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
Active 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?
Feral Feline
Well-known member
My thought is you should be offering this Q Tune as a kit to DIYers who want the last piece to the puzzle of a FULLY-DIY pedalboard!
Seriously though, the SMD version of the TL074 is cheaper than getting a couple TL072 through-hole ICs. The SMD footprint is super-compact.
I'd say it's the way to go if you've enough tuner-boardspace left.
The last op-amp in the TL074 could be used for power-conditioning/buffering whatever you want to call it.
Seriously though, the SMD version of the TL074 is cheaper than getting a couple TL072 through-hole ICs. The SMD footprint is super-compact.
I'd say it's the way to go if you've enough tuner-boardspace left.
The last op-amp in the TL074 could be used for power-conditioning/buffering whatever you want to call it.
Rpschultz13
Active member
That IS the plan. My partner @joulupukki and I Hope to offer a DIY kit… we’re getting close. Couple more months maybe. I think our tuning algorithm and smoothing is AS GOOD or possibly BETTER than the top 3. (Turbo, Peterson, Polytune3). I’m a tuning snob, but I find I prefer tuning with Qtune over the rest, surprisingly.
But I need to get this buffer figured out, with accessible dip switched to turn on/off. I’m kinda leaning toward the simple JFET buffer in post 1, sounded great to me.
Rpschultz13
Active member
Yeah LCD displays are notorious for noise. We found a 5khz noise in our display and was able to turn it off through programming. We have a separate ground for the display, we think this has the noise issue covered.
But I’ll try what you suggest.
But I’ll try what you suggest.
Rpschultz13
Active member
To do monitor output (tuning unmuted), I think I need a splitter. AMZ has a JFET splitter option. Where could I find an op amp splitter circuit?
PPCB has a splitter, but the schematic isn’t posted @Robert
PPCB has a splitter, but the schematic isn’t posted @Robert
Feral Feline
Well-known member
AMZ 2 channel Splitter
Collection of vero (stripboard) & tagboard layouts for 100s of popular guitar effects, with over 1000 verified designs. DIY your own boutique effects!
tagboardeffects.blogspot.com
Op-amp based
Op-amp
Also look into the Craig Anderton Spluffer, a splitter-buffer that's promising. Op-Amp based though.
Utility Boxes - Blend, Power, Looper, etc. - Craig Anderton 3-Channel Spluffer/Phase Switcher/Mixer
Craig Anderton 3-Channel Spluffer/Phase Switcher/Mixer. There are already a couple of similar utilities posted. This one is an all-in-one 3-channel buffer, phase inverter, and mixer. It has 2 wet...
guitar-fx-layouts.238.s1.nabble.com
Other Fodder for thought is any delay, chorus, flanger — They all split the signal...
Rpschultz13
Active member
Using the AMZ splitter, I think this works. Any suggestions?
Rpschultz13
Active member
I guess one question I have for this is, in TB mode, is this still considered True Bypass? Signal is still flowing through C6 and into the tuner through the Tuner Buffer. I would think the buffer creates a high enough impedance such that it doesn't affect the signal going through the True Bypass leg. Yes? No?
Rpschultz13
Active member
So then like this. Other side of relay disconnects that portion of circuit when in TB mode.
Rpschultz13
Active member
Based on other PPCB threads, the J113 seems to be an acceptable alternative to the J201. 10x cheaper.
Rpschultz13
Active member
I need (prefer) thru hole
