Traynor TS-25 highly suceptible to RF(?) noise

[garytoosweet]

Hey all,

I have a Traynor TS-25 that is highly susceptible to some type of noise (RF, EMI, something else?). I am very familiar with the Traynor TS series and have not had one behave like this before. I actually have a TS-25B and TS-50 here at the same time, and neither of them have this issue. I've worked on and owned TS-25's before and they didn't behave like this.

With nothing plugged in, the amp is quiet. When you plug in a guitar and turn the volume to zero, it's quiet.

However with a guitar plugged in and the volume up there is a loud buzz.

The noise is quieter when chassis is in the cabinet with steel panelling on the top and sides, but still present.

I have tried adding a small cap from input ground to chassis, no change.

The noise is only present on HIGH input. LOW input is ok.

All components on high input going into the TL071 test ok on the meter (2 diodes, C1, C3, R1, and R2).

All ground connections test good on the meter.

Amp sounds good, just the buzz.

There is a noisey 25kHz waveform present, scope shot attached (20us/div, .2V/div).

What else can I try? Looking forward to hearing your thoughts.

[Helmholtz]

25kHz is above the audible range (at least for adults) and guitar speakers can't reproduce a frequency that high.

Can you post a soundfile?

[garytoosweet]

25kHz is above the audible range (at least for adults) and guitar speakers can't reproduce a frequency that high.

Can you post a soundfile?

There's also noise down in the range of human hearing, but I thought the sine at 25kHz was odd and maybe related.

Here is a sound clip and another scope shot showing more noise at around 120hz (10ms/div).

The main 2200uf caps have been replaced. The 150uf caps for the 15V supply are original but test ok for capacitance and ESR with an LCR meter.

[The Dude]

If the noise isn't present with no input and/or with guitar plugged in and volume down, I'd be more likely to suspect the guitar is picking up the noise and not the amp. Maybe a nearby computer, phone, florescent or neon lights, etc. radiating into guitar pickups.

[garytoosweet]

If the noise isn't present with no input and/or with guitar plugged in and volume down, I'd be more likely to suspect the guitar is picking up the noise and not the amp. Maybe a nearby computer, phone, florescent or neon lights, etc. radiating into guitar pickups.

Yes it seems like that is the case to me as well. But it seems to come out so much louder on this particular amp than any other amp, including other extremely similar amps in the same series. All with the same guitar, same room, plugged into the same jack.

[g1]

That it quiets down in it's extra cabinet shielding makes me wonder if the transformer is the source of the noise getting to the pickups.

[J M Fahey]

The guitar may have a grounding or shielding problem, the cable may be low quality, there may be a nearby interference source as Enzo mentions.

Set guitar into full hum/buzz mode, meaning all pots on 10, and move it around, rotate it pointing at different angles, etc.

I suspect noise will change, with maximum and minimum positions, that might help you find the source.

Do NOT have your cellphone in your pocket or, start with it, then put it on a table or something at the other end of the room or plain turn it OFF. Any change?

That said, that Traynor has an unnecessarily complex input jack setup, cascaded series leaf switches connecting ground to where it´s needed, absolutely different circuits for each jack: normal (let´s call it old Fender style) is mixing them together through resistors (often 68k); here each goes to its own Op Amp input, and in different/opposite configurations: top one is "normal" , sort of, going to high impedance pin 3 of TL071; bottom one is low impedance (that might explain the lower hum/buzz level and on the other hand confirming the "antenna" theory) to pin 2.

To boot Top is not inverting, while bottom one is, so inputs in the same channel are out of phase.

What could go wrong? [rolleyes]

Traynor was cursed by Canadian Government: they asked for some kind of protection against cheap Imports, the answer was to give them a grant.

So far so good, pity is that the keys to the purse were held by a couple politician_90/engineer_10 type bureaucrats, who INSISTED that to deserve it, Traynor had to be "technologically advanced".

Good in theory, but as they say, "the Devil is in the details"

Every single year , on renewal date, they had to show that they had "advanced", so in the mix, besides real advances, they were forced to make circuits more complex every time just to "show something".

Notice Traynor circuits became more and more complex, specially in those excellent PA products, but also here as in that 6 transistor 3 band differential distortion clipper.

Also the "discrete Op Amp" driving Reverb, he *common base* reverb recovery circuit, etc.

Eventually it became impossible to keep up pulling rabbits from the top hat and the "help" stopped.
Oh well.

