Hello guys.
I have Peavey TKO 115 bass amp thats starts clipping at low gain and output volume. It was brought to me with this problem for repair.
If the treble control or higher frequencies on the EQ are turned down the amp can be pushed a little harder.
Any idea what might be going on?
Also, this amp is from Spain where they have 230V 50 Hz, the customer lives in a place where voltage is approx. 120V 60 Hz, so he used a 1:2 step up transformer to get to around 220V at 60 Hz. I told him that Herz aren't critical in this application.
Some time ago, I had a sound equipment and turn table from Germany with 220V, I also used a step up transformer and it worked just fine.
The customer asked me if using this trafo could be the cause of this clipping issue. The amp has a power consumption of 150W and the trafo delivers 300W, so it should be fine.
I have Peavey TKO 115 bass amp thats starts clipping at low gain and output volume. It was brought to me with this problem for repair.
If the treble control or higher frequencies on the EQ are turned down the amp can be pushed a little harder.
Any idea what might be going on?
Also, this amp is from Spain where they have 230V 50 Hz, the customer lives in a place where voltage is approx. 120V 60 Hz, so he used a 1:2 step up transformer to get to around 220V at 60 Hz. I told him that Herz aren't critical in this application.
Some time ago, I had a sound equipment and turn table from Germany with 220V, I also used a step up transformer and it worked just fine.
The customer asked me if using this trafo could be the cause of this clipping issue. The amp has a power consumption of 150W and the trafo delivers 300W, so it should be fine.
You sound like a pro. Check the ESR of the rail caps. Old dried up ones cause A/B amps to do exactly this.
Good advice and I would add: measure the amp.
Load it with a resistor same rating (ohms and power) as the speaker or worst case, use the original speaker as a load, it will be LOUD but 2 minutes are enough.
Maybe you can´t even reach clipping, Peavey amps have a very good compressor/limiter built in, then rise volume until you see it gets to a fixed value and no further, I am thinking around 22-24 VAC
Post results.
Load it with a resistor same rating (ohms and power) as the speaker or worst case, use the original speaker as a load, it will be LOUD but 2 minutes are enough.
Maybe you can´t even reach clipping, Peavey amps have a very good compressor/limiter built in, then rise volume until you see it gets to a fixed value and no further, I am thinking around 22-24 VAC
Post results.
Sorry, forgot to add the test tones:
https://www.mediacollege.com/audio/tone/files/250Hz_44100Hz_16bit_30sec.mp3
https://www.mediacollege.com/audio/tone/files/440Hz_44100Hz_16bit_30sec.mp3
They last 30 seconds, so set MP3 player to "repeat" or "repeat one" so you get continuous tone output, with a small glitch every 30 seconds .
A typical MP3 player or Phone "earphone out" puts out between 100 and 200mV RMS, fine to drive your amplifier at the instrument input.
Not enough if direct to power amp.
https://www.mediacollege.com/audio/tone/files/250Hz_44100Hz_16bit_30sec.mp3
https://www.mediacollege.com/audio/tone/files/440Hz_44100Hz_16bit_30sec.mp3
They last 30 seconds, so set MP3 player to "repeat" or "repeat one" so you get continuous tone output, with a small glitch every 30 seconds .
A typical MP3 player or Phone "earphone out" puts out between 100 and 200mV RMS, fine to drive your amplifier at the instrument input.
Not enough if direct to power amp.
indianajo: The caps aren't that old. This particular Peavey TKP should be less than 10 years old. Also, on the back is says "assembled in the UK". Not "made in ...". So my guess is that it comes from anywhere in the far east. PCB style and component arrangement also points in this direction.
Question: How can I measure ESR without a proper tool?JMFahey: I'm aware of the protection circuits on Peavey amps. I think it's called DDT. Really useful...
Those audio files are sine waves and too pure. I have a very old tone generator, with very odd frequencies (700 Hz, 70 Hz, ..., its from an old "Quad Eight" console) but basically the same. I'm thinking that pink noise would be more appropriated, since a bass note of 440 Hz has resonant frequencies as well.
Its hard to know the exact problem on the internet
but some educated guesses would be.
Cold or cracked solder connections to the board from tone/volume controls.
Some peaveys will have separate transformer taps for +15 -15 power supplys
for pre amp opamps. measure opamp voltage on pins.
peavey likely uses voltage regulators.
sometimes the power amp will also be opamp driven.
there can be a combination of regulators for the pre.
and the opamps on the power amp will have shunt regulators.
measure opamp voltage driving power amp. check large ceramic dropping resistors
and zener diodes in shunt regulators.
if there is a effect loop clean effect loop jacks.
includes switch contacts which can be hidden in jack.
with many combo amps, if headphones are inserted
the main speaker is disconnected.
so speaker connection run through headphone jack.
clean headphone jack and hidden connections.
if its a driven supply power amp , will have
15 to 16 volts for opamp from shunt regulator as mentioned above.
Then another 22 volts for bias supply. check 22 volt supply/capacitors
and often board ground connections will have oxidation for 22 volt supply.
clean board and chassis ground connections.
but some educated guesses would be.
Cold or cracked solder connections to the board from tone/volume controls.
Some peaveys will have separate transformer taps for +15 -15 power supplys
for pre amp opamps. measure opamp voltage on pins.
peavey likely uses voltage regulators.
sometimes the power amp will also be opamp driven.
there can be a combination of regulators for the pre.
and the opamps on the power amp will have shunt regulators.
measure opamp voltage driving power amp. check large ceramic dropping resistors
and zener diodes in shunt regulators.
if there is a effect loop clean effect loop jacks.
includes switch contacts which can be hidden in jack.
with many combo amps, if headphones are inserted
the main speaker is disconnected.
so speaker connection run through headphone jack.
clean headphone jack and hidden connections.
if its a driven supply power amp , will have
15 to 16 volts for opamp from shunt regulator as mentioned above.
Then another 22 volts for bias supply. check 22 volt supply/capacitors
and often board ground connections will have oxidation for 22 volt supply.
clean board and chassis ground connections.