Weird rat mod idea vetting

[jdoughty]

So I'm considering doing a rat with a couple notable differences:

• a 741 chip, the diy pedals vid I watched suggested this  will produce more highs, and I like the crispier sounds of the rat
• using a tc1044 to supply a -9v to the chips ground and a +18v to the positive terminal, increasing headroom (idea taken from electrosmash's analysis of the klon)

Additionally I'll probably use led clipping like the turbo rat or make it switchable, but that's a difference I understand.

What do you guys think? Adding headroom to the Rat would probably take some of the fuzz out of the gain knob... But I really want to see it first hand... (Cuz I'm nuts)

[GGBB]

General consensus seems to be that the lack of bandwidth - particularly at high frequencies - of the LM308 using a compensation cap in the RAT is what produces the characteristic RAT tone. I've not tried a 741, but have tried an OP07 which sounded similar but not identical. So if you want a different sound than RAT sound, a 741 will probably do that. I'm not sure headroom will make much difference since this is hard clipping anyway, but you can always try. Different clippers make a big difference since they change the gain-versus-clipping-threshold relationship and that ends up with a greater mid and upper mid hump for the same amount of distortion with higher Vf clippers.

[Fancy Lime]

Isn't there an old (70's?) Australian (?) Overdrive that uses just the 741's self clipping with out diodes? I forget the name, though.

Andy

[Rodgre]

Isn't there an old (70's?) Australian (?) Overdrive that uses just the 741's self clipping with out diodes? I forget the name, though.

Andy

Are you thinking of the original Crowther Hot Cake?

http://revolutiondeux.blogspot.com/2012/01/crowther-audio-hotcake-overdrive.html

Roger

[iainpunk]

General consensus seems to be that the lack of bandwidth - particularly at high frequencies - of the LM308 using a compensation cap in the RAT is what produces the characteristic RAT tone. I've not tried a 741, but have tried an OP07 which sounded similar but not identical. So if you want a different sound than RAT sound, a 741 will probably do that. I'm not sure headroom will make much difference since this is hard clipping anyway, but you can always try. Different clippers make a big difference since they change the gain-versus-clipping-threshold relationship and that ends up with a greater mid and upper mid hump for the same amount of distortion with higher Vf clippers.

i have done blind tests on guitarists, with a bunch of opamps, the difference between the LM308 and the OP07 wasn't heard by them at all. most of them thought the TL071 sounded the best but they found it sounding different from the others, and they thought the uA741 was the original LM308.... go figure.
the difference between the tones is best heard with the filter all the way open, so most bright, but its a minor diference, especially at high volumes.
the op07 and the lm308 have a low slew rate, only 0.3v/uS,
the 741 has 0.5v/us and the 071 has 20v/uS.
its this angle that determines the ''softness'' of the chips.

if you want to not make the IC itself clip, you lose a large part of the character. but if you insist, i recommend soft clipping using double the diodes you use for hard clipping. soft clipping with higher headroom before hard clipping prevents the IC from overdriving, and gives a smoother distortion than allowing the IC to clip.

cheers, Iain

[Fancy Lime]

Isn't there an old (70's?) Australian (?) Overdrive that uses just the 741's self clipping with out diodes? I forget the name, though.

Andy

Are you thinking of the original Crowther Hot Cake?

http://revolutiondeux.blogspot.com/2012/01/crowther-audio-hotcake-overdrive.html

Roger

Yes, that's the one!

[garcho]

using a tc1044 to supply a -9v to the chips ground and a +18v to the positive terminal, increasing headroom (idea taken from electrosmash's analysis of the klon)

why?

[iainpunk]

using a tc1044 to supply a -9v to the chips ground and a +18v to the positive terminal, increasing headroom (idea taken from electrosmash's analysis of the klon)

why?

headroom, less fuzzy distortion, especially with LED clipping, the distortion might get more ''open'' sounding

cheers

[Radical CJ]

using a tc1044 to supply a -9v to the chips ground and a +18v to the positive terminal, increasing headroom (idea taken from electrosmash's analysis of the klon)

why?

headroom, less fuzzy distortion, especially with LED clipping, the distortion might get more ''open'' sounding

cheers

This sounds like a similar idea to the DRV Inventions 1981, which is Rat-like but runs at 18v via a charge pump, and uses a TL072.

A question that occurs to me is that if you are trying to remove op-amp clipping characteristics with higher voltage, then why use the u741 and not something with less "character" such as a TL071 or NE5534?

I have never actually played a genuine 1981 or Rat, but have made my own clones of both useing the available schematics. Based on this (perhaps irrelevant) experience, the 1981 does indeed sound better at 18v than 9v (more crisp/less rubbery) but I prefer the Rat. I find that the 1981 picks up and amplifies any scratching on the strings way too much.

