Hello everyone,
My first post here. So far I've just been lurking and learning from the wealth of knowledge people have been sharing in the forums here.
Now, to the point. I have successfully built a few different guitar amplifiers. All of them employ solid-state rectification, but recently I have been interested in hollow-state rectifiers for the voltage sag they offer. While searching for a way to emulate the effect without having to install another socket or worrying about the available heater current etc., I found posts about using a resistor in the power supply whose resistance is close to that of a given rectifier valve. Certain users, however, claim that the sag caused by a simple resistor doesn't feel natural.
I have also stumbled upon a schematic by diyaudio user Gingertube posted here
https://www.diyaudio.com/community/threads/power-scaling.251971/#post-3841280
Question #1: Has anyone, apart from its author, built this circuit?
Question #2: If so, how does it respond to playing? How does it "feel" compared to an actual rectifier valve?
I appreciate any input,
Maciek
My first post here. So far I've just been lurking and learning from the wealth of knowledge people have been sharing in the forums here.
Now, to the point. I have successfully built a few different guitar amplifiers. All of them employ solid-state rectification, but recently I have been interested in hollow-state rectifiers for the voltage sag they offer. While searching for a way to emulate the effect without having to install another socket or worrying about the available heater current etc., I found posts about using a resistor in the power supply whose resistance is close to that of a given rectifier valve. Certain users, however, claim that the sag caused by a simple resistor doesn't feel natural.
I have also stumbled upon a schematic by diyaudio user Gingertube posted here
https://www.diyaudio.com/community/threads/power-scaling.251971/#post-3841280
Question #1: Has anyone, apart from its author, built this circuit?
Question #2: If so, how does it respond to playing? How does it "feel" compared to an actual rectifier valve?
I appreciate any input,
Maciek
That's pretty complicated, and may not be reliable. Why not just try a resistor first?
That circuit was a thing around 10 years ago, so no one here may have any experience with it.
That circuit was a thing around 10 years ago, so no one here may have any experience with it.
Thanks for the reply, rayma.
Tone and response-wise, it would probably make little to no difference to me personally because I have very little actual experience playing a valve-rectified amp loud. It might change sooner or later. However, sometimes people ask me to build them an amp and their requirements vary, hence my interest in Gingertube's circuit.
I'll wait. Maybe someone, perhaps even Gingertube himself, will chime in.
Tone and response-wise, it would probably make little to no difference to me personally because I have very little actual experience playing a valve-rectified amp loud. It might change sooner or later. However, sometimes people ask me to build them an amp and their requirements vary, hence my interest in Gingertube's circuit.
I'll wait. Maybe someone, perhaps even Gingertube himself, will chime in.
I had a KOC power scaler in one amp and ripped it out. Didn't sound good to me and was inducing hum and noise because of all of the extra wiring, which could have been the fault of the original installer (not me).
I've used Hall power scaling, called VVR, in many guitar amps. The fixed bias version tracks bias voltage, but is slightly less complex than the circuit you showed. It is useful for reducing volume and inducing some acceptable distortion, but only up to about 25% in my opinion - lower volumes really change the tone to something I don't like. With my amps that have VVR, I also use pre- and/or post-PI MV. Or, lower amp volume and a dirt pedal.
There are so many different ways of reducing amp volume while maintaining tone, but none seem perfect.
Also, I don't really consider the intent of these devices to induce or replicate rectifier tube sag, but they do make the amp a bit more compressed. Their main purpose is to reduce volume while permitting the amp to overdrive.
I've used Hall power scaling, called VVR, in many guitar amps. The fixed bias version tracks bias voltage, but is slightly less complex than the circuit you showed. It is useful for reducing volume and inducing some acceptable distortion, but only up to about 25% in my opinion - lower volumes really change the tone to something I don't like. With my amps that have VVR, I also use pre- and/or post-PI MV. Or, lower amp volume and a dirt pedal.
There are so many different ways of reducing amp volume while maintaining tone, but none seem perfect.
Also, I don't really consider the intent of these devices to induce or replicate rectifier tube sag, but they do make the amp a bit more compressed. Their main purpose is to reduce volume while permitting the amp to overdrive.
Thanks for sharing your experience, GKTAUDIO.
The circuit from the link I posted contains a sag potentiometer and if I understand the info there correctly, it does induce voltage sag. Actually, I found that post through a thread at AGGH where Gingertube gives a couple of hints on tweaking the response, among other things (I can link it if necessary).
I do intend to build it sooner or later (later than sooner, actually) and have someone more experienced test it. I just wanted to know if it's worth the effort.
The circuit from the link I posted contains a sag potentiometer and if I understand the info there correctly, it does induce voltage sag. Actually, I found that post through a thread at AGGH where Gingertube gives a couple of hints on tweaking the response, among other things (I can link it if necessary).
I do intend to build it sooner or later (later than sooner, actually) and have someone more experienced test it. I just wanted to know if it's worth the effort.
Semiconductors, especially transistors, in tube circuits can be problematic and unreliable, due to heat and voltage.
You don't want that in an amp that you build for a customer.
You don't want that in an amp that you build for a customer.
The MOSFET is static sensitive, which requires careful handling and installation. It is heatsinked to the chassis, so if you lose isolation, you'll have B+ on the chassis. Definitely should be designed/installed by someone who knows the issues involved.
Thankfully, I am aware of the issues you mentioned. Thank you for pointing them out nonetheless. Better safe than sorry.
I may not be sufficiently skilled to design MOSFET-based circuits, but I've used them in a number of projects, so I think I can assume I know how to handle them.
I may not be sufficiently skilled to design MOSFET-based circuits, but I've used them in a number of projects, so I think I can assume I know how to handle them.
And I do not, by any means, mean to sound like I know better. Most probably I don't.
I just wanted to make this clear because the written word may be interpreted in multiple ways.
I just wanted to make this clear because the written word may be interpreted in multiple ways.
Rather than having a circuit to introduce sag I would use a 6 position switch (or less) with a bunch of resistors. dumb but hard to muck up once the values are found.
Thank you for taking the time to reply, Printer2.
Sure, the simpler, the better. As far as playability or feeling is concerned, I guess it's all a matter of preference and/or acceptable compromise. I probably wouldn't be able to tell the difference. There seem to be people out there who can though, so I'm exploring my options for situations when I can't use the real thing, like when modifying an existing amp whose power transformer can't supply the voltage and/or current for a rectifier valve.
Sure, the simpler, the better. As far as playability or feeling is concerned, I guess it's all a matter of preference and/or acceptable compromise. I probably wouldn't be able to tell the difference. There seem to be people out there who can though, so I'm exploring my options for situations when I can't use the real thing, like when modifying an existing amp whose power transformer can't supply the voltage and/or current for a rectifier valve.
Not really sure there will be a difference in sound, I have about half a dozen 5Y3's, no desire to put them in an amp. SS and a sag resistor is fine for these ears.