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Old 26th August 2005, 05:54 AM   #1
bee696 is offline bee696  Thailand
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Default Input transformer for GC

Hi, Is it possible to add an input transformer for the GC? I'm now using non-inverted GC version. Any suggestion on the transformers will be much appreciated!! Thanks!
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Old 26th August 2005, 06:07 AM   #2
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Sure you could use an input transformer but why?
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Old 26th August 2005, 06:14 AM   #3
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Quote:
Originally posted by peranders
Sure you could use an input transformer but why?
High common-mode noise rejection, ability to accept balanced and unbalanced inputs without any compromises, ground isolation...?

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Old 26th August 2005, 06:18 AM   #4
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Default Re: Input transformer for GC

Quote:
Originally posted by bee696
Hi, Is it possible to add an input transformer for the GC? I'm now using non-inverted GC version. Any suggestion on the transformers will be much appreciated!! Thanks!
Sure.

The CineMag CMLI-15/15B would be a good candidate.

Just replace the shunt resistor you're using at the + input of the power opamp with a 15k resistor and just connect the transformer as shown in the datasheet.

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Old 26th August 2005, 06:24 AM   #5
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Steve, you are the right person to answer.... why don't you mention that you are selling audio transformers? Maybe something for bee696?
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Old 26th August 2005, 06:48 AM   #6
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Quote:
Originally posted by peranders
Steve, you are the right person to answer.... why don't you mention that you are selling audio transformers? Maybe something for bee696?
There are a few reasons for that actually.

First, the InterFace is currently out of production.

Second, if he's capable of building his own gainclone, he's capable of buying the raw transformers and implementing them directly which would be preferable (and significantly less expensive) to using something like the InterFace.

Third, I'm not a saleshack and don't take advantage of forums such as this to try and sell my commercial products (not saying you're saying that I am, just saying that I'm not).

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Old 26th August 2005, 07:23 AM   #7
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Still, in a home environment there is not often you have such nasty electrical envirnoment which calls for a transformer unless you have balanced output signals from the premap.
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Old 26th August 2005, 07:27 AM   #8
bee696 is offline bee696  Thailand
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Thanks so much!!!

Actually, I got the non-inverted GC kit, and I'm thinking what kind of input transformer is suitable?

My worry is the input resistor of the kit is 20K, so can I simply add the input transformer and connect it to 20k directly? as some of transformers are stated that impedance ratio is 10k:10k. Is it OK?

The reason why I want to add an input transformer is I found that input transformer is recommended in AA tube forum (Jensen is the best, as I know).

I have no idea on "CineMag", somethings in my mind in Lundahl LL1540 http://www.lundahl.se/pdfs/datash/1540.pdf, or Jensen
JT-11P-1 http://www.comtran.com/datashts/11p1.pdf. Pls help!! THANKS!!
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Old 26th August 2005, 07:34 AM   #9
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Quote:
Originally posted by peranders
Still, in a home environment there is not often you have such nasty electrical envirnoment which calls for a transformer unless you have balanced output signals from the premap.
Not sure what you mean by "unless you have balanced output signals from the preamp."

Nice thing about a good input transformer is that you get just about the same common-mode noise rejection when fed from an unbalanced source as you get when fed from an unbalanced source, which is typically significantly higher than you'd get with typical electronically balanced inputs.

Also, since most high end and DIY audio equipment uses safety grounded chassis often with the signal reference ground tied to the safety ground, you can have a fair amount of interchassis leakage currents which can produce noise.

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Old 26th August 2005, 07:42 AM   #10
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Quote:
Originally posted by bee696
Thanks so much!!!

Actually, I got the non-inverted GC kit, and I'm thinking what kind of input transformer is suitable?

My worry is the input resistor of the kit is 20K, so can I simply add the input transformer and connect it to 20k directly? as some of transformers are stated that impedance ratio is 10k:10k. Is it OK?
The CMLI-15/15B is ideally loaded with a 15k resistor. The 20k resistor wouldn't be any significant problem. Though it would be a simple matter to simply replace the 20k resistor with a 15k if you have some readily available.

Quote:
The reason why I want to add an input transformer is I found that input transformer is recommended in AA tube forum (Jensen is the best, as I know).

I have no idea on "CineMag", somethings in my mind in Lundahl LL1540 http://www.lundahl.se/pdfs/datash/1540.pdf, or Jensen
JT-11P-1 http://www.comtran.com/datashts/11p1.pdf. Pls help!! THANKS!!
All three are good quality transformers.

I don't have any direct experience with the Lundahls, though the one thing I don't like about them is that they're all PC moint types which tends to make them a bit messier to deal with.

I'd used Jensen transformers for years and used the 11P-1 in a commercial product of mine. But I found the CineMag transformers to be every bit as good as the Jensens but the CineMags cost significantly less.

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