# What's going on with my ProCo Rat build



## Cory Haynes (Dec 7, 2018)

So quick and dirty. I built a veroboard rat pedal it worked for a minute or 5. There was a brief lost period of time of pure distorted glory. it's my first full pedal build from scratch. Well my first pedal ever. Then it squealed in pain and died a fizzleing out death. I built this exact pedal.









Any ideas on where I should be looking? I'm going reflow all the solder tomorrow and ensure all the cuts are completely cut and nothing is touching that shouldn't be. But any educated help would be very much appreciated. The only part I didn't use the proper value on was the transistor, it called for a 2n5458 and I used a 2n5457. But I read for the purpose it serves in the rat that as long as it's an n-channel jfet I would be fine


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## ezcomes (Jul 28, 2008)

Interesting...i built this one too...only issue ive had is that it squeels with the gain over 2 o clock

It sounds like a joint has come loose...check all your solder joints...making sure the pins of the ic are soldered together as well

Good luck!


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## BSTheTech (Sep 30, 2015)

Waiting for Hammertime. Paging Doctor Hammer...


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## Cory Haynes (Dec 7, 2018)

BSTheTech said:


> Waiting for Hammertime. Paging Doctor Hammer...


Yeah how do we alert him to this thread. He knows his shit!


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## Budda (May 29, 2007)

You page him.

@mhammer in the rodent section please.


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## Guest (Jan 19, 2019)

I can't wait for this.


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## mhammer (Nov 30, 2007)

Jeez louise. I pop out to get some gas for the snowblower, in preparation for the deluge tonight, and all hell breaks loose.

1) I hate, hate, hate veroboard. It's hard to follow and takes up more room than it needs to.

2) Subbing a 2N5458 for a 2N5457 should not make any difference. Though not ALWAYS true, as a rule of thumb, when you have two similar-function transistors that are consecutively numbered (e.g. 5457/5458, or BC546/547/548) their difference is generally a matter of the higher-numbered one having a more generous spec along one or more parameters. Not always, but often.

3) The circuit does require an LM308, but will also work with a TL070, both of which require an external compensating cap (30pf). The 308 is the preferred chip, however, because of its gain limitations and how it behaves when you push the limits.

4) I have to go pick up my wife, so I'll leave you with this question: is the supply correct? Do you read +9v on pin 7?


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## BSTheTech (Sep 30, 2015)

mhammer said:


> ...and all hell breaks loose.


LoL


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## Cory Haynes (Dec 7, 2018)

mhammer said:


> Jeez louise. I pop out to get some gas for the snowblower, in preparation for the deluge tonight, and all hell breaks loose.
> 
> 1) I hate, hate, hate veroboard. It's hard to follow and takes up more room than it needs to.
> 
> ...


I'm making dinner but I'll have a look after. Thanks for pointing me in a direction.


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## mhammer (Nov 30, 2007)

Q: What are you powering it with? Battery? external supply?


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## Cory Haynes (Dec 7, 2018)

mhammer said:


> Q: What are you powering it with? Battery? external supply?


With a power supply sir


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## Cory Haynes (Dec 7, 2018)

mhammer said:


> Q: What are you powering it with? Battery? external supply?


I've been plugging it into a 1spot wall wort rated for 1700ma that I've plugged loads of other pedals into with never an issue


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## greco (Jul 15, 2007)

Cory Haynes said:


> With a power supply sir


Sir Mark Hammer! Congrats!

Well deserved...however, it does come with a whole new level of electronics diagnostic and consultative responsibilities.


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## Cory Haynes (Dec 7, 2018)

Alright @mhammer 

So a few questions and remember I'm new. Lol. 

So which way should the IC be orientated on this board. The 308s I bought don't have the dot at pin one just that little half moon at one end. But I've measured both spots of the socket pin seven could be based upon which way the IC is flipped. With the half moon facing the top of the board pin 7 of the socket reads 9.15 v. With the half moon facing down pin seven would read anywhere from 4.5 to 5v


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## mhammer (Nov 30, 2007)

greco said:


> Sir Mark Hammer! Congrats!
> 
> Well deserved...however, it does come with a whole new level of electronics diagnostic and consultative responsibilities.


