Is there a pair of transistors your would recommend that I can substitute for these small transistors?
I'm still trying to figure out if there is a name for these small transistors that are cylindrical with a flat on one side.
Since all of these transistors are connected between the -/+ 42 rails the transistors have to handle 84V?
BR
I'm still trying to figure out if there is a name for these small transistors that are cylindrical with a flat on one side.
Since all of these transistors are connected between the -/+ 42 rails the transistors have to handle 84V?
BR
My normal small signal devices are BC107 and BC177, but these aren't high enough voltage for some in the amp (see below).
No, only some of them - many only ever see a single 42V, and some less than that.
The amplifier is in current production, so those transistors should be available, from Fender if from no one else.
The small cylindrical transistors with the flat side are called TO92 packages. TO means "transistor outline" and most common shapes have a TO number.
None of your 2N400x series transistors are in the signal path. The actual amplifier circuits use Japanese series transistors. Your 2N4003 and friends do things like turn LEDs off and on, and act as switches turning 16v off and on to control things. Also a couple of them turn on and off the power amp mute. These are not critical types, and something like 2N4401/2N4403, or 2N3904/3906 should work.
I recommend if you replace the 2Nxxxx types with something else, you stick with American types. Electrically you can do fine with the BC series or some 2S Japanese serie4s parts, BUT the legs are in different order. AMerican types will go right into the holes, the other types will have to be mounted sideways or backwards so the leg pinout will fit the existing board holes.
The small cylindrical transistors with the flat side are called TO92 packages. TO means "transistor outline" and most common shapes have a TO number.
None of your 2N400x series transistors are in the signal path. The actual amplifier circuits use Japanese series transistors. Your 2N4003 and friends do things like turn LEDs off and on, and act as switches turning 16v off and on to control things. Also a couple of them turn on and off the power amp mute. These are not critical types, and something like 2N4401/2N4403, or 2N3904/3906 should work.
I recommend if you replace the 2Nxxxx types with something else, you stick with American types. Electrically you can do fine with the BC series or some 2S Japanese serie4s parts, BUT the legs are in different order. AMerican types will go right into the holes, the other types will have to be mounted sideways or backwards so the leg pinout will fit the existing board holes.
Enzo
Thanks for explaining these things to me. I figured out earlier today that these small transistors are TO92. Or should I say, I found some info that indicated that to me and then you confirmed what I found. Thanks!
I understand that the FM212R is still in production, which makes me wonder why these parts are so hard to find. They apparently have updated the parts they use or are running on previous stock. As for purchasing from Fender, they are real proud of their stuff. I don't think it would be feasible to purchase from them. Unless of course I can figure out exactly what it causing the problem and replace just that.
Thanks for leading me in the correct direction.
Thanks for explaining these things to me. I figured out earlier today that these small transistors are TO92. Or should I say, I found some info that indicated that to me and then you confirmed what I found. Thanks!
I understand that the FM212R is still in production, which makes me wonder why these parts are so hard to find. They apparently have updated the parts they use or are running on previous stock. As for purchasing from Fender, they are real proud of their stuff. I don't think it would be feasible to purchase from them. Unless of course I can figure out exactly what it causing the problem and replace just that.
Thanks for leading me in the correct direction.
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Transistors may be American types, but that does not mean they are made in the USA, in fact very few transistors are made here. Not all transistors are distributed in the USA. These could be among them. The Frontman series are imports. I can think of any number of times I wanted some part, and bumped into "not available in the USA".
I am not sure what you mean by proud of their stuff. You cannot just call Fender and order a part, but any Fender dealer or service center can, and there are places that sell Fender parts. Guitar, Amplifier, and Korg Keyboard Parts | NATIONAL PARTS DISTRIBUTOR FOR KORG, VOX, BLACKSTAR. PARTS FOR FENDER, GIBSON, GRETSCH, HOFNER, SWR, GUILD, AND MUCH MORE is an example.
But as I mentioned, these transistors are used in control circuits, so would have no effect on the sound quality, and most anything of sufficient ratings would work. I would just make a substitute if this amp came to my shop.
I am not sure what you mean by proud of their stuff. You cannot just call Fender and order a part, but any Fender dealer or service center can, and there are places that sell Fender parts. Guitar, Amplifier, and Korg Keyboard Parts | NATIONAL PARTS DISTRIBUTOR FOR KORG, VOX, BLACKSTAR. PARTS FOR FENDER, GIBSON, GRETSCH, HOFNER, SWR, GUILD, AND MUCH MORE is an example.
