Hi all, just wanted to post my findings...
Quote from wiki to begin
"Tube instrument amplifiers are often equipped with lower-grade transformers and simpler power regulation circuits than those of hi-fi amplifiers."
Based on this, I got my (old, but still quite nice) amp, and put a mains transformer across the output (used one of the 12V legs) and put the speaker across the other 12V leg. I mean, you can't get much lower grade than a cheap mains transformer, right?
I played through it for a while, and I really like the sound, so I thought it might be worth letting you guys know, so you can (if you so wish) give it a try.
Dad mentioned that, a long time ago, there were discussions about the differences between tube and SS amps, and one person pointed out that it's only the transformer that adds much difference.
I don't have an opinion of this theory, but, after trying it with my amp, it seems to have some merit.
I've probably gone a little OT, so, anyway...
I know most of you will have a mains transformer lying around somewhere, so give it a try. You'll be as surprised as I was.
Chris
Quote from wiki to begin
"Tube instrument amplifiers are often equipped with lower-grade transformers and simpler power regulation circuits than those of hi-fi amplifiers."
Based on this, I got my (old, but still quite nice) amp, and put a mains transformer across the output (used one of the 12V legs) and put the speaker across the other 12V leg. I mean, you can't get much lower grade than a cheap mains transformer, right?
I played through it for a while, and I really like the sound, so I thought it might be worth letting you guys know, so you can (if you so wish) give it a try.
Dad mentioned that, a long time ago, there were discussions about the differences between tube and SS amps, and one person pointed out that it's only the transformer that adds much difference.
I don't have an opinion of this theory, but, after trying it with my amp, it seems to have some merit.
I've probably gone a little OT, so, anyway...
I know most of you will have a mains transformer lying around somewhere, so give it a try. You'll be as surprised as I was.
Chris
You might like the sound, but it is hard to argue that the quality and clarity of the sound is improved. The magnetic core of an iron transformer does not increase in a linear fashion with the input current in the primary. An elementary physics experiment in electricity and magnetism demonstrates that.
I was a little surprised more people aren't doing so.
The sound it gives isn't really distorted or anything, but it sounds different. Not unclean, but certainly more flowy (I'm not making much sense, am I?)
Sounded good when I plugged a distortion effects pedal in.
I just wanted to let you guys know, so someone else could give it a go.
The sound it gives isn't really distorted or anything, but it sounds different. Not unclean, but certainly more flowy (I'm not making much sense, am I?)
Sounded good when I plugged a distortion effects pedal in.
I just wanted to let you guys know, so someone else could give it a go.
Hello Chris661,
I actually have done this before, and somehow, I think that even I was not the first one, even given my advanced intelligence. As mjf pointed out, McIntosh id use output transformers in some of their amplifiers. Anyway, my goal was more to build a push-pull MOSFET version of a typical tube amplifier. So the source of each mosfet went to one side of a center-tap transformer (also a step down transformer, like you used) and the output went to a little speaker. The distortion I got (OK, I was using an op-amp front-end to overdrive the MOSFETs) was not too shabby either, but all in all it failed to really produce a nice, "not-so-buzzy" tone.
Actually the earliest solid-state power amplifiers had to use transformers. I don't know if it was because the current limitation of transistors at the time was very low or because of impedance mismatch, but I've seem many an amp schematic with an output tranny, although most of those schematics, if not all, were Class-A topology.
Anyhow, an interesting experiment.
I actually have done this before, and somehow, I think that even I was not the first one, even given my advanced intelligence. As mjf pointed out, McIntosh id use output transformers in some of their amplifiers. Anyway, my goal was more to build a push-pull MOSFET version of a typical tube amplifier. So the source of each mosfet went to one side of a center-tap transformer (also a step down transformer, like you used) and the output went to a little speaker. The distortion I got (OK, I was using an op-amp front-end to overdrive the MOSFETs) was not too shabby either, but all in all it failed to really produce a nice, "not-so-buzzy" tone.
