# flatulent EH deluxe big muff pi



## kat_ (Jan 11, 2007)

I'm trying to fix up a 1978 deluxe big muff pi for a friend and I'm stumped.

It puts out a loud 60 cycle hum/buzz/fart sound. It doesn't matter if it's bypassed or not, it still puts out the same sound. The pedal has two outs. On the Fuzz Output the sound is constant no matter what, but on the Comp out the volume of the sound varies when the comp volume knob is turned.

Everything on the board looks okay - no burned out components or blown caps.

The pedal has a somewhat strange design in that it runs off AC power instead of an adapter. It has a small transformer inside the pedal. I'm wondering if that transformer is toast. Would a problem with the transformer possibly cause this noise? 

My other guess is something isn't grounding. I hope that's it.


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## keeperofthegood (Apr 30, 2008)

Needs to be re capped 

The ac power supply filter is done in. I think MHammer can walk a talk though of it better than I or anyone but I think pics will be requested


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## theelectic (Mar 11, 2006)

At this point ALL of the electrolytic caps in that thing should probably be replaced - they're 31 years old by now and at best, were designed to last 10 years. That they've lasted this long in a semi-working state is a bonus.

I don't think pictures are necessary - you'll probably find four or more capacitors on the board that are much larger than the others - 100uf or 220uf at 25V or more. They should lead to a rectifier which in turn leads to one side of the transfer. Replace those. In this case, you can replace a smaller value with a larger value (i.e. if you're replacing a 100uf, you can replace it with a 220uf if that's all you have on hand) but ensure the voltage rating of the new cap is the same as the old one or higher.


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## mhammer (Nov 30, 2007)

There's some technical info about it here: http://hammer.ampage.org/files/Device1-7.PDF and the schematic is posted around somewhere.

The advice about the caps is bang on. Electrolytic caps from that era are generally past their "best before date" by now, and have dried out and drifted off spec. All the more likely when there is a small transformer and AC supply inside the chassis that will give off at least a little heat.

Why do we suspect the caps? Because the caps are what helps to transform the AC power from the wall/transformer into DC power for the chips. And when the power is more like AC than DC, you get hum.

So, before you rip out all the caps, focus in on the ones most likely to matter, which are the ones in the power supply. My very grainy and hard to read schematic or the Deluxe BMP shows there will be 6 of them, two that seem to be somewhere in the 100-470uf range, and 4 smaller values that seem to be around 1-10uf or so. They will be near the transformer and the NE5354 regulator. Two of them appear to be tantalum type.

Score yourself some new caps (tantalum can be replaced with normal electrolytic here) of the same or larger values (e.g., 220uf can be replaced with 330uf or even 470uf in this application), and *make sure they have a voltage rating of 25v or greater*.

There is a high probability that replacing those caps will get the hum out of your life again. If it doesn't, we'll pick up again from there.


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## kat_ (Jan 11, 2007)

That's brilliant. Thanks guys.

I replaced the caps in one of my amps last year. I should have thought of that for the pedal. I'll post back once that's done.

Btw, mhammer - is your last name actually Hammer?


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## kat_ (Jan 11, 2007)

I replaced the four 100uf caps that are between the transformer and the regulator today. Absolutely zero change to the noise of the pedal. I was hoping for some change at least. Tomorrow I'll try to get some of the 10uf caps that are after the regulator. I'll also replace the 470uf that's elsewhere in the circuit just because it's the biggest cap on the board. Hopefully that'll start to clean stuff up.


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## mhammer (Nov 30, 2007)

kat_ said:


> That's brilliant. Thanks guys.
> 
> I replaced the caps in one of my amps last year. I should have thought of that for the pedal. I'll post back once that's done.
> 
> Btw, mhammer - is your last name actually Hammer?


Yes. First name Mark. the epicentre of Hammers is apparently Saskatchewan (there are 5 telephone listings in Swift Current alone), though I'm not related to any of them.


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## mhammer (Nov 30, 2007)

kat_ said:


> I replaced the four 100uf caps that are between the transformer and the regulator today. Absolutely zero change to the noise of the pedal. I was hoping for some change at least. Tomorrow I'll try to get some of the 10uf caps that are after the regulator. I'll also replace the 470uf that's elsewhere in the circuit just because it's the biggest cap on the board. Hopefully that'll start to clean stuff up.


