V-amp Tube Input Stage

[cr_XD]

hi, i've been searching hard and have not found a thread on this, but i can remember someone did it. Could he explain what was done, i suppose is bypassing the opamp input stages and put tube instead with the same level of gain. any ideas??

bye

[ansil]

hi, i've been searching hard and have not found a thread on this, but i can remember someone did it. Could he explain what was done, i suppose is bypassing the opamp input stages and put tube instead with the same level of gain. any ideas??

bye

if you are talkin about what i did some time ago [couldnt find it on search either] i did a tube preamp stage for my behringer. later i redid it and then later i took it out, and redid the amp normally and let a friend have it on semi permanent loan.

but mine was a V-ampire not the Vamp modeling station just to be clear. theres all sorts of room in the behringer for stuff like this. however the best thing to do is to replace the voltage tranny with a beter one, perhaps lighter. and basically you are using the back input and bypassing the preamp. essentially i jsut made it into a jcm800preamp that was the last version of it, before going to make it all tubepre and power, later it just got to the point i was worrying about the structural integrity of the chasis.

all in all i would do it again in a heartbeat.

try the hammond 229 transformers they are small and have ample voltage and current.

[cr_XD]

great, so using the return line in of the pre-dsp insert you jump the input stage, right? that's even better (no mingling inside), but what about impedances, the input impedance for that one is 20Kohm.

Now, what if i want to use the clean channel in my engl to go to that input and take the output from the vamp and put it to the poweramp of the engl?? any problems with impedances, i guess not.

the thing is i don't have it, but have just made my mind to buy something alike to play home. engl volumes are just toooooo loud.

the vamp seems a preatty good toy and really affordable, and for that price i don't mind playing with it. so i have nearly made my mind up. any suggestions??

do you think a mosfet pa would improve sound reasonably as to the engl pa (it is a screamer 50 btw)? cos i have just spoted a really cheap one with 150 watts!!!! (that's really much isn`t it, i'm not familiar with solid state real power)

thanks for the info friend, you guys are a huge library of information, i´m glad u share it with us ignorants

[ansil]

to be perfectly honest with you, i was trying to find my notes on it. but alas i can't seem to find it. at the time it was total expirament, i coudlnt' find values and didint' care to read what they were, i knew how to make the tube preamp and i found a place to hook in and out too, and well that was the begining of it, personally

[lovekraft]

Why is this project of any use whatsoever? Any tonal benefit you'd gain from the tube at the input would be completely swamped out by the digital modelling section (that's what it's there for!), and adding a high voltage power supply to a V-Amp isn't exactly trivial, nor is padding the output of even a single triode gain stage down to a level that the digital interface can swallow without choking. Keep in mind, Ansil does some of this stuff simply because he can - you can add tubes to your toaster, too, but it won't necessarily make your bagel taste any better! Just my $.02, adjusted for inflation!

Edited May 22, 2006 by lovekraft

[cr_XD]

Any tonal benefit you'd gain from the tube at the input would be completely swamped out by the digital modelling section (that's what it's there for!)

i´m not sure if i agree with that.

and adding a high voltage power supply to a V-Amp isn't exactly trivial, nor is padding the output of even a single triode gain stage down to a level that the digital interface can swallow without choking.

if i just replicate a preamp stage with the same levels and use a return input in the vamp that is design to receive those levels i don't see a problem

Keep in mind, Ansil does some of this stuff simply because he can - you can add tubes to your toaster, too, but it won't necessarily make your bagel taste any better! Just my $.02, adjusted for inflation!

i'm sure i want to try that bagel first

one last thing, the fact that i want to know what can be done, doesn't mean i´ve decided that way. before doing a whole preamp for this, i would definitely try my amp's first, that was not answered by the way. so here it goes, and i think this answers more than just the question but something already stated above:

Can i just plug my amp's effect's loop output into the pre-dsp input in the v-amp(i´m not sure if it's called liked that)??

thanks for the replys.

lovekraft, would love to know if i´m wrong, i´m an ignorant newby but i don't think it's that bad idea... can't wait to hear from you, bye

[ansil]

Keep in mind, Ansil does some of this stuff simply because he can - you can add tubes to your toaster, too, but it won't necessarily make your bagel taste any better! Just my $.02, adjusted for inflation!

