Electronics > Beginners
Op amp based preamp supply. Charge pump, single vs symmetrical & ripple
b_force:
--- Quote from: dazz on November 26, 2018, 03:48:24 pm ---
--- Quote from: Hero999 on November 26, 2018, 03:30:39 pm ---
Then I misunderstood. If you need 30V peak to peak, then you need a higher total supply voltage than 30V. A +/-16V supply won't do for the TL082, which needs a couple of volts of headroom on either supply rail, to avoid clipping, unless that's desired for the distortion effect
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Yes, it's built to distort, for rock'n'roll purposes! :-DD
More precisely, it's supposed to do both clean and distorted tones. That's what the gain pot is for
--- Quote from: Hero999 on November 26, 2018, 03:30:39 pm ---
The OPA2196 will be able to give 30V peak to peak from a +/-16V supply. If does have a lower slew rate, than the TL082, but it will be the lower audio frequency components which generate the largest voltage swings, so this is a non-issue.
http://www.ti.com/lit/ds/sbos869/sbos869.pdf
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I'm afraid it really needs to be an LM1458 as in the original circuit, or one of those TL082 with jfet inputs (which are supposed to clip more softly). Well, not really those 2, just one op amp with lots of mojo regardless of whether other types make more sense from an engeneering perspective. That's how guitar players roll :-//
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You don't want any distortion/clipping from your opamps. Also really don;t see where "sound descriptions" come from.
I have building these circuits for years.
Only thing you need to take care of is be able to drive enough capacitive load if it's a pedal.
dazz:
--- Quote from: Hero999 on November 26, 2018, 04:20:51 pm ---Do you have a specific type of distortion i.e. transfer function in mind?
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Well, it should be as close to the original as possible. Would posting LTSpice screenies help? Or perhaps I should post the .asc? I'm using a couple of "custom" models but I can zip them
--- Quote from: Hero999 on November 26, 2018, 04:20:51 pm ---
I think most op-amps will give fairly harsh clipping, as once the output goes beyond the limit, there will be no negative feedback. I suspect the clipping level may vary between op-amps with the same part number, because it's not a tightly controlled characteristic. By operating an op-amp at its clipping level, it's being driven past its deign specification.
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Well, there are many guitar effects and preamps that use opamps for clipping, I also heard that they clip harshly but many Marshall amps use them. The Tube screamer too, although I think the clipping diodes do most of the distortion there. I dunno, the Lead 12 works like that, so who am I to question Jim Marshall ;D
--- Quote from: schmitt trigger on November 26, 2018, 04:31:57 pm ---Another thing with using charge pumps, is that your negative output won't be completely symmetrical.
As the application circuit shows, there will be the diode's forward losses, plus any losses in the converter itself.
And indeed if not filtered correctly, the plain 7660 will generate an audible whine when used with sensitive audio circuits.
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Yeah, the asymmetry of the charge pump is what made me lean towards using it as a voltage multiplier to get from 9V to as close to 30V as possible, then use a heavily filtered virtual ground to ensure symmetry. I believe the load from the op amps will remain fairly stable so I don't expect the voltage supply to sag very much
BravoV:
Alternative consideration ...
https://www.analog.com/en/products/ltc3265.html#product-overview
Audioguru:
Yes, for the 50 years old extremely distorted sounds, you use 50 years old 1458 opamps (dual 741 old opamps). A fairly old but much newer TL082 or the lower noise TL072 are NEVER used for severe clipping because they produce the problem called Opamp Phase Inversion where the output suddenly goes positive when the input voltage goes to within a few volts from the negative supply. Its distortion is completely different to having ordinary clipping.
I see the circuit as an ordinary 2-opamps preamp with a passive tone controls circuit at its output. The 2 opamps can easily use a single polarity supply and the tone controls circuit can have an added input coupling capacitor.
b_force:
Yes, you do proper clipping with diodes, not relying on how the opamp clips.
That is asking for trouble.
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