Tweet
Every so often, you come across an amp whose misbehavior is somewhat baffling. Our Guitar Dept at CenterStaging, LLC in Burbank sent over a couple SVT-CL amps, one labeled 'F**KED....Horrendous Loud Noise when Turned on. Recent product, had the power tube Base Clamps, but had been in the shop before for initial set-up. So, I plugged it in, small Ampeg bass cab for test speaker and after it had warmed up, switched out of Standby.
Sure enough, LOUD Random Noise appeared, Master Volume was CCW, though that's ahead of the final preamp tube stage. Switched back to S/B, switched out of S/B, noise still there. I plugged in my shorting plug into the Power Amp Input jack, and that shut it up. Unplugged that, and the noise was still gone. Turned the Master Volume up and down, no contact noise at that stage. With the Master at Max CW, turned up the Volume pot and exercised it along with the tone controls, heard the usual residual noise (no input signal present). Plugged in the shorting plug into the Power Amp jack again, and exercised that jack, still no longer hearing this horrendous noise.
I dug out my one spare stacked Phone Jack for the Preamp Output/Power Amp Input jack assy to see what the normals looked like. These on my jack looked like a Rean style, the fixed blades of the Normals being straight up, and not at an angle that over time weakens and has to be tweaked upwards from the inside of the jack throat. Probing inside, felt like the CLIFF dual jack and not this Rean part that Neutrik sells these days, though only way to tell would be to remove the power amp chassis.
Using a new T/S plug, not wired, I inserted that so the input stage to the power amp would be open circuit. I did get a little bit of hum and buzz from the unterminated input circuit, but not that loud random noise that got it sent to me, and I heard when I first powered the amp up.
I powered it on and off numerous times, letting it sit idle for awhile, and it was now behaving like a normal working SVT-CL. Checked it again this morning it having sat idle over the weekend, and powered it up with the new T/S plug so the power amp input stage would be unterminated. No problems. I had applied some Caig Deoxit to the jack contacts with a long Q-tip, and exercised the jack with T/S plug numerous times. before setting it aside last Friday.
So, I don't know what the cause of this scarry noise is, not being able to reproduce it thus far.
SVT-Classic-Audio-Schematic.pdf
Preamp PCB Schematics (51911h2_).pdf
Power Amplifier PCB Schematics (419xxh2).pdf
S1CSTACKJACK.pdf
Preamp Out-Pwramp In jack.pdf
Sure enough, LOUD Random Noise appeared, Master Volume was CCW, though that's ahead of the final preamp tube stage. Switched back to S/B, switched out of S/B, noise still there. I plugged in my shorting plug into the Power Amp Input jack, and that shut it up. Unplugged that, and the noise was still gone. Turned the Master Volume up and down, no contact noise at that stage. With the Master at Max CW, turned up the Volume pot and exercised it along with the tone controls, heard the usual residual noise (no input signal present). Plugged in the shorting plug into the Power Amp jack again, and exercised that jack, still no longer hearing this horrendous noise.
I dug out my one spare stacked Phone Jack for the Preamp Output/Power Amp Input jack assy to see what the normals looked like. These on my jack looked like a Rean style, the fixed blades of the Normals being straight up, and not at an angle that over time weakens and has to be tweaked upwards from the inside of the jack throat. Probing inside, felt like the CLIFF dual jack and not this Rean part that Neutrik sells these days, though only way to tell would be to remove the power amp chassis.
Using a new T/S plug, not wired, I inserted that so the input stage to the power amp would be open circuit. I did get a little bit of hum and buzz from the unterminated input circuit, but not that loud random noise that got it sent to me, and I heard when I first powered the amp up.
I powered it on and off numerous times, letting it sit idle for awhile, and it was now behaving like a normal working SVT-CL. Checked it again this morning it having sat idle over the weekend, and powered it up with the new T/S plug so the power amp input stage would be unterminated. No problems. I had applied some Caig Deoxit to the jack contacts with a long Q-tip, and exercised the jack with T/S plug numerous times. before setting it aside last Friday.
So, I don't know what the cause of this scarry noise is, not being able to reproduce it thus far.
SVT-Classic-Audio-Schematic.pdf
Preamp PCB Schematics (51911h2_).pdf
Power Amplifier PCB Schematics (419xxh2).pdf
S1CSTACKJACK.pdf
Preamp Out-Pwramp In jack.pdf