35 years back, when doing my M.Sc. at University of Alberta, I served as one of the graduate student reps on university senate. I forget what the topic of discussion was, but I pressed my microphone button to speak on the matter. The corresponding light came on at the main desk, and the university president, Myer Horowitz (for whom the theatre is named), said "The floor recognizes Dr. Hammer". I smiled and said "That's good enough for me", as if the degree had been conferred at that moment.

Do they distinguish between "earned" and "honorary" knighthoods, the way they distinguish between earned and honorary doctorates? 

The One-Spot should not have caused any problems, in principle. But I have to wonder if the chip was somehow being "mispowered" in some manner. That is was power being applied to some part of the chip that would not normally receive such voltage? Was the 47R resistor in place to limit current draw?

Here is the schematic you should be following. Make sure your connections correspond to what is shown here.


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## mhammer (Nov 30, 2007)

Cory Haynes said:


> Alright @mhammer
> 
> So a few questions and remember I'm new. Lol.
> 
> So which way should the IC be orientated on this board. The 308s I bought don't have the dot at pin one just that little half moon at one end. But I've measured both spots of the socket pin seven could be based upon which way the IC is flipped. With the half moon facing the top of the board pin 7 of the socket reads 9.15 v. With the half moon facing down pin seven would read anywhere from 4.5 to 5v


The "half moon" should be facing what is shown as the "top" of the tagboard drawing. Note that the 100uf capacitor should connect to in 7 of the chip. The drawing shows cuts along the way, but the jumper itself should go from the + end of the cap to the contact point for pin 7.


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## Cory Haynes (Dec 7, 2018)

mhammer said:


> The "half moon" should be facing what is shown as the "top" of the tagboard drawing. Note that the 100uf capacitor should connect to in 7 of the chip. The drawing shows cuts along the way, but the jumper itself should go from the + end of the cap to the contact point for pin 7.


I've prodded and probed the hell out of this thing to the full extent of my abilities and knowledge. I ordered the op amps off Amazon. Can they be duds right from the get go? I'm in the process of rebuilding the whole thing double checking all the values as they go in. Using a lower heat soldering gun. I just wanna play the damn thing. If it turns out it was just dud components this will all have been an insanely frustrating endevour.


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## greco (Jul 15, 2007)

@Cory Haynes My friends an I are cheering for you...


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## mhammer (Nov 30, 2007)

Legitimate LM308 chips are still quite available. I think I got mine at Honson in Toronto.

You should learn how to make your own PCBs. It's not all that hard, and supplies are readily available these days. The toner-transfer method makes fabricating PCBs a piece of cake. The nice thing is that there are plenty of folks who provide tested working layouts for personal use, and the layouts have all the connections made between components. One still has to make a decent etch, and have the tools for drilling the boards, but for my money it's a damn sight less exasperating than trying to follow a veroboard layout.

Troubleshooting: One of your best allies in troubleshooting is having a schematic and understanding the building blocks of the circuit. So, for instance, the schematic shows a resistor near the input going to Vref (4.5V). That's for biasing the chip in order to fake having a +/-supply with a ground point. What that implies is that pin 3 should read 4.5V DC, when power is applied. If the guitar signal is actually reaching the chip, you should be able to get a reading of somewhere between 10 and 100milivolts of AC at pin 3. And so on. I find stripboard makes it harder to follow the circuit, and know where to get informative readings. BUt that's me.


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## Cory Haynes (Dec 7, 2018)

greco said:


> @Cory Haynes My friends an I are cheering for you...


Thanks man.


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## Cory Haynes (Dec 7, 2018)

mhammer said:


> Legitimate LM308 chips are still quite available. I think I got mine at Honson in Toronto.
> 
> You should learn how to make your own PCBs. It's not all that hard, and supplies are readily available these days. The toner-transfer method makes fabricating PCBs a piece of cake. The nice thing is that there are plenty of folks who provide tested working layouts for personal use, and the layouts have all the connections made between components. One still has to make a decent etch, and have the tools for drilling the boards, but for my money it's a damn sight less exasperating than trying to follow a veroboard layout.
> 
> Troubleshooting: One of your best allies in troubleshooting is having a schematic and understanding the building blocks of the circuit. So, for instance, the schematic shows a resistor near the input going to Vref (4.5V). That's for biasing the chip in order to fake having a +/-supply with a ground point. What that implies is that pin 3 should read 4.5V DC, when power is applied. If the guitar signal is actually reaching the chip, you should be able to get a reading of somewhere between 10 and 100milivolts of AC at pin 3. And so on. I find stripboard makes it harder to follow the circuit, and know where to get informative readings. BUt that's me.


