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Thread: Gibson maestro fuzz tone issues

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    Gibson maestro fuzz tone issues

    I have one here that I replaced the 3 transistors with the ones small bear sells http://smallbear-electronics.mybigco...zz-a-tort-pnp/.
    All I seem to get is howling feedback. So I bought another set thinking that maybe I ruined them installing without heat sinking them while soldering. With the new set I was careful about heat sinking and still it howls.
    This happens when using the resistors that come with the transistors.
    What is happening here? I've combed over this circuit countless times and nothing seems to be working.
    Can anyone shed some light on this pedal issue?

    thanks
    pete
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    Steve/Small Bear is not going to sell you something that has not passed the test, so we can scratch bum trannies.

    That said, it is possible that others have encountered a similar issue. I would recommend contacting SBE with a description of the problem. Be patient, because Steve has to deal with a LOT of correspondence, but you will get a reply. Alternatively, since the majority of pedal builders/folk are usually on the DIYstompbox forum, perhaps your problem would receive a well-informed and more prompt response there.

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    Old Timer olddawg's Avatar
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    The first thing I would check is the basing... that is always suspect. Substitutes are frequently different. Especially when you are dealing with old tech. What was the original problem? I would put the original transistors back in and trouble shoot from there.

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    You have to double and triple check the transistor pinout. I would have never swapped the resistors until it was working, they aren't that far from stock. Also make sure small bear is using the fz-1a, not the fz-1 for the parts location. He also has his own version of the fuzz with a positive ground. Do you have a transistor checker? If you are going to build any pedals you need one, gives you the pinout too.

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    I should have explained this better. This came to me not working at all and the transistors were not original. They are RS 101 9 (?) made in japan. I changed out the electrolytics and checked all resistors and pots. There was a wrong volume pot value which I replaced. So since there wasn't much else besides the wiring I thought I'd try new transistors. I'm getting sound now but it howls a lot.
    I have a transistor checker an Atlas DCA 55. I will go back and check my pin out on each of these. Thanks for reminding me to use that.
    I was going by the OC77 data on line.

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    Supporting Member mozz's Avatar
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    That pedal deserves a total rebuild, get rid of those film resistors. Here are a few pictures. You need to find (rca) 2n2613 or 2n2614. You need the leakage or it probably won't bias up right. The earlier model had a 500k pot with a 50k resistor in parallel.
    https://www.coda-effects.com/2016/12...-fz1-1966.html
    https://sites.google.com/a/davidmorr...stro-fuzz-tone

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    Supporting Member The Dude's Avatar
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    I got a kick out of, "If unit should ever need servicing, take it to a reliable radio man. The electrical diagram below should be shown the repairman to assist him in servicing the unit."

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  8. #8
    Supporting Member mozz's Avatar
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    You must have seen this before.

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    Supporting Member The Dude's Avatar
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    Yep. One of my fav's.

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    Senior Member nevetslab's Avatar
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    Quote Originally Posted by mozz View Post
    That pedal deserves a total rebuild, get rid of those film resistors. Here are a few pictures. You need to find (rca) 2n2613 or 2n2614. You need the leakage or it probably won't bias up right. The earlier model had a 500k pot with a 50k resistor in parallel.
    https://www.coda-effects.com/2016/12...-fz1-1966.html
    https://sites.google.com/a/davidmorr...stro-fuzz-tone
    Wow, that brings back memories!! I bought one back in 1966, using it on my Gibson EBO Bass and an Alamo Bass Amp...first of everything on my way to becoming a rock star (dream on!).

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by mozz View Post
    You must have seen this before.

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    Yep got one of those hanging on the wall. Coolest Label I've ever seen.

    nosaj

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by pontiacpete View Post
    I have one here that I replaced the 3 transistors with the ones small bear sells http://smallbear-electronics.mybigco...zz-a-tort-pnp/.
    All I seem to get is howling feedback. So I bought another set thinking that maybe I ruined them installing without heat sinking them while soldering. With the new set I was careful about heat sinking and still it howls.
    This happens when using the resistors that come with the transistors.
    What is happening here? I've combed over this circuit countless times and nothing seems to be working.
    Can anyone shed some light on this pedal issue?

    thanks
    pete
    Those solder joints don't look very good to me. Remember heatsink your transistors when soldering.
    nosaj

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    Binkie McFartnuggets‏:If we really wanted to know the meaning of life we would have fed Stephen Hawking shrooms a long time ago.

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    I quit working on those because I could never find a set of transistors that worked. You blow on those Ge transistors and their bias point changes

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    Quote Originally Posted by nosaj View Post
    Those solder joints don't look very good to me. Remember heatsink your transistors when soldering.
    nosaj
    Did the heat sinking as mentioned and no luck. Solder joints are good.

