NOS Rat Fairchild metal can LM308 op am giving lagging pick attack?

[Carpathian Whips]

Hello everyone!

My search brought me to this forum, and it looks like a treasure trove of good info!

I have a Rat clone pedal, with asymmetrical clipping and an NOS Fairchild metal can LM308 op amp.

I love the tone, however it seems like I'm having to deal with a slow pick attack, as in when I pick, there isn't enough immediacy to the tone being generated..it almost feels like a little bit of lag. It makes me feel like I have to work extra hard when playing solos almost! I guess the attack feels "soft" is the other way to put it making me feel like I have to work harder. I hope this makes sense.

Could the op amp have anything to do with it? I was thinking maybe I could change the op amp.

If this is the case what op amp would you recommend to keep the tone, but increase the pick attack immediacy and reduce the perceived lag.

I am running the pedal at 9volts, and up to 12 volts.

Many thanks.

[vigilante397]

Welcome to the forum

I'm having troubling picturing what you're talking about, any chance we can hear a demo of what you're describing?

[willienillie]

I doubt it's the opamp.  I've built Rats with the metal can Motorolas, different tone than the DIPs, but no problems.  I have one of the Fairchilds but haven't tried it yet.

Your description kind of reminds me of a recent Klon thread where one of the clipping diodes was bad.  Ge diodes in the Klon, but hard clipping (straight to ground) like a Rat.  So I wonder if the asymmetrical clipping is related to your issue.  I assume you mean two series diodes in one direction, one diode in the other direction.  If so, you can tack on a single diode in parallel with the two in series, and test it with symmetrical clipping.

[GGBB]

Being more specific might help. Can you post the clone schematic? Does this happen at any gain setting? Post voltages on the opamp and FET.

[Carpathian Whips]

Thanks for the responses guys.

I'd do a sound clip, but it is more of a "feel" or "response" thing with the attack being too soft, or the sag being too pronounced, when I'm playing a note, not really like a defect with the pedal or anything.

And I apologize, I should have been more specific about the pedal. It is a nocturne ubangi stomp. It is based on a white faced rat, reported to be tweaked for a better clean sound per the documentation. It also has an internal trim pot to dial up the mids, in addition to the symmetrical/asymmetrical switch. I actually like using it for higher gain, and turn up the mids trim pot to about 75%, whereas it comes set at around 45-50%. The tone is indeed glorious, but for the soft attack issue...which maybe I'm just idiosyncratic about.

Also I think that the higher the mids trim pot is set, the more of "my problem" that I seem to get..but I'm not certain about that, I have to take the back off the pedal and go back and try it out again.

But Tavo Vega, the builder, includes in the documentation for the pedal the suggestion that one may try different op amps, and that he likes the non metal can op amp better for higher gain, so this got me to thinking if there are any op amps that produce a faster attack/less sag.

But is sounds like probably not...but I had found a post where someone did attribute the issue I'm describing when they tried out the same metal can op amp, but wouldn't you know it, I can't find that post for the life of me...it was as a result of a google search and I don't even know what forum it was in.

I'm also going to hit up Tavo too over at Gretsch Talk to see what he thinks, but I thought I'd check with the collective brain of this forum as well since you guys know op amps, and I don't.

If nothing else, I found this place, and I'm really intrigued about learning how to solder and build some of my own pedals..with some sort of kits to start with most probably.

I really appreciate all of your responses.

BTW, who makes a good Rat kit that will allow me to build an asymmetrical RAT that sounds something along the lines of the Jam Rattler Rats?

[willienillie]

in addition to the symmetrical/asymmetrical switch

Well then, I'm sure you've already tried it with symmetrical clipping.  Rules out my wild guess theory above.

But Tavo Vega, the builder, includes in the documentation for the pedal the suggestion that one may try different op amps,

So there's a socket?  That's nice.  If you buy a DIP-package LM308, be aware that this is a chip that's somewhat rare and desirable, so there WILL be fakes out there (*cough* Ebay *cough cough* China).

