I was thinking of some Rat or Dist+ experiments, but I don't I want to use the LM741 nor the rare LM308.
Anyone knows a less noise, but low slew rate OpAmp?
I thought I saw some hints, but can't remember where.
A TL070 should be fine, in fact my "re-issue" Rat has one inside !!
sounds great, and I used one in the "Mongoose" too - very similar circuit
Marty.
TL070s are just as hard to find IME - I had better luck finding LM301's.
Quote from: spudulikeTL070s are just as hard to find IME - I had better luck finding LM301's.
Digikey has TL080s in DIP form which should be sufficant. Digikey is availible in the UK.
Andrew
I used a CA3130 in mine. I don't know how available those are - I had them given to me. Chances are they are out of production...
I've had ok luck with NTE replacements, even though they're expensive. I used an NTE1641 in place of an MN3007 in my Tonepad Small Clone, and didn't notice any difference when I finally ordered the MN3007 from Smallbear.
The NTE938M is listed at mouser as a replacement for the LM308, and they're $10 each.
Might work.
:shock: $10 :shock:
Thats £5.47. RSH sell LM301A at 45 pence each ...
You could use any single opamp, like a TL071, as long as it has the same pinout or you adjust your build to fit the new pinout.
These guys have the LM308 for 80p.
http://www.elclondon.co.uk/acatalog/ELC_Online_Catalogue_LM_SERIES_49.html
minimum order of 5 pounds though.
But what about the slew rate (seem to guarantee softer clip and smoother pick attack)? Should this be taken serious? the TL... series seem to have faster slew rate. Maybe they sound ok, but different. I don't know.
IIRC the slew rate of the TL070 can be adjusted with the extra cap it has that the TL071 doesn't. Same as the LM308. 8)
QuoteYou could use any single opamp, like a TL071, as long as it has the same pinout
If you do use a TL071, omit that 30pF cap between Pin 1 & 8. The TL071 is internally compensated, and that cap on that the LM308 requires isn't required with the TL071. And, IIRC, the cap that is internal to the TL071 is around 30pF as well. I think it was 27pF.
The thing that's kind of cool about the LM308 type opamps is that you can mess with different value caps. I don't know that there is any benefit in doing that, but the option is there. 8)
What WGTP said - ditto.
The TL070 with a larger compensation cap sounds the same EXCEPT it doesn't HISS so damn much.
By overcompensating the '070, it drops the slew rate to match the '308 which slews at an anemic 0.1v/us. Which just happens to sound good in this applcation for just the reasons you stated.
The noise of the TL070 is an order of magnitude better. You CAN hear that. And you'll like the quiet.
Steve Daniels at Small Bear stocks TL070s - go there. :)
Mr Coffee, what value cap did you use on the TL070?
I have some LM208, anyone use it?
Saludos, Marcelo.
To drop the slew rate of the TL070 from 13v/us down to the 0.1v/us of the LM308 requires overcompensation.
There is nothing sacred about 0.1v/us, BTW.
If 18pf yields 13v/us in a TL070, then 180pf slows you down to ~ 1v/us, assuming the charging current mirror doesn't saturate (which it probably will if you go for 0.1v/us)
Start there and work down to what sounds good to your ears.
This is about LISTENING and using your own artistic skills.
FWIW... and oh, YMMV. :)
Yes, from what I remember (long time ago I played with this stuff) 180p sounded about right with the TL070. The LM308 is a real p.o.s.. Don't waste your $$ or time with it, IMO. Nothing magic about it - just noisy and harsh. The TL070 sounds real good in this kind of ckt.
Doug
Quote from: Paul Marossy on May 24, 2005, 05:54:28 PM
I used a CA3130 in mine. I don't know how available those are - I had them given to me. Chances are they are out of production...
I tried a CA3130EZ in my Rat today. Really nice. :)
There is also the NE5534 that has a little nicer sound with the stock cap.
http://focus.ti.com/lit/ds/symlink/sa5534a.pdf
Hey, Hi and hello. I was asking the same question and this feed from 2005 came up. Anyone still here? Will anyone get an email notification that this was replied to so late in time? We'll see. Based on what I've gathered here. My lack of LM308 chips has given me 3 options for my Rat build. It's a Lil Mouse from BYOC. Calls for a LM 308 w a 33pf cap between 1&8. The best replacement would be a OP07, Same slew rate. Or... 3 options. An 070 w a 180pf cap, an 071 w no cap, or use a 741, and I'm not sure if the 741 gets a compensation cap. Thoughts?.... Hello? Anyone? hahaha years later?
