Is the Orman's Miniboost clean? Why does the computer simulation distort?

[JimRayden]

After seeing lots of discussion over Mini-Booster, I finally started to feel interest for that circuit. Being late, I can't use breadboard so I layed the schem down in a computer sim. At 200mV 1kHz, it distorts quite heavily. I'm using 2N5457's. When I raised the supply voltageto 18V, it gave a huge and perfectly clean boost but that's to be expected. But that little headroom at 9V? I couldn't have expected that.

Would anyone guess a reason for that? I was under the impression that the Miniboost was clean. Too bad my computer doesn't agree.

Another question: how much does this double-FET stage boost compared to Fetzer?

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Jimbo

[R.G.]

Everything is clean at some signal level, even germanium diodes.

As always Mother Nature insists that the Rules be followed.

A humbucker can easily put out a volt or more of signal. Active devices can only get so close to the power rails. There is only room in 9Vdc for a gain of a few times before you run out of power supply. There is nothing that will do more than about 3-9X gain on a 9V supply without distorting. Open that up to 18 and it's clean again.

[amz-fx]

Also, you may have the signal level up too high on the simulator...   a 100mv signal is a hot pickup output though the pick attack can be 1v as RG noted.   Try a lower signal level and see what you get.

Furthermore, the simulator always seems to give more gain than I have measured in the actual circuit with real transistors.   Sims always use ideal components and that's not real world.

More reading: http://www.muzique.com/lab/pick.htm  and http://www.muzique.com/lab/boost.htm

regards, Jack

[puffra]

After seeing lots of discussion over Mini-Booster, I finally started to feel interest for that circuit. Being late, I can't use breadboard so I layed the schem down in a computer sim. At 200mV 1kHz, it distorts quite heavily. I'm using 2N5457's. When I raised the supply voltageto 18V, it gave a huge and perfectly clean boost but that's to be expected. But that little headroom at 9V? I couldn't have expected that.

Would anyone guess a reason for that? I was under the impression that the Miniboost was clean. Too bad my computer doesn't agree.

Another question: how much does this double-FET stage boost compared to Fetzer?

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Jimbo

what simulator do you use?

[JimRayden]

Darn, where the hell did my reply go? And in general, why does the forum go down so often today? Aron is updating or moving something?

Jack, I was just reading the Mini-booster article. The text on the picture from the original National appnote pretty much explains it - the more gain the circuit has, the more "dynamic range you sacrifice", as it states. Starting to distort so soon and slamming the signal into 0V and 9V, I guess the circuit has quite a large of an amplification factor, right?

The question was, how much larger gain does the Mini-boost have compared to a simple JFET gain stage like the Fetzer?

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Jimbo

[JimRayden]

what simulator do you use?

CircuitMaker.

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Jimbo

[Transmogrifox]

I would agree with all of the above.

In addition:  It's surprising how much distortion you can have, and it still sounds "clean".  Some circuits you can put on the scope and see clearly that a signal level comparable to a guitar signal is clipping, but it doesn't sound like a "distortion pedal".  True, it sounds colored, and if you're listening the distortion is detectable, but it's not terribly crackly or fuzzy. 

With hot pickups, you can make the minibooster spit at you, no problems...but for most guitar signal levels it's clean.  It spits the most on the attack (naturally), which is a relatively short period of time so you don't really hear the fuzz since the decay level isn't high enough to clip much if at all.

[amz-fx]

The text on the picture from the original National appnote pretty much explains it - the more gain the circuit has, the more "dynamic range you sacrifice", as it states.

That's a little misleading since the statement applies equally to any amplifier circuit!

The question was, how much larger gain does the Mini-boost have compared to a simple JFET gain stage like the Fetzer?.

A lot more, and it depends on the particular jfet device that you are using.  A simple common source gain stage may amplify about 16x while a mini-booster could go 40x or 50x...  remove the C6 capacitor for a bit less gain.

regards, Jack

[Roobin]

Circuit maker is also a bit odd at times: I tried a simple, hard clipper, with diodes to ground, and it did nothing. Anyone else got any experience with Circuit Maker?

[JimRayden]

The text on the picture from the original National appnote pretty much explains it - the more gain the circuit has, the more "dynamic range you sacrifice", as it states.

That's a little misleading since the statement applies equally to any amplifier circuit!

Why should it be misleading then?

The question was, how much larger gain does the Mini-boost have compared to a simple JFET gain stage like the Fetzer?.

A lot more, and it depends on the particular jfet device that you are using.  A simple common source gain stage may amplify about 16x while a mini-booster could go 40x or 50x...  remove the C6 capacitor for a bit less gain.

regards, Jack

Thanks, you've been most of help.

Circuit maker is also a bit odd at times: I tried a simple, hard clipper, with diodes to ground, and it did nothing. Anyone else got any experience with Circuit Maker?

If you just tried to put diodes across a signal generator, it doesn't work that way. You'll have to put a resistor in series with the generator, so it basically turns the voltage differences (between sine and clipped) into heat.

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Jimbo