I have some metal can National Semicondutor LM308AHs that were made not too long ago (2010?), and unlike the old Motorola cans, they sound exactly like the plastic DIP chips to me.  So you might find a deal on those somewhere because they're not "vintage" yet.

For kits, there's BYOC (Build Your Own Clone), they tend to have good instructions.  I think they do a Rat-based kit.  If you're totally new to soldering, practice on something cheaper, nobody is good at it the first time.

[GGBB]

Please post pin voltages. You could have some FET cutoff going on - that would be consistent with the "soft attack" you describe. I highly doubt that the op-amp would have anything to do with that (but I've been wrong before).

[duck_arse]

ahh, I was going to ask if it has the fet output/buffer stage, but GGBB has me covered. except that he didn't say welcome to the forum, or that Carpathian Whips is an excellent name. for anything, probably.

[tubegeek]

No one has offered Mr. Whips a sausage yet? Seems downright rude. Welcome!

[Carpathian Whips]

in addition to the symmetrical/asymmetrical switch

Well then, I'm sure you've already tried it with symmetrical clipping.  Rules out my wild guess theory above.

But Tavo Vega, the builder, includes in the documentation for the pedal the suggestion that one may try different op amps,

So there's a socket?  That's nice.  If you buy a DIP-package LM308, be aware that this is a chip that's somewhat rare and desirable, so there WILL be fakes out there (*cough* Ebay *cough cough* China).

I have some metal can National Semicondutor LM308AHs that were made not too long ago (2010?), and unlike the old Motorola cans, they sound exactly like the plastic DIP chips to me.  So you might find a deal on those somewhere because they're not "vintage" yet.

For kits, there's BYOC (Build Your Own Clone), they tend to have good instructions.  I think they do a Rat-based kit.  If you're totally new to soldering, practice on something cheaper, nobody is good at it the first time.

Thank you for the warning regarding fakes!

Yes there is a socket specifically described for changing the op amp...the pedal was voiced for the low gain side of things and the maker described the gain tone as possibly better with the more modern LM308, but I did read somewhere that he thought the difference was maybe a bit subtle.

Also thank you regarding the advice for a kit and to first try my hack soldering skills on a cheapie at first.

I have to try the pedal again in Symmetrical mode and see if it is more "responsive". I am hoping to have another go at the pedal playing at normally loud levels this weekend.

[Carpathian Whips]

Please post pin voltages. You could have some FET cutoff going on - that would be consistent with the "soft attack" you describe. I highly doubt that the op-amp would have anything to do with that (but I've been wrong before).

Unfortunately I'm worse than a chump understudy when it comes to this stuff, and I don't know how I'd check this. I first need to get a volt meter probably right? I'm truly sorry to offend you with my ignorance and complete lack of electronics know how!

Can the whole slow slew rate be "slower" with the metal can LM308? Would slower slew rate possibly cause a more noticeable softening of pick attack ?

[Carpathian Whips]

ahh, I was going to ask if it has the fet output/buffer stage, but GGBB has me covered. except that he didn't say welcome to the forum, or that Carpathian Whips is an excellent name. for anything, probably.

Thank you so much for the input and nice words.

Regarding the name, it is the name of a music project I'm trying to get going. I'm Romanian by birth, and my Grandpa grew up in Transylvania in the Carpathian Mountains.. and the name just came to me.

You know, this whole Rat thing was very serendipitous because I'm becoming very convinced I need to get into electronics and pedal tinkering and building! It is so intriguing man!

[Carpathian Whips]

No one has offered Mr. Whips a sausage yet? Seems downright rude. Welcome!

Hey a friendly sausage! Man that has so many different connotations! 

Thank you very much for the warm welcome!

btw the other day I made this omelet, with feta cheese, mushrooms and polka kielbasa sausage that was the bomb!

