MAGNATONE M10 - 9-11 KHz Squeak when pushed into distortion
Hello all,
I hope everybody is doing alright
it's been a while since I've worked on any of my amps but I thought it was about time to get more serious about that MAGNATONE M10 I bought a couple of years ago and with which you guys helped me big time (as you always do) at the time of choosing the right POWER TRANSFORMER and REVERB TANK
i've been hearing lately some squeaks around 9-11 KHz when pushing the amp into a soft distortion (no pedals connected to the amp)
SOUND SAMPLE attached [Magnatone M10 Squeak.mp3]: has 3 parts. Flat EQ, +6 dB at the annoying frequencies, -10 dB at those frequencies (what i feel it should sound like)
I looked for mechanical sources to this squeak and could not find anything. Sweeped the SPKR and it seems to be fine (i might need to try taking the speaker out of the enclosure or even try a different speaker).
Next step was to hook a scope and see what's happening.
I fed the amp with a 100 mV RMS 400 Hz SINE
Hooked a 16 Ohm dummy load to the speaker output
Hooked the scope to the speaker output
(scope settings 0.5 V/div and 0.5 ms/div)
this is channel 1 (which includes the VIBRATO and REVERB, disengaged at this point) with the volume at 50%
there's this vertical shifting (or oscillation) which (i tested) is not affected by the VIBRATO speed (my initial thought was that the vibrato signal might be leaking even with the vibrato volume all the way down, but then thought this should be more of a HORIZONTAL shifting as this is a true vibrato and not a TREMOLO).
this vertical shifting occurs at whatever volume.
in that case if i engage the vibrato the shifting does look different (there is an X shifting added on top of the Y axis one). VIDEO 2
My understanding up to this point isthat the Y shifting is not generated by the VIBRATO circuit (i might be wrong)
looking for something on the scope that shows what we can hear on the sample file I pushed the amp's volume up to 75% until I saw the first "shoulder", with a second one showing up near full volume
Scope settings 1 V/div / 0.5 ms/div
CHANNEL 2 (no vibrato or reverb capabilities on this channel) shows the same Y axis shifting
My conclusions so far (apart from being clueless about what the scope is showing) are:
- there is a vertical shifting at the output that is not an amplitude change, hence i do not hear a volume change (a tremolo effect) when i am playing the guitar. but it's deffinitely something strange.
- channel 2 does not show the "shoulders" that channel 1 does but i can hear the same squeal coming out too.
I'd love to hear your thoughts / advice
thanks in advance!
PS: added schematic
https://www.magnatoneamps.com/schema...natone_M10.pdf
Hello all,
I hope everybody is doing alright
it's been a while since I've worked on any of my amps but I thought it was about time to get more serious about that MAGNATONE M10 I bought a couple of years ago and with which you guys helped me big time (as you always do) at the time of choosing the right POWER TRANSFORMER and REVERB TANK
i've been hearing lately some squeaks around 9-11 KHz when pushing the amp into a soft distortion (no pedals connected to the amp)
SOUND SAMPLE attached [Magnatone M10 Squeak.mp3]: has 3 parts. Flat EQ, +6 dB at the annoying frequencies, -10 dB at those frequencies (what i feel it should sound like)
I looked for mechanical sources to this squeak and could not find anything. Sweeped the SPKR and it seems to be fine (i might need to try taking the speaker out of the enclosure or even try a different speaker).
Next step was to hook a scope and see what's happening.
I fed the amp with a 100 mV RMS 400 Hz SINE
Hooked a 16 Ohm dummy load to the speaker output
Hooked the scope to the speaker output
(scope settings 0.5 V/div and 0.5 ms/div)
this is channel 1 (which includes the VIBRATO and REVERB, disengaged at this point) with the volume at 50%
there's this vertical shifting (or oscillation) which (i tested) is not affected by the VIBRATO speed (my initial thought was that the vibrato signal might be leaking even with the vibrato volume all the way down, but then thought this should be more of a HORIZONTAL shifting as this is a true vibrato and not a TREMOLO).
this vertical shifting occurs at whatever volume.
in that case if i engage the vibrato the shifting does look different (there is an X shifting added on top of the Y axis one). VIDEO 2
My understanding up to this point isthat the Y shifting is not generated by the VIBRATO circuit (i might be wrong)
looking for something on the scope that shows what we can hear on the sample file I pushed the amp's volume up to 75% until I saw the first "shoulder", with a second one showing up near full volume
Scope settings 1 V/div / 0.5 ms/div
CHANNEL 2 (no vibrato or reverb capabilities on this channel) shows the same Y axis shifting
My conclusions so far (apart from being clueless about what the scope is showing) are:
- there is a vertical shifting at the output that is not an amplitude change, hence i do not hear a volume change (a tremolo effect) when i am playing the guitar. but it's deffinitely something strange.
- channel 2 does not show the "shoulders" that channel 1 does but i can hear the same squeal coming out too.
I'd love to hear your thoughts / advice
thanks in advance!
PS: added schematic
https://www.magnatoneamps.com/schema...natone_M10.pdf
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