Beginner trying to design a hybrid tape head playback amp

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flancfuster

Member
Joined 2009
#1
While looking for a tube playback amp for reel to reel tape machines and reading some of the threads from here I couldn`t find any schematic to try.
After studying different schematics for playback (Ampex 351, Studer C37 and my Fostex E2), simulating and learning from them, I came up with a hybrid design ala Allen Wright.

Gain is around 57dB and can be adjusted by changing value of resistor R3.
R2 and C3 values are suited for my Fostex E2 tape head (taken from service manual schematic)
EQ can be adjusted using R7 and output level using R13/18.
EQ was calculated for CCIR 15ips.
Added a mosfet source follower to lower the output impedance.

I did some simulations in LTSpice and the figures looks pretty good.

Let me know what you think. Attached some photos and simulation file.

FYI this is my first attempt to design a circuit, I`m no EE, I`m just a self taught diyer.
schematic.jpg
EQ.jpg
THD.jpg
Layout.jpg
View attachment TAPE REPRO HYBRID.asc
 
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#3
I'm very impressed with your design so far and wonder if you have developed it any further in the last six months. I am also building a tube-based tape head preamp for my Otari MX5050. If you're a beginner, then I'm certainly a novice. I have built a prototype based on an Allied Electronics design from the mid-sixties, but am having issues with noise and clipping. I like that you have adapted a design by Allen Wright of Vacuum State. I use his Super reg and find it to be excellent in my Ultrapath line stage that I built.
How does your tape head playback amp sound!? Does it provide a significant improvement over the solid-state electronics of the Fostex or the Teac in your opinion?
 
#4
kmate said:
I'm very impressed with your design so far and wonder if you have developed it any further in the last six months. I am also building a tube-based tape head preamp for my Otari MX5050. If you're a beginner, then I'm certainly a novice. I have built a prototype based on an Allied Electronics design from the mid-sixties, but am having issues with noise and clipping. I like that you have adapted a design by Allen Wright of Vacuum State. I use his Super reg and find it to be excellent in my Ultrapath line stage that I built.
How does your tape head playback amp sound!? Does it provide a significant improvement over the solid-state electronics of the Fostex or the Teac in your opinion?
Click to expand...
Thank you for your kind words. The tube tape repro amp works perfect. There is no hum, noise whatsoever, I just need to connect a ground cable from Tape machine to tape repro amp. I still have to install it inside a chassis, probably two chassis, one for power supply to keep induced hum from transformer at minimum.
Regarding sound, I find it more to my liking than solid state. I'm probably biased, because I love the sound of Tesla PCC88. I have built a balanced phono preamplifier with them (see here) and it remains my reference phono stage. The sound of tape repro amp is detailed, non-fatiguing, linear and with great expansion on soundstage. Fostex, having 2Sk170BL in repro amp sounds better than Teac's transistor repro amp. Installing tube repro amp on Teac, takes the sound to another level, better than Fostex. Didn't install it yet onto Fostex, as I have to make some modification on wires coming from tape heads.
In conclusion, it's a keeper. Design wise, I was thinking to make a fully balanced version from tape heads to output, but that may be overkill.
 
#5
I have been keeping an eye on this thread too.

I'd like to make one from your design and try it out. I could make it from a board and the schematic. Do you have a spare board you could sell? Or a set of gerbers so I could have a board made?
 
#6
kmate said:
I'm very impressed with your design so far and wonder if you have developed it any further in the last six months. I am also building a tube-based tape head preamp for my Otari MX5050. If you're a beginner, then I'm certainly a novice. I have built a prototype based on an Allied Electronics design from the mid-sixties, but am having issues with noise and clipping. I like that you have adapted a design by Allen Wright of Vacuum State. I use his Super reg and find it to be excellent in my Ultrapath line stage that I built.
How does your tape head playback amp sound!? Does it provide a significant improvement over the solid-state electronics of the Fostex or the Teac in your opinion?
Click to expand...
I like another impressed follower would be interested in purchasing a blank PC board if if have spares.
regards,
 
#8
@fancluster, good job, just a question, wich Voltage are M+ (12V ?!) B+ (245V ?!) F+ (6.3V ?!) ...... I'm working to build your project (Reverse engineering from PCB picture), it's 95% finish, I wanna test with Revox B77 ... if you have some advise about fine tuning, I really appreciate .... many thank's PB
 
#12
Many thank's !!!! Any suggest for fine tuning with Revox B77 Head ?! the 64K resistor above the trimmer EQ Adjust looks like a mistake ... in the Right Channels (and circuit) 200K is the value. Another question, the 26K resistor is very difficult to find .... do you think 24K it's not ok ?!

Many Thank

PAOLO
 
#13
If you have the reproduce amp schematic from Revox B77, use the same value of the input resistor to ground in place of 56K from PCB. I suggest to omit the resistor (strap with wire) above trimmer EQ, if you have a way to measure frequency response try using 64K. 26K/3W resistor I found it at mouser. I suggest to use 27K instead of 24K
 
#19
If you have the reproduce amp schematic from Revox B77, use the same value of the input resistor to ground in place of 56K from PCB. I suggest to omit the resistor (strap with wire) above trimmer EQ, if you have a way to measure frequency response try using 64K. 26K/3W resistor I found it at mouser. I suggest to use 27K instead of 24K

sorry … you mean 27 instead of 26K (26 not available at mouser)
 
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