Ghost_Bass Posted February 27, 2012 Share Posted February 27, 2012 (edited) Hi, my guitarist has a Fender [s]Jazzman[/s] Jazzmaster Ultralight amp. It sounds lovely but it has too much volume on tap, so much that even with the minimal turn on the volume and gain controls just to get that first sound it's already too loud on stage. I have read something about fender using non-log pots that give lots of volume so i opened the amp and made a few mesurements. This is the amp in question: After opening it up i found the folowing writtings on the pots: upper channel (1): volume: 30C100K 0618 Q lower channel (2): gain: 30C100K 0618 Q volume: B100K 0642 Q From my understanding of pots i could already see that the volume pot on channel 2 is linear so this is one of the culprits for the too much volume on short turn but the C letter on the others left me intrigued so i mesured them with my multimeter. Next are the readings i obtained from all pots for 0%, 50% and 100% of turning the knobs: Ch1: vol: 0% - 96K / 50% - 33K / 100% - 0K Ch2: gain: 0% - 96K / 50% - 32K / 100% - 0K vol: 0% - 92K / 50% - 48K / 100% - 0K From this readings i see that the "C" pots work in the opposite way as the Log pots so i've serched a little more on the web and found this chart: [attachment=101100:pots-f4.gif] From this i think i'm right to assume that the "C" pots are antilog pots (never heard of such thing, please correct me if i'm saying something stupid). Back to the main problem, i want to change these three pots for Log pots so my guitarist can have a better control on his volume but another problem appeared, it seems that these aren't regular pots, they're called something like "fender snap in pots". Here's a pic: From the numbers on the original pots i guess i should be looking for something like some "A100K snap in pots" but i can't seem to find any on the web. The closest i've found was on banzai music and they only have the 250K or the 25K log pots: [url="http://www.banzaimusic.com/Hot-Rod-Deluxe-pot-250k-log.html"]http://www.banzaimus...t-250k-log.html[/url] [url="http://www.banzaimusic.com/Hot-Rod-Deluxe-pot-25k-log.html"]http://www.banzaimus...ot-25k-log.html[/url] so here are my questions for whoever may help me: - Will my idea of changing the pots for log ones is going to have the desired effect? - Should i be changing all the three pots? - Do you know where i can find the "A100K snap in" pots? - If i can't find any can i use any of the ones on banzai? Wich value? (here's another problem, i dont know if they're solid shaft, the ones i have here have one side filed like the one in the pic i've posted early) I'm very sorry for the long post and bad english but i wanted to give the most information possible. I would really apreciate some insight on this subject. Best regards Marco Edited February 27, 2012 by Ghost_Bass Quote Link to comment Share on other sites More sharing options...
MarkBassChat Posted February 27, 2012 Share Posted February 27, 2012 (edited) First you have to tell what exactly is the type of the amp; I haven't heard of Jazzman - is it maybe Jazzmaster Ultralight? That's true that Fender is known of using incorrect pots but it all depends how a pot is used in the circuit. In case of Jazzmaster, the pot (VOLUME CLEAN) is in negative feedback loop with the middle lead grounded. I think that this is the reason why they used unusual type of the pot (antilog) and this is not a mistake. Most probably changing the pot to log type will make it even worse. Have you tried the input #2? It is less sensitive (50% compared to input #1). In any case I would recommend to give the amp to someone who know electronics and can measure the signal and understands why it is to high (and he knows how to correct the problem). Mark Edited February 27, 2012 by MarkBassChat Quote Link to comment Share on other sites More sharing options...
