hello i have an early 90's peavey tko 115 1993.
i think the buzz is about some where between 100hz an 140hz (twice the power frequency im guessing.
*it is not in the power amp because if i plug line into " pwr in" the buzz stops when the pre is by passed.
*the sound is constant and is not effected by adjusting any of the controls. or by plugging a lead in or out.
* there is no ground lift switch on this model
If any one has any ideas what it could be and what to try that would be great, here is a schematic link
PEAVEY TKO115 SCH Service Manual free download, schematics, eeprom, repair info for electronics
thanks
i think the buzz is about some where between 100hz an 140hz (twice the power frequency im guessing.
*it is not in the power amp because if i plug line into " pwr in" the buzz stops when the pre is by passed.
*the sound is constant and is not effected by adjusting any of the controls. or by plugging a lead in or out.
* there is no ground lift switch on this model
If any one has any ideas what it could be and what to try that would be great, here is a schematic link
PEAVEY TKO115 SCH Service Manual free download, schematics, eeprom, repair info for electronics
thanks
Attachments
Start with the 15v power supplies, one probably has lost its filtration - ie high ripple.
make sure if the supplies are good that they both get right to the ICs. Go down the ICs and check each output pin for DC offset.
make sure if the supplies are good that they both get right to the ICs. Go down the ICs and check each output pin for DC offset.
thanks.
wondering do i measure op's offset output pin to ground chassis?
do you know if there is there a way to check dc ripple without an oscilloscope, also wondering if this is likely caused by a bad op or a faulty electrolytic coulping cap or if its more likely to from the ps filtering caps? if its worth guessing
Don't worry about what might cause it until you find out if you have it.
yes, all measurements of voltage are taken to ground unless otherwise specified.
Some meters will measure ripple on DC. Put the meter on AC and measure the DC voltage. After a second, the voltage number ought to settle to about zero if the supply is good. Any AC reading is ripple. Unfortunately some meters, mostly inexpensive ones, are confused by this. SO here is a test for your meter. get out a 9v battery, set your meter to AC volts, and measure the battery. if it settles to a zero reading, your meter will work. If you get some reading like 12 volts, then the meter is confused. The confused meter can sometimes be helped by adding a cap in series with its hot probe. I'd use a 0.1uf or 0.047uf from my drawers. The cap passes the AC of the ripple, but blocks the DC that confuses the reading.
yes, all measurements of voltage are taken to ground unless otherwise specified.
Some meters will measure ripple on DC. Put the meter on AC and measure the DC voltage. After a second, the voltage number ought to settle to about zero if the supply is good. Any AC reading is ripple. Unfortunately some meters, mostly inexpensive ones, are confused by this. SO here is a test for your meter. get out a 9v battery, set your meter to AC volts, and measure the battery. if it settles to a zero reading, your meter will work. If you get some reading like 12 volts, then the meter is confused. The confused meter can sometimes be helped by adding a cap in series with its hot probe. I'd use a 0.1uf or 0.047uf from my drawers. The cap passes the AC of the ripple, but blocks the DC that confuses the reading.
Oh, and before going nuts, also check that the hex screws that mount the circuit board are snug. SOme of them are part of the grounding.
+- 16V supplies are via 150R resistors and 16V zener diodes. Very simple. Measure the supplies and see if they are OK.
Loose connections, bad earths first suspects. Short circuit zeners next up and O/C capacitors on the supply next. Short circuit is the normal failure mode for a diode and may be what you have.
If +16 and - 1V, well you have it!
7815 and 7915 regulators are a good replacement for 150R resistors and 16V zeners 🙂
Loose connections, bad earths first suspects. Short circuit zeners next up and O/C capacitors on the supply next. Short circuit is the normal failure mode for a diode and may be what you have.
If +16 and - 1V, well you have it!
7815 and 7915 regulators are a good replacement for 150R resistors and 16V zeners 🙂
P.S I hope your back is strong for lifting this amp onto your bench. It's a heavy lump! Straight back, brace abs, breathe in and LIFT.
I found circuit diagrams if you need them.
I found circuit diagrams if you need them.
https://peavey.com/forum/viewtopic.php?t=39825
Apart from a missing "contour" switch, this circuit is probably almost the same as what you have.
I replaced the 150R resistors and 16V zeners for 7815 and 7915 linear regulators.
My guess is one of your zeners has gone short circuit, hence the buzzing.
Apart from a missing "contour" switch, this circuit is probably almost the same as what you have.
I replaced the 150R resistors and 16V zeners for 7815 and 7915 linear regulators.
My guess is one of your zeners has gone short circuit, hence the buzzing.
