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AMZ dual booster

11/9/1999 5:49 PM
Chris	AMZ dual booster Calling Jack or anyone who's built it! I'm interested in building this box-wanted something that will just push a tube amp into OD, given a degree of drive from the amp. How transparent is the booster- I want to hear the amp OD'd rather than colouration by the effect. Thanks Chris

11/9/1999 6:47 PM

Jack

quote:
"How transparent is the booster- I want to hear the amp OD'd rather than colouration by the effect."

It is very transparent. If you want an even cleaner sound you can increase the voltage supply to 12v, 15v or even 18v to get more headroom.

It will be much cleaner than using one of the many boutique overdrives that are often suggested for boosting the input to a tube amp since it should not be clipping the signal at all, nor does it have a mid-rangy response as do many of the TS derivatives.

regards, Jack

regards, Jack

11/9/1999 7:23 PM
R.G.	Clean Boosters in general I get a chuckle out of the quest for a clean booster. It seems that people expect that there's some magic one or two component circuit that gives a lot of boost and is "transparent" somehow. It's reasonable to point out that it's hard to get much cleaner and more transparent than an opamp within the range of its gain and slew rate limitation. With modern opamps those are very loose limitations indeed. While an amp like the LM833 may not have the high frequency response of a one- or two-component FET circuit up to maybe VHF radio range, it's quite happy with stuff up to the top and beyond audio. And while current-source loaded JFETs are very clean for non-feedback amps, they don't approach the linearity of an opamp. If you want headroom, run an LM833 from +/-15Vdc for a booster able to put out nearly as much signal voltage into an amp input as the amp will put out to a speaker - and anything between that and dead zero - with a lot of transparency. I realize that I just kicked over the can of worms again, and the group that believes that the only good opamp is a dead opamp will chime right in. Ah, well...

11/9/1999 7:23 PM

R.G.

Clean Boosters in general

I get a chuckle out of the quest for a clean booster. It seems that people expect that there's some magic one or two component circuit that gives a lot of boost and is "transparent" somehow.

It's reasonable to point out that it's hard to get much cleaner and more transparent than an opamp within the range of its gain and slew rate limitation. With modern opamps those are very loose limitations indeed.

While an amp like the LM833 may not have the high frequency response of a one- or two-component FET circuit up to maybe VHF radio range, it's quite happy with stuff up to the top and beyond audio. And while current-source loaded JFETs are very clean for non-feedback amps, they don't approach the linearity of an opamp.

If you want headroom, run an LM833 from +/-15Vdc for a booster able to put out nearly as much signal voltage into an amp input as the amp will put out to a speaker - and anything between that and dead zero - with a *lot* of transparency.

I realize that I just kicked over the can of worms again, and the group that believes that the only good opamp is a dead opamp will chime right in. Ah, well...

11/9/1999 7:56 PM
Gus	R.G. I think you are right about opamps if you keep the gain down so the opamp does not clip any decent opamp/circuit (1meg in z) is hard to "hear" the only thing I think I hear in buffers are cheap Electrolyic caps.

11/9/1999 8:33 PM

Jack

Re: Clean Boosters/semi-rant

quote:
"I get a chuckle out of the quest for a clean booster. It seems that people expect that there's some magic one or two component circuit that gives a lot of boost and is "transparent" somehow."

What tickles me is that most of the devices suggested for clean boost have diode clipping and/or heavy-duty frequency shaping, yet the claim is that they are transparent and let the feel of the notes come through.

Foo... the diodes are clipping the signal, even with the drive turned down and thereby producing a limiter effect. The top end is rolled off to reduce the "fizz" and the low end is rolled off to prevent flatulent tones on the bass.
That may be what sounds good but it is far from transparent or clean, and if you like that, then use it.