Let's hope. the hum does not have to result from ALL the caps being old and crunchy. It can be from merely one of them. The larger value ones are generally the more likely to go, though, so let's cross our fingers and hope the 470uf cap is the one.


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## kat_ (Jan 11, 2007)

Thanks for your help. I picked up a miscellanous assortment of just over 300 caps today so should be able to finish this (and some other things) off without any more trips to the store. I started playing around with pedals a couple of years ago without knowing anything about electronics beforehand. I learn a lot from every single project but I'm hoping it'll start to get easier at some point.

My last name is Hammer too.


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## kat_ (Jan 11, 2007)

I've replaced more than half of the caps on the board without any change at all to the noise. Seeing as the noise affects both the fuzz and comp outs and none of the other caps are shared by both circuits either every cap is bad or there's something else wrong. The other caps are all pretty tiny so I'm having trouble imagining them causing this loud of a noise. Do you have any other ideas at all?


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## keeperofthegood (Apr 30, 2008)

Hmm, I would still finish off the caps, they are simply known to fail and it doesn't hurt to recap. 

I would also suggest that it is time to bypass the AC all-together with a 9V battery. Doesn't need to be a permanent thing, but a testing thing  I am curious to know if it is line hum or not now.

As they say, walks like a duck, quacks like a duck, odds are its a chicken.


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## mhammer (Nov 30, 2007)

When it comes to older boards like this, my own inclination is to replace things a little bit at a time, just to avoid the heartache of lifted/fractured traces arising from the heat you have to apply to desolder something.

I've posted some schematics for it. One is a scanned factory schematic that is a little difficult to read but we know it's authentic. The other is a redrawn version which omits the power supply.

http://i414.photobucket.com/albums/pp228/Mark_Hammer/EHdeluxebigmuffpi_sustain.gif

http://i414.photobucket.com/albums/pp228/Mark_Hammer/bigmuffdlx.gif

I posted two other schematics I have of the individual fuzz and compressor sections (w/o PS included) but cannot vouch for their authenticity. Assuming they are accurate, there would appear to be issue changes where EHX went from using a JFET to adjust compressor level to a CA3080 to adjust gain. EHX labelled their in-house version of the CA3080 as EH1048, so if you see a chip with that number emblazoned on it, then you have the "other" version.

http://i414.photobucket.com/albums/pp228/Mark_Hammer/DeluxeBIgMuff-compressorsection.jpg

http://i414.photobucket.com/albums/pp228/Mark_Hammer/DeluxeBIgMuff-fuzzsection.jpg

Always glad to help out a fellow Hammer!:smile:


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## kat_ (Jan 11, 2007)

mhammer said:


> I've posted some schematics for it. One is a scanned factory schematic that is a little difficult to read but we know it's authentic. The other is a redrawn version which omits the power supply.
> 
> http://i414.photobucket.com/albums/pp228/Mark_Hammer/EHdeluxebigmuffpi_sustain.gif
> 
> http://i414.photobucket.com/albums/pp228/Mark_Hammer/bigmuffdlx.gif


The first of those schematics is what I've been using. 

Since the sound is identical from each output either there's a similar problem in each circuit or the problem is in something that's shared.

I really wish I could have seen this pedal before Andy's dad tried to fix it.


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## kat_ (Jan 11, 2007)

keeperofthegood said:


> I would also suggest that it is time to bypass the AC all-together with a 9V battery. Doesn't need to be a permanent thing, but a testing thing  I am curious to know if it is line hum or not now.


Where exactly should I put that in? Just after the regulator?


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## keeperofthegood (Apr 30, 2008)

I think I would like Mark's opinion of this as well, so MARK! What do you think of this approach and idea? 

Just had a thought. How is the AC being converted to DC? There are three 'simple supply' options usually found when using a transformer:

1) centre tapped transformer, with two diodes
2) un-centre tapped transformer with 4 diodes
3) same as 2, except using a 4 pin package 'bridge rectifier'

This is where a photo would benefit, looking at a few historical tracking sites I've not seen any with AC power supplies and the schematics don't detail any either. However, the chain is usually:

Transformer --> Diodes --> capacitor --> resistor --> capacitor

Sometimes the resistor is replaced with a three terminal regulator, for nine volts it would be LM7809 or LM7909 I think.