KiOgon Posted February 27, 2012 Share Posted February 27, 2012 (edited) There's probably nothing wrong with the amp, has it always been like it or has something changed? If you can attenuate the input level it should be OK & I'd leave messing with the internals to someone who knows what they're doing - no disrespect to you intended - but!! - certainly no point changing type of pots from manufacturer's design. BTW The impedance of the speakers used matches the amp I assume? Cheerz, John PS There's a guy just down the road from me that does Fender amp repairs (amongst others) & while it's generally sunny here - it ain't Portugal Edited February 27, 2012 by KiOgon Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted February 27, 2012 Author Share Posted February 27, 2012 (edited) Thanks for your replys, Mark, you're right, it's a Jazzmaster, i got confused whilst writting. There's absolutely no problem with the amp, it always was this way. The main problem is that my guitarrist lays with a Les Paul and it has a very hot signal and this little amp thingy is [email="250W@2Ohm"]250W@2Ohm[/email]!!! He uses a single 1x12" cab and it's stupidly loud at low settings of volume, so much that if he tries to lower a bit more on the volume knob (on both channels, both are very hot) the sound cuts out, I know that he can lower the volume on his guitar or even lower the pickups a little bit but then his guitar looses character... I just thought that having a log pot would smoother the volume control but i guess i was wrong, thank you for alerting me. It seems that the only way to solve this is to either get another guitar with less output or a 8ohm cab (his cab is 2ohm...). Before anybody asks, it really is too loud, he overwhelms the drums as our drummer plays very low and we want to keep it this way. Cheers Edited February 27, 2012 by Ghost_Bass Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 27, 2012 Share Posted February 27, 2012 R.S Components do snap in pots, but if the amp aint broke - why fix it????? The answer is a smaller amp, or you could try reducing the output. Would a pot wired between the effects send and effects return do the trick ? Quote Link to comment Share on other sites More sharing options...
Al Heeley Posted February 27, 2012 Share Posted February 27, 2012 I was thinking along similar lines. --^-- A small variable resistor in a stompbox as a passive gain reduction would be a 10 minutes solder job to tame the amp, effectively a second independant volume knob between guitar and amp - but it would need a little treble bleed cap and resistor on the pot so you didn't lose the highs on turning down the volume. Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 27, 2012 Share Posted February 27, 2012 OK, . a 470pf cap between the hot end and the slider, like the old Marshall SL100 mod ? But tbh, I was thinkig more of a set it and forget it job, who needs a guitard with 200+ Watts anyway ? Quote Link to comment Share on other sites More sharing options...
Al Heeley Posted February 27, 2012 Share Posted February 27, 2012 ..or sledgehammer to crack a nut, get a powersoak to attenuate the decibels while still allowing the amp to 'breathe' Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted February 27, 2012 Author Share Posted February 27, 2012 That would be a great idea but one problem... the amp doesn't have Fx loop! Here's the back pannel: I think i'll turn myself into the guitar, i'll lower his pickups a bit to see if it makes any difference, if not i gues we'll have to search for a new cab. He doesn't want to get rid of the amp because it sounds lovely. Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 27, 2012 Share Posted February 27, 2012 Strange animal isnt it. You could fit a pot in series with the hot end of the master vol, then set it and leave it, or replace it with a fixed resistor once you have it how you want it.. lose some volume, but effectively turn the master volume into a 'fine Vol' control. Are you sure theres not a fault with the amp if theres that much gain that you cant control it ? Is he using any effects between the guitar and the amp? Quote Link to comment Share on other sites More sharing options...
MarkBassChat Posted February 27, 2012 Share Posted February 27, 2012 Marco, You have several options but I must say that you forgot to mention few most important facts: - that your coleague plays Les Paul (this guitar has very strong signal), - that he uses 2 Ohms cab (with amp that is 250W), - that he likes the amp and you accept it even though 250W for a guitarist is not acceptable. The guitar that he has would sound well and be already very loud with e.g. 50W Marshall, or Rivera or any valve amp (even Fender Bandmaster - 40W). I would sell the amp and buy any of the amps mentioned here. If he insists to keep the amp, you have roughly three options: - decrease the sensitivity of the amp (by changing just 1 resistor in the input stage - R23 and using input #2), - add a high power resistor in series with the cab (e.g. 8 Ohms 50W - with a heatsink), - change the speaker from 2 Ohms to 8 Ohms (or change whole cab). But being frankly 250W power is rather suitable for a bass guitar and having such an amp for a guitar does not makes much sense (unless you are playing concerts like Woodstock) - I would get rid of it. Mark Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted February 28, 2012 Author Share Posted February 28, 2012 (edited) Hi Mark, the fact is that we all love the tone of this amp plus its size and portability, it's great for our stuff (we're a funk/soul covers band and we perform in pubs). He's not a shredder, he has the jazz school but i agree with you that the Les paul is sending way too much signal into the amp. I'll try to lower some input from the guitar first before we think about messing with the amp. Probably i'll lend him one of my 8ohm cabs for gigs and if it solves the problem i'll talk him into changing his cab. Can you recommend me any mods to the guitar that'll lower its output without loosing much character appart from lowering the pickups? Maybe using lower impedance pots and changing the caps? Brancini, he's only using a crybaby, all his other fx are form the amp. This amp is realy loud, my shuttle 9.0 (suposed to be 900W) is having trouble to keep up with him in that moments in the middle of a rehearsall when we kick in the OD and play a couple of rock chords just for the laugh. thanks for all your help so far Cheers Edited February 28, 2012 by Ghost_Bass Quote Link to comment Share on other sites More sharing options...