But as I mentioned, these transistors are used in control circuits, so would have no effect on the sound quality, and most anything of sufficient ratings would work. I would just make a substitute if this amp came to my shop.
Enzo
I have been reading a different article about SS amps that is way more informative that the last one I posted here. This fella has really got me thinking. I stiff don't get the whole picture and the whys and such of how power splitting via resistors etc. but I am getting there. The more I read the more I see and the more it makes sense.
I have a theory. My amp works for several minutes before the output transistors, well Q21 anyway, get hot and the amp stops working.
The sound is distorted on the clean and the drive channel. Now in this article, this fella explains a situation where you get oscillation. His description sounds like what my amp is doing. (Yes, Nigel has mentioned this possibility in past posts) The problem is, the oscillation this fella is talking about is in the power amp section. The distortion I am experiencing is on all three channels. This tells me the problem is right in the beginning of the preamp circuit. U1, U2, U3. Or one or more of the resistors in that section is not restricting.
Last night I was checking resistors in the power amp and found that R106, which is supposed to be 47 ohms was actually 3k2. And even though I went to Radio Shack yesterday to get some 47, 470 and 47k resistors when I got home I have two 47k and one 470. So I swapped in a 470 to see what would happen. Nothing!
Anyway, I am thinking maybe the same "problem" might be happening in the preamp.
I'll update tomorrow...
BR
Yeah, I think you nailed that one on the head. Import amp = import parts = pain in me ****!
Proud of their stuff = "high priced". Check any "Authorized Dealer" of any persuasion and you'll get quoted the "OH, you want factory parts? Step this way..." price.
I have been reading a different article about SS amps that is way more informative that the last one I posted here. This fella has really got me thinking. I stiff don't get the whole picture and the whys and such of how power splitting via resistors etc. but I am getting there. The more I read the more I see and the more it makes sense.
I have a theory. My amp works for several minutes before the output transistors, well Q21 anyway, get hot and the amp stops working.
The sound is distorted on the clean and the drive channel. Now in this article, this fella explains a situation where you get oscillation. His description sounds like what my amp is doing. (Yes, Nigel has mentioned this possibility in past posts) The problem is, the oscillation this fella is talking about is in the power amp section. The distortion I am experiencing is on all three channels. This tells me the problem is right in the beginning of the preamp circuit. U1, U2, U3. Or one or more of the resistors in that section is not restricting.
Last night I was checking resistors in the power amp and found that R106, which is supposed to be 47 ohms was actually 3k2. And even though I went to Radio Shack yesterday to get some 47, 470 and 47k resistors when I got home I have two 47k and one 470. So I swapped in a 470 to see what would happen. Nothing!
Anyway, I am thinking maybe the same "problem" might be happening in the preamp.
I'll update tomorrow...
BR
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"Proud of their stuff = "high priced". Check any "Authorized Dealer" of any persuasion and you'll get quoted the "OH, you want factory parts? Step this way..." price. "
Oh? Pardon me, but my shop is an "Authorized Dealer" for many brands, and I find it offensive to be accused of such an attitude. I don't charge any more for parts someone wants for themselves than I do for any repair. In fact, I support local amateurs wanting to learn. A guy walks into my shop looking for a 470k resistor, I usually just give him a couple. And advice is free. In fact, if you walked into my shop wanting those 2N4003 transistors, I would tell you I could order them, but I would also tell you what substitutes we could use, and I would have them in my drawers ready to go, no ordering required. COnsider I normally charge $60 an hour for the very diagnosis I give you for free. As do a bunch of other folks on this forum. It is easy to just label an industry professional as some sort of underhanded used-car-salesman cliche, but in reality the majority of us are honest prefessionals trying to help people.
Oh? Pardon me, but my shop is an "Authorized Dealer" for many brands, and I find it offensive to be accused of such an attitude. I don't charge any more for parts someone wants for themselves than I do for any repair. In fact, I support local amateurs wanting to learn. A guy walks into my shop looking for a 470k resistor, I usually just give him a couple. And advice is free. In fact, if you walked into my shop wanting those 2N4003 transistors, I would tell you I could order them, but I would also tell you what substitutes we could use, and I would have them in my drawers ready to go, no ordering required. COnsider I normally charge $60 an hour for the very diagnosis I give you for free. As do a bunch of other folks on this forum. It is easy to just label an industry professional as some sort of underhanded used-car-salesman cliche, but in reality the majority of us are honest prefessionals trying to help people.
