My new Music Man 410-65.

[Sea Chief]

30 years ago I drove a fair way t browse for a my 1st proper guitar amp. I was 19 & spotted a fendery looking older Musicman 210 for Ģ350 ( either a 65, or a 130 hd I cant recall ). Now I knew next to f-all about tube amps, but seeing blues dudes in my local pub with their peavy & h-h twin things which amazed me.. instinct told me try this one. Fell in love. Did everything I wanted, great tremolo, reverb, distortion, all sounding very decent & with that extra ' touchy feely thing too '. I saw by the "stand by" switch it was a tube amp, of somesort. Never heard of the name but that just added something to me. So.. went back next morning very 1st thing.. wasn't there. I was only one in shop the day before, so I knew someone heard my " demo" & snapped it up. Or maybe the owner didn't know quite how good it was/ often overooked etc & had it. Gutted.

Ive regretted this, like a pain if I thought on it " the one that got away " for 30 years! I mean the chances of finding one, over here, for Ģ350.. were nil. So Ive left it as a pain in back of my mind. A bit like a girl that got away who really floated your boat. Guitars? Never have quite the same allure to me/ get thru this one then that one.. all much the same' ish. Amps tho..

So my 50th comes up, I just sell a rubbish vox ac15 tbx, & have Ģ550. I look for a musicman. I find a 1976 410 for Ģ450. Eh? I can't quite believe it, at this price, being on Reverb/ listed for 2 years. Impossible. Most similar on ebay are min Ģ650 which was getting Ģ out of sight for me. Its in great nick. It has the extra 7025 tube. The quality.. I think slightly betters fender too. Omg.

So, after 30 years, I AT LAST have my Musicman ' back '.. the one that got away, ( & might have even bettered it with this one!). For my 50th (to myself). And Ģ30 to spare for new caps! How bloody happy am I!!

The other aspect this amp solves, is during this 30 years, Ive gone from amp to amp to amp, never satisfied as the distortion aspect hs never been possible ( without ear bleeding vol, or pounding tubes, or expensive attenuator "solutions" ; meaning I left distortion as an impossible hugely frustrating quest itself). This amp though.. however it does it ( a bit of magic, to me ) its distortion is absolutely fantastically useable too.

So my 30 year amp " journey".. even if it might not be your ultimate 66 fender super reverb pinnacle lustful amp.. is over. I'm so damn chuffed!

That is all. I just - had - to spiel it out. SC

[glebert]

Nice story, I am glad you got your amp. Sometimes you just have to treat yourself.

[Jazz P Bass]

Thanks for the post Sea Chief.

A warm story with a happy ending.

[Sea Chief]

Thanks chaps. Amazing how a boring black/ silver box can provide such fulfillment.

Does anyone know why, if its a solid state preamp, it can produce such decent distortion? I mean i dont suppose the two 6ca7 have anything to do with how it is created, & the 7025 is just a PI.. so it must be entirely SS made distortion. I dont find a pedal lurking about bolted inside anywhere, & nothing suggests 'additional distortion circuit' has been incorporated on the fairly sparsely populated pcb either.

Considering the countless avenues of ( universally hopeless ) distortion types Ive tried during my 30 year quest.. it seems absurd ive finally found my distortion, but, cant actually see where it comes from! I mean the knob that 'does it' doesn't say distortion on ( so.. maybe Im just imagining it then ?! ).

thanks, SC

[g1]

Nothing special about the circuit as far as overdrive/distortion characteristics. It's not the power amp (tubes), as you are playing at lower volumes with master set low. (edit: for this model it is the 12AX7 tube making distortion, see post #15)
And I don't think those LM307 metal can op-amps have any special magic, although you don't see them in many other amplifiers.

It's just that you have found an amp that distorts in a way that you like. Some owners don't like it and only like the clean sound. From what I remember, I thought it sounded pretty good (with ch.vol. up and master down) too.
But that's why we always go on about there being no right or wrong or 'best' circuit, just whatever sounds best to you.

[Sea Chief]

Nothing special about the circuit as far as overdrive/distortion characteristics. It's not the power amp (tubes), as you are playing at lower volumes with master set low.
And I don't think those LM307 metal can op-amps have any special magic, although you don't see them in many other amplifiers.

It's just that you have found an amp that distorts in a way that you like. Some owners don't like it and only like the clean sound. From what I remember, I thought it sounded pretty good (with ch.vol. up and master down) too.
But that's why we always go on about there being no right or wrong or 'best' circuit, just whatever sounds best to you.

To be honest g1 Im so cloth eared, or I havent the knowledge ( rather like a wine nerd can tell a good'un.. but an average jo cant really tell much difference to his Ģ5 bottle: IE the less knowledge makes some sense, perhaps ) to tell the difference between my distortion, & tube distortion. I think that - is - mostly testament to how good the amp's distortion aspect is designed on it (certainly by far the best ive heard in terms of vol/ master vol type of distortion on an amp.. by a huge margin).. less so my cloth ears, which can tell a tip top distortion say on a recording, at the drop of a hat.