[tubegeek]

btw the other day I made this omelet, with feta cheese, mushrooms and polka kielbasa sausage that was the bomb!

Two words: grilled swojska

[GGBB]

Unfortunately I'm worse than a chump understudy when it comes to this stuff, and I don't know how I'd check this. I first need to get a volt meter probably right? I'm truly sorry to offend you with my ignorance and complete lack of electronics know how!

Can the whole slow slew rate be "slower" with the metal can LM308? Would slower slew rate possibly cause a more noticeable softening of pick attack ?

No worries - I wasn't offended at all - sorry if I came across that way. And let me add my belated welcome - I was juiced up by thoughts of metal can LM308 RATs and didn't notice you were new .

If you'd like to give debugging a shot, click the "Debugging Page" link at the top or try the What to do when ... post. Yes - you'll need a "voltmeter" - digital multimeter or DMM - and some basic knowledge.

It isn't very likely that metal can vs PDIP LM308 are going to be drastically different in slew rate. Slew rate can have something to do with pick attack response, but what you have described seems different to me - more like the effect that compressors can have. And as I said that could be caused by misbiasing of the RAT's JFET output buffer. Could you possibly post a sound clip? It won't hurt to try a different kind of opamp with higher slew rate (and same pinout), and if it doesn't change the problem (note that it most likely will change the tone a fair bit) then that points to the JFET bias being the problem.

[PRR]

> I first need to get a volt meter probably right?

When you build a house, you can sorta tell if it is level, but even Jesus's "Dad" had a level (probably a string on a frame not a bubble level).

When you build electronics you can't see the electricity. _I_ can tell a 9V battery from a 7V battery on my tongue, but range and accuracy is limited and it hurts. Yes, you need a meter to get past "plug and pray". The $9 meters can be found for $3 and are just adequate for a first try. (They soon break and show no reading; they rarely show a wrong reading.)

> metal can vs PDIP LM308

These are surely the same die in different bottles. The metal job is likely to be selected for better DC specs which we do not care about at all. The die design/processing changed over the decades, and a *few* fancy buyers insisted on metal cans for extreme environments. So the metal/epoxy has no significance. Except everything is groovier if you know it is in the metal can.

[Carpathian Whips]

Unfortunately I'm worse than a chump understudy when it comes to this stuff, and I don't know how I'd check this. I first need to get a volt meter probably right? I'm truly sorry to offend you with my ignorance and complete lack of electronics know how!

Can the whole slow slew rate be "slower" with the metal can LM308? Would slower slew rate possibly cause a more noticeable softening of pick attack ?

No worries - I wasn't offended at all - sorry if I came across that way. And let me add my belated welcome - I was juiced up by thoughts of metal can LM308 RATs and didn't notice you were new .

If you'd like to give debugging a shot, click the "Debugging Page" link at the top or try the What to do when ... post. Yes - you'll need a "voltmeter" - digital multimeter or DMM - and some basic knowledge.

It isn't very likely that metal can vs PDIP LM308 are going to be drastically different in slew rate. Slew rate can have something to do with pick attack response, but what you have described seems different to me - more like the effect that compressors can have. And as I said that could be caused by misbiasing of the RAT's JFET output buffer. Could you possibly post a sound clip? It won't hurt to try a different kind of opamp with higher slew rate (and same pinout), and if it doesn't change the problem (note that it most likely will change the tone a fair bit) then that points to the JFET bias being the problem.

No worries you came across perfectly appropriately, it's just that I'm like Bambie caught in the headlights with this stuff. Many thanks for the kindly tips, I super appreciate it!
I'm going to have to dig out a voltmeter from somewhere deep in the garage, or buy one  , but I will get one for sure.
I'll have to record something..probably through the pedal directly to the amp, as I imagine that if I do it through a DAW or Garageband that may somehow mask things, maybe ?? I don't know how much will come across since you'll have no reference of when I'm actually picking the note though right? But I'll have to get motivated and do it. I do have a little Shure microphone that plugs directly into the iPhone, maybe I'll use that.
Thanks again for the knowledge.