Enzo
Enzo please dont be offended. I have run in to many "Authorized Dealers " with very high prices. Im sure you have too! Of course being in the auto repair industry, I see a lot of gouging, and I hate it! Perhaps my perception of dealers in the music eletronics world is slightly off center, fair enough?
The fact that you are here (as with others) helping amateurs with their woes shows your true colors. Its people like you, Fahrey, the Nigels and others that remind us that there are people that do give back to the community.
So please, dont be offended. I assure you, you are more than appreciated.
Now, about that twenty bucks...
Enzo please dont be offended. I have run in to many "Authorized Dealers " with very high prices. Im sure you have too! Of course being in the auto repair industry, I see a lot of gouging, and I hate it! Perhaps my perception of dealers in the music eletronics world is slightly off center, fair enough?
The fact that you are here (as with others) helping amateurs with their woes shows your true colors. Its people like you, Fahrey, the Nigels and others that remind us that there are people that do give back to the community.
So please, dont be offended. I assure you, you are more than appreciated.
Now, about that twenty bucks...
OpAmp U8
I have been having this idea that the fuzzy sound problem has to do with an OpAmp. I have some sockets and plenty of OA's so I removed them one at a time till I ran out of sockets. I'm short by two. I started with U1, installed a socket, inserted a TL072, plugged in the amp and tried it. Still fuzzy, U2 etc... I skipped u4 because it has to do with the reverb tank. U5 had a strange shinny pattern on top, I honestly expected that to be my problem. But I replaced it and nothing changed.
I should note here that two of the OpAmps are TL072 and the others are BA4560's. I have RC4580's which are nearly identical to the 4560's according to the datasheets.
The last one I changed is U8 and when I turned it on the amp was dead silent. No hum, no nothing. I thought for a moment I had shorted something and the amp wasn't on. But I cracked the volume on the guitar and there it was, smooth, no fuzz, sounding as pretty as the day I bought it. I played all three channels and it sounded wonderful! I kept checking the temp on the heat sink and it took longer this time but it was still getting hotter that "I" think it should. I still don't know what is normal. "Normal" must be pretty hot since it uses such a think heat sink. Anyway, I was playing and then suddenly it went fuzzy again. I checked the temp and it was about 135 on the heat sink. So... apparently the problem is on the same circuit as U8-B.
Last night and tonight I have been checking the value on each resistor beginning with R1. Most are right on the money (within 5%) but some are off by a noticeable amount and some are WTF off! Like thousands of ohms off. I am up to R115 so far. Below are my results so far. Those that are off but are in the ball park are not listed. Only the ones that are WAY off.
Those with no letter are ohms (<999) I'm sure that's obvious but...
Item listed actual
R19 47k 8.3k
R25 5.1k 21.8
R29 33k 3.07k
R31 220k 180k
R44 100k 44.1k
R50 47k 27.5k
R64 1m 93.1k
R88 47 80k
R106 fu47 3.3k changed to 470 - didn't have a 47ohm to install
R107 150 107
R108 390 107
R110 150 107
R111 390 107
R114 .22 0
R115 .22 0
That's all I have for the moment.
BR
I have been having this idea that the fuzzy sound problem has to do with an OpAmp. I have some sockets and plenty of OA's so I removed them one at a time till I ran out of sockets. I'm short by two. I started with U1, installed a socket, inserted a TL072, plugged in the amp and tried it. Still fuzzy, U2 etc... I skipped u4 because it has to do with the reverb tank. U5 had a strange shinny pattern on top, I honestly expected that to be my problem. But I replaced it and nothing changed.
I should note here that two of the OpAmps are TL072 and the others are BA4560's. I have RC4580's which are nearly identical to the 4560's according to the datasheets.
The last one I changed is U8 and when I turned it on the amp was dead silent. No hum, no nothing. I thought for a moment I had shorted something and the amp wasn't on. But I cracked the volume on the guitar and there it was, smooth, no fuzz, sounding as pretty as the day I bought it. I played all three channels and it sounded wonderful! I kept checking the temp on the heat sink and it took longer this time but it was still getting hotter that "I" think it should. I still don't know what is normal. "Normal" must be pretty hot since it uses such a think heat sink. Anyway, I was playing and then suddenly it went fuzzy again. I checked the temp and it was about 135 on the heat sink. So... apparently the problem is on the same circuit as U8-B.
