herr Grau  Germany
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Default EAR 834P mod - help identifying components

Hi hi,
I am currently in the process of modding a Douk clone EAR 834P. Not reinventing the wheel here, mostly just upgrades of coupling caps and whatnot .. Thorsten Loeschs Mod guide is well known and I am mostly keeping to it. Most components were easy to identify on the board, but some are really strange. Maybe somebody with experience with the unit can help me.

I have labelled a photo I am using for reference to the markings of the original schematic. I'm having trouble identifying the anode resistors of V1. They are supposed to be 330k, but I don't see them (maybe the two close to C8?..). I don't know where the 12 little 36k Resistors come in .. guessing they are somehow drawn together to substitute for a bigger resistor, but I don't yet know what and why. There is a single stray 68k Resistor close to V1 I can't place... And the strangest thing are two .. well I think semiconductors / transistors close to V1 labelled Q1 and Q2 (see last picture). What would they be doing there?...
Thanks a million.
Attached Images
File Type: jpg ear1.jpg (696.1 KB, 381 views)
File Type: jpg ear-2.jpg (536.9 KB, 365 views)
File Type: jpg EARphonocircuitcopy.jpg (72.6 KB, 393 views)
File Type: jpg ear3.jpg (969.8 KB, 366 views)

Last edited by Herr Grau; 8th July 2018 at 03:27 PM.
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Old 8th July 2018, 11:12 PM   #2
spaceistheplace is offline spaceistheplace
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EAR 834P mod - help identifying components
The schematic you are referencing is not precisely the same. Iím assuming Douk made some alterations.

Also, complicating matters the 834p schematic often circulating the web from one of the manuals which you reposted here is also not the same as the production 834p. Maybe the first iteration circa late 90ís but thereís notable differences now such as the JFETs you referenced.

I would ask Douk for a schematic of this design in particular or else you risk causing more harm than good.
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Old 9th July 2018, 07:03 PM   #3
Herr Grau is offline Herr Grau  Germany
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Thanks for your reply.
Yeah, I kinda noticed that it didnt quite fit the schematic around the first tube .. the rest is accurate though. And swapping parts for equal value never caused any harm, so...
Just trying to understand the thing entirely, since learning is one part of the reason I'm doing work on valve amps.
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Old 9th July 2018, 08:45 PM   #4
spaceistheplace is offline spaceistheplace
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EAR 834P mod - help identifying components
Get the schematic from Douk and post it here, then we can actually learn something.

Parts replacement isnít learning its blind repetition without a real goal in mind.

You will miss an opportunity to really improve performance this way.

JFETs may be the critical component to replace in matched pairs anyhow. Can you get part numbers off them? (Q1 and Q2)

Help me help you.
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Old 9th July 2018, 09:26 PM   #5
Herr Grau is offline Herr Grau  Germany
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I've written to Douk some days ago, but they are yet to reply. I don't quite count on getting a schematic.

And no, upgrading components to better ones of the same type doesn't teach you much. But first trying to understand everything you touch does. Which is why I'm trying to figure this out in the first place. Also, I want to make this information available. I think this amp is a hell of a bargain right now, and I want to give people the resources to upgrade it without them all having to do all the footwork and without even having to understand it - the same way many great people did for me many a time.

Regarding the Transistors, I will take a closer look when I open the amp up again. I'm needing it in working order these next days. I guess things will get much clearer once I've removed the board and can see the traces. Right now I'm suspecting the Transistors might be remnants of the not installed MC part, which in the Douk version is supposed to be a cheap step up amp encased to look like transformers... Will keep you posted.
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Old 9th July 2018, 09:36 PM   #6
rayma is online now rayma  United States
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Quote:
Originally Posted by Herr Grau View Post
I'm suspecting the Transistors might be remnants of the not installed MC part
Later EAR circuits have input transistors that the first tube cascodes with.
Looks like Douk updated their circuit as well.
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Old 10th July 2018, 05:57 AM   #7
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Quote:
Originally Posted by rayma View Post
Later EAR circuits have input transistors that the first tube cascodes with.
Looks like Douk updated their circuit as well.
I had very much feared someone would say that. Although I searched extensively, I have not found a schematic with that topology. Which advantages might this design offer over the original?
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Old 10th July 2018, 05:59 AM   #8
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Oh, and btw:
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Old 10th July 2018, 08:42 AM   #9
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EAR 834P mod - help identifying components
Please see if you can get the model numbers off of Q1 and Q2.

I would push Douk, perhaps say you need it for repairs.
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Old 10th July 2018, 09:57 AM   #10
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I will and I did.
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