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Old 21st January 2008, 11:18 AM   #1
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Default Line output as line input transformer?

Dear friends.

I have a project circling around in my head. It involves an input transformer before 1/2 5687 and interstaged to 300b.

I am looking for a 1:3 line input transformer that can also convert balanced signal to unbalanced.

I have found the LL1676 that can be used as 1:2 IT.
1:3 is more difficult for me to find, and therefore I was wondering about the OPTs that http://www.sacthailand.com/ sells.

The have a preamp output trannie which has the following data:

L-531S (Model nr.)(With balanced out)

5.0K:600R

1:0.33 (is this the same as 3:1 ??)

15-75,000Hz

http://www.sacthailand.com/Transformer_Interstage.html

Is it possible to use this in reverse so that (in my head that is) it can be used as input trannie with 1:3 step up? And balanced to unbalanced possibility?

Sincerely

BTW. I am quite a novice in these aspects.
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Old 21st January 2008, 04:10 PM   #2
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May I ask why you're needing a 1:3?

se
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Old 21st January 2008, 05:19 PM   #3
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Take a look at the Cinemag CM-25101 it is 3.1:1 and should work fine in reverse. They are about $80 USD each,
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Old 21st January 2008, 05:52 PM   #4
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Default Line out as line in

One problem you may encounter is hum pick-up. The signal levels in a line output transformer are high and hum pick-up is usually not an issue, so hum-bucking and shielding are not often used. When used in the input position, the signal levels are lower and hum may be a problem.

I ran into this when using a Jensen line-out transformer as an input to a 300B amp. It has a single-bobbin EI-core, and picked-up hum from a power transformer over 6 inches away. I cut a piece of square steel tubing (3" on a side) and mounted the transformer inside this. It cut the hum down by about 7dB, which was enough. A mu-metal shield or relocation of the transformer would be necessary for further hum reduction.

The Lundahl transformers use a dual-bobbin C-core design, which is much better at rejecting hum, so you may not have a problem here.

- John Atwood
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Old 21st January 2008, 08:05 PM   #5
DougL is offline DougL  United States
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Quote:
Is it possible to use this in reverse so that (in my head that is) it can be used as input trannie with 1:3 step up?
FYI, many transformers are resigned to operate one direction, and the windings are optimised for that usage. So in general, the transformer will work, but may not have the same frequency response specifications as it does in the other direction.

Quote:
And balanced to unbalanced possibility?
Just about any input transform can do either balanced or unbalanced. Its simply a matter of either wiring it up to the + and - on a balanced, or signal and signal return (ground) on an unbalanced connector.
Quote:
May I ask why you're needing a 1:3?
Steve's question is a good one. Let me rephrase it, any reason you need to make your preamp drive 9 times the capacitance?

HTH

Doug
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Old 21st January 2008, 11:03 PM   #6
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A bit tight schedule right now. Thanks for the answers.
Will answer a bit more tomorrow.

This project is initially an attempt on reverse engineering of the new Audio Note balanced products.

http://www.triodeandco.us/Welcome_fi...Amps080105.pdf

Sincerely

I have an AN m3 transformer coupled preamp so I guess it will match well.
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Old 22nd January 2008, 04:16 AM   #7
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Quote:
Originally posted by bambadoo
This project is initially an attempt on reverse engineering of the new Audio Note balanced products.
Ah, ok.

The CineMag CMMI-3.5C should give you what you want plus a little extra.

se
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Old 22nd January 2008, 06:44 AM   #8
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Dear friends. I got an email from sacthailand, and they told me it was not suitable in that place.

However my speakers are aprox. 108 db sensitivity, and I assume I have enough with a 1:2 step up?

When using 1/2 5687 I get approx 15x gain which seems a bit low, with a step up I get 30.

The reason for this setup is that I have a bunch of 5687 valves and 300b valves. Would really like to do something with them.

AN stuff has always interested me.

Sincerely
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