So about a week ago I finished my Mudbunny and I must say this thing rocks and is mean.. I do have one issue.. The pedal operates and sounds perfect but when I have the pedal on and my guitar volume rolled off there is a weird scratching noise coming from the amp(it happens on both my amps), the more gain the more noise... now I do understand that muffs do have white noise but this is above the normal high gain noise. It sounds like an old record player between songs, you know the sound of the needle scratching thru the speaker. I just reflowed every drop of solder in the pedal and no difference.
I ran thru the board with a audio tester and it seems like the noise appears after the first set of diodes and gets worse after the 2nd set of diodes, it goes thru Q3 and Q4 all the way to the volume pot and then out. I tried new trannies out of curiosity and that did not help. All the parts are high quality new parts from Small Bear.
Anyone got advice or help? An idea? ???
What kind of transistors did you use? When you replaced them, were the same type of trannies or different ones?
Also, what kind of diodes did you use in the build?
5089's both times, and I used the diodes that are recommended in the build...1n914, and 1n4001 for protection/polarity....
I'm thinking that your input cap is leaky or faulty. That might explain the noise. If it's failing, then DC could be creeping back to your guitar, and when you roll the volume down it causes the crackling.
The noise might be originating there, and then it's amplified through those subsequent gain stages.
so, basically try a new cap in C1?
Yep, I would try that first.
just got home from work and switched out C1 for a new cap and no difference, still have the same noise ???
Darn. Well, I think some voltage readings are needed. Maybe Q2 is misbiased somehow.
here is some more food for thought.... I just got done trying different trannies; 2n3904 and 2n5088 do not have the noise..... maybe the extra gain of the 2n5089's.....I actually really enjoyed the trying all the trannies....its the first time I have ever done that...... I love the 5089's the most, alot more aggressive and punchy...
any how... I do not have an operating multi meter right now so readings may have to wait....Does the info from above help or bring anything else to mind?
also I have already ran thru all the parts before I reflowed the solder and they are all correct
Well, I don't have much advice at this point. If 5089's are causing the issue then for whatever reason they are not working for this build. Having built the Gruntbox a few times, I haven't had a problem. I can send you some 5809s to try out...maybe a different stock will produce different results. Personally, my favorites are BC549. I just love them in a Muff!
Tell you what: PM me your address and I can send you some of both. I have plenty. Let's see if that helps solve the issue.
Issue resolved... I got the BC549's and the 2n5089's that Bean sent me in the mail, neither of those had the noise....so, I guess the 5089's I had were from a bad stock ???
I stuck with the BC549's, they were the quietest and had most clarity and punch......The MAYO is a GAIN MONSTER!!
Thanks MadBean... YOU ROCK!
Excellent. Yep, BC549 are the best Muff transistors I've come across :)
Brian- you use bc549B's? The "B's" have kinda low gain; I tried them in mine and didn't like them as much as the 5089s. About what hFe range do the ones you use have? Or do you have the mouser link to them?
EDIT: These are the ones I ordered. Are the ones you use different?
http://www.mouser.com/Search/ProductDetail.aspx?R=BC549Bvirtualkey51210000virtualkey512-BC549B
thanks
I have the "B"'. They do have "C" which are higher gain.
http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/BC549C/?qs=sGAEpiMZZMtvtNzZ3W%252bLwIHffn9J1%2fd6L7VProcj%2f2k%3d
I should pick some of those up on my next order.
I'm going to go back in & try the bc549s again when I get time. They sounded good, but IIRC it seemed like I wasn't getting the singing lead notes and the "big wall of fuzz" like with the 2n5089s. Just depends what you're looking for I guess.
The higher gain 549Cs are probably worth looking into as well. Thanks for your input.
I read a lengthy dissertation on the Muff circuits that was posted at BYOC a few years ago, prior to the 'legendary' crash, so I don't have a good link. I can probably scan my hard copy if you are interested, and I'll send you the PDF on request.
In any case, the author stated the mega gain trannies would have a nominal effect, the idea being something like, if a HFE of 350 clips going into the next stage, then all HFEs above 350 will have no additional effect, because 350 would be the limit. 'Bean can probably state it more clearly, but please try the BC549C's and report what you find.
For the record, I like 5089s, but I prefer BC549s.
cb
Yeah CRBMoA, I would definitely read that if you find the time to scan it.
Back when I was building my grunt, I roughly measured the hfe's of different some different transistors in my dmm. Here are those recorded results if anyone is interested-
bc549bs were about 300 on average
2n5088s were about 415 avg
2n5089s were about 730 avg
I couldn't tell any difference between the 5088 and 5089s, but both of those seemed to have noticeably higher gain & output than the bc549s.
If someone tries the 549c's please let us know the results....
I was able to tell a difference in gain between the 5088's and 5089's.....not alot of diff, main diff was the thickness and punch of the sound....... and the 549's seem to have plenty of gain and punch in my build... It is every bit as gainy as the 5088's in a creamy dreamer I just built for my cousin.... and I doubt jumping the emitter resistors on the Q2 and Q3 compaired to the 100R resistors is that huge of a difference....
I tried all the above mentioned in the mayo so I can see there being a certain gain cap that does not really help to go over....
If you find that article I would be interested as well ;D