How is the power out of the supply provided to the rest of the circuit? 9V DC across the last capacitor would be the spot to inject, that point should be 9V DC so placing 9V there should simply power the pedal. I would just use a battery clip and hand do the leads to the legs of the cap as this is just a quickie test to see if not using AC makes for the same sound. Of course >_> have to be careful to get the +/- right.

The thought I just had, if the rectifying diodes has/have failed and failed in an a 'closed' manner, then you would be getting AC or pulsating AC fed into the filter rather than rippled DC. This would overwhelm the filters ability to smooth. I think you also get a higher voltage out too when this happens. Easy enough to check too.


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## mhammer (Nov 30, 2007)

That the offending sound comes from both the fuzz section and compressor section suggests quite strongly that what they share in common - the power supply - is the source of the difficulty. I'm assuming that all caps you've replaced were of a suitable power rating, on spec, and installed with the right orientation. In which case, if they were, and the hum persists, then our next culprit is the regulator.

The NE5554 dual tracking regulator that is used in the Deluxe BMP can be seen in this datasheet: http://www.datasheet.org.uk/pdf-datasheets/Databooks-3/Book604-26435.pdf

The regulator essentially replaces a pair of individual 5v regulators (opne for V+ and the other for V-). In theory, the 5554 can be *functionally* replaced with a 78L05 and a 79L05. Of course, since these are two 3-pin devices, it is not a simple matter of replacing a chip with a substitute. Nor is it a simple matter to remove the existing chip or talk you through how to wire up the suggested substitutes on the board.

Still, is it possible for you to *carefully* desolder the NE5554 and remove it? Do you have braid, a bit of flux, and some suitable soldering iron that enables you to get in and out quickly?


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## kat_ (Jan 11, 2007)

I actually ran out of braid last night.

It looks like the 5554 is a bit tricky to get. I'm going to put this on the backburner for a bit. It's been frustrating me too much.

Today I took apart my old DX7 synth and did a small repair on it. It's all back together and working better than it has in years now. I really needed that today. Andy's not in any hurry to get this pedal back so I'm going to finish the amp I'm building before I go back to the pedal. 

I really appreciate everyone's help here. I will come back to this pedal. It's just getting moved to the bottom of the list for now.


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## mhammer (Nov 30, 2007)

Yes, the 5554 will be tricky to get, which is why the 78L05/79L05 fix seems most straightforward to me in terms of getting +/-5V to the chips.

Funny, flipping the hood of a DX7 and fixing that would be daunting for me. I have a non-functioning Juno 106 I picked up cheap about 5 years ago, and while I have flipped the hood several times, and scored all the schematics, I tend to quietly lower the hood and slowly back away.


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## kat_ (Jan 11, 2007)

In the DX7 I knew what was wrong. Actually fixing stuff is easy. It's the diagnosing that's magic.


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## kat_ (Jan 11, 2007)

mhammer said:


> The regulator essentially replaces a pair of individual 5v regulators (opne for V+ and the other for V-). In theory, the 5554 can be *functionally* replaced with a 78L05 and a 79L05.


I know it has been a long time but I'd like to come back to this and finish it off. The 78L05 is easy to get but none of the places I normally deal with stock at 79L05. Any suggestions where to get that? And if I do get it are you willing to talk me through what I need to do?


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## keeperofthegood (Apr 30, 2008)

kat_ said:


> I know it has been a long time but I'd like to come back to this and finish it off. The 78L05 is easy to get but none of the places I normally deal with stock at 79L05. Any suggestions where to get that? And if I do get it are you willing to talk me through what I need to do?


If you have no objections to eBay, there is a Florida seller that has "kits" of voltage regulators for a decent enough price I could recommend.


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## mhammer (Nov 30, 2007)

kat_ said:


> I know it has been a long time but I'd like to come back to this and finish it off. The 78L05 is easy to get but none of the places I normally deal with stock at 79L05. Any suggestions where to get that? And if I do get it are you willing to talk me through what I need to do?


A damn shame I didn't know this when I was in Calgary. I have wads of them, and would have gladly given you some. You can get them at Active. There are also LM340 functional equivalents too.

The thing about regulators is to keep on top of which pin is where on THAT particular version, and to make sure they can handle the current you want them to regulate. No harm in stepping up to the next level of current capability if that's all you can find.


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## bduguay (Jul 15, 2009)

We interupt this thread to ask Mark to check his PM's
Thank you for your cooperation.
B.


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