I appreciate the education I truly do. And I'm not opposed to trying my hand at etching a board. Your absolutely right though, veroboard can get the job done it seems but it like pounding nails with a 2 ounce hammer. I'm gonna keep bashing my head off the wall till I get this rat pedal licked then I think that may be the last of my veroboard building for awhile.


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## Todd MacCulloch (Mar 8, 2018)

After checking voltage to the chip, I find following through the schematic with an DIY audio probe, magnifying glass, and continuity mode to be my best friends when debugging.
The probe helps me find the first issue, the glass and continuity help me figure out the cause - bad joints and accidental bridges being the most common although sometimes the wrong component or component orientation.
Good luck!


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## jb welder (Sep 14, 2010)

Cory Haynes said:


> I ordered the op amps off Amazon. Can they be duds right from the get go?


Absolutely. Default should be to not trust obsolete chips coming from China. As we have heard about in other threads, they will counterfeit anything just to make a couple of pennies. After reading about so many people having problems with 'new' obsolete chips, I started thinking about it. Why would they have stockpiles of NOS chips from before China was a manufacturing giant? Why would they be building current versions of obsolete chips? 
The big problem with Amazon is they no longer show where they are shipping from, so I assume China unless told otherwise.

If you have to buy an obsolete chip and it seems they are all coming from China, be wary. Try to find a North American source like Mark mentioned. It can take some digging. Not all the chips coming from China are bad, but if it's a new hard to find or obsolete chip, and it doesn't work, chances are it's counterfeit or substandard.


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## Guest (Jan 21, 2019)

I used to go to garage sales and buy electronics from the 70's and 80's and gut them for opamps. I was looking for the JRC4558D and found many.


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## Cory Haynes (Dec 7, 2018)

Again. Your a solid group of dudes. I really do appreciate you guys paying forward your hard earned knowledge


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## mhammer (Nov 30, 2007)

Small Bear Electronics, in Brooklyn ( Small Bear Electronics ), was started by a member of the DIY stompbox forum, Steve Daniels. Steve has been a hobbyist in the field for many years. The business started out by Steve asking forum members "I can get a good deal on X. How many of you would be interested in buying one or more if I could get them for $x.xx?". As Steve located more and more good deals, the inventory started to take over the second bedroom in his apartment. Meanwhile he continued to work at a job as technical writer. Eventually, the volume of sales justified taking the big leap, and Steve started the business, eventually moving out of the 2nd bedroom into a space with room for all that inventory, and hiring 8 or 9 people to process orders, do some of the shopping, and manage financial affairs.

While he has a lot of commercial clients (many of them being "name" boutique houses), and they pay the bills with large purchases, he maintains a soft spot for hobbyists, and provides components for obscure pedals that no one else would carry. Equally important, all the chips and transistors are tested, and selected. You'll pay a little more for some things, and you'll wait a little while, but you'll know that you can trust what you've bought. Unfortunately, at the moment, he is out of stock on the metal can 308 chips. I have a couple of the plastic ones.

Tayda Electronics sells parts pretty dang cheap. They don't carry as broad a selection of the exotic pedal-specific stuff as Small Bear, but they carry a lot of things you'll find useful, quite cheaply. The drawback is that you can't be in a hurry, because stuff is getting shipped from Thailand. I find I usually need to wait 3 weeks or so for orders to arrive. They sell a Rat PCB ( RAT DIY PCB Guitar Effect ) but don't seem to carry the 308. 

