BOSS DS-1 Pedal

[ohm470k]

Hey Guys,

Stumbled upon this site while researching my issue and thought I would ask a question.

So I bought a Boss DS-1 Pedal on ebay with the hopes of modifying it, called the Keeley Mod, and reselling it. I knew it was not working properly from the start but figured it for an easy fix. However, I have run into a problem. If I turn the distortion to about halfway or less, I get a low sounding, low volume farty popping sound. Turning up the distortion allows the guitar to be heard. I did find that C23 was swollen and had almost blown the bottom out so I replaced it. Unfortunately, the issue remains. As part of the mod, I replaced/upgraded a dozen or more components and added in a switch. These were mostly caps, an led or two, and a couple of resistors. I was wondering if it could be one of the transistors and if anyone new a good way to find their equivalents, since only the 2sk30a seems available anywhere. I think I can use it to replace Q6, Q7, and Q8 if needed. But I am unsure about the rest.

These components have all been replaced as part of the mod or just my snoopiing around:
C1, C2, C3, C5, C7, C8, C9, C11, C12, C13, C14, C18, C19, C23, R14, R35, D1, D4, and D5.

Here is the schem:

 

[Arouse1973]

Hi there. Look up what's called motor boating. Might be what's happening.
Thanks
Adam

 

[KrisBlueNZ]

Hello there and welcome to Electronics Point

I agree with Adam that your description sounds like motorboating. It would be helpful for us to hear it though. Can you record a few seconds into your computer, convert to a mono MP3, ZIP it, and upload it here?

To attach it to a post, use the Go Advanced button, and click on the paper clip symbol. Browse to the ZIP file's location and select it, and click Upload. The forum has a file size limit of 97 kilobytes and it won't accept an MP3 file, which is why you have to ZIP it.

Failure of C23 could have been caused by connecting an adapter with too much voltage. D1 is supposed to protect the circuit against use of an adapter with the wrong polarity. Was it visibly damaged before you replaced it? Was it broken apart? If so, reverse voltage will have got in there and probably damaged the M5223 dual op-amp. This could concievably cause almost any kind of fault, including motorboating I guess.

Motorboating is normally caused by feedback through the power supply rails. What test equipment do you have?

What are you using as the power source? If you're using a battery, is it brand new? If not, replace it and try again.

 

[ohm470k]

Hello and thanks for the replies. I will try to make a recording but it will be a couple of days since I work 12 hour shifts and have a 10 month old daughter, as well as being married, lol.

I forgot to mention that the op-amp was the about the third thing I changed after D1 and C23. I also, socketed it so that someone could change it later for a different sound if they wanted. The motorboating never changed from the beginning to the end of these changes I just mentioned.

As far as tools, all I have at home is a soldering Iron and a meter... plus the normal screwdrivers and such. I would love to get it to work since I work for a German owned high end audio manufacturer as a tech, but they make a competing brand of pedal so that won't work. lol.

Like I said, give me a few days and I'll get the recording made. I would like to get this figured out without rebuilding the silly thing by almost changing everything I can't measure at home.

Thanks again, and I will be back soon.

 

[KrisBlueNZ]

Another suggestion: is there any sign of any sort of goop on either side of the board? Perhaps something spilled on it, or some adhesive residue? Any dirt or impurities? If so, clean the board with isopropyl alcohol and a toothbrush and a cotton swab. If it's on the component side, you might have to remove the components.

 

[ohm470k]

Ok. Here are the audio clips. Sorry it has been so long. I have been a little busy. I listed them in order of clean (no distortion) to farty popping sound (lowest distortion setting) to full distortion (distortion knob all the way up). The full distortion setting is better than at the low distortion setting but it's still not right. The clean tone is through the pedal with the effect off and sounds fine. I recorded this with my phone, but I think you'll here it all ok.

Oh, BTW, I am using a 9V battery to power it and the board is clean... other than a little flux from the mod.

 

[KrisBlueNZ]

OK, well, that's NOT motorboating.

Actually I think it may be the way the pedal is supposed to sound. It sounds like the pedal has a voltage threshold, and as parts of the signal exceed the threshold, this triggers the circuit to generate some kind of pulse or burst, to accentuate the loudest frequency in the signal. The threshold seems to track the signal level, so the extra sounds continue as the signal fades.