haaaaaaaaaaaaa i coudlnt' have said ti better myself. lol.

you know the little marshall is still running on 12volt heaters and havent' changed the tubes again yet.

lol.. dont' try this at home kids.

now if you want you can do some serious hacking on the thing but your mileage may vary. lol

full blown tube preamp. easy enough. preset eq. or pop a couple of holes in the chasis and mount them. i personal was thinking of just using bias style pots with the head adjustment. on perfboard to basically make a jcm 800 style preamp and eq. then plug it into the return of the unit and use the fx. pan all the fx hard right in the presets. disconnect the digital preamp on the left. and use the tube preamp and eq into a volume control into the left side of the stereo amp. its two lm3886's set up in a basic national.com pdf sheet.

not very hard to decipher. that way you can get great tube tone, digital fx [mediocre fx really but a bunch of them] a stereo power amp and pan each of them and still have midi control. however you would need ot do a few things if you wanted to midi control the gain section on the tube preamp. i am thinking led/ldr or perhaps the motorized pots. that woudl be cool theres a guy who has a cheap midi interface you can build i bleive its jon hollis.

also please take to heart what lk has said abovce. i will not try to talk you out of doing this. but i am INSANE i do some things simply because i have nothing better to do, and i don't always take accurate or any notes. alot of times its one off's. you have researched the behringers impeadance. somethign i should hvave done but i just went balls out.

guerilla tactics aren't always succesfull i have screwed up a lot of stuff in my time. but i again i did it when i was young so i dont' want to scare you. but at the end of the day, i would find a simple way of doign thigns unless you are insane as well then by all means.

I figured it out my kids the same way, he will take the longest route possible sometimes for no reasons. i laugh at this, his mothers annoyed by it lol. oh well. thats life.

hacking on a behringer isnt' that hard, building a halfway decent tube preamp to do one particular sound isn't that hard putting it together is where its sink or swim time.

sorry i am sleep deprived now,

msut get offline

ciao

ed

one last note, a trick i learned along time ago, was to split my guitar signal from say a stereo pedal [buffer still splits the signal regardless on or off] and send one side of it to a little preamp that i had for dirty sounds [old fender squier ss amp that was literly blown up.] and the other side went to the mxr bass amp that was also a fender, the preamp pedal ran into an eq which then went to the front of the bassamp and it was set really for the distortion channel but it had a few nice features. one was that if you didnt' put an fx send on the fx loop but you used an fx return, you could use the clean power [and or the eq section of the preamp depending on how you set the switches] of the bass amp and bypass the clean sound, most of the time i would set it up so that the clean side would be the straight amp maybe with some chorus or something into it and some reverb a nice sound really. and then the dirty would make it channel switching from a second amps output. a little noisy at the time but i had some nice vai/dreamtheater heavy gain sounding crunch. in reality if i had that same rig right now, i would use it over anything tube made as it had such a nice tone to it, and it was darn loud too. i have a crate right now that has the tube preamp and has a SS power amp, and i use only the powersection until i decide to sell it that is, got it in a real sweet trade.

ciao

ed

[lovekraft]

i´m not sure if i agree with that.

That's the great thing about free speech - you're guaranteed the right to disagree, even when you're dead wrong. Unless you bias a single triode stage so far out of its linear range that it distorts constantly or drastically limit its frequency response, it won't color the signal at all at normal input levels. What we think of as "tube amp sound" is a lot more complex than just running a single tube stage somewhere in the ciruit - it's the result of multiple stages interacting, and above all, transformers, power supply issues, speakers, etc.

...if i just replicate a preamp stage with the same levels....

OK, here's where we run into another problem - tubes have massive gain. A standard, correctly biased 12AX7 triode common cathode stage with a 100K plate resistor and a bypassed cathode (think standard Fender input stage) will give you about 35dB (56X input level) of clean, uncolored gain, of which you will have to throw away at least 75% to keep from frying the next stage in the V-Amp. That's a huge waste, using a tube and an expensive power supply to do a job that a sixteen cent opamp chip does equally well.

Then there are the heat and noise issues - since the tube gets quite warm, you'll have to have it mounted some distance from the digital circuitry, necessitating long signal and power leads which will be inherently noisier than the original setup. Sure, you can work around all these problems to some extent, but why bother, for a near-zero net gain in tonal improvement?