Last night and tonight I have been checking the value on each resistor beginning with R1. Most are right on the money (within 5%) but some are off by a noticeable amount and some are WTF off! Like thousands of ohms off. I am up to R115 so far. Below are my results so far. Those that are off but are in the ball park are not listed. Only the ones that are WAY off.
Those with no letter are ohms (<999) I'm sure that's obvious but...
Item listed actual
R19 47k 8.3k
R25 5.1k 21.8
R29 33k 3.07k
R31 220k 180k
R44 100k 44.1k
R50 47k 27.5k
R64 1m 93.1k
R88 47 80k
R106 fu47 3.3k changed to 470 - didn't have a 47ohm to install
R107 150 107
R108 390 107
R110 150 107
R111 390 107
R114 .22 0
R115 .22 0
That's all I have for the moment.
BR
In the section of the schematic where U8 is I assume that since the mid contour switch is shown to the left, that means that its in the "out" position or "Normal" and pushing it in makes the signal go through the section where U8 is?
But that section would still pay a part at all times wouldn't it, since it is connected to the circuit at all the times? Its just that the signal is directed through that section when the button is pushed in?
BR
But that section would still pay a part at all times wouldn't it, since it is connected to the circuit at all the times? Its just that the signal is directed through that section when the button is pushed in?
BR
I suspect your resistors are all fine, remember, this is not rocket surgery, the parts are not precision.
meanwhile your readings are way off, and notice your way offs are always lower than the resistor value, because of parallel paths in the circuits. Look at R19 47k. Look at the schematic. Since you no doubt took the readings with the amp off, that means JFET Q5 is ON, so the right end of R19 has a low resistance to ground. You can determine how low yourself, I'd guess under 100 ohms maybe. Now look to the other end of R19. A 50k pot to ground. R17 volume control. Turn it all the way clockwise (the arrow indicated clockwise) and you have 50k between the left end of R19 and ground. SO one end of R19 is essentially grounded, and the other has a 50k to ground through the pot. That puts 50k in parallel with the R19 47k. REsult would be about 24k. Rotate the control the other way and the wiper grounds the left end of R19. With both ends more or less grounded, your R19 will read like it is shorted, or close to it. SO that control affects your reading.
Now you can go back and look at the circuit for the other ones, and I bet you find similar situations. here is another: 150 ohm R107. Look at it. R108, R109 are in parallel with it. R109 is only 2/10 of an ohm, so ignore it. That leaves 390 ohms R108 in parallel with R107. DO the calculations for parallels and see how close that comes to your reading. I get 108 ohms on my calculator. Prety close.
Reading 0.22 ohm resistors is beyond the resolution of many meters, and they just read that as zero. Resistors like that are either OK, or they are burnt open. Yours are OK.
There are some apaproaches to repair: one is to simply replace every part in something, or at least in a circuit. That is called the sshotgun approach. It of course fixes any bad part problems, but misses connection issues or broken traces. Then there is replacing parts one by one, going down the rows. We call that an easter egg hunt. But look at the circuit, you have loop jacks - preamp out and power amp in. Your amp sounds bad. Instead of replacing a lot of ICs hoping to find a bad one, just play through the amp, and run a cord from the preamp out to some other amp. If it sounds bad in your amp, but the preamp sounds OK over in the other amp, then we know all the ICs in the preamp are working. If the preamop sounds crappy, then we look into it.
Likewise, when it sounds crappy, plug the guitar into the power amp in jack, so you are playing now through the power amp only. If that sounds punk, then the power amp is at fault. If it sounds OK, then the problem must be elsewhere.
We do those things to narow down where the problem must be. It maeks the search easier.