But the q I was entertaining, is how is it created? Where does it eminate from, if I dont see an OD pedal surreptitiously planted under the chassis, nor any obvious distortion ' circuit' on the pcb?

[pdf64]

I recall that you were enjoying the preamp overdrive of a Laney VC15 a few years ago, did you go off it?

[glebert]

95% of the distortion that people like is solid state (in some way). Some very notable "tube" amps use op amps and diodes for distortion, and almost all distortion pedals do, so who cares how it was achieved, just that it is the sound you want.

[J M Fahey]

Does anyone know why, if its a solid state preamp, it can produce such decent distortion? I mean i dont suppose the two 6ca7 have anything to do with how it is created, & the 7025 is just a PI.. so it must be entirely SS made distortion. I dont find a pedal lurking about bolted inside anywhere, & nothing suggests 'additional distortion circuit' has been incorporated on the fairly sparsely populated pcb either

Music Man uses a smooth clipping circuit.
The last Op Amp before the Master Volume has a 2diode 2 transistor 3 resistor network in its NFB which gracefully bends peaks down without flat topping or harsh clipping.

Check IC6a NFB


When peak voltage reaches about 13V, transistors turn on and clamp it, but it is NOT as brutal as if 13V zeners were used there, by any means.

Scope it and post screen image, very rounded tops and bottoms are quite visible.

Personally nothing aginst rounded tops and bottoms, of course.

Itīs less fuzzy here, still around IC6

[Sea Chief]

I recall that you were enjoying the preamp overdrive of a Laney VC15 a few years ago, did you go off it?

Hi pdf. No i liked that quite alot in fact, the only other mp in my quest whose distortion was useable & decent.. just the tiny cheapy controls & nasty cabinet, with laney on, was so uninspiring! Good circuit design that, i thought though.

[Sea Chief]

J M Fahey hey thanks for this. Interesting, alas I can only decipher a bit.. but it's still useful, & I know - where - now, IC6, it is being done. I see on the schematic where IC6 is, & the two volume 100 k pots are.

Is the reason the " vibrato channel " volume pot is a " double job " ( looks like two pots stuck together ) have something to do with it? Is this a double being an older form of reverse audio pot? Im sure I used an RA pot on my deluxe reverb build, which was a single type.

I will look into oscilloscopes using my ipad then.. I think this was mentioned as a possibility, interestingly.

Thanks for your help, SC

[J M Fahey]

Youīre welcome.

It works basically this way, and AFAIK itīs a MM invention,others have used it later:



IC6 here is wired like an inverting Op Amp.

Positive input is grounded, negative one substracts currents fed into it, to stay at zero volts all the time.

So if you apply a positive voltage to R40 10k , positive current will flow into pin 6.
That "should" make pin 6 more posutive.

Op Amp does not like that , tries to keep pin 6 at Zero Volts, so it injects exact same value current but opposite sign (in this case negative) from pin 7 (output).

Fact is, it does so through 100k pot (assume itīs set to maximum gain).

Now exact same current will drop 10X the voltage across 100k than it does across 10k, so stage will have 10X gain, opposite polarity, thatīs why itīs calld an inverting gain stage.

So far so good, and if driven hard enough, output will slam against rails (+/- 15V) and produce flat top harsh clipping.

Now the mystery network added.

Suppose you have positive output.

Normally "nothing happens", transistors are turned OFF (they are simply not biased) and feedback/"gain" current passes only through 100k resistor.

Remember that at all times pin 6 stays at 0 Volts so "same as ground".

BUT some of that positive voltage appears at Q2 base, through the resistor chain R41 - R42 - R43, turning it ON , as soon as Base reaches some 0.6V, so some 13V end to end.

Now that itīs ON, some current passes through it lowering gain.

Itīs not an abrupt change but a very smooth one, which nicely rounds waveform tops, without squashing them, and I guess you like that lack of harshness.

Same happens on the negative half.

That Op Amp trick is often used to round triangle waveforms into quasi sinewaves.



and here to make it certain it never really clips.
Not bad.

[Helmholtz]

Are we sure this amp has the soft clipper cell?
AFAIR, earlier versions having the 7025 driver/PI didn't have it.
MV was after the first 7025 triode (gain stage).

[Jazz P Bass]

Thank you Juan!
That was a very concise description.
Good to have you on board!

[pdf64]

Are we sure this amp has the soft clipper cell?
AFAIR, earlier versions having the 7025 driver/PI didn't have it.
MV was after the first 7025 triode (gain stage).

Yes, Sea Chief linked to the 2275 schematics for his model, that early version will be using the 7025 common cathode triode as the clipping stage for the preamp.
At low master vol settings, the power amp will be operating open loop.
https://www.thetubestore.com/lib/the...-Schematic.pdf
Whatever, thanks for the walk through the solid state overdrive circuit, Juan!