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    Quote Originally Posted by cjlectronics View Post
    I quit working on those because I could never find a set of transistors that worked. You blow on those Ge transistors and their bias point changes

    Ah ha i'm not the only one. If I can't find the RCA 2n2613 or 14s I'll pass on this repair. I don't see any sense and trying more NOS oc77s or whatever.

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    Old Timer J M Fahey's Avatar
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    Just thinking aloud:

    * soldering is horrible. Cold grainy solder, burnt wires, a solder iron burnt capacitor

    * what does "howling" mean?
    Do you get oscillation with input shorted and distortion pot set to 0?
    You do not but it appears as soon as you rise the pot and/or you plug a guitar there? ... please describe it better. Or upload a video.

    * triple check what´s there against schematic.
    Photocopy the one you have, measure voltages on all transistor pins, write them on schematic and upload it.

    * in principle howling is feedback and comes from a combination of gain and poor grounding/shielding.
    Dead/"bad" transistors will do the opposite: mute the pedal or at least have it show low gain or wonky sound.
    In a way, howling means transistors are "too good" or at least "good enough".

    * that fuzz is made out of 3 gain stages, which can work on their own, so start by lifting one leg of C3 , inject 100mV 1kHz into Q3 base, listen and scope output.
    By the way, howl should have disappeared.

    Then reconnect C3, lift one leg of C2, inject audio there, scope its collector and pedal output, has howl reappeared? etc.

    2 details: now you have a lot of gain, 2 cascaded stages, reduce signal injected to 10mV and 1 mV as needed with a simple attenuator , say 10k/1k and 10k/100 ohm.
    Do not trust original capacitors, use a film or bipolar one, say .47uF or thereabouts to inject signal into following stage.

    Then reconnect C2, lift 1 leg of C1, inject there, repeat tests.

    Going backwards, you will eventually plug into the input jack, repeat tests.

    Somewhere along the way howling must have reappeared, check wiring and grounding; if not, it´s a guitar problem, it feedsback/howls with all that gain.

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    Juan Manuel Fahey

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    Quote Originally Posted by mozz View Post
    You have to double and triple check the transistor pinout.
    And double check your transistor orientation as far as 1,2,3,Small Bear usually gives you the hfe and placement . Just a thought.

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    Old Timer olddawg's Avatar
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    I know these things are collectible.. but I’ve never used one I liked. The original came a cord with a plug on it hardwired on the output. I always wondered if that affected the functionality when people modified them with another jack. To me... you can MAYBE play an authentic “Satisfaction” riff and that’s about it lol.. The ultimate one trick pony. That said.. I know they can be made to work. I’ve owned several. Again.. as I and others have said... triple check the transistor orientation, resolder everything, check your grounds, and especially if it’s a 60s unit... don’t just assume the caps are all good.

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    Quote Originally Posted by olddawg View Post
    I know these things are collectible.. but I’ve never used one I liked. The original came a cord with a plug on it hardwired on the output. I always wondered if that affected the functionality when people modified them with another jack. To me... you can MAYBE play an authentic “Satisfaction” riff and that’s about it lol.. The ultimate one trick pony.
    One of my customers brought me a rusty FZ-1 to repair. It was as you describe, with a "flying lead" for the input. Both pots were shot, and the knobs disintegrated when I pried them off. Volume control had a click switch that disconnects the battery when turned fully CCW. I put in a true bypass DPDT foot switch & replaced a couple caps. Luckily transistors were still good, and the knobs were simply black Gibson knobs like you would find on a Les Paul, no trouble finding replacements. Germanium transistors were still functional, and the pedal runs on a single 1.5 volt AA battery. As you say, good only for the most rancid of fuzz tones - the intro to "Satisfaction" being a prime example. Owner does a lot of studio work and the FZ-1 just one more choice in his library of effects.

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    Supporting Member mozz's Avatar
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    Send it over here to PA, i'll fix it. I have made clones of the fz-1 and fz-1a. Any germanium with "some " leakage should work. If the leakage is not high enough it will work but sound gated and choppy. Leakage should be over 250-300, even higher.

    Like JM said, post your voltages.

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    Lifetime Member Enzo's Avatar
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    I recntly had a couple of those in my box. One was real gatey, you had to play aggressively through it. ie. get up to a level threshold.

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    Quote Originally Posted by J M Fahey View Post
    Just thinking aloud:

    * soldering is horrible. Cold grainy solder, burnt wires, a solder iron burnt capacitor

    * what does "howling" mean?
    Do you get oscillation with input shorted and distortion pot set to 0?
    You do not but it appears as soon as you rise the pot and/or you plug a guitar there? ... please describe it better. Or upload a video.

