Line out vs pwr scaling

[allsavy]

I've been toying with the idea of implementing pwr tube VVR in my amp to get bedroom level recording/playing . While the info online re VVR is appealing and befor I build a circuit, how might the VVR sound compare/differ to what a typical 2 resistor voltage divider at the speaker output as in a fender amp etc? (speaker sim notwithstanding)
My 40 watt amp probably puts out like 30 - 40 volts and the voltage divider values appropiate to give Line level output at around 2 volts.... seems to me that should be good enough to record direct or even drive a speaker for low level/big amp sound. ????

Question in my mind is how does dumping all that voltage not drastically affect the sound?

I'd have to fashion a dummy load to hear what is on tap at my existing line out to hear the diff but could someone shed some light.

btw... my line out voltage divider consists of 1/2 watt resistors!
compared to the big wire wound 10 watt resistors and 3 watt rheostat in my diy attenuater( which the tone goes up in heat).

how could they even compare ?
thanks, paul

[Cliff Schecht]

Reducing the power affects the sound in almost every situation. The speaker and whole output system in general react a certain way with each other. If you change one part of this "system", you're going to change how the entire system reacts and therefore change the sound as well.

[allsavy]

That reminds me of someone using dynamic dummy load made from a coneless speaker or something. Assume it helps address the loading issue so that line out will sound more like the amp.

weeber mass???

[MasterDisaster]

I have not tried the VVR3 but maybe Dana can fill in.

Power Scaling have a dynamic range of about 40db which should be enough for home use. I feel that this have less effect on tone that any attenuator I've tried but someone might disagree.
It works great on Marshall style amps but might not work as good on a Trainwreck as some of the sound and feel comes from stressing the output transformer.

Because you are actually lowering the output of the amplifier you might not get enough level from the line output using standard values.

Ted Weber's speaker motor attenuators do sound and feel differently compared to a resistive design but I am not sure that I prefer one over the other.

Mike

[UR12]

btw... my line out voltage divider consists of 1/2 watt resistors!
compared to the big wire wound 10 watt resistors and 3 watt rheostat in my diy attenuater( which the tone goes up in heat).

how could they even compare ?
thanks, paul

You can only get away with the 1/2 watt resistors in a voltage divider to provide a line level out. You will still need to have a speaker or resistive load plugged into the amp. If you go with the resistive load it will have to be gig enough to handle the power the amp puts out.

Reducing the power affects the sound in almost every situation. The speaker and whole output system in general react a certain way with each other. If you change one part of this "system", you're going to change how the entire system reacts and therefore change the sound as well.

I would have to dissagree with that statement to a point. The tubes in an amp have a linear portion of their characteristic curve that runs straight for a pretty wide range of voltages. As long as the tube is operated on a linear portion of that line it will amplify the same no matter what the plate voltage is. You won't get as much power at lower voltages but the tube will faithfully reproduce the signal. You are also reducing power when you turn your vol control. As long as everything is staying clean you get the same sound at a lower vol. You may loose something on the speaker end of things but that is why we add Tone controls to help adjust for the different settings. Distorted tones are a whole different ball game. Either way you have to over drive your tubes you can either run them at full voltage and run the crap out of them and then attenuate the speaker or you can vary the voltage and still have them distort at a lower voltage and power level. There is very little difference in the sound a amp produces running at lower voltages (as long as you keep the tube operating in a range it is happy with) and one operating at full voltage. The speaker is the main drawback along with the human ear, but having said that you should be able to drop the voltage on the tubes and then add a little treble or whatever to get the amp sounding like it did at higer levels plus you are not running the crap out of your power tubes and making them last longer. The biggest problem is that the speaker, when run at greatly reduced power levels, changes it's tone because it can no longer move enough air for our ears to be happy. This happens for any kind of attenuation method used to produce sound from speakers at low volumes. But I must say that for the voltage range between the speaker just moving enough air and max voltage there is IMHO very very little change in the sound the amp is producing.




Just my 2 cents

[Cliff Schecht]

That's sort of the caveat with guitar amps, we aren't necessarily operating over the linear region of the tubes curves. The attenuated sound really depends on the type of attenuation you're using, a voltage scaling circuit will react differently than a power attenuator. Lowering the voltages, especially in the power stage, is a better way of getting attenuation whilst retaining a characteristic sound. Not the simplest method to implement but it definitely has its advantages over passive power attenuation methods. But even this is going to change the sound because if you aren't pushing the transformer as hard, you're going to change the available bandwidth that the OT has and alter the sound accordingly. Maybe not a huge difference but it will be audible. With passive attenuators, you are still pushing the output section as it was meant to be pushed but since you're changing the load seen by the OT, it's once again going to change the sound a bit.