Master volume problem.

[Chuck H]

THD makes a lot of hoopla about their units. They certainly cost enough. I suppose I can forgive that since the design is rugged, practical and made domestically. Still, unless I'm wrong it's just a resistive attenuator. They have added bypass caps, bright switches and sagging light bulbs but that may be to the detriment of the sound.

IMO building an active load for attenuation is worth the effort if you want to turn down really low. Of course it will still not sound the same. All manor of things change like acoustic dynamics between the amp and guitar, the human ears less than perfect corrections for volume and room acoustics. Getting cranked up amp tone at low levels has been approached from so many different angles that it should be obvious by now that it's really hard to do and is never perfect, or even good enough. Even in this age of high gain master volume amps people are still trying to get cranked vintage amp tone. Recent developments would include Eminence's adjustable efficiency speaker and the glut of micro amps on the market. With all the more conscientious efforts that have been made it shouldn't be a surprise that a crude cross line master isn't panacea.

[Alan0354]

I opened the THD and partially copied the schematic, it's a lot more than resistive load. But there is a difference in the sound even when you lower to -4dB. At high attenuation, it's not that good. Still better than the regular MV though.

The 10 ohm resistor replacing one speaker only good for cutting the power in about half, like making my Pro Reverb into a Deluxe Reverb. I don't think the resistor work too well for any higher attenuation. I tried using a big adjustable wire wound resistor and drive the speaker with the tap. It did not sound that good. I don't have direct comparison, but from my memory, the THD is a lot better.

I did the MV just have have it, I did not expect to beat the THD, but I did not expect it to be that bad!!! I think the pre PI master volume works a whole lot better.

[Chuck H]

I opened the THD and partially copied the schematic, it's a lot more than resistive load.

How so? Are there inductors in there? If not it's just a resistive load.

I tried using a big adjustable wire wound resistor and drive the speaker with the tap. It did not sound that good. I don't have direct comparison, but from my memory, the THD is a lot better.

This is confusing because you say the ten ohm resistor sounds better than the THD. But the variable resistor (which can certainly be adjusted to ten ohms) doesn't sound as good as the THD.?.

I did not expect (the crossline master) to beat the THD, but I did not expect it to be that bad!!!

I've never liked them. I only use them as tacked in circuits for testing purposes and then remove them.

I think the pre PI master volume works a whole lot better.

That depends on the goal! If the amp is usually run clean and a stomp box is used for any clipping, or the stomp box is used to overdrive the preamp, then yes, a pre PI master works best. Basically, any time the distortion is to be generated before the power amp a pre PI master works best.

If power amp distortion is the goal an attenuator works best (Or possibly power scaling. But there are other criteria to manage and it isn't any better so why bother? (JM2C) With the post PI master you still don't get any power tube clipping. You only add the PI to the distortion chain. I think this is a bad idea because power tubes don't operate the same at all signal levels. A low input signal may not even drive the tubes into cutoff before the PI clipping for that cycle is clipping! So you actually get PI clipping that wouldn't otherwise be heard without this circuit. And to be honest, PI clipping isn't often idealized for tone. Add to that the complications of attenuating within the feedback loop and it becomes a mess of events that adds up to less than desirable results that change with settings.

Did I mention that I don't like post PI master volume controls?

[Alan0354]

How so? Are there inductors in there? If not it's just a resistive load.

I copied part of it, It's been a long time and I even have to find the copy of the schematic. There are inductors in it and capacitors.

This is confusing because you say the ten ohm resistor sounds better than the THD. But the variable resistor (which can certainly be adjusted to ten ohms) doesn't sound as good as the THD.?.

Remember the wire wound resistor in this case is like a volume pot and the speaker is tapping off the wiper. So the signal through the speaker also goes through part of the resistor. More important, I did that in 1980 on my Twin. I don't have the resistor to replicate the experiment. Also, I had it at high attenuation. The 10 ohm resistor in parallel with the speaker only reduce the loudness by about half, not like the volume pot style that attenuates all the way down. Remember I said I tried parallel 4 ohm with the speaker to get higher attenuation, that reduce the bass too much already. Bottom line, for small attenuation, it's not too hard, for large attenuation, nothing sounds that good.

I've never liked them. I only use them as tacked in circuits for testing purposes and then remove them.

I remove mine already.

That depends on the goal! If the amp is usually run clean and a stomp box is used for any clipping, or the stomp box is used to overdrive the preamp, then yes, a pre PI master works best. Basically, any time the distortion is to be generated before the power amp a pre PI master works best.

If power amp distortion is the goal an attenuator works best (Or possibly power scaling. But there are other criteria to manage and it isn't any better so why bother? (JM2C) With the post PI master you still don't get any power tube clipping. You only add the PI to the distortion chain. I think this is a bad idea because power tubes don't operate the same at all signal levels. A low input signal may not even drive the tubes into cutoff before the PI clipping for that cycle is clipping! So you actually get PI clipping that wouldn't otherwise be heard without this circuit. And to be honest, PI clipping isn't often idealized for tone. Add to that the complications of attenuating within the feedback loop and it becomes a mess of events that adds up to less than desirable results that change with settings.

Did I mention that I don't like post PI master volume controls?

Yes I remember you said you don't like PI MV.