Can you hear the difference?

[Chuck H]

Also, all system run by software, When we outsource programming to China, they learn and they gain experience in designing software of weapons, missiles and all the military weapons.

Ha ha!!! China isn't going to threaten us or bomb us. They're going to collect on our debt and own us!

This isn't to mention that outsourcing programming isn't half as informative (or detrimental to the US) as outsourcing the manufacturing of all our goods. China played this chess move two decades ago to posture themselves as the world leader in manufacturing. They simply can't be competed with and US and UK corporations are lined up to take advantage of the opportunity to line their pockets in direct proportion to the economic damage they do. China looked twenty years ahead. The people that are actually in charge in the US can't see past the next fiscal quarter. Guess who's going to win!?! And, to be fair, we shouldn't search for fault or some representation of evil in the winner just because we played badly and lost.

JM2C on that. (and I suppose this branch of the topic would be better moved to the "soap box")

[Alan0354]

Don't move this thread, I am more interested in the OT, forget politics.

I received the Classic Tone Marshall Plexi 3.6K OT. I am at the process of ripping out the old preamp in the Bassman and put in the new circuit for the Marshall build. I am going to experiment until I get the sound before building the circuit into the Marshall JCM900 Dual Reverb combo.

I have the Classic Tone Vibrolux OT in the Bassman and using 6V6 tubes. When I tested the new preamp, I am going to find a way to fast switching between the Vibrolux and the Marshall OT and set what is the difference in the sound. That's would be very interesting.

[J M Fahey]

I thought people have secret formula of scattered winding of OT like in pickups!!!

Pickups are a very important part of a musical instrument.
Given the *huge* inductance , byproduct of trying to maximize output so zillion turns of very fine wire, combined with relatively high self capacitance, plus interaction with guitar cables and amp input impedance, means that most have a very audible resonant peak smack within the audible range, a few KHz.
That which would be absolutely unacceptable even in the cheapest OT, is a desirable trait in the pickup because that gives it a recognizable "voice".
Although scatter winding is technically a poor way to do things (except in solenoids and similar coils where "sound" does not matter) it's a valid option in a guitar pickup, so it's acceptable and many have their own "secret sauce".
In the particular case of Fender pickups they stated that although even in the beginning precision winding machines were available, they were way too expensive, so they chose to use cheap pedal rheostat controlled sewing machine motors, coupled to the actual winding spindle with thin rubber bands so as to smooth torque transmission and act as "mechanical fuses" if something went wrong, and scatter wind with hand guided wire, as random as can be.
But it was part of the Fender sound.

An OT with a peak within the audio band is absolutely unacceptable.
Just for kicks and to know what would really happen, I once scatter wound a Fender type, 2 x 6L6 50W OT.

Problems:
1) it had a more than 6 dB peak around 8 KHz
2) distortion was buzzy, although some headbangers actually liked it (go figure)
3) the big problem that the unexpected or exaggerated phase shift at resonance made it quite unstable.
Connected one way it oscillated like an alarm siren, so that was the official wrong phase ... BUT ... connected the other way, it plain squealed at "mosquito frequencies" and lowering NFB a little it still showed on the scope a waveform where part of it ringed: unstable.

I couldn't use more than 6 or 8 dB NFB.

The solution was to apply a "fixed presence" circuit, which applied a little more NFB at most frequencies but removed it at higher ones.

I had that amp on a bare chassis in the shop and most tried it, out of curiosity.

We have an old Gaucho popular saying: "para cada botón existe un ojal" , literally meaning :"for every button, there exists a matching buttonhole *somewhere*" and sure enough, a guy LOVED it and bought it.

But it's not the right way to do it.

So you mean all the good OT are wound layer after layer like the picture? then what is the fuzz about different brands.....particularly MM that cost two to three times more?

Yes.
And transformers may be made barely acceptable, good or very good, like everything else.
As of MM iron, we don't have them here, but from what I hear, they are well made in general, and a few models are oversized.
3X the average price?
Well, that's a classic business decision, if they can sell at those prices, fine with me.
I recognize they make some models who nobody else does and in this market where now and then an old unobtainable amp needs repair or upgrade that's fine.