[Carpathian Whips]

> I first need to get a volt meter probably right?

When you build a house, you can sorta tell if it is level, but even Jesus's "Dad" had a level (probably a string on a frame not a bubble level).

When you build electronics you can't see the electricity. _I_ can tell a 9V battery from a 7V battery on my tongue, but range and accuracy is limited and it hurts. Yes, you need a meter to get past "plug and pray". The $9 meters can be found for $3 and are just adequate for a first try. (They soon break and show no reading; they rarely show a wrong reading.)

> metal can vs PDIP LM308

These are surely the same die in different bottles. The metal job is likely to be selected for better DC specs which we do not care about at all. The die design/processing changed over the decades, and a *few* fancy buyers insisted on metal cans for extreme environments. So the metal/epoxy has no significance. Except everything is groovier if you know it is in the metal can.

Roger that! I used to have/have a voltmeter somewhere...but after a few moves, I think it may have disappeared into the electrical ether, but I'll get a new one if I no find! I keep telling myself to get into this whole pedal tinkering and building thing, so it would be a nice thing to have a darn voltmeter!

Great info regarding the metal can vs the other...I may have been relating this earlier but I found some post somewhere, which I can't find now, where the poster mentioned a similar loss of pick attack/increased sag when they went to the very same metal can that I have, and now of course I can't find the post anymore..this is sort of what got me started on this whole journey, but just one post doesn't prove anything objectively of course.

Getting the scoop from all of you certainly argues strongly that it's likely not the Op Amp..but since it is socketed I'm thinking of just trying another Op Amp for sure..I'm not sure what priority this has at this point however. I'm just as likely to try another Rat, or even possibly try my hand at building one from a kit maybe.

[Carpathian Whips]

Don't know if this helps or not but here are some pics of the guts:

In these pics I set the trim pot, which affects mids, back to the stock setting as I wanted to see if the sag decreases when I do that but I haven't had a chance to try the pedal again like this..I'm thinking that maybe the increased sag/slower response/decreased pick attack thing started to be noticeable when I cranked the mids trim pot to 75% and started to run the pedal at 12v...but I'm not sure. I'll try to mess with it more tomorrow and go back and forth on the settings, including comparing 9v vs 12v operation.

[PRR]

I'm thinking your "attack" thing is just playing too loud. Many circuits "faint" when OVER-loaded and take a part-second to recover. Depending on recovery time, it might just shave the percussive attack and be OK after that.

me> even Jesus's "Dad" had a level (probably a string on a frame not a bubble level).

I got curious (dangerous) about what Joseph The Carpenter used to level-up the myrrh-shelf Mary asked him to build to keep her kid from eating the precious myrrh. I knew the spirit-level is a "recent" invention (1661 according to Britannica, but not used in trades until 19th century). Before that we had an A-frame with a weight on a string and a mark/hole denoting "level".
https://c7.alamy.com/comp/R0CP4C/a-reproduction-medieval-masons-level-at-gudelon-castle-treigny-yonne-burgundy-france-R0CP4C.jpg
I don't know why it is on a barrel of water. Maybe to compare to water level. However a level can be calibrated on any solid near-level surface. Put it east-west and mark the mark. Carefully turn it around west-east in the same place and mark the mark. Split the difference, that's close. Set it up again but add a shim so it hits the estimated center mark. Reverse and observe. If different, split the difference again. When you get "same" reading both ways, it's good.
In a variant, a vertical board with a plumb line and mark will tell when a wall is plumb.
Another reads level, plumb, and 45 degrees: http://videoshub.co/wp-content/uploads/2019/09/plumb-level-and-square-plumb-level-square-masonic-plumb-level-square-seattle.jpg
There was a folding pocket level,
http://diehandler.co/wp-content/uploads/2019/05/brass-folding-square-with-plumb-level-laser-rare.jpg