Lm108 or Lm208 are both mil spec and will work.
Guys. Has anybody tried Russian UD1408A (УД1408А)? Slew rate is like 0,05.
welcome to the forum, if you go with the 741, you definitely don't want that cap in there.
in double blind tests, most people didn't hear differences between my LM308 and OP07, but they seemed to prefer the 741's sound.
a key element in the sound of a rat is the SLEW RATE, this is how fast a chip can go up or down in voltage. the LM308 and OP07 both have 0.3v/us, the 741 has 0.5v/us. these are considered really slow, even by 1980's standards, the slowness mellows out the sound of the pedal a bit in a way a filter can't.
cheers, Iain
OP07 is pretty standard. LM741 isn't 'exactly' the same slew rate, but will probably sound great.
Another option, if you're willing to tinker more, is the NE5534 with an oversize compensation cap. I haven't tried this method yet, but I've heard other people on the forum using it with some success. it would take some trial and error to get right. I've been meaning to test it out with a scope myself.
A word of caution on the OP07: in a Rat, the chip itself clips. Some sound good when they do, others not. The problem with opamp clipping is that the chips are not designed for it. What's more, the chip names (LM308, OP071...) only signify the minimum specifications of the original spec sheet. That means that two chips of the same specs and name (two OP07 or two TL071 or whatever) from two different manufacturers are not necessarily technically identical. They are usually very similar but with things like clipping that occur way outside anything that appears on the datasheet, there can be significant differences. All that is a long winded way of saying: many people seem to like the OP07 in a Rat and the ones in the actual ProCo units sound good to me. But the OP07 that I have sound absolutely horrid when clipping. Fizzy, harsh, inharmonic, just awful. And no amount of circuit tweaking makes it better.
My favorite chip in a Rat, even before the LM308 is the LM301. NE5534 is really good too but needs some circuit changes.
Andy
Quote from: D_Ex_Patria on April 21, 2021, 02:20:50 PM
OP07 is pretty standard. LM741 isn't 'exactly' the same slew rate, but will probably sound great.
Another option, if you're willing to tinker more, is the NE5534 with an oversize compensation cap. I haven't tried this method yet, but I've heard other people on the forum using it with some success. it would take some trial and error to get right. I've been meaning to test it out with a scope myself.
the NE5534's compensation cap isn't slew rate changing, but its more of a normal filter function.
cheers.
Quote from: iainpunk on April 21, 2021, 04:19:54 PM....the NE5534's compensation cap isn't slew rate changing, ....
Sure it is.
(https://i.postimg.cc/vDNqFLVF/5534-SR-42.gif) (https://postimg.cc/vDNqFLVF)
(https://i.postimg.cc/FfSdzvPV/5534-MOF-42.gif) (https://postimg.cc/FfSdzvPV)
Well, here I go again...
I second the 5534 with more capacitance on the compensation capacitor. The 741 is just too damn noisy, unless you think hiss makes your sound "tube-ish". The TL070 has gotten really rare now, which is too bad for lovers of the Rat.
In substituting op amps, I've noticed that the output stage "sticking to the rails" when overdriven may also be part of the "sonic signature" of the old LM308 in the Rat circuit, and most modern op amps go out of their way to design that out (and do so quite successfully). The '308 is Really noisy (100+ nv/hz), and modern super-beta input op amps are totally different animals from the '308 - much quieter, modern-day slew rates, and overload gracefully.
So if you want to get the "spit" the fans of the Rat seem to love about it, you want to select an older, externally-compensated op amp. Maybe one like the NE5534, as suggested by D_Ex_Patria, which is low noise, externally-compensated, and IIRC, some manufacturers versions did stick to the rails (although I can't remember which any more), might be a good choice to make yourself a good modern day Rat.
The OP-07 is pretty quiet and slow, although the input current is compensated to get a low input-stage current, which may now work out so well in the Rat circuit, since it is one of the op amps where balanced input resistance is pretty much necessary to avoid major output offsets.
If a '5534 seems too hard to obtain, or doesn't "spit" enough for your taste, you could try an old LM301a that could easily be over-compensated to lower the slew rate to act like the '308, and since it has a very similar output stage to the '308, it may well "stick to the rails" in a similar fashion to get that "spit". And IIRC, it still is quieter than a '741.
