TL071/LM741

[Dr.EM]

Hi. As some of you may know, i'm working on a bit of a project, to build an analogue synthesiser. In it there will obviously be a fair few op-amps. I've decided that in less critical areas, I will use standard 741 chips (ie, for adding up control voltages). But also in there will be a mixer for the audio signals. For this I thought it might be better to use the TL071. I hear this is a FET op-amp, and just wondered whether it would work exactly as a 741 does? Also wondered whether op-amps can "crowbar" the power supply in any way. I have to use CMOS 555s because of this annoying effect. Thanks

 

[Nigel Goodwin]

Hi. As some of you may know, i'm working on a bit of a project, to build an analogue synthesiser. In it there will obviously be a fair few op-amps. I've decided that in less critical areas, I will use standard 741 chips (ie, for adding up control voltages). But also in there will be a mixer for the audio signals. For this I thought it might be better to use the TL071. I hear this is a FET op-amp, and just wondered whether it would work exactly as a 741 does? Also wondered whether op-amps can "crowbar" the power supply in any way. I have to use CMOS 555s because of this annoying effect. Thanks

You can generally just replace 741's with the TL071, as long as the circuit you're using doesn't do something 'really strange' that uses some obscure 'fault' within a 741.

The 071's cost very little, can you get 741's substantially cheaper?, there seems very little reason to want to use a 741 these days?.

I don't know of any HT problems with any opamps.

 

[audioguru]

If the input of a TL07x non-inverting amplifier is overdriven and gets to within about 2V from its negative supply, it suddenly inverts. You might be able to use it as a weird frequency-doubling effect. :lol:

In order for the original 555 to have 200mA output sink and source, its totem-pole output draws hundreds of mA from the supply for the moment it switches, even without a load. That is why its datasheet says that a supply decoupling cap is mandatory. :shock:

 

[Dr.EM]

Actually, your right about the 071s, didn't think they would be so cheap. Will probably use them throughout. They are static sensitive devices though, do I need to be careful with them? I've never got static shocks in my house, and most people pay no attention to it anyhow, but its just a little concern of mine. Good that there is no problem with the crowbarring.

The 555 switching is pretty terrible on the TTL one. It says up to 400ma in switching, the CMOS is only 4ma. If I were running 2 oscillators together with the normal type, they "soft sync" even on frequencies a long way apart.

 

[audioguru]

Hi Dr. EM,
The TL07x is cheap because it has been used in many consumer audio products for many years and is probably made and sold by the millions each year.
It has Jfet inputs, not Mosfets, the datasheet doesn't even mention ESD sensitivity and I have soldered hundreds by hand and have had tens of thousands installed into audio products without a failure. I get big electrostatic sparks at home and work in winter.

I've never had two 555 oscillators running at the same time on the same pcb. It's cool that they sync together. I don't use many 555's, I have used much simpler Cmos digital gate and inverter oscillators instead for many years. :lol:

 

[Dr.EM]

Oh right. The JFETs I got came in static bags and everything, just assumed.

The main reason for my using the 555 (or 7555 to be accurate) is the voltage control pin, it makes voltage control very easy :lol:. You like the soft sync effect? I will be installing a hard sync on the oscillators, but I don't want soft sync as one of the coolest things about analogue synths is detuning the oscillators just a bit to get "phatt" sounds :shock:

 

[audioguru]

Hi Dr. EM,
You might be interested in this self-tuning filter. I don't know what the pot does:

 

[Dr.EM]

Interesting, what would you use something like that for? My synth will use the old voltage controlled Moog filter, sounds great 8)

 

[audioguru]

Hi Dr. EM,
The self-tuning filter would do the opposite of fuzz, it would make a guitar sound nice and smoooooooth. A velvet guitar, something like a flute.
It would probably make your voice sound restricted like a very bad telephone connection. :lol:

 

[Dr.EM]

Oh right, thats pretty cool then. Would sound nice with a good reverb after it i'd imagine. Does it re-tune on different incoming frequencies, or levels?

Ordered 10 TL071 chips btw, enough to take advantage of a decent price break.

 

[audioguru]

Hi Dr. Em,
I think the filter will follow the frequency of a single input. If you feed it a chord, it would probably get confused and who knows what it will do.