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Output Transformer Primary Impedance Affect on Tone
I was reading TUT4 (I think) that details various transformer set combinations for 50W amps.  With that section was statement about how some builders/players favor the sound of high impedance primaries over lower ones and visa versa.  I've experimented with different primary impedances 5E3 designs but I'm not sure if the difference in impedance was great enough to experience a big difference and I didn't do it with two amp sitting side by side. To my ears the higher impedance transformer seemed to sound little softer and warmer but that could have been my imagination. 

What has been other people's experiences? Also given the same supply voltage what effect should we expect between say a higher and lower impedance primary as far as tone? 

Wouldnt the high impedance make less power if B+ is the same? maybe that gets you to clipping sooner too.
(12-07-2022, 02:27 AM)nauta Wrote: Hey
Wouldnt the high impedance make less power if B+ is the same? maybe that gets you to clipping sooner too.

Different impedances of primary have different suggested Va (B+) values but most are lower than the supply voltages that most guitar amps have. My question is that given that the supply voltages are adequate for full power for either transformer what is the possible tone difference?
Hi Guys

The differences between OTs are many. If you try to narrow them down by taking samples from a single product line by a single manufacturer, even then you may not be making a "scientific" comparison, even if the same person designed every unit in the line. For example, Hammond has many OTs in the 1650-series, but these were designed by different engineers over a period of time, and then modified later by different engineers. Different techniques were used on different models.

The narrowing to given product line DOES give you a comparison of what is available, which in the end is what matters.

Because the tube has a nominally-set transconductance, the amount of current it wants to push through the OT is set for a given grid-1 voltage change given Vs and Va are stable. Changing the OT impedance means the effective voltage gain of the tube is different with each OT sample. Whatever fixed PA circuit you use, if it has feedback or not, the impact on how hard the circuit is driven or how it tries to accommodate the changed load varies.

Each OT design has its own parasitic elements and these impart distortions to the signal trying to pass through it. Combine this with the circuit adaptations above and you have a very unpredictable situation tone-wise. This means you cannot make a general statement, such as "going to high-z adds harmonics", which would be the intuitive notion. Higher turns ratios DO introduce stronger parasitic impacts in general, but it cannot be assumed to be a guarantee of tonal shift.

I know from talking with many techs and builders that for a given build where they have tried a range of primary values for OTs, that they can hear a difference and choose something specific for the build. This may sacrifice power, but amps are designed for tone. You may find the impact is greater in simpler circuits, particularly where other distortion mechanisms have been dealt with, particularly grounding and wiring.

You really have to try it for yourself.
Thanks for the reply! It's helpful. I have some idea about how different sectionalization schemes and grades of laminations affect the sound from a book on transformer design I read. Most manufacturers don't publish info about either the lamination types used or how a transformer is sectionalized which goes to your point about the Hammond 1650 series. My guess would be that various "clone" transformers are even less consistent.

There are a lot of factors involved so I can see your point about how unpredictable it may be.

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