Guitar Related Electronics - Where to Start

[thegreenlaser]

My guitar amp's been acting up for the last year or so, and as I'm finishing up the second year of my electrical engineering degree, it's been occurring to me that my inability to do anything to even try to fix it is pretty sad. I'm pretty sure that something like this isn't outside of the range of my abilities, I just have no idea where to start. So my question is, where do I start if I want to be able to understand how guitar electronics (amps, pedals, pickups, etc.) work, to the point where I can do simple repairs and maybe even try my hand at designing effects boxes? I'm hoping there's at least a few people here who tinker around with their guitar equipment who can help me out.

Thanks.

 

[turbo]

What kind of guitar amp? If you can locate and buy an old Fender Champ or some other simple tube-based amp, you'll have a perfect test-bed for your tinkering. The amps are simple and the components are large enough to allow you to solder and de-solder them at will. Once you get up into the solid-state models, I can't help you, except for the in-guitar electronics.

 

[yungman]

Well, I was a musician for a long time, I just happen to be designing music electronics in the last half a year and I designed two guitar tube amp before. So give it to us!

Name your problem, provide the schematic ( if you don't have it, go on the web, there are a lot of schematics there. If it is a more common amp, chances is I have it).

 

[thegreenlaser]

@turbo: It's a tube amp: Traynor YCV-50, though I don't know if it's simple or not. Even still, I've done very little with electronics outside of school as of yet, so I don't really know what I'd do with a simple tube amp if I had one. I guess that's my main issue here.

 

[thegreenlaser]

Well, I was a musician for a long time, I just happen to be designing music electronics in the last half a year and I designed two guitar tube amp before. So give it to us!

Name your problem, provide the schematic ( if you don't have it, go on the web, there are a lot of schematics there. If it is a more common amp, chances is I have it).

I do appreciate the offer, but I'm more looking for advice about how I could get started learning about this type of thing so that I can do it myself. (Though maybe getting help fixing this problem is as good a place as any?)

If you don't mind me asking, how did you get into designing music electronics?

 

[yungman]

The main issue is school don't teach tube amp. I don't have Traynor schematics, Traynor is quite a common amp. You should be able to get the schematics. As I said, get the schematic, name the problem and we go from there.

 

[turbo]

OK. That seems to be a decent amp by a decent company. The first thing that you ought to do is get some basic documentation (schematic and wiring diagram) so that you can start chasing down the problem(s). Hopefully, Traynor has not gone to all printed-circuit boards, so you can swap components easily. Good luck and come back for more if I can help.

 

[yungman]

I do appreciate the offer, but I'm more looking for advice about how I could get started learning about this type of thing so that I can do it myself. (Though maybe getting help fixing this problem is as good a place as any?)

If you don't mind me asking, how did you get into designing music electronics?

I designed my first tube amp in 1978! Info was still around at the time! Go on line or someone might have a pdf copy of the old RCA Receiving Tube Manual. There are a lot of theory and description that you can learn.

Tube is really similar to N-JFET in a lot of ways. Grid is like the gate, cathode is source and plate is drain. Grid is usually lower voltage than the cathode like gate is usually lower voltage than the source in normal biasing.

For pentodes, there are two more input that is set at certain voltage. For your purpose, ignor them at the moment. You'll go quite far just imagine tube as N-JFET and read the schematic. You better know the rest of the components!

Now now, don't people jump on me about tube vs JFET, this is the real basic way of looking at it for the purpose of the OP.

 

[jim hardy]

by all means get several tube manuals in your library.

http://www.ebay.com/sch/items/rca tube manual?_dmd=1&_sop=12

You learn 10X more by hands-on than from just studying. When i was in college(and slide-rules dominated the earth) the professors were bemoaning the loss of hands-on lab classes from undergraduate curriculum.

i started college in 1964 and still prefer tube manuals from that era . Of course they're what i learned from in high school. The 1964 edition has a delightful 15watt hi-fi amplifier schematic . I built one from old TV parts and used it for decades. Hammond still makes transformers for DIY tube audio hobby market (Bless their hearts). Guitar guys like tubes...

This digital clock from Ramsey should be an attention-getter in any modern EE department :

http://www.ramseyelectronics.com/images/hk/NIXIE-w.gif

http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=NIXIE

 

[yungman]

I forgot to mention, there are books out that specifically for tube amp. I have the "Designing Power Supplies for Tube Amp. by Merlin Blencowe. And I saw other guitar tube amp books. Go on Amazon and look for some of those.

But if you just want to trouble shoot the amp, you don't need to get so deep into this. Of cause if you want to get into tube amp, it's a different story. But I doubted there is a job market for tube amp at all. There are too many tinkerers that modify tube amp to the Nth degrees. I left music electronics as of 1979 and only got back half a year ago where I don't work anymore and can afford to do for the fun of it for no money.

When you read more schematics, you'll find all tube amp circuit basically evolved from one or two classic amps from the 50s. The Fender Bassman, Vox AC30 are two of those. Marshall pretty much Fender Bassman with a few value change. Mesa is just cascading a few of the preamp stages of Fender design to get the distortion. Their so called Simu cast is nothing more than combine different pairs of tubes in and out to reduce power.

