Music Man 410 trem prob.

[Sea Chief]

Hi chaps,

Ive just bought a sweet vintage mm 410-65, sounds gorgeous.. but for the tremolo. Its doing a sort of double-pulse, instead of a strong single pulse. Da-da... Da-da... Da-da... etc ( a strong usual pulse followed immediately by a lesser sort of ghost pulse). Ruining the effect totally.

Any ideas? Do these use a roach like fenders i wonder.. certainly not tube driven being ss preamp stage, i think. It does have one 7025 PI tube, but i dont think related to tremolo circuit?

schematic here (my chassis number is 2275-65.. but i cannot find the PI 7025 tube on this schematic, oddly):

https://www.thetubestore.com/lib/the...-Schematic.pdf

Many thanks if you could help, SC

[Jon Snell]

Phase Invertor circled.

For the tremelo check around the JFet T1. The circuit uses a transitorized Colpitts oscilator that feeds the JFET with the oscillations and modulates the drive to IC7 pin 3 via TR1.
If it sounds odd, check the linearity of the waveform with your oscilloscope.

[Sea Chief]

Phase Invertor circled.

For the tremelo check around the JFet T1. The circuit uses a transitorized Colpitts oscilator that feeds the JFET with the oscillations and modulates the drive to IC7 pin 3 via TR1.
If it sounds odd, check the linearity of the waveform with your oscilloscope.

Ob crumbs Hi Jon thanks for reply.. but I don't have an oscilloscope. Id bet its this linearity aspect being on the c*ck though..

Would the idea of just replacing this Colpitts oscillator be viable? Any idea of complexity, & cost in parts for me to do? ( ie instead of sending amp off to a tech).

Aprreciated, SC

[Sea Chief]

Aha from your schematic area highlighted, very kindly thank you Jon, I can finally see the 7025 mentioned!

On the right track then, with the right schematic for my amp. Thx

[J M Fahey]

You can use your computer, an App and a signal attenuator as a Scope.
I suggest one, there´s many online, search for "Software Scope" .

Read this thread, it´s well explained there.

https://www.thegearpage.net/board/in...-ones.1620645/

Attenuator schematic is missing (image site erased it) but I´ll add it later.

[Leo_Gnardo]

SC: "sounds gorgeous.. but for the tremolo. Its doing a sort of double-pulse, instead of a strong single pulse. Da-da... Da-da... Da-da... etc ( a strong usual pulse followed immediately by a lesser sort of ghost pulse"

IIRC there's a trim pot (pre set for Brits) to adjust the balance of the trem LFO signal. Important to identify the correct pot so as not to inadvertently change bias instead. They're both blue discs maybe 15 mm diameter.

Somebody let SC know. I'm on his ignore list. Small wonder because as we all know he likes to ignore good advice. And I got tired of delivering it to him. But I'll make a brief exception just for today because I'm in an inexplicable good mood. Don't worry that will fade soon I'm sure. Good luck campers!

[g1]

Sea Chief , there should be an internal trim pot for the tremolo mounted on the circuit board, as mentioned by Leo_Gnardo above (you would be well advised to remove him from your ignore list so as not to miss out on pro tips).

According to the service bulletin the trim pot is "second to the left (looking from the front)". Mark it's setting before you touch it so you can set it back to the way it was if need be. Try tweaking it a little bit either way and see if it makes any difference.
If any doubt about which trimmer, post a picture of the circuit board.

[52 Bill]

Before adjusting the trim pot, try turning down the intensity control. Usually it will bring the effect back down to typical trem sounds.

[Sea Chief]

Sea Chief , there should be an internal trim pot for the tremolo mounted on the circuit board, as mentioned by Leo_Gnardo above (you would be well advised to remove him from your ignore list so as not to miss out on pro tips).

According to the service bulletin the trim pot is "second to the left (looking from the front)". Mark it's setting before you touch it so you can set it back to the way it was if need be. Try tweaking it a little bit either way and see if it makes any difference.
If any doubt about which trimmer, post a picture of the circuit board.

Hi g1.. a trim pot! Music ( man ) to my ears! Woohoo!

Yes I thought i had undone all from my ignore list, must have missed one: thanks to Leo gnardo for this info/ will of course undo from list.

Fantastic.. will delve into it pm today. Im gonna do a general thread on this amp/ these mm's.. im a real fan.

thx alot chaps, SC

[Sea Chief]

Before adjusting the trim pot, try turning down the intensity control. Usually it will bring the effect back down to typical trem sounds.

Great thanks Bill.. sounds like you've been under the hood on one of these mm's.

[loudthud]

This thread is old, but the info is good : https://music-electronics-forum.com/...issues?t=12356

[J M Fahey]

Indeed.

I love it when I see threads 10-15years old where Forum members were *already* so accurate and well informed

[Sea Chief]

This thread is old, but the info is good : https://music-electronics-forum.com/...issues?t=12356

Thanks for this, it gives alot about fets & 2N transistors.. but not-so much on the trimpot?

Is the idea in my case, to badically just twiddle the trimpot whilst tremolo on, & hopefully tweak it until it settles into a normal trem effect? Thx SC

[Sea Chief]

Are these main caps here showing signs of 'leaking' ? Ie some beige gubbins has popped through the top, same on other one. Thanks SC

[Sea Chief]

Here's my internals.. which trimpot would it be to tweak? Thanks SC