I am concerned for your power amp. 47 ohm R88 measures 80k? Then it is effectively open. Q12 passed excess current to burn that part. Likewise Q18 and/or Q20 havwe burnt out R106. Please do not put 470 ohm resistors where 47 ohm ones belong. That will increase the voltage across the part, and at the very least would indeed make the thin run MUCH hotter.
meanwhile your readings are way off, and notice your way offs are always lower than the resistor value, because of parallel paths in the circuits. Look at R19 47k. Look at the schematic. Since you no doubt took the readings with the amp off, that means JFET Q5 is ON, so the right end of R19 has a low resistance to ground. You can determine how low yourself, I'd guess under 100 ohms maybe. Now look to the other end of R19. A 50k pot to ground. R17 volume control. Turn it all the way clockwise (the arrow indicated clockwise) and you have 50k between the left end of R19 and ground. SO one end of R19 is essentially grounded, and the other has a 50k to ground through the pot. That puts 50k in parallel with the R19 47k. REsult would be about 24k. Rotate the control the other way and the wiper grounds the left end of R19. With both ends more or less grounded, your R19 will read like it is shorted, or close to it. SO that control affects your reading.
Now you can go back and look at the circuit for the other ones, and I bet you find similar situations. here is another: 150 ohm R107. Look at it. R108, R109 are in parallel with it. R109 is only 2/10 of an ohm, so ignore it. That leaves 390 ohms R108 in parallel with R107. DO the calculations for parallels and see how close that comes to your reading. I get 108 ohms on my calculator. Prety close.
Reading 0.22 ohm resistors is beyond the resolution of many meters, and they just read that as zero. Resistors like that are either OK, or they are burnt open. Yours are OK.
There are some apaproaches to repair: one is to simply replace every part in something, or at least in a circuit. That is called the sshotgun approach. It of course fixes any bad part problems, but misses connection issues or broken traces. Then there is replacing parts one by one, going down the rows. We call that an easter egg hunt. But look at the circuit, you have loop jacks - preamp out and power amp in. Your amp sounds bad. Instead of replacing a lot of ICs hoping to find a bad one, just play through the amp, and run a cord from the preamp out to some other amp. If it sounds bad in your amp, but the preamp sounds OK over in the other amp, then we know all the ICs in the preamp are working. If the preamop sounds crappy, then we look into it.
Likewise, when it sounds crappy, plug the guitar into the power amp in jack, so you are playing now through the power amp only. If that sounds punk, then the power amp is at fault. If it sounds OK, then the problem must be elsewhere.
We do those things to narow down where the problem must be. It maeks the search easier.
I am concerned for your power amp. 47 ohm R88 measures 80k? Then it is effectively open. Q12 passed excess current to burn that part. Likewise Q18 and/or Q20 havwe burnt out R106. Please do not put 470 ohm resistors where 47 ohm ones belong. That will increase the voltage across the part, and at the very least would indeed make the thin run MUCH hotter.
"In the section of the schematic where U8 is I assume that since the mid contour switch is shown to the left, that means that its in the "out" position or "Normal" and pushing it in makes the signal go through the section where U8 is?"
Yes
"But that section would still pay a part at all times wouldn't it, since it is connected to the circuit at all the times? Its just that the signal is directed through that section when the button is pushed in?"
The signal always goes TO U8, selected or not, but when in the normal setting, the output of U8 has nowhere to go. It goes to the switch, but the switch is set the other way, so U8 has no effect on anything.
Yes
"But that section would still pay a part at all times wouldn't it, since it is connected to the circuit at all the times? Its just that the signal is directed through that section when the button is pushed in?"
The signal always goes TO U8, selected or not, but when in the normal setting, the output of U8 has nowhere to go. It goes to the switch, but the switch is set the other way, so U8 has no effect on anything.
Enzo
I will do as you instruct when I get home.
Im thinking someone had me do the preamp out to another amp but I dont remember the result. Im thinking it was clear but I will verify when I get home.
I meant to ask about how the resistors are affected by being connected to the circuit
But I forget. I figured the circuit was affecting my readings but I wanted your input before I began removing resistors.
I will do as you instruct when I get home.
Im thinking someone had me do the preamp out to another amp but I dont remember the result. Im thinking it was clear but I will verify when I get home.
I meant to ask about how the resistors are affected by being connected to the circuit
But I forget. I figured the circuit was affecting my readings but I wanted your input before I began removing resistors.
Enzo
I apparently wasn't clear in what I was saying.
When I said the section with U8 would still affect the sound: I wasn't talking about the OpAmp. I can't expect it to be doing much because the signal, as you said, goes through it but hits a dead end at the Mid Contour switch,
What I actually meant was the signal is still going through R201, 202, 203 and C201 & 202. So I was making the assumption that section was still being used since it leads to ground.
