So the curves are NOT from a test tape, right - SO the effects of the tape head are NOT being considered. Too bad.
Have you thought about using a flux loop to include the head.
Believe that the 56K (R8/23) resistor across the 100nf cap rolls off the lows. It's a compromise between "total" LF rolloff and allowing more lows at the expense of head bumps. Might want to play with it.
As mentioned - head "loading" (R/C) can affect the highs - especially around 20-30Khz. Values Revox chose are fine.
Have you thought about using a flux loop to include the head.
Believe that the 56K (R8/23) resistor across the 100nf cap rolls off the lows. It's a compromise between "total" LF rolloff and allowing more lows at the expense of head bumps. Might want to play with it.
As mentioned - head "loading" (R/C) can affect the highs - especially around 20-30Khz. Values Revox chose are fine.
The plots are taken with monitor switch to tape while recording so I guess both heads are included?
I'm not sure what a flux loop is. 🙂
I tried a 39k for R8/R23 because they are found in other versions of the record board but as you said it only affects the lows.
I tried the head loading as suggested here but that also didn't affect the bump.
Indeed the frequencies above 15-20k got up.
I'm not sure what a flux loop is. 🙂
I tried a 39k for R8/R23 because they are found in other versions of the record board but as you said it only affects the lows.
I tried the head loading as suggested here but that also didn't affect the bump.
Indeed the frequencies above 15-20k got up.
Two questions:
a) what happens when you swap the playback channel inputs at head leads?
b) have the switches been cleaned?
a) what happens when you swap the playback channel inputs at head leads?
b) have the switches been cleaned?
Two answers:
a) the curves are different but I didn't try to adjust them. I can swap them again and take some plots if you like.
b) yes, the interconnection board, all switches and pots has been cleaned completely including the large fast / slow switch.
Latest I did was fine tuning by ear and the results are pretty good on both speeds.
a) the curves are different but I didn't try to adjust them. I can swap them again and take some plots if you like.
b) yes, the interconnection board, all switches and pots has been cleaned completely including the large fast / slow switch.
Latest I did was fine tuning by ear and the results are pretty good on both speeds.
It would be nice if you would do that.
Then it should be a bit more clear whether the problem is in the channel signal amplification area or in the tape/PBhead combo.
Will do but you will see the unadjusted results.
I rather not turn all 10 pots again, now that I found a certain sweet spot. 🙂
I rather not turn all 10 pots again, now that I found a certain sweet spot. 🙂
Sorry, this does not make sense.
If you have tuned your device into your comfort zone then measurements really do not count 🙂
I made them anyway so I'll post them, one never knows what it's good for. 🙂
Swapped playback head channels:
Slow speed:
Fast speed:
Swapped playback head channels:
Slow speed:
Fast speed:
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Here are the plots with normal connected channels:
https://www.diyaudio.com/community/...revox-b77-frequency-curve.414076/post-7713261
Swapped: In low speed we see a better responce in the high regions, particularly the left channel (which is now red instead of green)
In high speed we can see the same behaviour: better high frequency response but both channels deviate at about 1kHz.
https://www.diyaudio.com/community/...revox-b77-frequency-curve.414076/post-7713261
Swapped: In low speed we see a better responce in the high regions, particularly the left channel (which is now red instead of green)
In high speed we can see the same behaviour: better high frequency response but both channels deviate at about 1kHz.
Oh, it's marked on top of them.
First is always slow speed, second is fast speed.
Red is right channel, green is left.
On the swapped channels, red is left, green is right.
All are taken at -20dB
First is always slow speed, second is fast speed.
Red is right channel, green is left.
On the swapped channels, red is left, green is right.
All are taken at -20dB
The last discussion was about swapping the channels (tape/head vs PB amplifier chain/board channel)...
In this post https://www.diyaudio.com/community/...revox-b77-frequency-curve.414076/post-7714393
I swapped the wires L & R of the playback head.
In this one https://www.diyaudio.com/community/...revox-b77-frequency-curve.414076/post-7714436
I reverted back to normal (L = L & R = R)
I swapped the wires L & R of the playback head.
In this one https://www.diyaudio.com/community/...revox-b77-frequency-curve.414076/post-7714436
I reverted back to normal (L = L & R = R)