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Old 17th July 2012, 07:27 PM   #381
sonidos is offline sonidos  United States
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@RNMarsh

What do you think of locating the xformer and filter caps in a separate box away from the circuit? This is the approach that JC took in his Blowtorch pre-amp. where you see he had the psu separated from the pre-amp.

However, I would definitely put my regs on same board as head amp or close as possible for this head amp.
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Old 18th July 2012, 02:16 AM   #382
RNMarsh is offline RNMarsh  United States
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@RNMarsh

What do you think of locating the xformer and filter caps in a separate box away from the circuit? This is the approach that JC took in his Blowtorch pre-amp. where you see he had the psu separated from the pre-amp.

However, I would definitely put my regs on same board as head amp or close as possible for this head amp.
I didnt know JC did that -- havent seen a Blowtourch. But, I use the same method. two xfmrs and rect and filt cap in a seperate box. Run the two raw dc to the amp/pwr supply with PSright beside the amp circuit. Better would be to make both reg ps on same pcb as amp. -RNM
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Old 18th July 2012, 03:08 AM   #383
sonidos is offline sonidos  United States
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Behold, from the original thread, the CTC Blowtorch.

John Curl's Blowtorch preamplifier

I did notice one thing when I read the Blowtorch thread a couple of years ago. The amount of the room in the chassis. My guess is we should aim for a chassis that just fits. The Goldilocks Principle - just right. Not too big, not too small.
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Old 18th July 2012, 02:12 PM   #384
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Default thank you...

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Originally Posted by RNMarsh View Post
For perfectionist way -- I always advocate having the power supply reg right at the amp circuit. .. shortest distance from circuit and ditto for the grounds.
Integrate the pwr supply onto the amp pcb is best way. Or, second best, locate the pwr supply pcb right close to the amp pcb.
although still theres question left in my mind I find your design are worth keeping...thank you again for the contribution and will follow this thread...

regards,
joel
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Old 20th July 2012, 02:09 AM   #385
sonidos is offline sonidos  United States
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Default junk!

The 2n5457 from Tayda Electronics are junk. Looking at face of TO-92, it's GSD. It should be the reverse per the Fairchild and OnSemi datasheets. Using the set up recommended by Richard Marsh, I got 11.2 mA, or about 11.2 V across the 1k resistor.

As per the datasheet, I tied gate and source to ground. I set +15V to the drain...darn things overheated!

The 8 pcs. of the 2n5460 measured right in the middle of the datasheet for Idss. 3.5mA so I feel better about those. I've got about 40 pcs. of each jfet on order from Futurelec. I'll keep you posted on those.
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Old 20th July 2012, 02:43 AM   #386
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Default Egg on my face!

I must have had a wire set up wrong. Looks ok now.

p jfets measuring about .84 volts. The 2 or 3 n jfets I checked are about .83 volts.

I feel better now. Please forget my previous post.
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Old 22nd July 2012, 06:29 PM   #387
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Well, I have receive the new MJE200/210 from On Semi. The result...quite disgusting again. Total I have 400 pieces and 0 pairs. If I mix from both Fairchild and On Semi I could get 4 pairs... out of 400. Not very good!!

I look around to find other possibilities from what I have at home. I find this:
- BD139/BD140: Seems quite adequate - same body and pin-out, similar characteristic
and, what is even more important, MUCH easier to find complements. Out of 80
pieces, I found 13 perfect pairs.
- 2SB649/2SD669: same body and pin-out, not so similar characteristic. The sad part
is that for the parts I have the Vbe is not equal for PNP and NPN groups. One is
0,70v and the other 0,72v.
- 2SA1306/2SC3298: not very good, different body, different pin-out and dissimilar
electrical characteristic. But, maybe?

Could you please Mr. Marsh tell me your opinion about this candidates? Thanks in advance.

Javier
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Old 22nd July 2012, 06:46 PM   #388
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Originally Posted by Unomas View Post
- 2SB649/2SD669: same body and pin-out, not so similar characteristic. The sad part
is that for the parts I have the Vbe is not equal for PNP and NPN groups. One is
0,70v and the other 0,72v.
I have used the 2SB649AC/2SD669AC with success -- the late Randy Stone's favorite driver transistor for lateral mosfets.
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Old 23rd July 2012, 03:28 PM   #389
sonidos is offline sonidos  United States
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@Unomas

As I said before, when I started refurbishing my Adcom 535, it was hard to get PNP/NPN matches and Anatech told me to just do the best that I can do because what we're talking about is an improvement in THD.

I plan to do the same on this project - just get as close as I can with what I have. I'm sorry you have spent so much money with very little payoff for your hard work. Best wishes going forward - sonidos (btw, I am also Javier )

jackinnj - those Hitachis have really shot up in price. Yeeowwww. I'm glad I bought several for my Adcom a couple of years ago. I wonder if the Hong Kong specials are any good on ebay.
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Old 23rd July 2012, 04:01 PM   #390
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by Unomas View Post
Well, I have receive the new MJE200/210 from On Semi. The result...quite disgusting again. Total I have 400 pieces and 0 pairs. If I mix from both Fairchild and On Semi I could get 4 pairs... out of 400. Not very good!!

Could you please Mr. Marsh tell me your opinion about this candidates? Thanks in advance.

Javier
The output transistors just needs a beta of greater than 100. take the highest Hfe from the mje200 and the lowest from the mje210.... but do get a match on the Vbe --something like .72 should be easy to find. The topology, currents and transistor will take care of the rest. On the 2N 50xx types, they can be matched for Hfe and Vbe. The jFETs are matched only by the .8 v method shown. that should be all you need to do to get great performance. -RNM
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