    * triple check what´s there against schematic.
    Photocopy the one you have, measure voltages on all transistor pins, write them on schematic and upload it.

    * in principle howling is feedback and comes from a combination of gain and poor grounding/shielding.
    Dead/"bad" transistors will do the opposite: mute the pedal or at least have it show low gain or wonky sound.
    In a way, howling means transistors are "too good" or at least "good enough".

    * that fuzz is made out of 3 gain stages, which can work on their own, so start by lifting one leg of C3 , inject 100mV 1kHz into Q3 base, listen and scope output.
    By the way, howl should have disappeared.

    Then reconnect C3, lift one leg of C2, inject audio there, scope its collector and pedal output, has howl reappeared? etc.

    2 details: now you have a lot of gain, 2 cascaded stages, reduce signal injected to 10mV and 1 mV as needed with a simple attenuator , say 10k/1k and 10k/100 ohm.
    Do not trust original capacitors, use a film or bipolar one, say .47uF or thereabouts to inject signal into following stage.

    Then reconnect C2, lift 1 leg of C1, inject there, repeat tests.

    Going backwards, you will eventually plug into the input jack, repeat tests.

    Somewhere along the way howling must have reappeared, check wiring and grounding; if not, it´s a guitar problem, it feedsback/howls with all that gain.
    Thanks for all this Juan. I had pulled all of the transistors and decided to return it to the shop that it came from until you wrote all of this. Believe it or not I've worked on many of these and have not had this kind of problem and was able to get them out of here within a reasonable amount of time. This time I have 2 of these, the other is an absolute mess compared to this one. No transistors no board just a hand full of components held together with electrical tape. Anyway, you convinced me to give it another go. I'll be back.....
    Thanks.

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    Old Timer J M Fahey's Avatar
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    Cool
    Worst case, fully rebuild it.
    10/15 parts?
    One of the few cases where I actually suggest shotgunning, big time

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    Juan Manuel Fahey

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    Here it is, completely re-built without the resistors that came along with these transistors(Q1 OC77 Q2and 3 OC75). Checked all the pinouts with the transistor checker. So I think everything is in correctly. I decided to start with the resistor values in the original FZ-1, this is why it's probably not working. But it doesn't oscillate at all when turning the volume pot however there is no distortion or fuzz. It's passing a clean signal only There's -3 volts getting to the collector of Q1, nothing on collector of Q2 , -2.1 on collector of Q3.
    Got hit with a lot of amps, this is what I have so far.
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    Does it pass a clean signal without the 3v supply ??

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    You mean when the unit is off or the stomp switch, switches off? Yes.
    It sounds exactly the same except when the effect is in on position the volume pot does something. Not much a sweep though

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  27. #27
    Supporting Member mozz's Avatar
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    First schematic you posted was fz-1a, this is fz-1. There are differences. The resistors from factory and the resistors from small bear are not that far from each other, both will work to at least get some sounds.

    If you have no voltage on Q2c, you have wiring problems, open or shorted resistors or caps. Once again, bad transistors or bad pinout.

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  28. #28
    Old Timer J M Fahey's Avatar
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    PLEASE do not say "no voltage" but "0 Volts" or whatever.

    IF you meant zero volts on Q2 Collector, first:
    If you have no voltage on Q2c, you have wiring problems, open or shorted resistors or caps. Once again, bad transistors or bad pinout.
    are quite possible, but also Q2 may be saturated/overbiased.
    Notice that Q3 is dropping 0.9V across 10k even with base grounded through 10k and NO bias.

    So:
    1) check Mozz´s suggestions.
    2) remove the 470k bias resistor and recheck.
    Please post V-C-E voltages for all 3 transistors.

    "Normally" not needed but Germanium is a very crude semiconductor material (and that´s an understatement) so we must assume *nothing*.

    I cringe when I see the DIYAudio people insisting on Germanium "because it sounds like Tubes" and even currently designing a RIAA preamp around Russian Military transistors ... surely that label alone must carry mucho strongo Mojo

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    Does MEF have a knucklehead ranking? After hours with this thing I notice this is the FZ-1. Says it on the front. Duh. Hence the new schematic.
    Anyway moving on, sorry about the vague 'no voltage' reading. I definitely should know better than that by now. How many years have I been reading this forum. Oh only 1 decade.
    Here's another, the 470K wasn't 470k but more 470ohms. .. ... .... sorry guys, please be patient.
    Now the voltages:
    Q1
    c -2.9
    b -1.2
    e -1.1
    Q2
    c -1.9
    b -.06
    e 0 ground
    Q3
    c -1.2
    b .5
    e 0 ground

    It's back to making this really loud whistle as soon as the volume is upped a bit.

    thanks
    pete

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  30. #30
    Supporting Member mozz's Avatar
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    What are your gains and leakages measuring for all the transistors? 470k is the correct value.

