Rpschultz13
Active member
Anyone care to compare/contrast the PPCB Mini JFET Buffer with others. It's really simple. What are it's limitations?
Wanting to add it to a True Bypass tuner.
Wanting to add it to a True Bypass tuner.
PPCB Mini JFET Buffer
- Thread starter Rpschultz13
- Start date
JTEX
Well-known member
Compared to a (good) op-amp buffer, this will have:
- less headroom (the output can't swing rail-to-rail)
- more distortion (if it matters)
- much poorer power supply rejection (if there's noise in the power, it easily makes it into the signal)
- higher output impedance
- depending on the op-amp it's compared to, it might actually draw more idle current, if it matters.
On the plus side, it might be quieter than many op amps, and maybe marginally easier to build.
- less headroom (the output can't swing rail-to-rail)
- more distortion (if it matters)
- much poorer power supply rejection (if there's noise in the power, it easily makes it into the signal)
- higher output impedance
- depending on the op-amp it's compared to, it might actually draw more idle current, if it matters.
On the plus side, it might be quieter than many op amps, and maybe marginally easier to build.
JohnnyCreepy
Member
Rpschultz13
Active member
Good read. So which version (fet or opamp) would color my tone the least?
It looks like the PPCB one I show above, is the front end of the Dr. Quack Envelop Filter.
It looks like the PPCB one I show above, is the front end of the Dr. Quack Envelop Filter.
Rpschultz13
Active member
Here's my tuner, I have 2 prototypes. The one on the right I've modified to add a J201 fet buffer (post #1) on the output. Currently the board has an LM358 and uses 1 op amp for the tuning circuit gain and the other as a buffer into the ESP32 that processes the tuning.
I played through it on my acoustic, sounds great to me. It does what a buffer should. Without it, my signal going into the amp (without any other pedals/buffers) is weak and I have the gain it up a fair bit. But with it, the signal is much stronger. When I put it in my pedalboard there is no noticeable difference because there are other buffers involved.
This AMZ page says op amp buffers are even better then fet buffers. It mentions a TL071, and I wondered about using a TL074 instead of the LM358. Having a single TL074 could give 2 op amps to the tuning circuit, 1 for an output buffer and have an extra one for who knows what.
Conversely, the fet buffer is extremely minimal part count and would be simple to add. A TL074 would take more board space.
Thoughts?
I played through it on my acoustic, sounds great to me. It does what a buffer should. Without it, my signal going into the amp (without any other pedals/buffers) is weak and I have the gain it up a fair bit. But with it, the signal is much stronger. When I put it in my pedalboard there is no noticeable difference because there are other buffers involved.
This AMZ page says op amp buffers are even better then fet buffers. It mentions a TL071, and I wondered about using a TL074 instead of the LM358. Having a single TL074 could give 2 op amps to the tuning circuit, 1 for an output buffer and have an extra one for who knows what.
Conversely, the fet buffer is extremely minimal part count and would be simple to add. A TL074 would take more board space.
Thoughts?
