Say you had a PRRI with JBL & a Rocktron Velocity 300...

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Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby lunasparks » Wed Aug 18, 2010 5:17 pm

...Let's talk more "optimal" solutions as well, but would it be possible to do something like the following? And I emphasize the "Possible" in that question....

PRRI main speaker jack to dummy load
Ext speaker jack into some kind of DI box --> Rocktron --> JBL installed in the PRRI cab

An initial issue with my idea is that the Rocktron will be receiving the powered tone from the PRRI--although with signal converted and hopefully tone preserved (!)--and maybe there's some weirdness with basically having the signal go through two power amp stages on its way back to the speaker?

Now my understanding is that even if I did something along this line of thinking the better solution would be to convert the 2nd speaker jack to a line out and then proceed as described (I think). But let's pretend for the moment that's not an option.

Why would I want to do this? Let's say I can't really mic the amp easily with the band and I like the clean on my PRRI at 3 on volume. Goal would be to just power up the clean tone and spit it through my JBL K110 (being careful not to push it too hard, obviously).

Any thoughts on this thought experiment?

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Re: Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby JonnyBoy » Wed Aug 18, 2010 5:29 pm

It is not a good idea to send a full power signal ready for speakers into another power amp. Your best way to do this and why many around here have modded the preamp signal tapped to go to another poweramp source is the highest fidelity and tone retention when using outside amplification. the other way may give you something, but I couldn't think that is the optimal procedure for amplifying the prri's signal. IT may even screw up the Rocktron or at least sound horrible.
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Re: Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby SarnoMusicSolutions » Wed Aug 18, 2010 5:34 pm

With a good power soak type load (8-ohm) providing a post-power-tube line level signal to feed to the Rocktron power amp to the JBL's, you could take advantage of the Princeton's ability to overdrive it's 6V6's. That could be cool. If you know you want to run clean, then I'd probably go simpler and tap the preamp signal before the the Princeton's power section. But what you suggest could be cool, just as long as the load on the Princeton doesn't ruin the sound. Most power soaks I've heard are not that pretty, but it's been a while, and maybe someone's got a good one these days.

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Re: Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby lunasparks » Wed Aug 18, 2010 5:42 pm

JonnyBoy - would a DI Box not tame the signal before it hit the Rocktron to prevent a dangerous mess? Agreed that who knows what it would sound like.

Brad - I've never used a dummy load so I guess I don't understand the way they could screw up the tone headed to the Rocktron via second jack. Would you mind explaining a little more what's going on here that could damage the plan? Second, since we've already broached the "optimal" discussion, I guess I'll ask how difficult is it to do the preamp tap?

thanks again!
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Re: Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby JonnyBoy » Thu Aug 19, 2010 8:26 am

I am sure it would help, I am not so sure about tame with the DI. I have heard of using two amps before, but I would argue that amps already are refined to sound their best alone, and if volume is what you are after (a PRRI that is loud as hell) the preamp is probably the best way.

The preamp tap is a simple procedure of taking a lead off the last preamp tube's circuit before it goes into the power amp, usually off a resistor or capacitor within the circuit, not straight off the tube itself. I think with a Reissue you would have to have some knowledge of the amp's circuitry to find it. You can logically deduce, Like I did with my TR reissue, from the old schematics where it is. What is funny, there are a few points you can tap in there to get the preamp signal, some better sounding than others, some almost identical to the best sound, some that won't give you anything, and some may fry your amp or part of it. But for the most part, you can find it with a little logic and power thinking. You are trying to find the signal that has been processed after the last preamp tube and has been properly processed to enter the power amp section. Some of the experts around here may be able to give you a clearer picture of what I am trying to say, I am not an electrical engineer nor pretend to be.
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Re: Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby strumminsix » Thu Aug 19, 2010 8:36 am

What is your need? I hear lots of folks hear talk about what can be done or how to do things but what you can do and what you need are 2 different things.
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Re: Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby lunasparks » Thu Aug 19, 2010 9:40 am

JB - thanks again for the thoughts. I'm not an engineer either and it makes me a little queasy thinking about digging into the circuit too much--thus my attempt at a "creative" solution. Would doing a preamp tap disable the normal operation as a combo or can both the line to power amp and onboard 6v6 section be preserved? This dual function is important to me (I don't need an external power amp for practice).

Which brings me to strummin....good point on clarifying my need. I think JonnyBoy got pretty close: "a PRRI that is loud as hell."

