RAT chip differences

[yeeshkul]

Guys i am new to Rats. I understand the vintage models used LM308AN. They are considered to be rare and expensive. Chinese seem to produce them again though. Do you have any experience with the sound?
How did the original chip look like - i mean how to recognize the original from the current production?

[pinkjimiphoton]

well, the originals were round metal cans. but i don't think the rat used them, as it came out way after they started making "modern" chips.

i personally don't believe in mojo. put a socket in and try what you have til ya find something you like.

that said, i prefer metal can lm301's in a rat circuit. super smooth n buttery. but not much different from any other similar opamp. most of it comes down to the rest of the circuit.

dunno if that helps at all, but 99% of the time you could sub any compatible chip for any compatible chip and nobody could tell the difference.

[yeeshkul]

Yeah, i am not much into mojo myself. I will start with LM308 in metal can from smallbear.

[Steben]

low slew rate opamps

[yeeshkul]

Yes i understand that ensured The Rat was sounding sweeter than Boss DS.

[Steben]

It is not only the slew rate of course. Any non-feedback-clipper (i mean, not like boss OD or Tube screamers) will have the opamp clipping itself at a certain point, which adds to hard clipping effect. Some opamps don't do this fluently, resulting in their own character. That's why some distortion circuits have diode to ground clipping typology, while having feedback diodes around the opamp as well, this eliminates most of the opamp clipping. In a rat (or dist+ fe), the opamp clips freely.

[yeeshkul]

How does the opamp clipping add to the diode clipping? The diodes come the last and will clip it down to aproximately 0.7V ...

[Steben]

It is subtle. Yet discussing opamp differences is always about the subtle.

No bandwagon (small signal) diode is a perfect hard clipper. There is always a variable "on resistance", which is logarithmic. Even with diodes to ground, there is always a small dynamic range.

Most higher voltage Zener diodes have a much smaller resistance along with the higher treshold, which means a very big ratio between the clipped signal and the dynamic portion above the treshold; in other words: they are much harder clipping than silicon diodes.
Schottky and certainly Germanium diodes have a much smaller ratio, which means the dynamic range is much higher, resulting in softer clipping.

Now, since there is a small dynamic range, the changes in the signal in front of the clipper are translated into this small range.

[yeeshkul]

Thank you for explaining this Steben 

[Mark Hammer]

The Rat applies a max gain of just under 3200x to mids and highs (starting around 1500hz).  That equates to roughly 70db.  The datasheet indicates it will juuuuuussst do 70db "open-loop gain) at 1khz, but starts to be more limited as you go higher in frequency (when using a +/-15V supply).  Maximum voltage swing is +/-14V (with that 15V bipolar supply), so we'll assume it runs out of any additional amplification when it comes within one volt of either rail.  So, on a good day, with the wind at your back, it will output 3.5V on either side of Vref, using a 9V supply.  Ask yourself how many times your input signal can fit into +/-3.5V.

At pretty much anything other than Gain at minimum, you're asking ore out of that op-amp than it is capable of.  One might suggest that the diodes are merely supplementing the opamp clipping, rather than the reverse.

[mickeybellinello]

Hi to all,

I just bought a metal can LM308H but I realized that there is also an LM308AH.

Which are the differences between those two?

Thanks

[GGBB]

Hi to all,

I just bought a metal can LM308H but I realized that there is also an LM308AH.

Which are the differences between those two?

Thanks

Still the same differences as when you asked in the other thread 

https://www.diystompboxes.com/smfforum/index.php?topic=122573.msg1157068#msg1157068

[roseblood11]

I use the cheap OP07, and I can't hear any difference compared to the LM308.
T. Rex Dr Swamp used that chip, too.

[mickeybellinello]

Hi to all,

I just bought a metal can LM308H but I realized that there is also an LM308AH.

Which are the differences between those two?

Thanks

Still the same differences as when you asked in the other thread 

https://www.diystompboxes.com/smfforum/index.php?topic=122573.msg1157068#msg1157068

I apologize but when I received the other thread notification I missed my reply post.
Thanks Again!

[Invertiguy]

Having just received a UA308HC in the mail from Small Bear, I decided to do a shootout between it and a few other opamps (LM301, CA3130EZ, and OP07) in my Aion Helios build. The differences are subtle, and it sounds like a Rat no matter what chip is in there, but I definitely notice a difference between them, especially when the chips themselves are driven to clipping and the diodes are switched out of the circuit. My least favorite of the bunch was the OP07- it works, but just sounds "congested". The CA3130EZ and LM301 are both very nice, although in very different ways. The CA3130EZ is balls-to-the-wall aggressive (and also rather noisy) and has a strong attack, but seems to cut out on long sustained notes once the signal passes a certain threshold whereas the LM301 is a lot more smooth sounding and will sustain for days. The UA308HC, which is supposed to be an LM308 equivalent, was a strange one. Soundwise it somewhere in between the CA3130EZ and the LM301, but it exhibited a weird characteristic on faster-picked runs where it would cut off the attack of each note, like it was struggling to keep up. This went away when I backed off the guitar volume a bit so it may be related to the active pickups in my guitar or maybe a quirk of my build, but I still thought it was strange as none of the other chips did anything of the sort. Might have to look into getting an actual LM308N or LM308AH to see if it does the same thing, but for now I'm perfectly content with the LM301. In any case, I just thought I'd share my experience with Rat chip swaps, and I'd definitely advise socketing the chip and trying out a few for yourself!

[Steben]

The mixed attack might just be that low slew rate.