Hope they make good money, they've worked hard for that.

BTW, what do the hifi OT that are different from OT of guitar amp. I know they have the screen grid tap, but is there any secret in the winding pattern? I don't know anything about audio OT.

Designing an OT is a compromise.

Few turns, not enough inductance (in parallel with load), no bass. Period.

Many turns, good bass, but high capacitance, combined with high "losses/parasite inductance" meaning inductance which is not properly coupled to the other side and lies in series with load: kills highs.

To boot, both combine for a resonant peak, which may lie just above 20 KHz, not that easy to hear ... but which complicates very necessary NFB.

The answer to both high capacitance and losses inductance is to *split* windings in sections, which is very annoying and time wasting, it takes time to reset winding machine, choose another spool, etc.

As in: I wind OT , both for self use and for repairs so I have a small notebook with the "formula" of many.

Even "cheap" despised JCM 900 original OT is:
half primary (thin wire) / 0 to 4 0hms secondary (thick, different advance screw and gears) / quarter primary (thin again) / 4-8 and 8-16 secondary windings (thick) / quarter primary (thin).

As you see, machine has to be reset, mid winding, 4 times.
An Industrial Engineer hated thing.

Hi fi transformers of the highest quality may have windings split up to 20 times !!!!!!!!!!!

Of course, many are flat up to 100 KHz
While at the same time they reach down to 30 Hz and below.

[J M Fahey]

Some examples:

1) "cheap" Hi Fi , "good" guitar transformer,split in 5:


2) good Hi Fi, increibly good guitar OT, split in 7:


3) you-will-never-see-it-in-a-guitar-amp audiophile OT split in 20 sections:

It includes 2 cathode NFB windings like Marantz and Mc Intosh used in some top models.

EDIT: see that the last example does not just have "4 ohms" and "8 ohms" taps but multiple taps, brought out to tagboards, which can be wired for different desired impedances, even real weird ones.
Primaries also go to complex tagboards.

[Alan0354]

Hey Juan,

Thanks for the detail information. You really shed light on the limitation of scattered winding. Yes, the worst thing for NFB is the unwanted poles and zeros that cause phase shift. But how about running without NFB? That should fix the instability problem. But still it might not sound good having peaks in the OT.

Now I see, so the main difference between low cost and high end OT is the number of sections, but within the section, it is still wound left to right and right to left with paper in between. Dividing into more sections can increase inductance ( better low end) without too much increase in inter winding capacitance ( better for high end).

Thanks.

[stokes]

I dont think its fair or even reasonable to try to compare OT's,or any tube amp lstening on computer speakers.I think in order to fully judge a tube amps "tone" you have to actually have the guitar in your hands to also get the "feel",which is half the formula of good "tone"

[Alan0354]

Of cause the ultimate test is to play and listen real life. BUT, if there is a huge difference, you can hear it no matter it's through a recording......hell, you can hear it in a hand held radio with 3" speaker. Point is, they are all close enough. If you have to listen over again to judge, it's close. It's all about taste more than real quality.

I can say, the difference is so so much smaller than comparing different speakers. With speakers, there is no if and buts, you hear a distinct difference. For OT clips here, I am sure you can make do with any of these by a little tweak.

I really understand what Juan said about you cannot tweak a resonance peak and other tricks with the OT that you can do with pickups and speakers. Your hands is really tied on this....Which implies the difference is not going to be very distinct. I am guessing that the difference is like different brand of tubes. Yes, there is a difference, but you can make do.

[Alan0354]

I opened the Classic Tone Marshall OT and see how it's wound. I think it's split into 4 sections. Here are a few pictures:

A) Primary
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B) Secondary
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See whether you can make sense out of it.

[J M Fahey]

Canīt really see small detail which requires very good light and a jewellerīs loupe (no kidding) , even less through the insulating translucent mylar tape , but the main details are visible anyway.