It's not that hard to try out different compensation caps to find what sounds good before you "button it up". Put in a IC socket for the op amp, and use two machine pin sockets to plug in various compensation caps while you listen to how different values make it sound. You can solder the "golden" cap in to the socket pins if you like, but unless you're using a big old silver mica cap or something, the socket pins will hold it just fine through on-the-road rock and rollin'.
Let us know what you decide sounds best to you afterwards. Your findings may end up in the design of the iteration of Rat pedals!
Bart
My Texas Instruments NE5534 do something additionally interesting in a Rat. If the bias resistor is too large to supply enough bias current and the input coupling cap is small, then the opamp clipping becomes strangely fuzzy and dark. In a good way, I really like it. The reason, I speculate wildly, is that when the output hits it's limits (or one of them), more current is drawn from the inputs than should be as per the datasheet. This causes the non inverting input to drift, making the signal very asymmetrical. If the input cap is large, it can temporarily supply some charge to counteract that. For a noticeable effect compare a 22n input cap and 2M2 bias resistor with a 220n cap and 470k resistor. This may not work with all NE5534 from different manufacturers or even different batches.
Andy
Edit: mind you, this effect becomes less noticable if you overcompensate too much.
QuoteMy Texas Instruments NE5534 do something additionally interesting in a Rat. If the bias resistor is too large to supply enough bias current and the input coupling cap is small, then the opamp clipping becomes strangely fuzzy and dark. In a good way, I really like it. The reason, I speculate wildly, is that when the output hits it's limits (or one of them), more current is drawn from the inputs than should be as per the datasheet.
Biasing shifting on the NE5534 is a common issue with the large resistors. It does have a significantly higher bias current than most opamps. (FWIW, the app notes have a scheme to inject current into the inputs.)
I built a dual op amp rat last year (switchable from LM308 to CA3130). Here are my notes/musings from the op amps tried - tests done via headrush gigboard, fendery cleans and headphones. Note that I ended up bumping up the pin 6-2 feedback cap on the CA3130 to 1nF to kill the oscillation after 2PM on the distortion dial. I lost some of the aggressive pick attack but it's still noticably more aggro than the LM308.
cheers,
Brett
LM308
• Stock, it's a warm, rich tone. Some settings a little woolly?
TL070
• I used a 150 pf compensation capacitor. Very hard to tell the difference between this and the LM308 using headphones and floor modeller. Makes an excellent and classic Rat.
TL071
• obvious difference to stock chip. Retains a lot more high-end and has a metallic pick attack. Thinner, probably more aggressive tone. I like it as a point of contrast.
LM741
• Quite similar to LM308 and makes an excellent Rat. Retains a little more high-end - possibly a little more focused/less woolly than the LM308 at identical settings. I really like it.
CA3130
• Wow! Needs at least a 330 pf compensation cap to tame the high end. But when you get there, it's great. More aggressive, modern and gainy than the LM308, with an oscillation whistle at about 2pm on the distortion pot on one pickup (middle position ok). The additional gain is especially noticeable when you wind the guitar volume back a little- it certainly cleans up slower than the stock chip. A great option if something a little wilder is required. Personally, I think it's my favourite.
NE5534
• less drive and thickness but more clarity/crispness than LM308. Retains an aggressive pick attack with more high-end and would certainly cut through a mix. Perhaps veering more towards overdrive. Probably the least rattiest but a nice contrast with the stock chip.
LM301
• very close to the 308, but with a little more clarity on the unwound strings and certainly less wooliness at high distortion settings. I like this and it would make an excellent rat
Quote from: bmsiddall on April 21, 2021, 10:21:12 PM
I built a dual op amp rat last year (switchable from LM308 to CA3130). Here are my notes/musings from the op amps tried - tests done via headrush gigboard, fendery cleans and headphones. Note that I ended up bumping up the pin 6-2 feedback cap on the CA3130 to 1nF to kill the oscillation after 2PM on the distortion dial. I lost some of the aggressive pick attack but it's still noticably more aggro than the LM308.
cheers,
Brett
YESSSS the CA3130 is so great! especially when omitting the original clipping diodes, since this opamp has a CMOS inverter as output stage, it does genuine soft clipping.
am currently building/designing a distortion/overdrive using the CA3130 or CA3160 for its perticular output characteristics, and the fact that it can be exploited for great sounding tones when you have only the output stage in an open loop configuatation.
cheers, Iain
Quote from: Prive on May 31, 2005, 08:15:36 PM
I have some LM208, anyone use it?