Learn the basics and read some of the schematics and you'll see what I mean.

 

[thegreenlaser]

Thanks for the advice everyone! I think I've at least got some places to start now. I'll come back if I need more information/help.

 

[Bobbywhy]

thegreenlaser,

Just from the above comments I can count about 100 years of combined experience with this kind of equipment. Add in my 40+years and you have plenty of able and willing folks.

You only said your amp was "acting up". Exactly what are the symptoms? Include as much detail as possible, and maybe we can help you troubleshoot it!

Bobbywhy

 

[jim hardy]

where do I start ...

you need a multimeter and a tube manual.

once you have figured out how tubes work, from reading the tube manual, you will know what voltage to expect at each pin.

Then you measure voltages in your amplifier.
Then you use laws of kirchhoff and ohm to see what doesn't make sense.

Google took me right to the service manual for a YCV50 amplifier

but they interject themself in the link, i hate that
http://www.google.com/url?sa=t&rct=...ptpJ_XPS740qlfIew&sig2=Q6FCrduCYvZrU58dnxp-uw

i think you can download it from here
http://www.traynoramps.com/default.asp?p1=7&p2=0&p_id=30

http://www.traynoramps.com/downloads/servman/smycv50b.pdf

and it looks like a wonderful manual.

Go man, GO !

old jim

 

[turbo]

Just from the above comments I can count about 100 years of combined experience with this kind of equipment. Add in my 40+years and you have plenty of able and willing folks.

Just between the two of us, we have over 80 years tinkering tube amps.

 

[Bobbywhy]

My first radar set, the AN/APQ-72, was made by Westinghouse. In 1963 it was mounted in the nose of our F4B Phantom fighter jets. It was built with 100% vacuum tubes, and was remarkably accurate and reliable, considering. Often when the flight crew "griped" about some problem we couldn't duplicate it on the ground. So we would open up the radome, extend the radar set, lower each unit, and tap on the individual tubes with a screwdriver handle while one guy in the radar operator's seat monitored the 'scope. This simulated the in-flight vibration. Many times we could isolate the problem like this. We then replaced that unit, retested, and signed off the "gripe" as fixed.

 

[yungman]

you need a multimeter and a tube manual.

once you have figured out how tubes work, from reading the tube manual, you will know what voltage to expect at each pin.

Then you measure voltages in your amplifier.
Then you use laws of kirchhoff and ohm to see what doesn't make sense.

Google took me right to the service manual for a YCV50 amplifier

but they interject themself in the link, i hate that
http://www.google.com/url?sa=t&rct=...ptpJ_XPS740qlfIew&sig2=Q6FCrduCYvZrU58dnxp-uw

i think you can download it from here
http://www.traynoramps.com/default.asp?p1=7&p2=0&p_id=30

http://www.traynoramps.com/downloads/servman/smycv50b.pdf

and it looks like a wonderful manual.

Go man, GO !

old jim

Thanks
Now I got Traynor schematic in my collection.

 

[thegreenlaser]

Well, since I have all this experience offering to help me...

The issue is specifically that it randomly cuts between normal-sounding and muddy sounding. (roughly every 30 seconds or so it will switch) If I use a volume pedal to keep the final output at the same volume, the effect is more noticeable when the master volume is higher.

If I remember correctly, I tried re-seating all the tubes in case they were corroded or not connected correctly, but it had no effect.

 

[davenn]

I would be starting off by looking at any of the electrolytic capacitors. They will dry out with time and give all sorts of weird faults. BE AWARE they are all rated for several 100's of Volts they do bite if not discharged!

Dave

 

[yungman]

Do you mean the channel switching or some sort of effect switching by itself? Find out exactly what function is switching and look at the schematic. If so, you might not have a tube amp problem, you might have a relay control problem instead. Some amp has LED to show the status of what your setting, does the LED switch also?

If you want to, find the particular schematic of your amp from the pdf Jim Hardy posted, tell us what model is your amp. Test and find out exactly what function causing the problem and go from there. It is likely not the tube circuit at all, you might not have to learn the tubes.

Does the "muddy" mode gets much louder? I remember Mesa has a tone circuit like Fender and they have a relay open the last leg to get a lot more middle ( muddier) but a lot louder for over driving. I am just guessing here without a schematic.

 

[thegreenlaser]

I'm fairly certain it's not one of the switches turning on and off. It's definitely more like the clarity of the sound is just disappearing intermittently. I'll maybe check to see if I can replicate it by turning some of the tone knobs down all the way?

@davenn how would I go about checking the caps? I'm assuming I could use a multimeter to check if they're charged, but how would I check if they're working?

 

[jim hardy]

I'm assuming I could use a multimeter to check if they're charged, but how would I check if they're working?

Measure the ratio of DC to AC across them.

Good ones will be like: DCreading = 10X ACreading
bad ones like only 2X or so.