But I have a couple of modifications...the basic idea is that I'd like to never have the volume on the head above, say, 3-4--where tone is best for what I'm doing these days. But I'd like to be able to project that tone (or something close to its level of clean) at a high wattage/dB levels, and to be able to do so on the fly, at my discretion, in a live setting. This gets at some of my earlier posts about live sound in general, which I'll continue to improve and experiment with, including just mic'ing the amp and trying to figure out how to make it work in a PA and monitor setup where I don't have control. It's just this kind of volume flexibility + clean preservation I have in mind and which led me down my hypothetical road.

Finally, ideally I would like the solution to not involve diving into the circuit for further mods on the PRRI itself--I'm still a newbie. So, I know it's a lot to ask. :shock:

In any event, after further research I ordered the goods to try out my idea this morning (less than $50, so not a big loss if it turns out to sound like a turd). If it's crappy then at least I'm left with the option of doing a preamp tap...or just upgrading the the SMS one of these days. Keep your fingers crossed I don't fry the whole thing!
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Re: Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby SarnoMusicSolutions » Thu Aug 19, 2010 9:47 am

For some reason, power soak devices have often sounded like shit. They sound choked and cold compared to the full power to the speaker load. They never quite emulate a speaker well, and if you want that tap as a line signal, they can also sound weird if you're hoping for the sound of the amp overdriven a bit, it just doesn't translate as well as actually driving a speaker. Worth a shot, but I've always been left cold by the attempts.

Regarding tapping a preamp output from the Princeton Reverb, it's a bit different than with our Twins and Deluxes because there's no "mix node" where the 2-channels come together. That's normally how and where we tap. The Princeton is a 1-channel amp, so we'd have to approach it a bit differently, but not THAT differently. I recently upgraded the signal path in Jay Farrar's DRRI, and the results were pretty good. Didn't even mess with tubes or bias, just the signal path component quality. And I ditched that bright cap that's fixed to the volume pot. That adds unnecessary amounts of crisp. Just doing a good capacitor and plate resistor upgrade in a RI Fender makes for a nice improvement. In theory, you should be able to make a fine tube preamp out of one for our Jerry purposes.

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Re: Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby strumminsix » Thu Aug 19, 2010 9:55 am

lunas - I'm pretty sure Tom (tigerstrat) has his preamp tap setup in such a way that he can either run out to a the external poweramp or use the onboard poweramp. I think that'd be a pretty slick setup for you right there.

I'd highly suggest that route so you have a great grab and go amp but could easily output to an external poweramp for more watts but still use the existing speaker!
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Re: Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby tigerstrat » Thu Aug 19, 2010 12:54 pm

strumminsix wrote:lunas - I'm pretty sure Tom (tigerstrat) has his preamp tap setup in such a way that he can either run out to a the external poweramp or use the onboard poweramp. I think that'd be a pretty slick setup for you right there.


I actually don't have the switching jack for my Showman Reverb's pre out, so when I do want to run power tubes (very rare) I have to insert a dummy plug in the pre out jack. Cheesy but it works.
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Re: Say you had a PRRI with JBL & a Rocktron Velocity 300...

Postby lunasparks » Fri Aug 27, 2010 9:38 am

Update: so getting my PRRI "loud as hell" more or less works. Here's what I did:

Main speaker connected to non-inductive dummy load from Parts Express (there's the load)

Ext. speaker out to a cheapish speaker-level to line-level converter (DI box didn't work because it generates a too-low mic level signal as the output/ input to the V300)

from line level converter into the Rocktron Velocity 300 input. Rocktron speaker output to JBL in the Princeton cab.

Now I set the tone stack and volume on the PRRI for the preferred tone and from that point forward volume is managed with the Rocktron. End result is a clean PRRI sound that can get loud as hell without going into overdrive.

Below is a link to a tone comparison where I just put the Rocktron volume near the clean amp volume (around 4). Idea is to get an idea of basic tone loss vs. clean thru PRRI. With the converter, V300, and cables in between there's some loss on the top end. Maybe my ears are fatigued, but until I can get the SMS one of these days (or figure out how to preamp tap the PRRI) I may be able to use this setup for gigs where I generally don't get opportunity to mic the amp and not have to worry about whether I can maintain a clean tone all night.

Sure, it's kind of a weird thing to do, I guess, but more or less I was just curious how it would work out....

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