Tube Amps / Music Electronics
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|10/25/2000 4:15 PM|
Give me a TL072 op amp and I'll give you a booster that will blow your doors down. Seriously, I've been playing with some simple non-inverting amplifier circuits lately and I've been amazed at the tones you can get. I'm starting to like this better than a lot of the JFET stuff I've done. The EQ'ing works differently than the typical amplike JFET source circuit shelving. I've been able to get nice clear highs and tight lows with no mud - a problem I was having with some of my JFET circuits.
Think about it- what's an opamp overdrive usually consist of? op-amp->clipping circuit->output stage and maybe a tone circuit as well. Take the opamp stage, that's where you get the gain and voicing, and blast your tube amp with that. Throw the rest of that stuff away - you don't need it. You think you need it, clipping circuit, tone control, hot output stage, but you don't- not for a booster. The opamp puts out plenty of gain to drive your amp. Just EQ it and blast it out there and let your amp do the rest of the work.
"Warm Boost", yeah, I like that. (I was thinking "Slightly Soiled Boost", maybe???) With a 9v supply you will exhaust headroom at a certain point and a FET-based opamp will add some warmth of it's own. If you want more headroom, bump up the supply voltage.
Bottom line, if you have a tube amp, try throwing out that wicky-wacky and simplify.
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|10/25/2000 6:14 PM|
>Give me a TL072 op amp and I'll give you a booster that will blow your doors down.
The problem is when you have a fairly clean amp that's powerful.
That's when you want the compression aspect of a warm boost.
I suspect when you can really drive the amp, that's when something like the Micro Amp and others really come into play.
In your case, your amp is already compressing, for people with fairly clean amps with power, they need a warm boost!
Uh when my 2X12 Celestian Greenbacks come in, my amp will be plenty LOUD and I will really need that "warm" boost!
|10/25/2000 6:55 PM|
I'm a little confused... By "fairly clean with power" do you mean an amp that doesn't break up smoothly when it's overdriven? In that case, I agree. Before I re-tuned and modded my amp, the breakup was harsh and I could only push it so hard with a pedal. The rest of the distortion/compression had to come internally from the pedal. Since the mods it will take any reasonable signal level, assume the "personality" (EQ and voicing) of the booster circuit, and produce a smooth overdrive.
I don't think there's any way around a "warm" boost, unless you really limit the gain of the booster. Even at at 24 or 36 volts, if the gain is high enough you can get some clipping in the op amp. Of course, hi fi isn't the goal here.
|10/25/2000 7:29 PM|
OH, I just meant that since you are lucky and get to push your 10 watt amp UP, then you are already running a great compressor!
For people like me, even though my amp has lots of feel at moderate volumes, I could still use a little more compression. My amp can get really loud so I need a warm "boost".
Oh wait, I see the problem - I used the "boost" term in the wrong context, yes, I meant a circuit capable of boost, but as Mike Fuller said, gives you the feeling of playing at louder levels without the louder levels - i.e. compression and feel.
Unfortunately, unless I am playing really loud, I cannot max out my amp like you - it's too LOUD.
I'm sorry, I'm talking about something totally different from you!
In your case, the amp is distorting so you need CLEAN signal to boost the amp.
In my case, the amp is not maxxed out, so I need a more dirty/WARM signal to give it more feel. Hah!
|10/26/2000 2:50 PM|
Okay, so what you're saying is that your amp doesn't compress well unless you're cranking it. I have absolutely no perspective on this. This is the first tube amp I've owned since my first amp, a Silvertone amp-in-a-case, back in 1972 (yikes!). The tube amp revolution came and went about 2 or 3 times before I woke up... (I figure if I stay far enough behind, I'll be in style about every 10-20 years...)
Anyway... Most of the time I don't crank the MV to 10 or anything. It's a good tone but I don't use it a lot, at this point I'm more intrigued by preamp distortion. So I run the MV around 5, which yeah, would be way too loud for a 50 or 100 watt amp around the house. When I first started with this amp I was all shy and didn't want anyone to hear me so I ran the MV around 2-3. With a 50 or 100 watter, this is probably more the level you are running, I suspect. Big tonal difference between that level and 5. At 4-5 it seems to come alive, open up, start singing, etc. So I think I see what you mean there.
Well, "clean" is a relative term. My goal is to get the majority of the clipping and distortion from the amp. (That's why I like the term "warm", it's more accurate, to me.) If the booster distorts a little in the process, that's fine, as long as it adds to the fun. But I'm trying to avoid diodes and multi-stages that purposely try to generate clipping (and yeah, compression) in the booster. Nothing wrong with that, I just want to see what the -amp- sounds like when it's driven.
Anyway, no right or wrong tonewise with this stuff. I just need to do this for myself, part of my "tone learning curve". And this is getting me real close to the tone I've been after.
|10/25/2000 6:55 PM|
Thanks, I appreciate all the input. I'm assuming you mean just the opamp gain stage as in the Shaka IV. You lost me on the supply voltage - headroom thing but I'm just a hack that's just learning. "Slightly Soiled Boost", that's a cool name; how about "Bacon Strip Boost" or "Skid Mark Boost". Sorry to be crude; couldn't resist. I'll probably try a Booster 2.5, Sweet Thing, Shaka IV, Screamer+, and the Hotbox. Even I should learn something from all that!
|10/25/2000 7:37 PM|
What Doug means is that the more voltage you give the op amp or JFET (within its limits), the more clean headroom you have before clipping. Therefore, the less you give it, the more clipping will occur - of course the signal has to be large enough to drive the circuit, but that's the basic idea.
An interesting experiment I did was drive the Shaka HV circuit with a voltage regulator - everything from 5V->30V - interesting how the circuit reacts to the different voltages.
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