Actually the earliest solid-state power amplifiers had to use transformers. I don't know if it was because the current limitation of transistors at the time was very low or because of impedance mismatch, but I've seem many an amp schematic with an output tranny, although most of those schematics, if not all, were Class-A topology.
Anyhow, an interesting experiment.
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Certainly.
The amp I'm using is a class AB thing, designed to be clean, with bass, mid and treble controls.
As I said - it doesn't give a huge load of distortion, just makes things sound smoother. The SS harshness has gone (it's a late 70s amp), replaced with something nicer.
As stated above, adding the transformer introduces new and interesting non-linearities (checked this using a scope, set to sum, connected to before and after the transformer) - more difference at the lower frequency strings.
I didn't want to experiment on my little Fender amp, so I bought something faulty off ebay - that way, I don't mind if it explodes.
I like it so much it's now my main amplifier. Shame it doesn't go so loud - you run into all sorts of nasties at 7/10 on the volume control. I expect it's the power supply, but for what I paid for the amp, it's probably not worth upgrading much.
Chris
The amp I'm using is a class AB thing, designed to be clean, with bass, mid and treble controls.
As I said - it doesn't give a huge load of distortion, just makes things sound smoother. The SS harshness has gone (it's a late 70s amp), replaced with something nicer.
As stated above, adding the transformer introduces new and interesting non-linearities (checked this using a scope, set to sum, connected to before and after the transformer) - more difference at the lower frequency strings.
I didn't want to experiment on my little Fender amp, so I bought something faulty off ebay - that way, I don't mind if it explodes.
I like it so much it's now my main amplifier. Shame it doesn't go so loud - you run into all sorts of nasties at 7/10 on the volume control. I expect it's the power supply, but for what I paid for the amp, it's probably not worth upgrading much.
Chris
You solved the mystery of how everyone that just anyhow add opt to their output apparently get a better sound.
I'm not discounting those that made actual design considerations when using opt, but those that just add them when unneeded be it to replace capacitors or not.
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FWIIW... Carver had a series of amplifiers that were built to do that. (eg. TFM25 or M1.0t) The TFM is an acronym for Transfer Function Modified. You can Google 'The Carver Challenge' and should be able to find some stories on it. They used a null comparator circuit to compare the output to a target amplifier. By adjusting certain things like output resistance and spectrum of harmonic distortion levels it was possible to null the difference between the two to more than 70 db. While not identical most people would not be able to tell the two apart.
All too easy to snag one off of eBay or Audiogon. If you want to do it yourself, sorry I cannot help anyone with that.
All too easy to snag one off of eBay or Audiogon. If you want to do it yourself, sorry I cannot help anyone with that.
The series resistor concept I had experience before, thanks to a friend with expertise in making headphone amps - usually don't have coupling capacitors but a resistor in series to avoid short-circuit when plugging in the TRS connector. The expensive Caddock resistors sound more extended and dynamic than the stock ones, smooth in comparison.
An interesting paper about tube-sound emulation:
http://www.peavey.com/support/technotes/hartley/chapter_3.pdf
And yes, the output transformer is an important part of it. And no, don't take an expensive HiFi output transformer for a guitar amp, it would not give satisfactory results. The ones used for guitar amps can't be called crappy, but "deliberatly low grade" would possibly be agood description. So your mains transformer might actually be a good chaice for this purpose.
In Elektor they once introduced a bridge-type amp using a mains transformer. This might also be an interesting solution for a guitar amp. It could do 70 Watts from a 12 Volt power supply without any further step-up measures..
Regards
Charles
http://www.peavey.com/support/technotes/hartley/chapter_3.pdf
And yes, the output transformer is an important part of it. And no, don't take an expensive HiFi output transformer for a guitar amp, it would not give satisfactory results. The ones used for guitar amps can't be called crappy, but "deliberatly low grade" would possibly be agood description. So your mains transformer might actually be a good chaice for this purpose.
In Elektor they once introduced a bridge-type amp using a mains transformer. This might also be an interesting solution for a guitar amp. It could do 70 Watts from a 12 Volt power supply without any further step-up measures..
Regards
Charles
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