Trainwreck Expres - Air brake, PPIMV, VVR, etc

[JPGraphX]

Hey guys!

I would like to know what is your setup for attenuating your Trainwreck Express.

I would like to install a VVR but I'd like to have more info about what is possible, what are plus/minus for every type of attenuation.

Thanks!!

JP

[M Fowler]

I built the Airbrake but don't care for how it sounds with the Express.

I'm trading my 5b6 Cage amp #2 to a friend for a Bad Cat Unleash so we'll see how much better that works to attenuate.

[katopan]

Your preferred choice definitely depends on how much you want to attenuate. I've heard other people's Expresses, one with LarMar master volume and the other with VVR. They both sounded great turned down a bit. I didn't get to hear them any lower so don't know how low they go before sounding too different.

I love VVR but didn't build it into my Express. I could understand that it'd do a great job just based on how well it works in my other amps.

But I wanted a solution where I could play my Express at very low home friendly volumes (TV volume). I built an external reactive dummy load (resistors, inductor and bass boost caps) which except for the height of the resonance peak, follows the speaker impedance that I was modelling after very well. So to the amp it electrically looks like a speaker. I put a line out tapped off that with volume control and a Tweed style tone control. I feed the line out into an old solid state bass amp combo that I changed out the speaker to a V30 for re-amping. So a real guitar speaker is creating the sound at the end of the chain. The tone control can be set to get the same tone as at full volume. If you play a bit louder than TV volumes it sound phenominal. Below TV volume where you can start to hear the strings acoustically over the speaker output, it suffers because the speaker is being driven so little. That's consistent with all the methods I've tried with other amps in the past (VVR, L-Pad, autotransformer attenuator) so no way around that. Works better than anything else I've tried for super quiet home friendly playing.

Unleash, Ultimate Attenuator, Ho's Attenuator, etc do the same sort of thing but with the SS re-amp power amp included. Except I already had the SS combo sitting around and building a reactive dummy load was cheap.

[KellyBass]

I've built 2 xpress amps that I equipped with VVR's. Both amps are professionally owned and have been gigged with fairly hard for the past 4 years or so with no reliability problems. I did, however, end up changing out a pair of resistors that determine the amount of attenuation. After battling DC leaking onto the pots and, worse, hearing the amp at bedroom volume, I made the change. Stock, the VVR will take your HT from 400v to 40v. By increasing the value of 2 100k resistors, you can adjust the drop. I can't remember what value I ended up using, but the attenuation is somewhere around 25%. Nowhere near bedroom volumes, but hey, it's an express! This way, the amp retains most of it's character and there's no audible DC on the pots. The VVR knob is labeled "loud" and "louder"!

[JPGraphX]

Cool! I don't need bedroom level, only small venue/bar volume.

I'll need some info about that vvr setup. You've used Dana hall's vvr?

[LeftyStrat]

katopan, did you base your reactive load on the Randall Aiken article? I'd be interested in the details.

There was a huge long thread on TGP that I think around page three has some clips with excellent results. The difference between a purely resistive dummy load and the reactive load was night and day.

[KellyBass]

Yep, I used Dana's and scaled the pre and power tubes. If I remember right, you can just scale the power tubes, but that requires a master volume so the preamp tubes' signal, running at normal voltage, doesn't blast away at the power tubes running scaled. But, I never use master and volume in the same sentence so that wasn't an issue.

Switching the 100k's to ??? (I should keep better notes) let's say 600k, would give you a b+ of 240v give or take....and that's approximately where I ended up. This should work very well for you. Both amps regularly play at a big outdoor festival one night, a small club the next. It took a while to get the guys to use them, but now I see them reachin' around to the back of the amp at the start of most every gig I attend.

Aw crap! There's a tornado heading this direction. Gotta love Oklahoma in the spring.

[katopan]

Lefty, I designed my own circuit. Modelled it in LTSpice to fit as close as I could get over a published speaker impedance curve. Then validated with a frequency spectrum plugin. It's a simplification compared to Aiken's, but more complex than just a resistor and inductor. I added resistors and caps to give some bass end impedance increase, but not the full resonant peak like Aiken's goes to the trouble to create. Typical rolloff of an amp and speaker is coming into play by the frequency of the resonant peak, so it's less important to get an actual peak and more important to just have a bit of a curve in that area. Full build thread over on Wattkins. It sounds great and delivered exactly what I was after.

[KellyBass]

That sounds interesting. I'm gonna re-visit that Aiken article... and check out the Wattkins thread as well. I'd love to try my luck with my own circuit...been meaning to at some point. I have noticed that there is a bit of "flattening" that takes place as you attenuate. It's nice to know why and it makes sense. I like the idea of rolling it back in. Plus, there are some mounting requirements wit the VVR. It'd be nice to have some flexibility there and still feel confident that the the mosfet is thermally happy.

[LeftyStrat]

That sounds interesting. I'm gonna re-visit that Aiken article... and check out the Wattkins thread as well. I'd love to try my luck with my own circuit...been meaning to at some point. I have noticed that there is a bit of "flattening" that takes place as you attenuate. It's nice to know why and it makes sense. I like the idea of rolling it back in. Plus, there are some mounting requirements wit the VVR. It'd be nice to have some flexibility there and still feel confident that the the mosfet is thermally happy.

This is the thread I mentioned on TGP:

http://www.thegearpage.net/board/showth ... ?t=1072793

It's long but worth the read. At the bottom of page four is a clip comparing reactive vs purely resistive.