MarkBassChat Posted February 28, 2012 Share Posted February 28, 2012 What is special about Le Paul is that it has a very strong signal, which easily overdrives the input stage of an amp. So any modification to the guitar will change it's sound. Les Paul is a perfect match with e.g. 50W Marshall so using 250W amp is questionable. What about listeners or owners of the pubs you play? Do they accept the sound level your colleague can produce? I wouldn't modify the guitar, I would rather decrease the gain of the input stage of the amp and add a resistor in series with the cab. Mark Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted February 28, 2012 Author Share Posted February 28, 2012 He doesn't play too loud live, but he can't fine tune his volume wich is a bit frustrating, a tiny touch on the knob and boom! On rehearsalls we keep his amp far away from us. We're looking for the least expensive way to do something to solve this problem. Tell me, i would you lower the input stage gain? In regard to the resistor on the cab i think that he would probably get a 8Ohm cab instead and sell his. Cheers Marco Quote Link to comment Share on other sites More sharing options...
MarkBassChat Posted February 28, 2012 Share Posted February 28, 2012 (edited) [quote name='Ghost_Bass' timestamp='1330425959' post='1557100']Tell me, i would you lower the input stage gain? [/quote]You have to find out the schematic and read it. I already mentioned that one of possibilities is to decrease R23 resistor - from 68k to e.g. 22k and use input #2. Another option would be to decrease R16 resistor from 33k to 22k. [quote name='Ghost_Bass' timestamp='1330425959' post='1557100']In regard to the resistor on the cab i think that he would probably get a 8Ohm cab instead and sell his. [/quote]You have to understand that it will not be the same as adding a resistor in series. With 8 Ohms cab 100% of the output voltage will be still delivered to the cab (only the power will be lower). With a resistor in series only a fraction of the output voltage will be delivered to the cab. I don't even mention that buying a resistor costs less than a new cab. Mark Edited February 28, 2012 by MarkBassChat Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 28, 2012 Share Posted February 28, 2012 [quote name='MarkBassChat' timestamp='1330462939' post='1558001'] You have to find out the schematic and read it. I already mentioned that one of possibilities is to decrease R23 resistor - from 68k to e.g. 22k and use input #2. Another option would be to decrease R16 resistor from 33k to 22k. You have to understand that it will not be the same as adding a resistor in series. With 8 Ohms cab 100% of the output voltage will be still delivered to the cab (only the power will be lower). With a resistor in series only a fraction of the output voltage will be delivered to the cab. I don't even mention that buying a resistor costs less than a new cab. Mark [/quote] Sound advice - sorry, couldnt resist that. If it was me, I'd go for less gain. Putting a resistor in series with the speaker will reduce the volume, but you'll still have the problem of control, or lack of it. Just less volume. Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted February 29, 2012 Author Share Posted February 29, 2012 [quote name='MarkBassChat' timestamp='1330462939' post='1558001'] You have to find out the schematic and read it. I already mentioned that one of possibilities is to decrease R23 resistor - from 68k to e.g. 22k and use input #2. Another option would be to decrease R16 resistor from 33k to 22k. [/quote] Thanks Mark, i'll try to see if i can identify that resistor and if it's possible to replace it myself. I'll post pics of my findings. I've already managed to get the schematic for the amp from here: [url="http://support.fender.com/schematics/guitar_amplifiers/Jazzmaster_Ultralight_59000.pdf"]http://support.fender.com/schematics/guitar_amplifiers/Jazzmaster_Ultralight_59000.pdf[/url] [quote name='BRANCINI' timestamp='1330467403' post='1558088'] Sound advice - sorry, couldnt resist that. If it was me, I'd go for less gain. Putting a resistor in series with the speaker will reduce the volume, but you'll still have the problem of control, or lack of it. Just less volume. [/quote] I'm just looking for some mod that'll lower the volume a bit so that the guitard can have a little more tweakability on the volume knob. We don't need a big reduction, the volume he currently has is suitable for gigs but it's a pain for him to set it just right. I'm just looking to make him more confortable with the amp. He's already thinking in not taking his cab to gigs and just DI form the amp and hear from the monitor... but we prefer to mic his cab to PA because the Les Paul is too bassy. I'm already starting to see a culprit for this problem... it has an important part in every problem/solution i can think of... maybe is time to convince him to get a Telecaster?!! Thank you all, i really apreciate all the info you're giving me. Cheers Quote Link to comment Share on other sites More sharing options...
