Hello, I am making a preamp of a Marshall JCM800, but i have some questions , I was reading that the Marshall output transformers are smaller than they should and go into saturation to help distortion, I got some small audio transformers from 2.5k to 8 ohms,
these:
my idea is to make a 250v preamp pedal and use the transformer as if it were an output but with a 12ax7 and make it go into saturation so that the preamp has the sound of a jcm800 preamp with the saturation of the output transformer but without the power tubes, all in one pedal
My questions are, can I use it as a 12ax7 output transformer? How can I make this little transformer go into saturation? Does it really make a difference to have the transformer saturated?
these:
my idea is to make a 250v preamp pedal and use the transformer as if it were an output but with a 12ax7 and make it go into saturation so that the preamp has the sound of a jcm800 preamp with the saturation of the output transformer but without the power tubes, all in one pedal
My questions are, can I use it as a 12ax7 output transformer? How can I make this little transformer go into saturation? Does it really make a difference to have the transformer saturated?
Welcome to the Tubes / Valves threads.
I like your premise, but you need more data on the circuit and the transformer.
Then there is the issue of what it will sound like.
Perhaps the Instruments and Amps threads will have more knowledgeable responses on Guitar amplifiers and sounds.
The results of using that transformer and a 12AX7, depends on the transformer specifications.
Is it for AC only, or is it rated to work with some DC?
How much DC?
A 12AX7 does not have a lot of current.
But using any 2.5k Ohm load on a 12AX7 can produce lots of distortion even without any saturation of the transformer.
But that distortion may sound completely different than the distortion of lamination saturation.
You did not say if you will use the transformer as a voltage step-down, or just use the primary as a choke.
And that brings up another issue, what is the inductance of the primary?
The low frequency notes may roll off early, no low string notes.
Too many variables to know the possible outcome.
I like your premise, but you need more data on the circuit and the transformer.
Then there is the issue of what it will sound like.
Perhaps the Instruments and Amps threads will have more knowledgeable responses on Guitar amplifiers and sounds.
The results of using that transformer and a 12AX7, depends on the transformer specifications.
Is it for AC only, or is it rated to work with some DC?
How much DC?
A 12AX7 does not have a lot of current.
But using any 2.5k Ohm load on a 12AX7 can produce lots of distortion even without any saturation of the transformer.
But that distortion may sound completely different than the distortion of lamination saturation.
You did not say if you will use the transformer as a voltage step-down, or just use the primary as a choke.
And that brings up another issue, what is the inductance of the primary?
The low frequency notes may roll off early, no low string notes.
Too many variables to know the possible outcome.
Transformer saturation depends principally on the core cross section, the ac voltage applied and the frequency. Small cores saturate at lower voltages so the one you have will probably saturate at less then 10V rms, maybe even as little as 3V rms. If you are going to load the secondary with 8 ohms then you need to be able to drive 10V rms into 2K5 which you will not do with a 12AX7. I suggest you try an ECC88/6DJ8 configured as an SRPP with 5 to 6mA quiescent. This will easily drive 10V rms into 2K5 and saturate your little transformer.
Cheers
Ian
Cheers
Ian
Not really, Marshall always used proper sized transformers, well designed and made by their suppliers: Dagnall and Drake.
Fender too, often using high quality Schumacher iron.
Only exception might be in very early late 40´s amps, or their single ended student amplifier Champ, the smallest cheapest one, not the average one.
And transformer saturation as a "sound" component is sort of a Myth.
Transformers do saturate, but at lowest frequencies as said above, but the saturation we love comes from power tube saturation, a very different thing.
And which happens at any frequency, as soon as tubes get saturated and chop signal tops.
Too small OTs simply chop Bass frequencies, big time.
As a side note, 2k5 is WAY too low for 12AX7 (hey, it´s too low for 6V6 or 6BQ5), typical 12AX7 transformers need from 25k to 50k and that for parallel sections to double the current.
Search for Fender reverb transformers to have an idea of what you´ll need.
And even so, they are designed for parallel 12AT7, which handle lots more current than 12AX7.
And agree this should be moved to Instruments and Amps section.
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I agree transformer saturation as a'sound' is a myth but transformer distortion as a 'sound' is discussed endlessly on the pro audio forums. There are plenty of products and projects that claim to impart that certain something only transformers bring to table. As a rule most of them exploit the BH curve shape but stay well away from true saturation. Of course the distortion they produce mostly odd harmonics (third and above) in contrast to the mainly second harmonic produced by audiophile SE amps.
Cheers
Ian
Cheers
Ian
I highly doubt that your little coils are gapped, they will saturate with DC. To avoid this, cap couple it as Icsaszar suggests.