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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
Follow Ups:
Hello again Charles,I mispoke regaring the signal output of my Tascam 42B tape playback head. It is 30 ohms impedance rather than 50 ohms. Sorry bout that sir.
bob
An African American audio, classical & jazz music lover. I love all great jazz, classical and folk music. Am also a lover of 1/2 track (15ips) reel to reel tape decks.
Edits: 03/24/13
Good afternoon Charles (Mr. Stellavox), As always, you are a wonder sir and honest to a fault. Again, I so wish I could afford the King Cello. What a musical thrill that would be. Not being able to do that, I thought I would ask the tech if he could do so. He felt that he could do it basing it on a very excellent phono pre amp he had built. I will never believe you would have anything negative to say about anyone, especially someone in our beloved audio area.
As we speak, I note you have a brand new King Cello Pre Amp out for consumption and that's wonderful. It is my dream to just get to hear one playing one of the better reel to reel tapes. Again, I am hoping that someone brings another audio show here to Georgia. I am sure if that were the case there would be more presenters using reel to reel tape as a playing medium.
Charles thank you so much for taking away from your busy schedule to respond to my need for information. I do appreciate. I am sure someone who has actually used a SUT in a tape head pre amp will respond sir.
bob
An African American audio, classical & jazz music lover. I love all great jazz, classical and folk music. Am also a lover of 1/2 track (15ips) reel to reel tape decks.
How much CAN you afford? As I posted last August (you responded), the deHavilland 222 that I own and love seems to be just the ticket. Price then was $2295. I bought mine without tubes for $2200. Plenty of gain, quiet as a tomb, NAB/IEC choice, sounds fantastic with my Otari, modified with tape head output and Bottlehead's tape path mod kit.
You might scroll down and re-read the thread.
Hello Mr. Pogue,
I more than appreciate this post. I am familiar with, but never heard, the dHavilliand 222. I truly believe it's a fabulous tape head pre amp, but, as a government retiree living on a fixed income I must be very careful with expenditures. This is the reason I thought to have one build that would fall within what I could afford. The project is coming along. I have already begun to purchase recently recorded reel to reel tape and I can't argue about the prices. So I am looking to have a working tape head pre amp once it's completed. I know you're going some good listening. Put on a tape for me (smile).
bob
An African American audio, classical & jazz music lover. I love all great jazz, classical and folk music. Am also a lover of 1/2 track (15ips) reel to reel tape decks.
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