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yeah heavy my mate who played bass used to get me to carry his one for him all the time,
I used to play metal through it. I have two of them stacked, a tko 80 scorpion and a tko 115 bw.
the tko line out to the bw power amp is good set up for driven sound and the bw line out to tko 80 power section is set up or a good clean sound so i only have to swap a few leads around and not change the settings.
I run 6 string guitar through them. the tko 80 is better because it goes to 30khz, the other only 20khz. tko80 has the better speaker.
thanks for the help
thank you for all the advice, I have a good meter, the power rails to all the ops are pretty close and there doesnt seem to be any ac at the ps caps in the power supply.
op's(4558's) U1,2,3,4,9,10,11,5, all measured -15.60v & +15.36v.
U 7 and 8 measured -14.79v & +14.89v. I havent measured U6 (LM308ON) yet.
All the dc off sets were near perfect except U7 pinout2 measured 0.195vdc
and U11 p-out1 measured 0.012vdc.
Recently i replaced all the electrolytic's and replaced the audio ceramics with film and it was still quiet and a much clearer sound though I wouldnt bother doing this again.
after doing this. i cant remember if the noise developed on its own a few weeks or so later, I had recently swapped the 4558's to try opa2134. I think the gain on the 2134's were alot higher and amplifying the noise.
I swapped U7 (0.195v offset) and U8 which are the op's between the preamp tone etc and the power stage since the tone and volume controls did not amplify the problem.
swapping them back to 4558's lowered the buzzing considerably to hardly being bad.
I swapped all the others back as well because i was worried they were just cheap rubbish. though it almost eliminated i dont think it was the problem, the higher gain op's just amplified it more. so i left one 2134 in the eq section which seemed to colour the sound a bit. but not as strong as having all 2134s.
anyhow the only two things i could put it down to is u7 dc offset which i have no idea how to correct ,
or is it possible it is interference being picked up, i replaced two pots at one stage and i only had small type audio pots so i had to run short wires from the pcb to the pots, the other thing is i used the normal style caps in place of axial caps so more of the lead is exposed than normally would with axials, could the slightly longer leads pick up the buzzing sound? or is it more likely the dc offset at 195ma?
cheers
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The gain in an opamp circuit is totally dependent on the feedback resistor used, and won't change by just rolling op amps. The OPA2134 should be MUCH quieter than the 4558s; if not, something else is wrong. Do the opamp circuits have bypass capacitors on all the power pins? Perhaps the faster 2134s are causing oscillation; you should be able to see this with a scope on the op amp output pins.
hello, they are not on each vcc+ & vcc- .
i think they are only at the start on the ps that feeds all of them.
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On the schematic and PCB layout you will see decoupling capacitors on pins 4&8 of each op amp. The leads are quite long and it's not like modern design though. The newer op amps aren't that new either so I would have thought OK.
The pots you replaced - cases earthed? - same value ohms?
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I think it is most likely the pots, they arent shielded and the original design used external shielding on the pots, i only had small plastic backed pots for the two values i needed so i used them.
trying to remember what order I replaced things in. i think this may have been what happened,
first I recapped the amp with film etc and the frequency response improved greatly with no noise,
then i replaced a few pots that hadnt been replaced so I could match the dials to the ones that had been replace by the last owner (Peavey use a small shaft size)
that may have introduced bit of noise though not really noticeable ,
then went from the original 4558s to 2134s which amplified the noise which was already in the back ground because swapping back to 4558s made it hardly noticeable again.
I will get track down some shielded pots because i think this may be the problem, cheers
Hi, I've the same issue as described above in the first post. It's a friend's amp that I'm trying to fix.
I've got 32mV at U3 output and 3.85V on the negative leg of C118 (which is U5 audio in) , it gives me 28.75V on U5 output...
Not familiar with these amps, more experienced in hi-fi ;-)
Any advice will be welcome,
Cheers,
I've got 32mV at U3 output and 3.85V on the negative leg of C118 (which is U5 audio in) , it gives me 28.75V on U5 output...
Not familiar with these amps, more experienced in hi-fi ;-)
Any advice will be welcome,
Cheers,
Hi Phil. May I suggest you start a new thread for your amp repair. i gets confusing repairing two amps in the same thread, plus this thread has gone to sleep. Furthermore this thread was about a TKO115 and you offered a schematic for a MAX115. Different circuits.
By your schematic, did you mean C116 rather than C118? The power amp is an LM3886, and those mostly either work or they don't. DC on the output? If you have both power supplies, then it points to a bad IC.
By your schematic, did you mean C116 rather than C118? The power amp is an LM3886, and those mostly either work or they don't. DC on the output? If you have both power supplies, then it points to a bad IC.