The 308 is considered a "lesser" op-amp. Although the circuit will work with a TL071, the 308 is the original, and possibly the preferred chip, largely _because_ of its shortcomings. The Rat applies gains of several thousand, when the gain control is dimed. Datasheets for chips will often show the "gain-bandwidth" product, also termed "open loop gain". Here's the one for the LM308. It shows the absolute maximum gain you can extract from the chip, as a function of frequency. Happily, it shows the curve for a compensation cap of 30pf, which the Rat uses. Note that a voltage gain of 1000x is 60db. The chip can manage that out to about 600hz, according to the graph. But note as well that I said the Rat has a maximum gain of just over 3000x for the mids and highs. 3000 is around 70db. Clearly, the LM308 can manage that much gain if amplifying 100hz. But there is no way it can manage that much gain for stuff even as low as 500hz, and certainly not for the content above 1khz, which is what distortions will add. By contrast, a TL071 is good for 60db amplification out to around 5khz.

Think of it like running. Lots of folks can sprint real fast for 20ft. Some can sprint fast for 20ft but run out of breath for anything farther. And still others can run fast for 400m. The LM308 runs out of steam easily for what it is asked to do. And that's what provides its distinctive tone. Using a "better" chip may well deliver something quite usable, but not the "true" Rat tone.

Hope that made sense.


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## Todd MacCulloch (Mar 8, 2018)

I forgot to mention, I don't have a dedicated signal generator when using the audio probe. I use my looper pedal.
I record a quick passage on the looper and then run the looper into the circuit being tested.
I plug the probe output into my practice amp (mine has headphones which is nice).
Where I touch with the business end of the probe completes that portion of the circuit to the amp.


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## Cory Haynes (Dec 7, 2018)

Yup. So rebuilt the whole damn thing and the 100uf cap litterally started to smoke. I was super careful with everything. Sighs.


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## mhammer (Nov 30, 2007)

Was that the same 100uf cap used previously, or a brand new one? I ask because maybe the dysfunction before was due to that same cap.

But good on ya for being willing to start from scratch.


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## Cory Haynes (Dec 7, 2018)

mhammer said:


> Was that the same 100uf cap used previously, or a brand new one? I ask because maybe the dysfunction before was due to that same cap.
> 
> But good on ya for being willing to start from scratch.


Brand New everything. Veroboard does kinda suck. And I'm not being a sore looser. It just by it's very nature can leave a ton of loose ends. And I'm down to one remaining (possible a dud) 308 chip.


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## mhammer (Nov 30, 2007)

If you can whip up a simple unity-gain board with a socket. You can try out the chip in that and simply confirm that it works.

As I mentioned earlier, the Rat circuit will "work" with a TL071 (which won't need the 30pf compensation cap) . It won't sound exactly like an original Rat, but it will confirm for you that it's the circuit, not the 308 chip, or that its the chip, not the circuit. And TL071 chips are in great abundance and a whole lot cheaper than 308s.


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## Cory Haynes (Dec 7, 2018)

mhammer said:


> If you can whip up a simple unity-gain board with a socket. You can try out the chip in that and simply confirm that it works.
> 
> As I mentioned earlier, the Rat circuit will "work" with a TL071 (which won't need the 30pf compensation cap) . It won't sound exactly like an original Rat, but it will confirm for you that it's the circuit, not the 308 chip, or that its the chip, not the circuit. And TL071 chips are in great abundance and a whole lot cheaper than 308s.


So if I aquired a tl071 I would just run a jumper where the 30 pf cap was? And I'll look up unity gain boards, I've never heard of one before


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## Cory Haynes (Dec 7, 2018)

mhammer said:


> If you can whip up a simple unity-gain board with a socket. You can try out the chip in that and simply confirm that it works.
> 
> As I mentioned earlier, the Rat circuit will "work" with a TL071 (which won't need the 30pf compensation cap) . It won't sound exactly like an original Rat, but it will confirm for you that it's the circuit, not the 308 chip, or that its the chip, not the circuit. And TL071 chips are in great abundance and a whole lot cheaper than 308s.


After a search I can't find anything showing me how to build a unity gain board . If anybody could send me a link as to what to build it would be greatly appreciated


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## jb welder (Sep 14, 2010)




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## Guest (Jan 24, 2019)

http://www.learningaboutelectronics.com/images/Voltage-follower.png

The image did that httpS where it adds the s for secure site of some sort, and if the site doesn't have the s, there is an error... So I linked to it.


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## jb welder (Sep 14, 2010)

Thanks Player, still does that nonsense where you have to remove the 's' from https, so I'll just upload the pic.


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