Wil Posted February 29, 2012 Share Posted February 29, 2012 [center]What about a volume pedal between the guitar and amp?[/center] Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted February 29, 2012 Author Share Posted February 29, 2012 [quote name='Wil' timestamp='1330524412' post='1558815'] [center]What about a volume pedal between the guitar and amp?[/center] [/quote] We tried it, it cuts too much of the guitars character... i'll start by lowering the pickups to the point they still retain the timbre and see if that makes any significant change. Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 29, 2012 Share Posted February 29, 2012 (edited) Simple way to attenuate the signal would be a resistor in series with his guitar lead, might affect the sound a bit as he wont be driving the amp so hard. A bit like amps used to have years ago, 2 input sockets per channel, one attenuated and one not. Try 68K in series, if thats not enough, maybe a 68K across the input to tha amp as well. tbh other than that, it just looks like its just one of those things thats more trouble than its worth. Only way to keep the same sound or close to it would be a power soak type of thing..HEAFTY resistors in a potential divider setup across the output, but it would run very hot. Edited February 29, 2012 by BRANCINI Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted February 29, 2012 Author Share Posted February 29, 2012 (edited) Yes, you're right. i'll see in the weekend what we can do to lower the input. I'm hoping that it won't be necessary to mod the amp but putting a resistor on one of the inputs seems like a good idea and it won't mess much with the amp's circuits. Just one question, the resistor should be on the hot wire, right? Cheers Edit: On the other hand maybe it's a more sound move to place the resistor in the guitar rather in the amp! It's easier to solder on the guitars jack and there won't be a PCB getting in the way! Any suggestions on the kind/brand of resistor i should be looking at or any one i could pick from a electronics store would do the trick just fine. Edited February 29, 2012 by Ghost_Bass Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted February 29, 2012 Share Posted February 29, 2012 (edited) My way would be to make an adaptor with a short 8" or so length of lead with a jaack line socket and a jack plug, Put one resistor in the socket. one in series with the inner wire, and if you need to, one across the both terminals of the plug, a bit of ingenuity with heatshrink sleeving and your done, Use physically small resistors and it will all fit nicely, But have a play with it first before you make a permanent job, easier to alter it that way. Edited February 29, 2012 by BRANCINI Quote Link to comment Share on other sites More sharing options...
Ghost_Bass Posted March 7, 2012 Author Share Posted March 7, 2012 Just to give some closure to this, last weekend i sat dow with my guitard at the rehearsal to try to solve things without messing with the amp. I started explaining him all the options you've sugested me and when i told him about putting a resistor in "Input 2" he said "I don't use that channel, it's atenuated" !!!????!!!!!!!!!!!!!!!.... F*ck!!! Apparently input 1 is louder than 2 (like having passive/active inputs on your bass amp) so i convinced him that he would not ruin the amp and we plugged to input 2. Problem solved!!! F*ck*ng guitards......... Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted March 7, 2012 Share Posted March 7, 2012 Some people just never look for the simple option. bit like the old story of the lorry stuck under a bridge. Quote Link to comment Share on other sites More sharing options...
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