I did as you directed: Guitar connected to the Power Amp In, sounds fuzzy.
Preamp Out, the sound is clean in the second amp. So, you have narrowed it down to the Power Amp section.
I'm going to test the resistors in that area before I head to town to get some 47ohm resistors and any others that appear to be damaged.
BR
I apparently wasn't clear in what I was saying.
When I said the section with U8 would still affect the sound: I wasn't talking about the OpAmp. I can't expect it to be doing much because the signal, as you said, goes through it but hits a dead end at the Mid Contour switch,
What I actually meant was the signal is still going through R201, 202, 203 and C201 & 202. So I was making the assumption that section was still being used since it leads to ground.
I did as you directed: Guitar connected to the Power Amp In, sounds fuzzy.
Preamp Out, the sound is clean in the second amp. So, you have narrowed it down to the Power Amp section.
I'm going to test the resistors in that area before I head to town to get some 47ohm resistors and any others that appear to be damaged.
BR
Revision
Not sure what happened but I have to revise how the amp is acting.
Preamp out into my other amp, its fuzzy. I don't know if it changed or I got it wrong earlier. Guitar connected to Power Amp in is muffled but its not distorted.
Between this afternoon and now: I just replaced the 470 ohm I had installed in R106 with a 47.
I pulled R88 and checked it. I got 80 ohms. I installed a 47.
I fired up the amp and its fuzzy. About like it was before. And there is a buzzing sound now. If I turn my guitar away from the amp the buzz lessens but its definitely still there.
I played for about 10 minutes though. I kept checking the temp on the outputs and it slowly went up. It just stayed there about 110 to 115 for 4 or 5 minutes and then it started creeping up.
I hooked the premap out to the other amp played for a minute the I hooked the guitar to the power amp in. (I removed the preamp out cable)
Like I wrote above, Its clean but muffled with the guitar in the PA in. Fuzzy with the preamp to the second amp.
That means it has to be one of the resistors doesn't it?
I was checking the voltage at Q18, 19, 20 and 21. They are all running -+ 43 volts.
It seems to me a transistor is staying on and not being regulated. Based upon what I have been reading about regulating transistors, opamps etc.
The heat is taking longer to run away but its still running away. Can't remember the term. Thermal run away or something like that. And the two something that is supposed to be the most common cause of overheating.
I'll keep reading.
BR
Not sure what happened but I have to revise how the amp is acting.
Preamp out into my other amp, its fuzzy. I don't know if it changed or I got it wrong earlier. Guitar connected to Power Amp in is muffled but its not distorted.
Between this afternoon and now: I just replaced the 470 ohm I had installed in R106 with a 47.
I pulled R88 and checked it. I got 80 ohms. I installed a 47.
I fired up the amp and its fuzzy. About like it was before. And there is a buzzing sound now. If I turn my guitar away from the amp the buzz lessens but its definitely still there.
I played for about 10 minutes though. I kept checking the temp on the outputs and it slowly went up. It just stayed there about 110 to 115 for 4 or 5 minutes and then it started creeping up.
I hooked the premap out to the other amp played for a minute the I hooked the guitar to the power amp in. (I removed the preamp out cable)
Like I wrote above, Its clean but muffled with the guitar in the PA in. Fuzzy with the preamp to the second amp.
That means it has to be one of the resistors doesn't it?
I was checking the voltage at Q18, 19, 20 and 21. They are all running -+ 43 volts.
It seems to me a transistor is staying on and not being regulated. Based upon what I have been reading about regulating transistors, opamps etc.
The heat is taking longer to run away but its still running away. Can't remember the term. Thermal run away or something like that. And the two something that is supposed to be the most common cause of overheating.
I'll keep reading.
BR
If turning the guitar affects the hum, it is coming from the guitar, your pickups may be picking up the magnetic field of the power transformer. Turn the guitar volume control to zero, kill the hum?
Use some other signal for testing. A CD player maybe. I use a line out from my cheap bench stereo receiver. Once I think the amp is fixed, THEN I play guitar through it to verify it sounds OK.
Use some other signal for testing. A CD player maybe. I use a line out from my cheap bench stereo receiver. Once I think the amp is fixed, THEN I play guitar through it to verify it sounds OK.
Wait a minute. The amp sounds fuzzy when the preamp out is hooked to the other amp.
