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Old 13th December 2010, 08:38 PM   #1
djn is offline djn  United States
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Default IS there any OTL pre amps out there?

I am thinking about building a pre amp but don't really need that much gain. I thought about a DHT pre amp but then started thinking about going OTL pre amp. I've never heard of one.....any help?
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Old 13th December 2010, 09:10 PM   #2
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Generally, preamps don't use output transformers. They use output coupling capacitors.
You could design a preamp without output coupling capacitors if you used bipolar voltages on the preamp. I'd be afraid of too much residual d.c. voltage on the output of the preamp as the tubes reach operating temperature and as they age. Readjustment of the bias would be necessary on a regular basis.
In general ... not a good idea. A tube failure could put a huge amount of d.c. on the output.
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Old 13th December 2010, 09:26 PM   #3
DF96 is offline DF96  England
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You have never heard of an OTL preamp because almost all preamps are OTL, so it doesn't need to be said.
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Old 13th December 2010, 10:03 PM   #4
djn is offline djn  United States
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OK, here is where I am coming from knowledge wise. The last and only pre amp I had was a John Hogan Line Stage. "line stage" might be different than pre amp....I don't know. But the Hogan line stage has OTs so I assumed all pre amps had OTs.

Thanks for the clarification.
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Old 13th December 2010, 10:52 PM   #5
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So- do you want to know how to set up a tube preamp with a direct-coupled output?
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Old 13th December 2010, 11:00 PM   #6
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Quote:
Originally Posted by atmasphere View Post
So- do you want to know how to set up a tube preamp with a direct-coupled output?
Why, yes I do. I was thinking OTL just to keep the signal path simple. Derect coupled sounds even cleaner.
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Old 13th December 2010, 11:08 PM   #7
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Did you have anything in mind besides a direct-coupled output?
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Old 14th December 2010, 12:07 AM   #8
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Quote:
Originally Posted by djn View Post
Why, yes I do. I was thinking OTL just to keep the signal path simple. Derect coupled sounds even cleaner.
Try this: SYclotron Audio The Heretical Preamp
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Old 14th December 2010, 01:13 AM   #9
djn is offline djn  United States
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Quote:
Originally Posted by atmasphere View Post
Did you have anything in mind besides a direct-coupled output?
Well, to be honest, I've been running my system (which I just sold off) with only a passive volume pot going into a Behringer 3400 then to three amps, each with a volume pot to balance the volume between drivers.

So, this whole preamp is new to me. Just before I got ride of everything, I put the Hogan line stage right in front of the 3400 and the system really came alive.

So in the new system I wanted to include a preamp/line stage.....if there is a difference.

I am building three amps at the moment. A 12HL7/GM70, a PP E-linar 807, and a Tim Mellow OTL.

I am also building a three way tube crossover.

My speakers are the big Heil on top, a large Tractrix horn with the TAD 4001 for mid, and a vented box with TD15M for midbass, and a pair of subs with Martin Logan Sub drivers.

I am using a passive volume pot/selector switch before the pre.

SO, I could use some advice as to what to include in the preamp.
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Old 14th December 2010, 01:18 AM   #10
djn is offline djn  United States
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Quote:
Originally Posted by dsavitsk View Post
Interesting read. I think I need to print that one out and do some studing.
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