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Old 13th May 2006, 12:08 AM   #1
jovan is offline jovan  Yugoslavia
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Default Passive preamp with utc transformers

Hi there,

For several months i've got the big problem of my curiosity!

So, i have an passive preamp, which i get as a gift earlier, when i didn't have interests about hifi like today. Then he said to me that making of that preamp was expensive to him, and that sounds great. This pream is based on two step attenuators, two UTC LS 12 , and two UTC LS37 transformers. I used this preamp with two old Meridian monoblocks, but now i don't have amplifier.
Couple days ago i found my new love in the hifi world- single ended tube amps! Till than, i was always listen SS amplifiers, but since that moment, when i heard musicality of SE amps, i came on idea to buy/or to find someone to make me SE amplifier.
My questions are:
-Can i use this passive preamp in combination with tubes?
-Can i use these UTC transformers in building of integrated SE tube amp?
- Are these transformers good ?
I'm asking all this, because i saw that the only place, where anybody mention UTC transformers is this TUBE forum.

Thanks a lot! Sorry about my bad English....
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Old 13th May 2006, 03:09 AM   #2
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Quote:
- Are these transformers good ?
haha, the very best you will ever find.

Yes, use it in an integrated amp. LS12 should give you lots of "free" voltage gain (almost 34dB from a single transformer, if you connect it 50ohms:120kohms). WOW, thatīs plenty!

Maybe you could include a riaa filter in the amp and drive the transformer directly from a phono source. Those tramsformers are 80% nickel core (mumetal / permalloy) and will handle very low signals with very low distortion.

canīt find info on LS37.
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Old 13th May 2006, 08:23 AM   #3
jovan is offline jovan  Yugoslavia
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Thanks ,

I was made a mistake-it isn't LS37, it is LS30x....Sorry, i'm little bit stupid for electronic .........

Here is my preamp:
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File Type: jpg pasiva_165.jpg (79.5 KB, 701 views)
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Old 14th May 2006, 06:34 AM   #4
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LS 30x is a multiple line to multiple line. All low impedance. I canīt understand what itīs doing there thought. I wouldnīt use it for this purpose. can you draw a schematic of the unit?
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Old 14th May 2006, 01:45 PM   #5
jovan is offline jovan  Yugoslavia
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, i can't, because i don't know how ...I don't know anything about that electronic woodoo(for me) things at all.Sorry!
But i will make a photo of pramps inside, and i'll take it here.
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Old 14th May 2006, 01:52 PM   #6
jovan is offline jovan  Yugoslavia
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Here si the picture:
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Old 14th May 2006, 03:40 PM   #7
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It seems to me a bit depends on which way the xfmrs are set up!

Perhaps it is 600 ohm in ---> 600ohm out ---> attenuator ---> 600ohms ---> High Z ---> out

That being In-->LS30 ---> atten --> LS10 --> out

The other way doesn't make much sense, since the high Z (gain) side of the LS10 would then be driving a 600 ohm xfmr. BUT, if the load on the opposite end of the "600 ohm" transformer was 47kohm, would it matter? (probably not)

Take an ohmeter and determine the total resistance of the attenuator.

Figure it out... there is an input wire, a ground, and a wire going to the moving part (the wiper). Measure from the input wire to ground.

Also take note of which RCA jack is labeled INPUT and which pins of which xfmr it goes to! Then look up the UTC transformers online and see what the pinout is, and that will tell you the impedances.

Now you will have learned something.

In the mean time, use it with your tube amp - it will be very good.

Be happy you have such a nice thing.
If you don't like it anymore, send it to me. I will pay the shipping.

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Old 14th May 2006, 11:10 PM   #8
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Quote:
Perhaps it is 600 ohm in ---> 600ohm out ---> attenuator ---> 600ohms ---> High Z ---> out
yes, now I see. Most probably you are right.

It makes for a really nice unit. I wouldnīt mess with it. Do not take it apart. From the pics itīs really well built, and the parts it uses is fantastic. Think like this: If you take it apart to use it in a unit, you loosemany possibilities. It would be much better to make some different tube preamps and keep the preamp separated. So, you could use it with any of your tube amps, and you also could use your tube amps without the transformers... Got it?

Just keep the high impedance output cable very short. The preamp should stand close to the amplifier input, and use a cable of no more than a meter. Use good quality shielde cable, but do not get crazy about it...

The advatage of transformers is that you could also build some amps with balanced inputs, and connect the transformer hi- side in balanced fashion.

Also, good for all push pull amps. no phase spliters, no nothing. All stages push pull. Good for no feedback amps.
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Old 14th May 2006, 11:38 PM   #9
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by bear

If you don't like it anymore, send it to me. I will pay the shipping.


no,Bear-I'm closer,so I'll pay less for shipping
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Old 15th May 2006, 12:36 PM   #10
jovan is offline jovan  Yugoslavia
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Thanks for the answers, a lot!!

I'll you it in combination with Pass First Watt maybe, or with some tube amp...I'll see. If i decide to sell it, i'll send you a message about it; but, it could be complicate, because i don't know how much it's worth... Thanks again, and if there is some good ideas, i'm here!
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