The Dual Booster will probably sound better in this application if the low end is rolled off by changing C5 and C6 to 1uF or even 0.56uF. The high end response can remain since there is no clipping diodes to generate "fizz". I use this version all the time with a tube amp and its much less muddy than my old TS-9.

regards, Jack

11/9/1999 10:34 PM
Mark Hammer	Re: Clean Boosters in general Clean booster, jumbo shrimp, tight slacks. What do these three things have in common? I empathize with Chris' desire to aim for a tone that is pleasingly natural, but the way he framed it alludes to some common misunderstandings. Let's start from the beginning. When you "boost" there are a few things that can be accomplished. One is that the signal comes as close to maximum as available headroom can withstand. This will likely (assuming good design) improve the S/N ratio, and provide greater overall efficiency/volume with the same equipment. Moving beyond the limits of headroom may start out clean, but end up dirty if headroom on the next stage is exceeded. Recommendations to use a heftier supply voltage are wise. Even if the schematic says 9v, if you can get away with 12 or 15 or 18, do it. Most op-amp based devices can accommodate 18v. If there is room for a second battery in the chassis, unsolder the battery snap lead to the inpout jack and solder it in series with another battery snap for jack-switched 18v. A second accomplishment is really more one of buffering than boosting, however many "boosters" also have a buffering effect, and many buffers can also appear to boost the signal because of the preservation of high end (i.e., it cuts through more, ergo it must be louder). Now designing a unit to accomplish one or more or all of these goals can't be done in a vacuum. If you have ultra-hot humbucker pickups, the odds of ANY boost, no matter how pristine, NOT resulting in distortion somewhere in the chain are slim if you are anyone but Chet Atkins. If anything, I would vote for a compressor/limiter as my "clean booster", because it will increase average level in a relatively clean manner without necessarily running up against headroom issues on the next stage. I guess the long and the short of it is that when you decide that a "clean boost" is what you want, you haven't finished ordering. And that's true regardless of whether the semiconductors involved have 3 legs or 8. By the way, in hifi circles, it is common to strive for op-amps that have higher slew rates, since it is assumed they would introduce less coloration by being able to respond to all requested signal swing across the complete spectrum. In most conventional guitar uses, especially where a sluggish 12" speaker is the destination, slew rates of more than what one sees in a garden variety 4558, are essentially functionless.

11/9/1999 10:34 PM

Mark Hammer

Re: Clean Boosters in general

Clean booster, jumbo shrimp, tight slacks. What do these three things have in common?

I empathize with Chris' desire to aim for a tone that is pleasingly natural, but the way he framed it alludes to some common misunderstandings. Let's start from the beginning.

When you "boost" there are a few things that can be accomplished. One is that the signal comes as close to maximum as available headroom can withstand. This will likely (assuming good design) improve the S/N ratio, and provide greater overall efficiency/volume with the same equipment. Moving beyond the limits of headroom may start out clean, but end up dirty if headroom on the next stage is exceeded. Recommendations to use a heftier supply voltage are wise. Even if the schematic says 9v, if you can get away with 12 or 15 or 18, do it. Most op-amp based devices can accommodate 18v. If there is room for a second battery in the chassis, unsolder the battery snap lead to the inpout jack and solder it in series with another battery snap for jack-switched 18v.

A second accomplishment is really more one of buffering than boosting, however many "boosters" also have a buffering effect, and many buffers can also appear to boost the signal because of the preservation of high end (i.e., it cuts through more, ergo it must be louder).

Now designing a unit to accomplish one or more or all of these goals can't be done in a vacuum. If you have ultra-hot humbucker pickups, the odds of ANY boost, no matter how pristine, NOT resulting in distortion somewhere in the chain are slim if you are anyone but Chet Atkins. If anything, I would vote for a compressor/limiter as my "clean booster", because it will increase average level in a relatively clean manner without necessarily running up against headroom issues on the next stage.

I guess the long and the short of it is that when you decide that a "clean boost" is what you want, you haven't finished ordering. And that's true regardless of whether the semiconductors involved have 3 legs or 8.

By the way, in hifi circles, it is common to strive for op-amps that have higher slew rates, since it is assumed they would introduce less coloration by being able to respond to all requested signal swing across the complete spectrum. In most conventional guitar uses, especially where a sluggish 12" speaker is the destination, slew rates of more than what one sees in a garden variety 4558, are essentially functionless.

11/9/1999 8:52 PM
Stan Bailey	Re: Clean Boosters/semi-rant Chris; I built one and it gives a good clean boost. However, I was getting some distortion when the pot was around 10:00. Perhaps it was the 4558 using. I fixed the problem by dropping the NFB pot down to 10K. Stan

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