PPIMV on 2204/2203 type amps.

[hdahs]

What is the benefit/purpose of adding a PPIMV to an amp that already has a traditional master volume i.e. the 2204/2203? The reason I ask is that those type MV's seem to work and sound fine, so why add another?

The only PPIMV I have heard was on a Retro-King 50 watt, on loan from a friend, and to be honest I didn't like it much, as compared to a traditional MV. Upon inspection, found that this amp did not have the 5.6K grid stoppers installed, so I installed them, and that seemed to help some.

I'm considering implementing a switching 2204/1987 preamp in my 50 watt Metro, ala Neikeel's 2203/1959 setup, which turns Volume II into a master Volume, and am wondering if adding a PPIMV to this is necessary or worth it.

Thanks

[neikeel]

I use my amps as a 2 in 1 (a 100watter and a 50watter).

With the switch engaged you get 2204 tones (pure) when you set the PPIMV to 10 (ie totally out of circuit). You then use the traditional pre-PI MV as on a 2203/2204. To get the amp 'cooking' the master sounds best to me above 5 on the dial which can be quite loud, I have found that nudging the PPIMV down to 8 or 9 (NO LOWER) takes the edge off the volume without all of the side effects (fizzines, loss of Presence control) of a clamped down PPIMV.

Similarly in 1987 mode if you disengage the switch and crank the pre-PI MV to 10 to get pure plexi tones. You then use the PPIMV to dial the volume back a little (again always above 7 on the dial). You can always scrub off a tiny bit of volume with the pre-PI MV if you want.

The only compromise between 2204 and 1987 is which NFB set up you use and whether you put a 0.68uF cap to bypass the 820R on V2a. I prefer 47k/8ohm and 0.68uF cap of a plexi over the 100k/4ohm no bypass cap of a metal panel/2204 so I stick with that, your ears should decide or put a switch on the back for both/either. I am not a fan of lots of microswitches on my amps (or ones with dozens of dials like TSLs or Mesas etc) but you choose!

[demonufo]

The benefits come in spades to those that don't have the room to crank their amps right up, since the 2203 and 2204 still sound way better cranked, since the pre phase inverter master volume by it's very nature, only gives pre-amp distortion, and it's not until you crank the master volume that the phase inverter (and subsequently the power tubes) have to work themselves into power stage distortion.

By adding the PPIMV, you get to bring more of the delights of power stage distortion at lower volumes than otherwise necessary.

The PPIMV, particularly the LarMar are a useful addition to these amps IMO.

[hdahs]

Thanks for the responses, gentlemen. Between them, I have most of the answers I was looking for.

@Neil. I'm not a big fan of amps with TMK (too many knobs) disease. Simpler works better for me. You referred me to the layout for your 2 in 1 setup, which is what I will follow. Looking at the diagram, do you see any reason why I couldn't just remove both Normal channel jacks, and use a full size pot, and separate DPDT toggle? I would never use the Normal low jack anyway, and I dont care the size and terminals on the available push pull pots.

@demonufo - Thanks for the detailed opinion on the PPIMV. I never gave much consideration to the PI circuit being part of the power section, or the way it distorts, contributing to the overall sound. Correct me if I am wrong, but the PPIMV doesn't allow any more power tube distortion does it? I am under the impression that the only way to achieve this is to have the amp cranked, and use an attenuator to ease the pain factor. I guess having both types of master volume on the amp would allow more flexibility, and enable me to hear the sonic differences between the two types. Like I said my reservation was, that in the one setup I heard, I wasn't enamored with the sound, as it sounded kind of buzzy, and choked to my ears. The lack of 5.6K grid stoppers probably didn't help. And as Neil said, naturally it sounds better turned up too . But the standard Pre PIMV ala 2203/2204 never sounded bad to me, or with any of the buzzy, choked sound. But there are obviously a lot of happy users of the LarMar, so it seems to be worth a try.

[demonufo]

Yeah the PPIMV is just really increasing the function of the phase inverter within the power stage. And a PPIMV cranked right back will sound really fuzzy (ie, just the PI distortion without the blanket of the natural power tube distortion on top of it). For this reason, a few people like lower gain tubes in the PI (another thing worth experimenting with) like for instance the 5751.

A PPIMV wound back too far is not particularly nice sounding IMO, which is why those that need to go down to bedroom levels are better off with an attenuator AS WELL as a PPIMV (again, most attenuators I have seen don't sound all that great cranked right down to neighbour friendly levels).

Everything sounds better louder IMO, simply because of the way each individual part of the equation reacts (guitar, strings, pickups, tubes, transformers, rectifiers, speakers, even your ears). And there are a lot of satisfied LarMar users, but I can almost guarantee that most of these people use the PPIMV moderately, rather than winding back all the way.

[waggclan]

A good combination of a lower power PI preamp tube (5751) inefficient speakers and a PPIMV should do the trick on a 2204.

I've got an Aracom but never used it on my 50w amps.