[iainpunk]

well, the 308 or 741 have an abhorrently slow slew rate. this mellows out the tone.
another idea i saw being mis-implemented on Reddit was using a slew-limiting circuit for the opamp, to soften the tone even more. he made a big mistake in placing the slew rate limiter before the gain stage, thus making it fast again through the gain that came after it. but the concept is great! i might add such a slew limiter on future projects

this can of course be juggled around to be non-inverting, and use the exact feedback loop of the RAT or whatever you want


cheers, Iain

[jdoughty]

Wow, these are some fantastic ideas and questions.

I can answer a few questions quick.

Why the 741? I bought a large number of them for dod 250 style pedals. The tl071 may be a good one to get later to try though!

Why try this concept in general? First, curiousity! Honestly it's the primary driver, especially after reading about the klon's power pump trick and about pettyjohn's pedals using 36v, made me super curious about how different these circuits could be made to sound.

Secondly, the fuzzier end of the rat to me is the least useful. I like it, but not as much as the low to moderate gain so maybe this would get that as the ceiling?

[Radical CJ]

Wow, these are some fantastic ideas and questions.

Why the 741? I bought a large number of them for dod 250 style pedals.

A good enough reason for me! I'm always experimenting with what I have in abundance, and am in a similar boat with a bag of JNR4558s. I don't even think they are genuine (very cheap from ebay), and the 4558 is not a high performing op amp anyway, but they've been sounding good in a lot of projects.

I also have a big bag of NE555s, and you'd be surprised by how many uses can be found for those: square wave tremolo, square wave fuzz, bypass with soft switching, charge pump, and what might be the world's ugliest octave down...   

[iainpunk]

and what might be the world's ugliest octave down...

is it the frequency limiter that's the second half of the atari punk console?
i have build one of those frequency limiting fuzz-things, but i like it set at around 300Hz, and play barre-chords. it gives a glitchy fuzzy, broken noise wall, where the original chord kinda peeps through. fun little pedal for noise, Jesus and Mary Chain sounds, death metal chuggin' etc...

[Radical CJ]

and what might be the world's ugliest octave down...

is it the frequency limiter that's the second half of the atari punk console?
i have build one of those frequency limiting fuzz-things, but i like it set at around 300Hz, and play barre-chords. it gives a glitchy fuzzy, broken noise wall, where the original chord kinda peeps through. fun little pedal for noise, Jesus and Mary Chain sounds, death metal chuggin' etc...

I haven't previously heard of the Atari Punk Console, but looking at the schematics the second chip is indeed doing a similar thing, but for pins 6 and 7 put 22k to 9v and 3.3uf to 0v, and 10n from 5 to 0v. According to datasheets this set up can be used to divide a known frequency, but in practice it works for a range of the guitar, with notes outside that range produceing other divisions such as fifths down, or out of tune thirds. Some notes dont change, and some get scrambled into just fuzz noise. On my breadboard I run another 555 into it which is configured into a schmitt trigger, and blend the outputs to get the square wave fuzz plus the octave (or other note) down. Worth considering that the guitar signal allready needs to be very loud to trigger the schmitt trigger.

But... to circle back to the theme of the thread. Here is a link to a page with a schematic of the 1981 (Rat like on a charge pump). It may inspire useing additional u741s for buffering and improving output impedance. http://effectslayouts.blogspot.com/2019/06/1981-inventions-drv.html

[iainpunk]

a good opamp for the RAT circuit is the LM358, it has a slow slew-rate, which smooths out the tone a bit more, plus, its a double opamp, so you can use one side for the output buffer!

cheers, Iain

[jdoughty]

I was surprised the 1981 uses 42 tl072s, holy cow that would cut into my 741 supply.

[jdoughty]

I do love the sound I'm hearing in that 1981, but I'm wondering if I can cut out an opamp

[iainpunk]

the opamp that gives the ''buffer out'' connection can be left out if you use true bypass.
then there is the first gain stage and the second, you could take off one extra opamp if you combine then in to a single gain stage. its just a matter of experimentation of what you put in the feedback loop. i recommend starting with copying what the ProCo Rat has, and then changing the values until you are satisfied.

i personally like putting LED clipping in the feedback loop of a rat with normal diode clipping,
this makes sure the opamp doesn't clip to the rails, but soft clips instead, this takes out some of the harshness without losing gain and grit.

cheers, Iain

[jdoughty]

How well do you guys think a pot connected to the 18/9 volt would work to allow blending the two voltages?

[soggybag]

From what understand the 1981 Inventions DRV is a Rat with a charge pump. It's a little like the Rat and. A little like the Klon: http://effectslayouts.blogspot.com/2019/06/1981-inventions-drv.html