I build both TS-808 and Sans Amp GT-2. I like much GT-2, who doesn't have diode inside it. I think the distortion is generated by opamp saturation. Anyone know another knd of overdrive works in this way? I like to see the schematic...

I am sure there are some others that do this, but can't state specifics. I do a mod to the MT-2 Metal Zone that removes the clipping diodes tho' and overdrives the op amps instead. One of the obstacles to doing this and getting good sound is slightly overdriving multiple stages of gain. If you just slam an op amp you would get fuzz. So you need multiple op amps which rases the parts count and thus the price for a factory unit.

Greybeard

Black Cat OD at Fuzz Central
 There are others that overload' OA's for distortion
 I've tried it, and prefer the diodes in...
 But I never seriesed OA Gain stages and 'stepped' up the clipping at each stage, or messed around with that much, just pulled them from a TS or DIST+ Type and boosted the front end...I know I like using diodes for clipping...can't say much beyond that other than I read somebody loves his Black Cat but I don't see many OA clippers without diode designs.

...euhm... what about the infamous LM386-chips?
They distort quite nice!

I haven't built one yet (LM-386) but I do hear that they sound good. But I also understand, and correct me if I am wrong, that it really isn't an op amp but an actual amp. Splitting hairs I know.

Greybeard

In general for op amps, I would say that diodes clip better BUT there is the Black Cat and the Hotcake so as usual it depends on the circuit.

Quote from: GreybeardI haven't built one yet (LM-386) but I do hear that they sound good. But I also understand, and correct me if I am wrong, that it really isn't an op amp but an actual amp. Splitting hairs I know.

Greybeard

Opamps are all "amps", but most of them are small signal ones. I mean LM386 is a "power" amp, while most opamps are preamps. But they all are the same basic circuit (phase splitter, - and +, etc...)

Quote from: Steben
Opamps are all "amps", but most of them are small signal ones. I mean LM386 is a "power" amp, while most opamps are preamps. But they all are the same basic circuit (phase splitter, - and +, etc...)

OK, so we are going to split hairs then. Excuse me for not using the word "power" amp in my post.  :wink:

We were talking about producing clipping in an "operational amplifier" (Op Amp, OA, etc) not power amps. Just because the LM386 comes in an 8 pin package it would not automaticly be classed Op Amp.

IMHO that is.

Greybeard

Check out the Mockman at ROG.  It can be used with or without diodes in the feedback loop.  Experiment.  Using a 100K to 220K resistor at the input will reduce the mid-rangey tone.  Try LED's, SI's, GE's and combinations.  

Quote from: Greybeard

Quote from: Steben
Opamps are all "amps", but most of them are small signal ones. I mean LM386 is a "power" amp, while most opamps are preamps. But they all are the same basic circuit (phase splitter, - and +, etc...)

OK, so we are going to split hairs then. Excuse me for not using the word "power" amp in my post.  :wink:

We were talking about producing clipping in an "operational amplifier" (Op Amp, OA, etc) not power amps. Just because the LM386 comes in an 8 pin package it would not automaticly be classed Op Amp.

IMHO that is.

Greybeard

I understand ;-).
Yet, the LM386 can be used as an OA by not using the watts (just as in a Dist+ or TS. There are a lot of preamp Overdrive design that use only one LM386.

Other than the LM386, I think many forumites have negative opions about op amp clipping.  As Aron pointed out, several well thought of distortions do not have clipping diodes with the op amps.  I suspect it is a matter of tweeking the op amp differently without the diodes to get good results.  

Usually an opamp switches pretty quickly, creating a fizzy output. The sansamp runs the fizzy signal into a thingy that lengthens the rise/fall times of the output waveform:


before:
 _   _   _
_| |_| |_|

after:
 _   _   _
_/ \_/ \_/


This prevents harshness but also sacrifices high-frequency response, since it also acts as a low-pass filter if too much is applied. That can be good for direct recording, though. There are better ways to do it, but that's the basic gist of it.

Quote from: aronthe Hotcake

Have you the schematic??  :shock:

Quote from: Joe DavissonUsually an opamp switches pretty quickly, creating a fizzy output. The sansamp runs the fizzy signal into a thingy that lengthens the rise/fall times of the output waveform:

Code Select Expand


before:
 _   _   _
_| |_| |_|

after:
 _   _   _
_/ \_/ \_/


This prevents harshness but also sacrifices high-frequency response, since it also acts as a low-pass filter if too much is applied. That can be good for direct recording, though. There are better ways to do it, but that's the basic gist of it.

What about the **308 opamps as in the rat? Famous about their slow slew rate. Could they be usefull in series (eg. a pair) without diodes?

Quote from: GreybeardI am sure there are some others that do this, but can't state specifics. I do a mod to the MT-2 Metal Zone that removes the clipping diodes tho' and overdrives the op amps instead. One of the obstacles to doing this and getting good sound is slightly overdriving multiple stages of gain. If you just slam an op amp you would get fuzz. So you need multiple op amps which rases the parts count and thus the price for a factory unit.

Greybeard

Can u give me a note on how to mod the MT2  by using saturated opamp?

The op amp in the RAT distorts plenty before the signal gets to the diodes.  I suspect many of the diode to ground type distortions have a lot of op amp distortion going on and that may have more to do with it's sound than other factors, i.e. diodes in the loop sounding different or slew rate limiting.  

Quote from: wui223Can u give me a note on how to mod the MT2  by using saturated opamp?

I put the whole mod and a sound clip on another forum. You can find it here   http://indyguitarist.com/forum/viewtopic.php?t=63  I hope  :wink:

there are quite a few follow ups also, check out the whole thread.

Greybeard