Driver Board for the ST-70 Using Common Mode Feedback PI

the thermionic watercooler

Postby Geek » Sun Dec 06, 2009 3:43 am

Hi Guys,

Tom - If you can mod it for a trioded 6EJ7, go for it!

Personally I would either make an adapter, chopping traces is a headache even for experienced folks.


Bill - Intro cost: $25.50 for either octal or noval version. I'll par it with the KTA board ($27.50) after the first run is done.

Artwork is proprietary to my partner. The circuit is "Copyleft", so if you reverse engineer a Gerber for it, you can post/redistibute it at no charge.

I'll work on a BOM first thing Monday (I'm entertaining tomorrow). I usually wait until I work on the documents, but I'll fast track that one ;-)


nyazzip - Two reason's I don't bother: 1) I have a symbiosis with my partner for PCB's and 2) the quality level of the work his professionals do would cost three times as much from any other factory.


Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Postby tomlang » Sun Dec 06, 2009 8:19 am

nyazzip, great story!

I was thinking the same thing as MashBill and was gonna make a BOM but I really didn't have all the info wrt component sizes required and I thought Geek might have it already.

I wanted to breadboard part of the circuit in the meantime.

Geek, not thinking of chopping traces more along the line of mounting chassis sockets and mounting your board underneath with jumpers going up. Exciting project, I need to order the China Chassis today (4-6 week lead) and get crackin'!
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Postby Geek » Sun Dec 06, 2009 9:47 pm

BoM fellas :-)


Resistors:
(all 1/2W, 5% unless noted)

2 - 20 ohms
2 - 100 ohms variable trimmer. Digikey CT6EP101-ND or equiv.
10 - 220 ohms
6 - 1K
2 - 1.2K
2 - 10K
4 - 22K, 2W, metal oxide
4 - 47K
2 - 100K
4 - 150K
2 - 470K, 2W, metal oxide
4 - 1Meg



Capacitors:
(voltage ratings can be higher than listed)

2 - 1.5n, 50V film
8 - 100n, 630V film (polypropylene pref.)



Semiconductors:

2 - IRF710
4 - 2N3904
2 - 1N4739A, 9.1V zener



Valves(noval board):

1 - 5751 or 12AX7
2 - 6CG7/6FQ7
3 - PCB mount noval sockets

or

Valves(octal board):

1 - 6SL7
2 - 6SN7
3 - PCB mount octal sockets



Misc:

2 - Heatsinks, Aavid Thermalloy 504222B00000G, Digikey HS104-2-ND or equiv.
2 - sets insulating pad/hardware if you want the sinks electrically isolated.


R3 - NFB resistor. 47 ohms I would say is maximum and gives 18dB NFB. High D.F.
for hard to drive speakers (like 3-ways), but for 2-ways or fullrangers, I'd
start around 22 ohms and tweak to taste from there. (one for each channel)
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Postby tomlang » Thu Dec 10, 2009 4:08 pm

Geek, what is the lead spacing of the caps on the board?

5% ok? thanks
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Postby Geek » Thu Dec 10, 2009 8:11 pm

716P size, like the original.

I got news they are in the mail to me. We may have them soon into in the New Year.

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Postby MashBill » Thu Dec 10, 2009 9:39 pm

I'll par it with the KTA board ($27.50) after the first run is done.


This statement is confusing to me. Can you explain this better? Do we need the KTA board too?

Good news on the delivery.

Thanks,
Bill
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Postby Geek » Thu Dec 10, 2009 11:12 pm

No. I was only referring to the price.

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Postby tomlang » Sat Dec 12, 2009 10:52 pm

Geek:

1. Octal Socket, Ceramic, P-ST8-193 from AES fit your board?

2. For those of us 6SL7'ly challenged, do you think a 6SN7 will have enough gain for triode stage if one has a "good" preamp ahead of it?

thanks!
Last edited by tomlang on Sun Jan 31, 2010 11:36 am, edited 1 time in total.
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Postby Geek » Sun Dec 13, 2009 4:20 am

Hi Tom,

Yes. They are the same as I have.

Please don't use a 6SN7 for the 6SL7. The 6SL7 circuit is DC coupled to the 6SN7 drivers and things would likely not be Zen for too long on the board :-\

I have some used and maybe a NOS 6SL7's around here if you are in need.

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Postby burnedfingers » Sun Dec 20, 2009 12:23 pm

How do I order an octal one?
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Postby Geek » Sun Dec 20, 2009 5:24 pm

Boards are in!

I just finished "proofreading" the octal one last night for errors. Looks good. Noval will be "proofread" in a couple days.

Documentation for these will be done in the new year, as my time is extremely limited until then.

How do I order an octal one?


You PM me your country (if international), state (if US) or postal code (if Canadian) along with your PayPal email and I send you an invoice.

Given their value, they go insured airmail, which (based on one board) will be $7.20 for USA.... exact +$0.50 for the bubble envelope.
(Canada varies with every postal code and International varies with each country region).

First bach of boards are at the $25.50 intro.

Cheers!


** edit **

Here's pics to give you an idea of the quality of these:
http://geek.scorpiorising.ca/contrib/Ge ... al_Top.png
http://geek.scorpiorising.ca/contrib/Ge ... Bottom.png
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Postby MashBill » Sun Dec 20, 2009 5:53 pm

Great news! They look great! PM sent.

Bill
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Postby tomlang » Sun Dec 20, 2009 6:08 pm

I can't find C6 on the schematic (bypass cap across R4?).
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Postby Geek » Sun Dec 20, 2009 6:25 pm

tomlang wrote:I can't find C6 on the schematic (bypass cap across R4?).


C6 is not implimented in this schematic version. It's on the board for a future modification I'm experimenting with.
(has to do with tweaking NFB)

PM replied, Bill Image

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Postby burnedfingers » Mon Dec 21, 2009 5:32 am

Sent you payment for an octal board. Is there a schematic that I could download so that I can get parts ordered?

Thanks,
Joe
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