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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 24th Sep 2019, 8:53 am   #21
Michael Maurice
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Default Re: New amplifier for reel to reel

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Unless you can come up with a better solution than the original manufacturers then in most cases you'd be best repairing the original cards.
My thought was prompted by the fact that I need another 8 cards for the MTR90 now that I have a 24 track playback head for it. Used working cards seem to go for around £100 each but my machine is an early Mk1 which is slightly different to the later Mk1s and Mk2s so anything I buy would need to be modified anyway.
But this is a totally different scenario to that of the O/Pís. In this case, youíve very little to lose.
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Old 24th Sep 2019, 11:27 am   #22
Ted Kendall
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Default Re: New amplifier for reel to reel

I still think building from scratch is doing it the hard way in this case. Granted, the original Mk I was no beauty and was heavily revised, but there is more in common with the subsequent versions than not.
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Old 24th Sep 2019, 10:12 pm   #23
jamesperrett
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Default Re: New amplifier for reel to reel

Logically you are almost certainly right Ted - it would probably take me ages to actually do anything but I miss having an electronics design project to really get my teeth into.
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Old 25th Sep 2019, 9:00 pm   #24
hillmanie
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Default Re: New amplifier for reel to reel

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Here's the expensive ready-made end of the market!

this is pretty easy compared to recording when intimate knowledge of the heads in use is required.

ch
Expensive? I'll say. One I see is $9k !!
Re pre-amp is it fair to say that even if you bought advertised as 'tape head pre-amp' you'd still have to re-design it to match to your heads? Do the characteristics of tape heads differ much?
TT
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Old 26th Sep 2019, 5:27 am   #25
TIMTAPE
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Default Re: New amplifier for reel to reel

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Originally Posted by wd40addict View Post
Here's the expensive ready-made end of the market!

this is pretty easy compared to recording when intimate knowledge of the heads in use is required.

ch
Expensive? I'll say. One I see is $9k !!
Re pre-amp is it fair to say that even if you bought advertised as 'tape head pre-amp' you'd still have to re-design it to match to your heads? Do the characteristics of tape heads differ much?
TT
Heads for older valve tape machines were usually high impedance and so a modern preamp would need a FET type front end. The repro head in a Tascam 122 Mk III feeds a FET front end preamp. Similarly in a higher end Akai GX cassette deck I have. I suspect the heads are of somewhat higher impedance than in run of the mill cassette decks.

But it also relates to tapes and tape formats. High speed, wide track open reel tapes were not too critical as the signal off tape was relatively strong, and that signal (including tape noise) could mask the preamp noise. But slow speed, narrow track recordings (not least cassettes) had a weaker signal so the preamp needed to have very low noise so as not to add noise to the weak signal off tape. I modded the replay preamp on my Revox A700 mainly to lower preamp noise in the slower tape speeds and with quarter track tapes. I doubt it would make any audible improvement for 15ips wider track "pro" recordings.

One of the 'advances' in tape machines was a switch which muted the play head preamp except when the tape was playing. It made it appear that any noise heard (including hum) was solely from the tape, for when the tape was not moving, the preamp seemed silent. On some of my machines I've disabled this switch so I can hear truthfully the noise the playback preamp contributes. It may seem like tape noise but it isn't.

So like some others here, I modify for an audible, measureable benefit, or for more reliability. Why else would one do it? Boredom perhaps.

Last edited by TIMTAPE; 26th Sep 2019 at 5:42 am.
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Old 26th Sep 2019, 9:09 am   #26
wd40addict
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Default Re: New amplifier for reel to reel

It was the high level of hiss that led me to design my own electronics for my Brenell pictured above.

Prior to this I had used a Collaro / Magnavox 363 deck with the playback section of the Practical Electronics tape link circuit. This design dated from the 70s and used an FET for high impedance input feeding a 741used for gain and EQ. It sounded ok, but sadly the noise level from a blank tape was only slightly higher than the amplifier itself!

Eventually the 363s rubber died so I started to look round for a decent 3 motor deck to try my own ideas out. I found the Brenell and built an op-amp based playback pre-amp. This was much quieter than the PE design. Eventually I also added full featured record amplifiers.
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Old 26th Sep 2019, 1:52 pm   #27
TIMTAPE
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Default Re: New amplifier for reel to reel

Interesting to hear someone else having worked on the same issue of playback preamp noise. Bulk erased tape's residual noise (especially later Low Noise tapes) is indeed a good reference point for the preamp's noise, especially when a listening test is coupled with viewing on a sensitive VU meter and Spectrum Analyzer.

A simple improvement I made was to various Japanese battery powered portable recorders I used to own, which had Germanium transistors. Not so bad in many areas of the amp but for preamplification, usually pretty noisy. I sometimes replaced just the first stage Germanium PNP transistor with a BC 559 and simply rebiased it for best performance. One transistor and one resistor. No other changes. Since the preamp doubled as the mic preamp, that was now less noisy as well.
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