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Old 11th April 2013, 09:05 PM   #3561
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I was about to decide on this, with 380 x 140 x 32mm heat sink per side. But would like to explore other alternatives.

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Old 15th April 2013, 08:55 AM   #3562
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Quote:
Originally Posted by Nelson Pass View Post
Try a Jensen JT-123-ALCF as a 1:4 autoformer.

Quote:
Originally Posted by Zen Mod View Post
two things , unfortunately :

1. I'm not Pa

2. yes , with Jensen , being xformer sans CT secondary , you must use one per leg

3. looking at schm you posted in #3390 , connection is like attached :

4. #3 and #4 are just to confuse you , considering two things mentioned
Quote:
Originally Posted by Nelson Pass View Post
By that drawing, autoformer would be

BRN to GRY

VIO to BLU

GRN to YEL

RED = GROUND

ORG = OUT

BRN = IN

Correct me if I'm mistaken, ZM

Sorry to dig up these old posts.

If I were to replace C1 and C2 with an interstage transformer, is R3 and R4 still necessary?

And, would this be a suitable transformer?

EDCOR - XSM10K/10K
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Old 15th April 2013, 03:02 PM   #3563
6L6 is offline 6L6  United States
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I've got mine biased properly and running in stereo - (Changed R9 to 4.75K, bias pot has lots of range now)

Oh, wow... It's completely transparent.

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Old 15th April 2013, 03:39 PM   #3564
generg is offline generg  Germany
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Quote:
Originally Posted by Navyblue View Post
Sorry to dig up these old posts.

If I were to replace C1 and C2 with an interstage transformer, is R3 and R4 still necessary?

And, would this be a suitable transformer?

EDCOR - XSM10K/10K
is suitable...... but you have no gain by the xformer, donīt you want gain?

in the case you want, take a 1:4 or 1:5 xformer
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Old 15th April 2013, 03:59 PM   #3565
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Originally Posted by generg View Post
is suitable...... but you have no gain by the xformer, donīt you want gain?

in the case you want, take a 1:4 or 1:5 xformer
Thanks.

Sorry for the elementary question, when a transformer steps up, does it comes with extra penalty such as gain stage (i.e. distortion)? I suppose the extra current draw by the preceding stage is insignificant.

Also, can R3 and R4 be eliminated?
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Old 15th April 2013, 04:24 PM   #3566
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In post 2994 Zen mod shows a f4 without the buffer stating about a 10k load . Then the voltage on the rails could be raised some with out a problem I take it . giving more than 25 watt class A with in reason.
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Old 15th April 2013, 04:34 PM   #3567
flg is offline flg  United States
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Yes. There will be tradeoffs, the driving source should be many times lower source impeadance than the primary:secondary > load impeadance(3 FET gates and the biasing R's). You should go to: http://www.jensen-transformers.com/a...%20Chapter.pdf
So, when N.P. uses a buffer to drive a transformer, now you will understand why? Basically, if you want to do a turns ratio for the gain, you need a super buffer. You can probably get away with the best N and P JFETs in your drawer and use a B1 style (but you could do better). That might net you 15 ohm source Z. Squared times the turns ratio would give you the output Z of the secondary. And what is left on the input of the F4? 10k?
(15*15)*4(or 5)= your source impeadance into the F4 output stage. Are you only using it for midrange?
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Old 15th April 2013, 05:46 PM   #3568
generg is offline generg  Germany
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Quote:
Originally Posted by Navyblue View Post
Thanks.

Sorry for the elementary question, when a transformer steps up, does it comes with extra penalty such as gain stage (i.e. distortion)? I suppose the extra current draw by the preceding stage is insignificant.

Also, can R3 and R4 be eliminated?

the transformer step up is the main source of distortion as Nelson mentions in the M2 owner manual, but ....... many advanced people write that the distortion of such a small xormer, you might even go for a 1/4W version, is often more pleasant than the distortion of a regular gain stage.

And when you read the reviews of M2 for instance at Tone Audio there is much praise of clarity and darkness combined by this solution.

You can take the same input buffer like in F6, with or without degeneration (mind the voltage and Idss hints!) and drive the Jensen. Recommended input about 600R and output about 10k from your first Edcor try....
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Old 16th April 2013, 04:17 PM   #3569
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Thanks guys. I think I'll stick to the default this time round.

Is 1/4W resistor all around enough for the amp circuit? I am not sure about the current passing through R5 and R22.
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Old 16th April 2013, 08:46 PM   #3570
generg is offline generg  Germany
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1/4W is good for R5 and R22.
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