Real "paper" insulation, old style construction, of course donīt know steel composition and heat treatment but looks very clean cut and without burrs, which indicates good steel.

Anything else, only unwinding it, counting turns, measuring diameters, but of course itīs unnecessary unless you want to start making them (ahem!) .

In a nutshell, looks good, well made.

FWIW Iīll post a couple pictures:

1) A nineties JCM900 OT.
Made by Drake, you can see the modern plastic bobbin and all wires are brought out to tags:

Funny thing is that people way back then used to hate JCM900 and love (reedition) Plexis and JCM800 ... all 3 used the same OT (duh !!!! , thatīs what Marshall had available )

2) a Mesa Boogie Triple Rectifier OT (really pulled from a "200W" 6 x 6L6 Bass amp but itīs the same, itīs larger than the Dual Rectifier one).
Classic construction, paper insulation, even same thin wood wedge inserted on a side to prevent coil movement:


3) both together for size comparison, by an original early 80's Twin Reverb PT.
Wonder why people complain Twins are heavy


Sorry about the mess, the cleaning lady arrived late that day

[Alan0354]

Ha ha, I thought my room is bad!!!

I was just wondering what is so bad about plastic bobbin in you do layer by layer with paper in between like the JCM900. I thought I read somewhere that the JCM900 OT is different from the plexi. I could be wrong, but I thought my 74 Plexi had an OT that stood up, not lying down. The plastic bobbin in your picture cannot by in the bell housing that can stand up.

Is your JCM900 OT a 50W. My JCM900 Dual Reverb 100W OT looks huge. Do you think even the 100W OT is the same as the Plexi 100W? It is laying down though.

Also, in the pictures, you can see spacer between the core and the paper bobbin. In another word, the extra thickness of the plastic bobbin should not matter.

I am very curious to open the Classic Tone Vibrolux OT when I swap the Marshall one in.

[Chuck H]

There's nothing "wrong" with plastic bobbins, per se'. It's the manufacturing process associated with the plastic bobbin transformers that's typically lacking. So... Plastic as a construction and insulation material isn't bad. The plastic bobbins are generally used as a uniform starting template for quick and dirty manufacturing. Often straight wound or with very few layers. Often the plastic is thicker for stability on the machines and that makes a difference too. The plastic itself doesn't do anything bad to a transformers performance. Conversely, paper, as a construction material, doesn't do anything positive for transformer performance. But... The materials are still indicative of construction method, spacing and other tolerances. It's easier to know you're PROBABLY getting a better product if it's made the "old" way (paper) rather than the "new" way (plastic). It's an erroneous association being applied to the materials themselves by the general public, as promoted by the "boutique" profiteers.

I think Hammond uses plastic bobbins on many of their products that are known to sound good. They are one of the old guard transformer manufacturers that has modernized to stay competitive while maintaining a strong mission standard. Plastic is not a detriment in their product. Most transformers with plastic bobbins are indeed cheap crap though.

So disregard "plastic" as a moniker for "crap" and pay more attention to performance specs, customer review and manufacturer reputation (and perhaps longevity).

[Alan0354]

Just a FYI, I took out the original OT from the Marshall Dual Reverb. I notice it's a two separate primary. BUT the primary is not winding in single layer, then separated by paper before winding back like the Classic Tone OT. It is plastic bobbin and the primary is just continuous winding on top of each other. What I try to say is each of the section of the primary is a thick layer of winding on top of each other. So it is cheaper made......and this is the original Marshall OT.

[J M Fahey]

So it is cheaper made......and this is the original Marshall OT.

I told you so

To be more precise: It's the JCM900 Dual Reverb OT .

They used quite different 100W`(and 50W) OT designs along the last 50 years .

You can't look at one and say : "oh !!!`now I know what they are" because you have just one sample.

FWIW `they once used big expensive very high quality Partridge transformers ... what Hiwatt and Orange used customarily.

Marshall had been sent 2 or 5 samples ... he used them but never made an order.

I wonder who's the lucky guy who got them.