Apart from the general signal flow, it's not clear to me (from the schematic) what exact effect the circuit should be having on the signal. In particular, I have no idea what the astable multivibrator in the bottom left corner is for. So I can't say for sure that the circuit is designed to produce that effect.

Based on what you've told us, I think it's clear that the pedal has been powered with reverse polarity. You've replaced D1, C23, and the op-amp, which are the components most likely to be damaged by reverse power supply voltage. Other components that could have been damaged would be the JFETs, and the transistors. Replace them if you want.

Before you do that, see if you can borrow (or try out, at a store) another pedal of the same type, to see whether it's supposed to sound like that or not.

 

[ohm470k]

Thanks for the replies!

Well it's definitely not the way it is supposed to sound. Here is a demo I found on youtube. All the mod is supposed to do is better the tone and get rid of some of the background noise. As well as give some different sounding clipping. It's definitely not supposed to pop before or after the mod, which it has.

What about one of my first questions on finding transistors to replace the ones I mentioned not being available? That seems like my next logical step.

Thanks again.

 

[KrisBlueNZ]

2SC2240-GR (Q1,2,3) is a low-noise NPN with the standard Japanese pinout (E,C,B from left to right looking at the flat side with the pins downwards). Current gain for the -GR version is 200~400, although that's only significant for Q2.

If you want to keep the same pinout, your options are limited. I did a search on Digikey and found the Fairchild KSC1845F at http://www.digikey.com/product-detail/en/KSC1845FTA/KSC1845FTACT-ND/4213845 which is a good choice but with somewhat higher current gain, which is not significant.

Digikey don't have many transistors with the Japanese pinout; you might be able to find a better option from a Japanese supplier - you might even be able to get the original type.

If you don't mind crossing over two of the wires (put insulation on one of them, of course), there are other options. Again these are from Digikey.

Fairchild BC549C http://www.digikey.com/product-detail/en/BC549CTA/BC549CTAFSCT-ND/3478139
ON Semi BC549C http://www.digikey.com/product-detail/en/BC549CG/BC549CGOS-ND/1475811
Fairchild BC550C http://www.digikey.com/product-detail/en/BC550CBU/BC550CBUFS-ND/975565
ON Semi BC550C http://www.digikey.com/product-detail/en/BC550CG/BC550CGOS-ND/1475813

These C-suffix devices all have current gains of 420~800, which is higher than the originals, but again it shouldn't be a problem.

2SC2450-GR (Q4,5) can be replaced with any general purpose NPN, including the KSC1815F (if you want to keep the same pinout), or the BC549C or BC550C, or BC547B (all of those BCxxx devices have the Europena pinout, CBE), or the 2N3904 (American pinout, EBC).

I will check out the YouTube clip in a few days when I have my broadband access back.

 

[ohm470k]

Thanks Kris for the reply. I have a bunch of random transistors that I'll sift through first and order if I need to. I'll let you all know the results.

 

[KrisBlueNZ]

Make sure you use transistors that are specifically flagged as low-noise for Q1~3.

Does anyone know whether transistor noise gets worse with age with modern devices? If it does, that would be a good reason to buy new parts.

 

[ohm470k]

Well I replaced the fets, the transistors in the signal path, and Q4 and Q5. Still doing the same thing. However, I let the battery run down on a pedal I built a week or so ago and, low and behold, it sounds very similar to this pedal!

So, it seems that there is not enough voltage getting through unless the distortion is all the way up. I may be able to look at this thing a little more in the next couple days.

 

[KrisBlueNZ]

I checked out the YouTube clip and you're right, there's no sign of that "popping" sound. But they didn't show the full range of adjustment on the controls, so that MAY not be a fair comparison.

It could be useful to trace the signal through the circuit from left to right and see where this sound appears. Record some clean guitar, loop it, and feed it into the pedal. Adjust the pedal for the most noticeable popping sound. Then disconnect the amp from the output and use it (or another clean amp) to follow the signal from the input, through Q1, then Q2, then U1A, U1B, and Q3 and see which stage adds the effect. That MIGHT help us pinpoint the cause.

 

[dts6gc]

Hi all,

I am experiencing a very similar sound issue on my DS-1. Was there ever a resolution to this issue?

 

[ohm470k]

If I remember correctly, it was the piano and possibly the low battery. Can’t recall much else. Sorry.

Sorry to hear Kris passed in 2015 as well.