Isnt fuzzy if I hook the guitar to the pa in. Yet the heat sink is getting hot. Q21 seems to be the one running the hottest. Does that make any sense at all? Or is that two different problems?
Man dude this stuff could overwhelm someone real easy.
Isnt fuzzy if I hook the guitar to the pa in. Yet the heat sink is getting hot. Q21 seems to be the one running the hottest. Does that make any sense at all? Or is that two different problems?
Man dude this stuff could overwhelm someone real easy.
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Do you have or can you borrow some other amplifier with FX loop jacks? It mi8ght be useful to you to hear what it normally sounds like to play the guitar into the power amp in (FX return). And what it sounds like to play its preamp out (FX send) into some other amp.
In a solid state amp like this, yes, I'd say the majority of tone is generated in the preamp, and the power amp is basically ther to propel the speaker with that preamp signal.
ANything is overwhelming if you are not familiar with it. A bunch of writing in Russian looks incomprehensible, but learn their alphabet, and the words under the picture of a sandwich on the wall in a Moscow McDonalds reveals itself to say "Beeg Meck." Which we can figure out the meaning of, I suspect. This power amp is indeed pretty complex, especially for what it does. But circuits are circuits, and no offense, but your understanding of this at a circuit level is relatively weak. Experience will make it look more friendly.
DOn't confuse symptoms and parts. The essence of our effort is to isolate the problem, or problems. AMp sounds fuzzy connected to another amp? Isn't funny if you connect the GUITAR to the PA? Do you mean if you connect the preamp out to the PA? I am not sure what you are reporting. I expect the guitar itself plugged into the PA to sound clear. I expect a good preamp to sound clear into the PA as well, so that is a good test of it. recognizing the preamp could be on a distortion setting, but I hope we all get that part.
When connecting the preamp to some other amp, we need the other amp to be on a prety clean setting. Obviously we can overdrive the other amp with the relatively hot signal from the preamp out. We don;t have to play loud to hear if the preamp signal is funny or not.
You say "Yet the heat sink is getting hot." Well heat sink getting hot has nothing to do with how the preamp sounds herre and there. Q21 is an output transistor for the power amp, and if it were funny, yes, it could distort what comes out the speaker. But not what comes out the preamp.
Q21 may indeed be what is geting hot, it ought to be the same hotness as Q20. But getting hot doesn't tell us it is bad. It might be, but it can also be hot because Q19 is turning it on too hard. For Q20,21 to work right, Q18,19 have to be right, and for them to work right, Q12,13 have to be right, and Q11, and Q9, and so on.
In a solid state amp like this, yes, I'd say the majority of tone is generated in the preamp, and the power amp is basically ther to propel the speaker with that preamp signal.
ANything is overwhelming if you are not familiar with it. A bunch of writing in Russian looks incomprehensible, but learn their alphabet, and the words under the picture of a sandwich on the wall in a Moscow McDonalds reveals itself to say "Beeg Meck." Which we can figure out the meaning of, I suspect. This power amp is indeed pretty complex, especially for what it does. But circuits are circuits, and no offense, but your understanding of this at a circuit level is relatively weak. Experience will make it look more friendly.
DOn't confuse symptoms and parts. The essence of our effort is to isolate the problem, or problems. AMp sounds fuzzy connected to another amp? Isn't funny if you connect the GUITAR to the PA? Do you mean if you connect the preamp out to the PA? I am not sure what you are reporting. I expect the guitar itself plugged into the PA to sound clear. I expect a good preamp to sound clear into the PA as well, so that is a good test of it. recognizing the preamp could be on a distortion setting, but I hope we all get that part.
When connecting the preamp to some other amp, we need the other amp to be on a prety clean setting. Obviously we can overdrive the other amp with the relatively hot signal from the preamp out. We don;t have to play loud to hear if the preamp signal is funny or not.
You say "Yet the heat sink is getting hot." Well heat sink getting hot has nothing to do with how the preamp sounds herre and there. Q21 is an output transistor for the power amp, and if it were funny, yes, it could distort what comes out the speaker. But not what comes out the preamp.
Q21 may indeed be what is geting hot, it ought to be the same hotness as Q20. But getting hot doesn't tell us it is bad. It might be, but it can also be hot because Q19 is turning it on too hard. For Q20,21 to work right, Q18,19 have to be right, and for them to work right, Q12,13 have to be right, and Q11, and Q9, and so on.