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    Old Timer olddawg's Avatar
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    If they are germanium transistors you should have .3v across a forward biased emitter/base junction. If you don’t the transistor isn’t conducting.

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by olddawg View Post
    If they are germanium transistors you should have .3v across a forward biased emitter/base junction. If you don’t the transistor isn’t conducting.
    That´s the textbook case but as you see the transistors are conducting, even if apparently no or wildly insufficient bias

    * Q1 is passing 110uA (which is fine) even with meager 100mV bias

    * Q2 is passing 666uA even with meager 60 mV bias.

    * Q3 is passing 170uA .
    It shows 2 "impossible" readings:
    a) impossible 500mV bias
    b) which we do not know where it comes from, since there is no resistor to feed base current from -2.9V rail to Q3 base ... which to boot is grounded through a 10k resistor

    The explanation for all these anomalies is that germanium transistors are lossier than an oxygen tank with exhaust tube "covered" with a handkerchief.

    Imagine invisible internal resistors connecting Collector to Base and you will be near enough.

    OK, now that we solved the DC problem, let´s test the AC/functional side.

    The howl means the Fuzz pedal is healthy and has (lots of) gain, let´s tame that.

    Please do the tests suggested in post #16 and post results

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    Juan Manuel Fahey

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    Old Timer olddawg's Avatar
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    Quote Originally Posted by J M Fahey View Post
    That´s the textbook case but as you see the transistors are conducting, even if apparently no or wildly insufficient bias

    * Q1 is passing 110uA (which is fine) even with meager 100mV bias

    * Q2 is passing 666uA even with meager 60 mV bias.

    * Q3 is passing 170uA .
    It shows 2 "impossible" readings:
    a) impossible 500mV bias
    b) which we do not know where it comes from, since there is no resistor to feed base current from -2.9V rail to Q3 base ... which to boot is grounded through a 10k resistor

    The explanation for all these anomalies is that germanium transistors are lossier than an oxygen tank with exhaust tube "covered" with a handkerchief.

    Imagine invisible internal resistors connecting Collector to Base and you will be near enough.

    OK, now that we solved the DC problem, let´s test the AC/functional side.

    The howl means the Fuzz pedal is healthy and has (lots of) gain, let´s tame that.

    Please do the tests suggested in post #16 and post results
    Yeah.. I guess.. there is always some alchemy going on with old germanium transistors. Don’t see them much except it old fuzzes, Rangemasters, and the occasional vintage car radio restoration. I had a Rangemaster clone at one time that was usable.. but even as a kid in the early 70s.. these legendary boxes, fuzz faces, etc, never seemed to live up to their reputations.

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  34. #34
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by olddawg View Post
    I had a Rangemaster clone at one time that was usable.. but even as a kid in the early 70s.. these legendary boxes, fuzz faces, etc, never seemed to live up to their reputations.
    Oh,if you use them on their own, they are cheesy.

    "brushing shoulders" fames from being used by KILLER very creative Guitar players, and for the exclusive use of driving a Plexi or AC30 balls to the wall slamming tjem with 20X the signal they expected.
    What you hear is pure power tube distortion, driven by a guitar *boosted* 20 to 40 dB preamps ... which sometimes also distorted on their own, but that´s not the point.

    A few famous players used fuzz or raw distortion pedals (think MXR Dist+ or Big Muff and the odd Fuzz) into clean amplifiers and sound was ghastly ... think Rolling Stones, some American Rock bands in the late 60´s or the buzzy "Jerry Garcia" sound.

    As a free sample, here´s a record from our early Argentine Rock music, 1969.
    They are using all the "proper" stuff: Gibson 335 into a 100W Plexi and 2 x 4x12" , probably Greenbacks ... but also some nasty Fuzz (most certainly Germanium based) and the marshall used "clean" .
    Surprisingly the background guitar has quite an acceptable crunch but the lead Guitar sounds like a mosquito on crystal Meth.


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    Juan Manuel Fahey

  35. #35
    Old Timer olddawg's Avatar
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    But of course.. still the old pedals were always hit and miss... even old VOX wahs. I tried most at some point or another... probably the worst was the “Fender Blender” (which I don’t think was germanium) imho, which people seem to be falling themselves over lately. AND.. amp performance varied as well. I always wrote it off as 20% tolerance randomness and the vagarities of germanium devices.

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