...Can i just plug my amp's effect's loop output into the pre-dsp input in the v-amp...??

If you mean can you use the V-Amp in your F/X loop instead of before the amp's input, absolutely, with the caveat that you'll have to pay attention to level matching - if your F/X loop runs at line level, you may have to pad the V-Amp's input (so it doesn't clip the pre-DSP stages) and boost the V-Amp's output to drive the F/X return to full volume. You can do all that very cheaply without ever breaking open the V-Amp's case.

I don't want to give you the idea that I'm just dissing your great idea - I'm just trying to show you how tortuous it is to implement, especially with no guarantee that it will make any difference whatsoever. I apologize if any of this sounds harsh or condescending - that was not my intention. This remains, however, an extremely impractical idea, and I calls 'em like I sees 'em. Good luck with that KT88 bagel toaster!

[ansil]

hey lk did you see that guy who was using a toaster to drop the voltage in his amp. forget exactly what he was doing exactly saw a link along time ago. anyway, thought i would say hey. and ask you if you rmemebered that.

ciao

picked up some killer molex connectors too.

and a flat screen 17" monitor if the guy from ebay will ever email me back. it needed a powersupply

[cr_XD]

ok, i understand what you mean. i´ll clarify my intentions:

i don't intend to open and handle the gutts of the v-amp but carry on the mod externally. this means making a preamp to go pre-dsp of the v-amp. the power amp stage is not in my scope.

and i don't mean to make a clean preamp, i want it to colour the signal a bit, i'm not a freak tube that wants to have tube just because i like the glow. i think this is not imposible, and working a circuit similiar to the real-mctube or a fender input stage isn't hard, is it??

anyway, this means all the problems you see are not that BIG problems.

the only problem i can have is that in the end there is no difference between the input stage of the v-amp and the tube's preamp. or that i cannot use it because the level is way too high. but anyway i´ll end up with something i can use as a pedal or something to overdrive and get some ugly dist.

my idea is much more simpler than ansil, just because i know so less than him XD.

i think it's a good idea what i want, and it is inside my 'can do'.

i thought by the messages that maybe i hadn't explained clearly what my intentions BASED on ansil´s project were. what do you think of it????

[lovekraft]

Yes, that's a better (and more practical) idea, but let's take it one simple step further - if you build the preamp from, say, the AX84 High Octane and pad/gain-match it to a decent speaker sim, like Runoff Groove's Condor, you can get rid of the V-Amp altogether. I still think we need to more clearly define the problem you're trying to solve before we can find the most appropriate solution.

[cr_XD]

if you build the preamp from, say, the AX84 High Octane and pad/gain-match it to a decent speaker sim, like Runoff Groove's Condor, you can get rid of the V-Amp altogether.

there is no problem, the thing is that i was weighing up wether to buy the v-amp, and the fact that i could use a tube input stage to make a little tubey and use the effects on it, sounded a reason to buy it and yet have a new project to make XD. However, you don't like the idea, you think the v.amp will kill any tube sound out, is that true. not that it's gonna put me off buying it, it still is a great tool for home practice and recording, but all this thread is just to feed my anxious ignorance and curiosity , thank you for your time, i hope you are not disapointed with me...

[lovekraft]

I actually quite like the V-Amp for a lot of things - I prefer most of the patches to similar ones in the POD (yechh!!), but then I absolutely love my PSA-1, and it's 100% analog and sandstate, so go figure. The only point that I've been trying to get across is that the V-Amp is designed to work on a clean guitar signal and give you the sound you want from there, so if anything, I might use an old tube studio mike preamp at the output to warm things up a bit, but not at the input. You are free to do whatever you'd like - I simply don't think that this approach will get you a positive result even close to equalling the effort and expense involved. I've learned the hard way (repeatedly) that digital equipment doesn't react to being overdriven in a good way, and my personal experience with mixing analog and DSP has given at best mixed results. Keep in mind, Ansil's the mad circuit-bender around here, while I'm just an engineer-wannabe who worries about frequency response, noise and can it handle being stomped on every night for a 230 date tour, so we have completely different agendas and approaches. If the idea appeals to you, and you can afford the time and expense, even if you have to write it off as an educational experience, then go forth with my blessings!! And, for the record, I'm never disappointed in anybody who's still thinking!

If you decide to go for it, let us know how it turns out.