Enzo
Enzo
I don't have anyone around here with an amp I can borrow. The only fella I know of just told me his amp is at his collage dorm so I am out of luck on that.
My Spider Jam amp has an auxiliary input for feeding in a mic or keyboard or another guitar. It also has a software setting to either have the drive and effects that are associated with the guitar input, also applied to the auxiliary input. I set it to be free from the guitar input effects, which gives a pretty clean signal. The SJ does not have an effects loop I am sorry to say.
I plugged my guitar into the FM212 1st input. and connected the Preamp Out to the SJ Aux input. The + speaker terminal shows 2.0 mV at idle (speakers attached)
I had to unhook the Fender speakers because I couldn't tell what was what in the sound. The sound is clear from the SJ. Its not perfectly smooth but the signal isn't fuzzy. Its just not the same sound that normally comes from my Fender speakers.
I made sure that the Fender is set to the clean channel. Of course I had to try it in overdrive too (its a guy thing I assume. lol)
I then removed the preamp out cable, reconnected my speakers and plugged the guitar into the (PA) Power Amp In jack. The amp sounds muffled but it is distorted. (or fuzzy as I have been calling it) Its not prominent like when I am playing through the amp normally but it is fuzzy and the harder I pluck or strum the strings the more fuzzy it gets. But I think that is to be expected isn't it?
Someone said earlier in this thread to connect the PA out to the PA in.
I don't get what plugging a guitar cable from the Preamp Out to the Power Amp In is supposed to accomplish. They are already connected together.
Yes sir you are correct! I am getting there. I am seeing how things flow, its the understanding the biasing and splitting resistors and why they act the way they do and how this over here affects that over there. But the more I read the more its starting to gel - as they say.
Playing the amp normally and on the clean channel, I have noticed that the heat sink stays about 108 to 110 or so. Its when I engage the overdrive that it starts getting real hot.
So are you saying I should back track from Q17 removing each one and testing them? I downloaded a short paper on testing transistors with my DVOM yesterday.
Thank!
BR
Enzo
I don't have anyone around here with an amp I can borrow. The only fella I know of just told me his amp is at his collage dorm so I am out of luck on that.
My Spider Jam amp has an auxiliary input for feeding in a mic or keyboard or another guitar. It also has a software setting to either have the drive and effects that are associated with the guitar input, also applied to the auxiliary input. I set it to be free from the guitar input effects, which gives a pretty clean signal. The SJ does not have an effects loop I am sorry to say.
I plugged my guitar into the FM212 1st input. and connected the Preamp Out to the SJ Aux input. The + speaker terminal shows 2.0 mV at idle (speakers attached)
I had to unhook the Fender speakers because I couldn't tell what was what in the sound. The sound is clear from the SJ. Its not perfectly smooth but the signal isn't fuzzy. Its just not the same sound that normally comes from my Fender speakers.
I made sure that the Fender is set to the clean channel. Of course I had to try it in overdrive too (its a guy thing I assume. lol)
I then removed the preamp out cable, reconnected my speakers and plugged the guitar into the (PA) Power Amp In jack. The amp sounds muffled but it is distorted. (or fuzzy as I have been calling it) Its not prominent like when I am playing through the amp normally but it is fuzzy and the harder I pluck or strum the strings the more fuzzy it gets. But I think that is to be expected isn't it?
Someone said earlier in this thread to connect the PA out to the PA in.
I don't get what plugging a guitar cable from the Preamp Out to the Power Amp In is supposed to accomplish. They are already connected together.
Yes sir you are correct! I am getting there. I am seeing how things flow, its the understanding the biasing and splitting resistors and why they act the way they do and how this over here affects that over there. But the more I read the more its starting to gel - as they say.
I understand what we are trying to do. I do my best to use the lingo used in this thread when I report things. I apologize for not being clear enough at times.
Yes, I understand this. I mention the heat because the heat sink gets so blazing hot. I am using a laser thermometer. The heat sink gets over 140degs. I don't know what normal temp is but that is frickin' hot to me.
Playing the amp normally and on the clean channel, I have noticed that the heat sink stays about 108 to 110 or so. Its when I engage the overdrive that it starts getting real hot.
Q21 runs several degrees hotter than Q20.
So are you saying I should back track from Q17 removing each one and testing them? I downloaded a short paper on testing transistors with my DVOM yesterday.
Thank!
BR