Source for 708N chip to upgrade Rat 2?

[Enzo]

This is not my area of expertise, but in applications like overdrive/distortion pedals, the op amps are operated outside of their polite "quality audio" conditions. They are used in ways the data sheet doesn't cover, and the manufacturer doesn't specify operational data. That in my mind explains why two ICs will sound different. And it also might explain what g-one mentioned, a newer "better" IC doesn;t work as well. The better design handles undesired - from their point of view - conditions, but those conditions are what we here are looking for.

[Steve A.]

Enzo:

I ran across a webpage on the RAT that explained/theorized that what made the RAT so special was that the LM308N could not keep up with the signal properly- along the lines of two wrongs do make a right when it comes to music electronics.

Steve

P.S. I'll post a link to that page if and when I find it again.

[Enzo]

More or less what I was saying. Op amps all work pretty well within their design parameters. The effect guys select specific ICs based on how they react to using them outside the designed parameters.

[Chuck H]

I think I read a similar article. The biggest factor was determined to be slew rate. The lm308n has a very poor spec. Of course this is WITHIN the operating parameters, so there is still all the goodness that happens outside those parameters to factor in too. Although guys designing with other chips and intentionally buggering it's operation to reduce slew rate report good results too.

The NTE938m is "equivalent" to the lm308n. I found one report from a guy that used it side by side with the lm308n and said it sounded good. He didn't say if it sounded different though. At last check the NTE938m could be had at Mouser for about $10.

[dai h.]

re: the IC, it appears they used NS and Motorola. I think mine (bought around mid 80s) used a Motorola (it's boxed up and don't feel like digging it out at the moment and couldn't find the paper I drew out the schemo and component info on). Pretty confident it was the same as this one:

THE?????????????Pro Co : ????RAT

(gut/PCB pics of a couple of other units for comparison) :

THE?????????????Pro Co : ????RAT

THE?????????????Pro Co : ????RAT

THE?????????????Pro Co : ????RAT

THE?????????????Pro Co : ????RAT "????????"

THE?????????????Pro Co : ????RAT

THE?????????????Pro Co : ????RAT

THE??????THE????????????Pro Co : ????RAT "????????"

THE????? Premium Selections????????Pro Co : ????The Rat "Original Large-Box"

THE??????THE????????????Pro Co : ????The Rat "Original Large-Box"

THE??????THE????????????Pro Co : ????The Rat "Original Large-Box"

THE??????THE????????????Pro Co : ????The Rat "Original Large-Box"

[Chuck H]

Units # 2, 6 and 7 are interesting in that they have the old case graphics but the later board layout with a hole for the LED (but no LED installed)?!? I've only seen that on the "Vintage The Rat reissue. Never on a 'no led' small box unit. Repairs maybe? Or perhaps someone figured to cash in by sticking a reissue board into a broken collectible?

Other than that the pics seem to confirm Steve's findings. The original large box units all had the NS chip, the earliest "white face" units had the NS chip while later "white face" and all the "black face" models have the Motorola chip.

Mine was a "white face" unit but I remember it being a fairly aggressive sound. I'm leaning toward mine having been a later "white face" with the Motorola chip.

[dai h.]

Chuck, in the description for this one:

THE?????????????Pro Co : ????RAT

it says the PCB is a Rat II board ("a highly unusual model w/estimated date of production around '87-'88"). Could have been an easy solution when they need to make some Rat I, I suppose. Seems plausible since I think it'd be pretty hard to damage one so catastrophically, and (although the prices are pretty high), maybe too much trouble to fake one (unless you happen to be sitting on a lot of broken ones--but as I mentioned broken Rats seem to be less likely than not due to the super robust build).

[Chuck H]

Haha! I didn't use a translator (Easy enough but I was lazy). Indeed, I don't figure ProCo threw away left over cases when they started a new model! Fender was notorious for such things too.

EDIT: Check this out! No post #s but it's about 2/3rds down the page. Poster says his RAT2 is from '87 and his Rat1 is from '88!?! That's odd enough but the pics also confirm the transitional model.

http://www.harmonycentral.com/t5/Eff...228436/page/23

[dai h.]

maybe a sign of their (Pro Co's) success? Or just a crossover period of making both. Maybe a good practice (to enable some dimension/layout compatibility, use common parts) if the occasion arises (as seen in the apparent examples). The early Marshall PCBs are like that, with alternate markings for different models.

p.s. (Chuck I can read Japanese because I am one of themz... )

[Chuck H]

The early Marshall PCBs are like that, with alternate markings for different models.

Yes, I've owned several.

p.s. (Chuck I can read Japanese because I am one of themz... )

I know. We've both been here (on the forum) a long time. I, however, am pitifully unilingual.

The poster in my link indicates that he preferred his RAT2 to the Rat1. It could be an indication that the new design was done with some care in listening and the actual presence of the LED as part of the circuit has an affect!?! That WOULD be the only difference between his two circuits. More likely it's just unit variance or his personal tastes though.

I've never played a RAT2 with the Motorola lm308n. Since the redesign included that chip, a new layout, unknown (to me) circuit alterations and the LED I'd like to try one some time. It could be that the early RAT2's are as good as the early Rat1's? Later RAT2's used the newer National Semiconductor chip. The same chip most modders got their hands on for replacing the chips in later models. But since that particular model was designed with the Motorola chip, and seems to be preferred to later units, all the different Rat incarnations may be very chip specific. So... A summary of what I think "I've" observed from this thread so far would be...

The early big box and small box Rat's were designed with the old logo NS chip and people seem to prefer it to the later Motorola chip.

The RAT2 was a redesign with the Motorola chip, new layout, LED and maybe other stuff and people seem to like those too.