Saludos, Marcelo.
Same chip - tighter specs. Ditto for LM108.
There are other "308" chips if you can find them at a reasonable price. Or at least one that I know of (and own) - Fairchild UA308.
Quote from: mozz on April 21, 2021, 09:40:09 AM
Lm108 or Lm208 are both mil spec and will work.
Actually that's not accurate. They are higher spec than 308, but the manufacturer data sheets do not indicate that they are "military" spec. Instead, they indicate to "refer to RETS108X for LM108 military specifications". I think this means that a military spec approved LM108 was available, but stock LM108 units are not tested for military spec ratings. TI chips that are truly military spec usually have an "M" in the suffix, but I don't know if that was also true with other manufacturer's like National (whom TI bought out).
Well here is the numbers. Better temp difference is always in the mil spec compared to a consumer part.
The LM108 is guaranteed from -55C to +125C, the
LM208 from -25C to +85C, and the LM308 from 0C to
+70C.
Here are the mil numbers.
JM38510/10104 LM108
Here's a cross reference from mil to consumer
JAN MIL-M-38S10 - bitsavers.org
I have a lead for purchasing NOS LM308 chips. If in the US feel free to PM me.
I wanted to take a moment just to thank everyone who chimed in with details about each of these alternatives. I know this was a thread specifically about substitutes, but I'm scribbling furiously in my notebook about op-amp properties that could come in handy outside of just replacing the 308.
Quote from: D_Ex_Patria on April 24, 2021, 09:54:53 AM
I wanted to take a moment just to thank everyone who chimed in with details about each of these alternatives. I know this was a thread specifically about substitutes, but I'm scribbling furiously in my notebook about op-amp properties that could come in handy outside of just replacing the 308.
there are two factors i consider when using an opamp for clipping, the ''knee'' of the clipping, and the slew rate. i have been looking in to extremely slow opamps (like the MCP6042 dual) and slew rate reduction circuits to use as gain stages or after another distortion stage.
for the knee, you can use a CMOS (ca3130 ca3160, both quite expensive) output opamp with a relatively heavy load (about 1 or 2kohm) to soften the curve, or use a cheaper cmos inverter IC.
(https://i.postimg.cc/vxZLbJqB/cmos-output-vs-gain.jpg) (https://postimg.cc/vxZLbJqB)
the down side is that the cmos knee and slew rate reduction are hard to have at the same time without making it really complicated.
cheers, Iain
purely anecdotal and i have been told that i'm totally wrong by folks, but in the circuit i built lm308 and lm318 both sounded the same to me. both were about the same price from some us-based ebay seller when purchased a year or two ago
Quote from: thetragichero on April 24, 2021, 05:30:48 PM
purely anecdotal and i have been told that i'm totally wrong by folks, but in the circuit i built lm308 and lm318 both sounded the same to me. both were about the same price from some us-based ebay seller when purchased a year or two ago
i can assure you that they sound quite different when running to the rails without diodes or tone control (that's how i test IC's for distortion character.) the 308 is quite soft/subdued* compared to the extremely bright 318. this is also confirmed with the data sheets; 308 and its extreme slowness, 0.3v/us is the slew rate ''filter'' high end out, the 318 has 50v/us (IIRC) which leaves all the high end in.
the difference between chips is mainly hearable in the upper high end, and having the tone/filter taking out high end makes the difference smaller and smaller the further you turn up the filter (or turn down a traditional tone control)
cheers, Iain
i'm not saying the lm308 is soft/subdued on its own, but you get that impression when comparing with faster chips
ahh i tested in a rat-type circuit with clipping diodes and a baxandall tone circuit afterwards. very unscientific but all i really cared about was how it worked in that particular case. suppose it doesn't help the conversation as much as i thought
While stripping old circuit boards for parts, i found LT1013 dual opamps, slew is 0.2-0.4 v/us. I don't know what it was used for but other specs may be good while slew is low.
Quote from: thetragichero on April 24, 2021, 07:54:27 PM
ahh i tested in a rat-type circuit with clipping diodes and a baxandall tone circuit afterwards. very unscientific but all i really cared about was how it worked in that particular case. suppose it doesn't help the conversation as much as i thought
you actually contribute more than you think, by demonstrating that in a more complex circuit, the IC doesn't matter as much as it does in a simple circuit.
cheers