Weird awful feedback

[Helmholtz]

How much do you have to roll back volume or tone to stop it?

What is normal feedback?

Don't you have a possibility to try a buffer or something like a tubescreamer or even a buffered tuner pedal?

(A buffer is an active electronic circuit the provides low output impedance wihout changing the signal.)

[daniel_pt]

How much do you have to roll back volume or tone to stop it?

What is normal feedback?

Don't you have a possibility to try a buffer or something like a tubescreamer or even a buffered tuner pedal?

(A buffer is an active electronic circuit the provides low output impedance wihout changing the signal.)

I don't use pedals... don't like the step dance. I plug the guitars directly into the amp and that's it!

But i can try to use the HeadRush MX5 outof the fx loop and use it between the guitar and the amp.

I recorded with the iPhone a small sound sample of the difference between neck and bridge pickups.

It starts with the bridge, then i change to the neck and finish with bridge again.



EDIT: with MX5 between the guitar and the amp, no squealing feedback...

[Helmholtz]

EDIT: with MX5 between the guitar and the amp, no squealing feedback...

That confirms my source impedance theory.
A stand-alone buffer doesn't need to have a switch and would surely help.
Easy to build one yourself.

It seems clear that the amp is close to the edge of self-oscillation, especially as it oscillates with open input.
That's certainly due to extreme gain and probably non-optimal layout.

Did you try a different guiar cable? Some cables don't have perfect shielding.
Do the preamp tubes have shields?
Is the speaker chassis grounded?

[daniel_pt]

That confirms my source impedance theory.
A stand-alone buffer doesn't need to have a switch and would surely help.
Easy to build one yourself.

It seems clear that the amp is close to the edge of self-oscillation, especially as it oscillates with open input.
That's certainly due to extreme gain and probably non-optimal layout.

Did you try a different guiar cable? Some cables don't have perfect shielding.
Do the preamp tubes have shields?
Is the speaker chassis grounded?

Tried different cables and different guitars... only happens with this one.
pre-amp tubes are shield.
speakers are inside the cabinet and i didn't check them in a long while... i might try a different cable for speakers thou...

Btw, i have the gain know at 12... i could go a lot higher, but 12 is already enough

[Helmholtz]

Buffer (= impedance converter) is my best advice

[daniel_pt]

Thank you Helmholtz
I'll dig about that.

One last curiosity is that I have one other guitar also with passive Seymour Duncans and this annoying feedback doesn't occur with the exact same amplifier settings!

[Helmholtz]

One last curiosity is that I have one other guitar also with passive Seymour Duncans and this annoying feedback doesn't occur with the exact same amplifier settings!

Does that guitar also have the "Jazz", as different PU types have different resonant frequencies and impedances?

[daniel_pt]

Does that guitar also have the "Jazz", as different PU types have different resonant frequencies and impedances?

Indeed... in the other guitar, I have a pair of Seymours SH-6 and they have am higher impedance than the SH-2/Jazz...
So, I guess the "mystery" is solved...

SH-2

Jazz Model

Four Con.

Neck: 7.72 k Bridge: 7.9 k

Neck: 8 KHz Bridge: 7 KHz

Alnico V Bar

SH-6

Duncan Distortion

Four Con.

Neck: 12.7 k Bridge: 16.6 k

Neck: 6.5 KHz Bridge: 5.5 KHz

Ceramic Bar

I just don't recall having this issue in the past. I used to play with this guitar as I just play any other...

[Helmholtz]

Indeed... in the other guitar, I have a pair of Seymours SH-6 and they have am higher impedance than the SH-2/Jazz...

The numbers look like DC resistance (so not kHz but k Ohm).
PU impedance at the resonant peak is much higher and not related to DCR.

I just don't recall having this issue in the past. I used to play with this guitar as I just play any other...

Well, only you can know if something changed with the amp.

It might make sense to check the input tube for microphony.

[Chuck H]

Tried different cables...

What cables did you try? Were they different units of the same cable because it's the cables you use or were they actually different types of cables? Length?

[daniel_pt]

The numbers look like DC resistance (so not kHz but k Ohm).
PU impedance at the resonant peak is much higher and not related to DCR.




Well, only you can know if something changed with the amp.

It might make sense to check the input tube for microphony.

I used the pencil poking method already, but no sound came out from the speakers...

It can be something with the amplifier indeed, i just have no idea of what!
i already troubleshoot enough stuff with my work and tbh i have no patience for troubleshooting this ahah

I think I'll just let it die of age

[daniel_pt]

What cables did you try? Were they different units of the same cable because it's the cables you use or were they actually different types of cables? Length?

Same brand, different size...

I even used my longest one to hide behind doors and it still feedbacks like crazy *sigh*

[Chuck H]

Same brand, different size...

I even used my longest one to hide behind doors and it still feedbacks like crazy *sigh*

Shucks. I was hoping a longer cable might help since it lowers the resonant frequency and a high resonant frequency is an aspect that stands out for the problematic pickup.

FWIW Helmholtz suggestion of a buffer should be fine since it works. I'm a plug and play guy myself, like you, but I've never heard any note worthy change in tone when using a buffer.