Most DMM's read only the AC component when selected to AC
but analog meterss have internal diodes so will idicate DC when selected to AC.
Better analog ones like Simpson 260 have a jack labelled OUTPUT that connects a capacitor inside the meter to block DC, for making exactly this measurement.

Your amp is a hybrid some transistors and some tubes.
As suggested by the radar fellow above, I'd "thwack" (pardon the technical term) the tubes while powered up and listen to see if one has gone microphonic on you. That causes positive feedback and distortion.

Then start learning your amp by downloading that manual and checking power supply voltages.

I have a Simpson 260 and consider it a necessary wardrobe accessory for serious tube guys.

old jim

 

[yungman]

I'm fairly certain it's not one of the switches turning on and off. It's definitely more like the clarity of the sound is just disappearing intermittently. I'll maybe check to see if I can replicate it by turning some of the tone knobs down all the way?

@davenn how would I go about checking the caps? I'm assuming I could use a multimeter to check if they're charged, but how would I check if they're working?

Have you look at your amp and find the schematic from the files Jim Hardy posted? Without that, all talks are cheap. We are guessing here.

Does it gets louder when go into muddy sound? If only the sound get muddier, no distortion unless you hit the strings hard, I don't think you have a filter cap or tube problem. You might have an intermittent solder connection. Don't assume anything, get the right schematic and go from there.

The first step is going to have to open the amp and tap the components with a wooden stick. But be careful, every time you turn off the amp, make sure you keep the STANDBY switch on and just turn off the power. The Standby switch cut the HV to the power tube. If you turn the Standby off, you will not discharge the big filter caps even you turn off the power and it can be very dangerous. Keep the standby on and turn off the power, the tubes will still conduct as the filaments are still hot, that will discharge most of the stored energy in the filter caps. In order to be safe, I actually tie a lead from the chassis onto a straightened paper clip tided on a wooden stick to short out all the filter caps before even touch the inside.

 

[thegreenlaser]

Measure the ratio of DC to AC across them.

Good ones will be like: DCreading = 10X ACreading
bad ones like only 2X or so.

Most DMM's read only the AC component when selected to AC
but analog meterss have internal diodes so will idicate DC when selected to AC.
Better analog ones like Simpson 260 have a jack labelled OUTPUT that connects a capacitor inside the meter to block DC, for making exactly this measurement.

Your amp is a hybrid some transistors and some tubes.
As suggested by the radar fellow above, I'd "thwack" (pardon the technical term) the tubes while powered up and listen to see if one has gone microphonic on you. That causes positive feedback and distortion.

Then start learning your amp by downloading that manual and checking power supply voltages.

I have a Simpson 260 and consider it a necessary wardrobe accessory for serious tube guys.

old jim

I have a DMM, so hopefully it should be easy to measure AC and DC independently. So as far as exact process goes, would I just measure the AC voltage and DC voltage across a capacitor to see if it's still good? Would this have to be done while the amp is on or do I have to use some sort of test circuit? Sorry for being a little slow with this... I've never really done anything like this, so I'm trying to learn as much as I can.

Have you look at your amp and find the schematic from the files Jim Hardy posted? Without that, all talks are cheap. We are guessing here.

Does it gets louder when go into muddy sound? If only the sound get muddier, no distortion unless you hit the strings hard, I don't think you have a filter cap or tube problem. You might have an intermittent solder connection. Don't assume anything, get the right schematic and go from there.

The first step is going to have to open the amp and tap the components with a wooden stick. But be careful, every time you turn off the amp, make sure you keep the STANDBY switch on and just turn off the power. The Standby switch cut the HV to the power tube. If you turn the Standby off, you will not discharge the big filter caps even you turn off the power and it can be very dangerous. Keep the standby on and turn off the power, the tubes will still conduct as the filaments are still hot, that will discharge most of the stored energy in the filter caps. In order to be safe, I actually tie a lead from the chassis onto a straightened paper clip tided on a wooden stick to short out all the filter caps before even touch the inside.

I've looked at the schematic... I just don't really know what to do with it. I think I recognize most of the components, and in theory know how to analyze them in a circuit, but I really don't know how the schematic helps me isolate the problem. That was kind of my motivation for starting this thread.

It definitely just gets muddier, and not more distorted.

Now when you say tap with a stick, do you mean tap things while the amp is on to see if I can recreate the problem by bumping a component?

 

[yungman]

1) you need to tell us what schematic in Jim's link.
2) When it get muddy, does it get louder?
3) Yes, use a wooden stick to tap the components and see whether you can make it to fail.
4) Look at the tone control circuit area.

I need to look at the schematic and then step by step look at it with you. Do you have a scope?

 

[jim hardy]

So as far as exact process goes, would I just measure the AC voltage and DC voltage across a capacitor to see if it's still good? Would this have to be done while the amp is on or do I have to use some sort of test circuit?

yes, that should get you started. Make the measurements with amp powered up. Be careful - when you're beginning it's easy for a probe to slip and short to chassis. Watch out around those tubes.

Old volume and tone control adjustable resistors can get intermittent. Do any have a 'dead spot' where they make a scratchy noise when turning them ?