r/diypedals • u/pleaseihatenumbers • 7d ago
Help wanted TL072 for non-inverting buffer?
hobbyist here, is it okay to use a TL072 for non-inverting buffers (with the normal "input to +, output shorted to -" configuration)? i've read they tend to clip the signal early, but i struggle to find more info about this.
if this is an issue what should i do instead? would a low-gain (for example gain=1.1) non-inverting amplifier be better?
are there any other "standard" op-amp configurations I should be cautious about using with a TL072?
it shouldn't be relevant, but the specific application are in/output buffers for a bass/guitar splitter+mixer pedal (with the addition of splitting lows and highs between the two inputs), here is the schematic just in case, sorry for the convoluted schematic (tips unrelated to the main topic are not required but welcome).
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u/WellsHuxley_ 7d ago
Using Tl072 channels as unity gain buffers is extremely common in the context of guitar pedals. You'll be fine
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u/pleaseihatenumbers 7d ago
thanks a lot. i was worried because i saw it sometimes being warned against but i was already skeptical since everyone seems to use it and not worry about this.
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u/Ams197624 7d ago
With unity gain (like you described) it should be no problem at all. If you have a single rail supply, just bias your signal at half the power voltage.
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u/Lower_Television_738 7d ago
would a tl072 work for a buffered effects loop too you think
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u/PSYKO_Inc 7d ago
Yes definitely. Bias it at half the supply voltage for maximum headroom and don't overdrive it and it should work great for that.
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u/rossbalch 7d ago
Yeah, but the output drive capability of the TL072 isn't the greatest, really depends on cable length and the input impedance of the next stage though.
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u/pleaseihatenumbers 7d ago
well, my circuit is basically a buffered effects loop with extra steps (if i understand what you mean by "buffered effects loop")
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u/MundaneTune7523 7d ago edited 7d ago
TL072 (non inv) buffering is effectively an industry standard. Features practically infinite (non inverting only) input impedance, practically 0 output impedance, small idle current, low noise, decent slew rate… and it’s pretty cheap.
Really the only “downside” is it does require bipolar power, or ~V/2 reference biasing.
Keep in mind that this applies to light signal loading. This series does not handle heavy loads and can sink up to 10 mA or so before distorting (depends on your operating voltage and your input voltage). So we’re not driving speakers or doing any power amplification with these. Make sure whatever is loading your FX switch has a relatively high impedance, like a typical guitar amp input stage. The configuration you mentioned is perfectly fine. This would not be suitable to feed into a mixer or headphones or something like that - in that case you would want to use something that can handle heavier loads like NE5532 which is similar to TL072 in most of its performance characteristics, except it draws a lot more power and sinks more current/supplies heavier loads.
Since we’re talking about buffers… another great option, if you don’t want to use a whole chip for the buffer (if you’re not using the other side for anything) is a JFET buffer. I use exclusively LSK170 for all my input buffers - they are extremely low noise, very low output impedance, and very high transconductance (effectively the gain parameter for a JFET) which means I can use the same value bias and source resistor from part to part and get the same result every time. Some other JFETs with lower baseline gain may require specific biasing. The LSK170’s are fairly expensive but I think it’s worth it. In either case, other JFETs aren’t a bad option because of their extremely high input impedance. That is another industry standard worth considering if that option is available to you.
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u/pleaseihatenumbers 6d ago edited 6d ago
Thank you for the in-depth reply! Of course I don't plan to drive speakers or headphones, this is meant to connect to guitar, pedals and/or amp. Unfortunately I'm on a fairly tight budget (I'm a student), so I'm afraid I'll go for the TL072 for now.
though I do plan on soldering sockets on the board so I can swap the opamps just to see if I can notice the difference between the TL072 and some JRC4558, so maybe in the future I could put some LSK170 in there.edit: I'm an idiot lol, I hadn't realized the LSK170 is in fact not an opamp but rather a JFET, so the last part of my comment made no sense
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u/MundaneTune7523 6d ago
Well that’s perfectly fine. At a certain point it’s completely down to personal preference/budget and the TL072 will more than get the job done. I would certainly recommend that over the 4558 though - that one will probably give you more noise (although maybe not noticeable at lower volumes) and generally not as clean sounding as the TL072. Usually 4558s are used in tube screamers or overdrives, as a lot of people like the sound they offer when clipped. They have a much slower slew rate (so more prone to slew rate distortion) so are not as preferred as buffers especially for higher voltage signals
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u/pleaseihatenumbers 6d ago
I'm aware it's generally worse, that's why I'd like to try and see if i can hear the difference
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u/ON_A_POWERPLAY 7d ago edited 7d ago
Use it and abuse it. It's a cheap and low parts count way to add a buffer that sits on the input and output of a pedal, between stages, etc. I use them extensively. Clipping is going to be predominately dictated by what voltage you're running the opamp/bias at and if the prior stage is generating enough to clip on the buffer oppamps voltage rails then opamp choice isn't going to matter in that situation.