[garytoosweet]

I brought the TS-50 I have back to the bench and tried it with all other variables the same, there is almost no buzz, it sounds like a healthy amp. When switching between the two amps I noticed the TS-25 has WAY too much gain. The signal is just way hotter than it should be. The amp is far too sensitive. With the Gain turned up you can get pretty heavy distortion sounds, like a cranked DS-1, Metallica type of tones. This amp should not be capable of that.

That it quiets down in it's extra cabinet shielding makes me wonder if the transformer is the source of the noise getting to the pickups.

Using the cable as an antenna with one end plugged into amp and moving other end around, I am able to pick up the transformer noise when close to it, but it's a lower frequency (60hz, presumably?) and doesn't seem related to the buzz. When the 1/4" plug in is inside the chassis, the buzz completely disappears. The chassis is completely open on the bench.

Set guitar into full hum/buzz mode, meaning all pots on 10, and move it around, rotate it pointing at different angles, etc.

Noise definitely changes a lot, but seemingly without much rhyme or reason. I turned all other electronics in the room off. No cell phone, etc. No change. No doubt it is noise being picked up from pickups, though.

Interesting bit of Traynor history there, JM. Love to hear it.

[g1]

When switching between the two amps I noticed the TS-25 has WAY too much gain. The signal is just way hotter than it should be. The amp is far too sensitive. With the Gain turned up you can get pretty heavy distortion sounds, like a cranked DS-1, Metallica type of tones. This amp should not be capable of that.

I would start with that issue, and hopefully you get lucky and kill two symptoms with one fix.
You also mentioned that the noise is not bad with the low jack. They look like special jacks with isolated switches on the schematic. Are they both stock and the switches are doing their thing?

[garytoosweet]

I would start with that issue, and hopefully you get lucky and kill two symptoms with one fix.
You also mentioned that the noise is not bad with the low jack. They look like special jacks with isolated switches on the schematic. Are they both stock and the switches are doing their thing?

Yeah I'm thinking it's likely all symptoms come from one issue - just too sensitive.

I've checked it out pretty thoroughly and not sure I'm going to find an issue.

The actual LOW jack is just a plain mono (non-switched jack). Looks stock. I tried grounding the tip of the LOW jack when using the HIGH input but didn't make a difference. The HIGH jack is switching and working.

I ended up adding a 1000pf cap from TL071 Pin 3 to ground which seemed to help some. Believe this should form a low pass filter cut off around 16kHZ.

I once had a JCM 800 with similar issues. I tried everything, had been recapped, all new tubes, lead dress was fine, no caps leaking, resistors in spec etc etc. Eventually I added a 10pf or so cap between plate and grid of V1 and it tamed the amp and solved the issue. Still sounded like an 800 should. I heard that some of them come from the factory with this cap, and some don't. I'm not sure what is making some amps more sensitive than others.

[g1]

Looking again, the schematic (TS25) of those input jacks makes no sense.. That you found a regular jack at the low input lines up with the TS50 schematic, where at least the high jack switch appears able to do something. (see attached)
So you still are at the point where you can get much more gain out of the 25 than the 50 ?
I would compare them and see if the big gain increase is already showing up at the output pin of the TL071. If so, I would look at the feedback loop around that chip.

[garytoosweet]

Comparing the TS-50 and TS-25 side by side.

With a 100mV p-p (~40mV RMS) sine on the input, GAIN set to 10, EQ's at noon, Reverb/Master at 0. No load.

Pin 6 (output) of the first op-amp:
TS-25: 5VAC
TS-50: 1VAC

The TS-50 is set up a bit different than the schematic. The opamp is a LF351N instead of the TL071. R3 feedback resistor is 680k. R1 and R2 are 100k's. Gain pot is 50k. Clearly from factory.

The TS-25 is set up as per the schematic with a 10k input, 1.5M feedback resistor and 1M gain pot.

The sine on both amps is clean up to the 6 transistor circuit, with the much hotter signal on the TS-25 getting clipped like crazy.

Only had a few minutes this weekend with it but will continue diving in this week.

EDIT (slightly more thinking on this):

Plugging these numbers into an opamp calculator quickly.

The TS-25 with matching numbers on the schematic should have a gain of approx. 150. 40mV in, 6V out.

The TS-50 with the values in the actual amp calculates a gain of approx. 8. 40mV in, 300mV out.

Obviously I am seeing more voltage in the TS-50 but these numbers are pretty close. Point is the set up in the TS-50 will provide much less gain than the TS-25. The TS-25 is the relatively early, original late 70's design and the TS-50 is the later revision from the early 80's.

Possible the amp was redesigned to cut the gain by that much?