Building a Dundovic tape playback preamplifier

SeleniumFalcon

Thanks for your list, I'll print it out and use it to search on eBay. I have the Kind of Blue tape, I was buying some used records at a shop on 31st Street in Baltimore and as I was paying I saw this tape. I asked about it and the owner said, "you can have it, nobody's buying tapes any more". Of course this was a few years ago before the recent interest in certain ones. I see them selling (or asking) for around $500.00.
I too, have more 2 track tapes than anything else. I started collecting them along time ago, I even bought a tape from J. Gordon Holt in beautiful shape for only $80.00. At the time I was guided by a tape enthusiast named Rich Brown who advised me to find a high speed 2 track Revox A77. I bought one off of a retired recording engineer and that started my efforts to refurbish tape recorders. He also sold high quality copies of safety master tapes and I collected them as well. Then he recommended the Stellavox SP7 deck which I bought from another collector named Charles King. At that time The Tape Project started up and collectable tapes began spiraling upwards. So, I found myself trying to find a way to get the most from 4 track tapes which had more recent (a relative term) artists.
Thanks agin for your list, it's good to know another tape enthusiast.

Jetmaker737

That's very cool that you got Kind of Blue for free. I paid $300 for the 4-track version in May 2022. It has gone for as high as $424 in the 4 years I have been tracking prices. The 2-track version has gone for as high as a whopping $1034! Prices went crazy during the pandemic, they've now cooled off a bit.

AVHead

SeleniumFalcon wrote: »

I prototyped the circuit so I could see if it actually worked.

I noticed you mentioned elsewhere that you added the Shure M64 pre in flat mode after this tape pre to get some more gain. Since you prototyped this, I was wondering if you might have tried different load and emitter resistor values (and probably the feedback network too) to see if you could extract some more gain out of the tape head pre itself ?

SeleniumFalcon

No, I didn't think to do that, it would have been a good idea. I believe I initially connected the Dundovic to my system, by itself, and just increased the volume on my preamp until things sounded loud enough (around 10:00 o'clock I think). Then I connected a tube based gain stage that I built for a Dolby B project and wasn't happy with the resultant sound. Then I tried the Shure and there was no noise degradation and I could reduce the Dundovic volume, which seemed to improve distortion and headroom, and the combination sounded so good, I left things alone and didn't experiment further. Then, I think I got side tracked working on playing this combination with a Dolby 422 decoder (I was collecting Dolby B prerecorded tapes) which has a different calibration process than I was used to. I'm easily distracted.
In hindsight I should have determined the output of the Crown playback heads (I believe I measured 1.0mV) and duplicated this on my test signal generator and measured the total gain and tried to determine how much gain I needed.

AVHead

0.1mv does seem quite low. It would require a lot (78db!) gain to get it up to .77v.
Was that on unloaded heads ? or loaded into the pre ?
If loaded then it might be worth checking if they are being loaded too high (low input impedance of the pre).

SeleniumFalcon

Wrong decimal place it should be 1.0mV, sorry.