I'm using my TU-8600S with a preamp, which allows me to connect to multiple sources and produces a more dynamic bass. The gain is now too high. I have to turn the volume knob on the TU-8600S to 2-3 o'clock position to make the noise from my preamp inaudible.
I'm wondering if we can replace the 12AX7 with a lower gain variant such as the 5751 so that we can turn the TU-8600S volume pot to maximum position, effectively taking it out of the circuit. The volume will be controlled only by the preamp.
Any thoughts?
I'm wondering if we can replace the 12AX7 with a lower gain variant such as the 5751 so that we can turn the TU-8600S volume pot to maximum position, effectively taking it out of the circuit. The volume will be controlled only by the preamp.
Any thoughts?
I am afraid it is not that simple for various reasons.
- Elekit amps use some global negative feedback. If you change the gain of the amp then the feedback needs to be adjusted accordingly as bandwidth and phase compensations depend on its amount. The TU-8200 is very sensitive to changes to the feedback level and, not surprisingly, the design value provides the best sound overall. The 8600 must be very similar.
- The 5751 has about 30% less gain in an average circuit configuration than the 12AX7, and the change to the amp's sensitivity will be even less with the negative feedback applied. That difference is insignificant.
- You can achieve similar result by removing the cathode bypass caps, but that also impacts feedback levels as well as distortion characteristics.
- Elekit amps use some global negative feedback. If you change the gain of the amp then the feedback needs to be adjusted accordingly as bandwidth and phase compensations depend on its amount. The TU-8200 is very sensitive to changes to the feedback level and, not surprisingly, the design value provides the best sound overall. The 8600 must be very similar.
- The 5751 has about 30% less gain in an average circuit configuration than the 12AX7, and the change to the amp's sensitivity will be even less with the negative feedback applied. That difference is insignificant.
- You can achieve similar result by removing the cathode bypass caps, but that also impacts feedback levels as well as distortion characteristics.
Thanks. That's a good point. Using a different tube will shift the operating point and bias, and it gets more complicated with the NFB. I don't know if it is for better or for worse.
I was thinking that there are always some manufacturing variability, and different tube manufacturers may have even larger differences. 30% difference in mu is not small but I don't know how it compares to the variability in the tube itself.
I don't have any 5751 at hand, so I was thinking if anyone has already tried it or has tried something similar.
I was thinking that there are always some manufacturing variability, and different tube manufacturers may have even larger differences. 30% difference in mu is not small but I don't know how it compares to the variability in the tube itself.
I don't have any 5751 at hand, so I was thinking if anyone has already tried it or has tried something similar.
I have used them without issue in place of the 12ax7 or as a pair in place of the 12au7. Also have used all across as well for all 3 tubes. Didn't go out looking for them specifically I just have some lying around. Yes you get gain differences and whatever but if you have em slap em in and enjoy the changes, amp won't blow up.