Later logo NS chips were readily available for a long time and people bought them and stuck them in their later pedals with most reporting improvement but I don't see as much raves as I do hype about the actual lm308n moniker.

New Chinese lm308n chips suck.

Conclusions... Use the old logo NS lm308n in for the old layout. Use the Motorola for the second layout. Avoid the third layout models (unless you already own one). Steve reports good results with the later logo NS chip. Ignore all other lm308n's and beware of counterfeits.

Notes... The lm308 cans seem to have a mixed reputation but nothing bad. Just not always great.

[dai h.]

The poster in my link indicates that he preferred his RAT2 to the Rat1. It could be an indication that the new design was done with some care in listening and the actual presence of the LED as part of the circuit has an affect!?! That WOULD be the only difference between his two circuits. More likely it's just unit variance or his personal tastes though.

Chuck AFAIK the Rat II has some slightly different values (hope I'm recalling correctly), with a 2.2M right at the input (probably no difference except less of a 'pop' when switching), a 2.2M closer to the OPA input (vs. 1M on the Rat I), plus a bigger output cap (10uF for the II vs. 1uF for the I). So, (differences adding up to) slightly more bottom?

As far as some (very amateur-ish) experimentation, I tried replacing the Rs and alu electros with metal film and "Black Gate" caps, which seemed to weirdly sound okay through a crappy (IMO--and harsh "solid state sounding" due to topology and whatever) Boss GL-100 (early amp simulator) but when I took it over to an in-law's and tried it through some low-end Marshall Valvestate (IIRC), it seemed (VERY EMBARASSINGLY) thin sounding (so I later replaced all the old parts).

Also, tried OP07 (long ago before the "official" newer versions), and it seemed sort of "nicer" subjectively, but wasn't really struck that it was an improvement.

Also tried sticking adhesive-backed copper foil on the top back of the chassis (portion with the pots and jacks, etc.) on a big box Rat I reiss. (along with different clipping diodes on a rotary switch), and weirdly seemed a bit smoother sounding (maybe totally fooling myself and I don't even remember why I tried that). In hindsight I wonder if I improved the RF rejection or something (i.e. made all the ground points the foil was connected to lower R and L so made it more difficult for RF to develop a voltage across and get into the audio--Rats also have a direct connection of jacks to chassis which I understand is better to keep out RF (as opposed to say an insulated jack with thin trace or wire running to circuit ground which allows potential RF to develop a voltage across and get into the audio and intermodulate creating musically unrelated tones, or "Breaker one niner, you got a smokey on your six, over").

[Steve A.]

P.S. Check this out. I think these are fakes! Vintage Motorola LM308AN LM308 OpAmp DIP8 x 1pc | eBay

I reported this listing to eBay as being a counterfeit item. Not that they would ever do something about it but I gave it a shot. It would probably also be good to post a warning on TGP unless someone has already done so. I hate to see people ripped off in a scam!

Steve

[Chuck H]

Way to step up, but...

How to prove they're fakes? It's a hell of an accusation without proof! They do look like Motorola chips. They're a slightly different designation than the coveted lm308n (being lm308an). Looky here. I think this is a genuine part, though a different dual op amp. Look at the case shape, dimple, "M" placement, etc.

5 LM2904 Dual Op Amp Wide Temp Range Genuine Motorola | eBay

[Steve A.]

How to prove they're fakes? It's a hell of an accusation without proof!

Ahhh... but in the virtual world of the internet a party is presumed to be guilty until proven innocent.

I know absolutely nothing about Motorola LM308N's except for the 3 ones that I bought with 1984 date codes and the 1987 one in the picture posted previously by O C Disorder which are as I described:

"LM308" on the top line
the Motorola logo and the letter "N" on the middle line
a date code on the bottom line.

http://music-electronics-forum.com/a...-semi-corp.jpg

Perhaps someone has some Motorola chips from the 90's and can tell us if they changed their numbering format from the one in this picture.

I consider all of this to be along the lines of bullshitting around the watercooler, a campfire or a keg of beer where the First Amendment gives me the right to talk shit and make an ass of myself.



Steve

P.S. My doctor tells me that I need more exercise so I have made a point of jumping to conclusions whenever I can...

EDIT It was the first eBay link you posted coming from China that I thought looked fraudulent (just my own inexpert opinion):

Vintage Motorola LM308AN LM308 OpAmp DIP8 x 1pc | eBay

The second auction you linked to was from a US address, evidently an electronics parts dealer who made no claims as to the worthiness of the chips in guitar effects pedals and who said that they may be different from the ones in the pictures. He sounds like a reasonable eBay seller to me.

5 LM2904 Dual Op Amp Wide Temp Range Genuine Motorola | eBay

Condition of Goods
Unless otherwise noted above:
NOS (New Old Stock) or better, clean, unused
30 day Non-DOA, Good-on-Arrival Guarantee
Untested, but NO JUNK or suspect parts
PCB parts are thru-hole, NO SMD/SMT
Small parts may be bulk packed
Manufacturers and Date Codes may vary

Important: The parts we sell are categorized as new because they are unused, but many of our parts are those rare, hard-to-find, discontinued, manufacturing surplus and / or old stock commonly known in the parts business as 'NOS' (New Old Stock). Some of our stock pictures show date codes which may vary from the actual product shipped.

[Chuck H]

+1
And I still think they are fakes!!! I just wouldn't want to see my comrade bringing a knife to a gunfight, if you get my meaning. The finish is too smooth, the print is too bold and that doesn't even address the address!?! All the LM308's I know about were made in the USA and suddenly there are buckets of NOS hiding in Chinese warehouses?!? Indeed! I'm the guy that brought it up. I don't need convincing, but if there's a chance I'm wrong I wouldn't want it to reflect poorly on you!