In Reply to: RE: Tube Tape Head Step Up Transformer posted by Music Man Bob on March 23, 2013 at 07:54:01:
Bob,
Apparently, under "normal" listening conditions your tech indicates that the preamp has a hiss problem. So, the desired signal isn't being amplified or "lifted" enough above the noise (hiss) so that that it becomes un-noticeable. We have here what in technical terms would be called a poor signal-to-noise ratio. To alleviate this, you need more gain. Gain however doesn't come without a noise penalty. The tech could try and get more gain out of the preamp but that then dissolves into the tube types used and how much gain you can eek out of them. Another way is to use a step-up transformer at the input, which can give you gain "without much noise" (I won't say noiseless). Step-up transformers are used extensively with moving-coil phono cartridges in tube preamplifiers, as the cartridges have a much lower output than moving magnet cartridges and require 10 to 15dB more gain. A step-up transformer can provide this gain with miminal added noise. I have used transformers in microphone preamps but have no experience with them in the phono world. Since your tape head output impedance is around 50 ohms you could probably get away with a microphone step-up transformer that has an input impedance as close to that as possible and with as high a step-up ratio as you can find. Realistically, you may have to settle with a step-up ratio of ten to one and perhaps an input impedance of 150 ohms or so (will have to load the secondary properly for best transient response). Undoubtedly other inmates could make better suggestions based on their own experience. I don't have the specs on the LL-1536 but do know that Lundahl makes some great transformers. Finally, I don't mean to question your tech's knowledge; he is on the right track but we're obviously entering new territory here.
Charles
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Follow Ups
- RE: Tube Tape Head Step Up Transformer - stellavox 03/23/1314:47:23 03/23/13 (4)
- RE: Tube Tape Head Step Up Transformer - Music Man Bob 11:49:58 03/24/13 (0)
- RE: Tube Tape Head Step Up Transformer - Music Man Bob 15:08:10 03/23/13 (2)
- RE: Tube Tape Head Step Up Transformer - Dave Pogue 17:12:17 03/23/13 (1)
- RE: Tube Tape Head Step Up Transformer - Music Man Bob 17:22:43 03/23/13 (0)