Quiz about a mosfet booster

[tca]

I've been testing several mosfet boosters (only one device) and I would like to propose some experiment (I'll reveal the complete circuit in a week).



You will find several mp3 files that represent different bias points. You are asked to choose, or not, one that you like the most in two options, small input signal and hot input signal.

Here is the clean bypass signal: clean0.mp3

Small input

- clean1.mp3
- clean2.mp3
- clean3.mp3

Hot input

- od1.mp3
- od2.mp3
- od3.mp3

Here is the quiz. You can only vote one time. You can see the results after voting.

Enjoy your listening! And comment away.

Cheers.

[bool]

clean would be something inbetween the 1 and 2, and OD is 2 .. no contest

I was down this route many times so it's somewhat obvious to me..

One thing I must ask: are you -sure- that you want to connect the input cap directly to the gate thus skipping the gate stopper resistor and it's function? I would connect the cap to junction R3 R4 R5, but that's only me...

[tca]

R3 and R5 sets bias and R4 the input impedance, the circuit does not seem to oscillate at high frequencies, and so the typical 100Ohm resistor at the gate could be removed (and btw, yes, there is also a Zener missing from source to gate).

[GibsonGM]

Clean1 and OD3 for me. 

[deafbutpicky]

clean1, overdrive2. Let me guess, they're taken in reverse order...

One thing I must ask: are you -sure- that you want to connect the input cap directly to the gate thus skipping the gate stopper resistor and it's function? I would connect the cap to junction R3 R4 R5, but that's only me...

no big difference concerning the high input impedance of the mosfet, right?!

[tca]

clean1, overdrive2. Let me guess, they're taken in reverse order...

Each pair (clean1, od1), (clean2, od2) and (clean3, od3) correspond to the same bias. The only difference in each pair between clean and od is the amplitude of the input signal: clean A=0.35V, OD A=1V.

[tca]

Responses so far (with 125 views):



Thanks.

[GGBB]

I can't hear any differences - all three sound identical in both small and hot input cases.  Am I losing my hearing? 

[kingswayguitar]

I can't hear any differences - all three sound identical in both small and hot input cases.  Am I losing my hearing? 

ditto

[GGBB]

I can't hear any differences - all three sound identical in both small and hot input cases.  Am I losing my hearing? 

ditto

Thank-you.  (Misery loves company.)

[pappasmurfsharem]

I can't hear any differences - all three sound identical in both small and hot input cases.  Am I losing my hearing?  

ditto

Thank-you.  (Misery loves company.)

Playing through my Creative Labs Titanium HD (Arguably one of the best consumer level PC sound cards)
And through my studio monitors they all sound the same to me.

Putting Clean 1 and Clean 2 in audacity there on a few of the audio upswings there was a hair difference. Literally like 1-2 pixels

[tca]

I can't hear any differences - all three sound identical in both small and hot input cases.  Am I losing my hearing?  

ditto

Thank-you.  (Misery loves company.)

Playing through my Creative Labs Titanium HD (Arguably one of the best consumer level PC sound cards)
And through my studio monitors they all sound the same to me.

Putting Clean 1 and Clean 2 in audacity there on a few of the audio upswings there was a hair difference. Literally like 1-2 pixels

I know they sound similarly, but they are in fact different. Here is the voting so far:



Thank you for all the votes!

[slacker]

Clean 1 and 2 seem to have a bit more low end than 3, for example the low notes in the first phrase sound fatter, apart from that I can't hear much difference.

[alfafalfa]

To distinguish between them you should (imoh) record the clips with the same volume level.  Clip 1 clean is much louder than 2  & 3.

Alf

[Ben N]

The only one that really stood out for me was od 3, a clear winner--no SS-ey distortion artifacts, nice smooth overdrive. Clean 3 was a bit dull to my ears. I picked clean 2, but honestly there was little to no difference from clean 1. Both I thought lost a little bit of sparkle compared to bypass, but in a nice way for a boost--that tiney bit of edge that can get harsh when it gets loud. Assuming od3 and clean3 were biased the same, this makes sense.

[deadastronaut]

i like the Hissssssssssssssssssssssssssssssssssssssssss.... 

[tca]

So here the final outcome:



Thanks for all responses...

[tca]

... and here is the circuit:




Settings:

R1 = 100k
(clean1, od1), R1/R2= 1
(clean2, od2), R1/R2 = 3/2
(clean3, od3), R1/R2 = 3

I've added a tone Garnet type tone control (no loss). If you build it use a trimpot for R2 (with value R2=R1) and adjust to taste. Any IRF* will work, just trim R2. There is no need for a heatsink. You can also add a zener from source to gate, but I never broke a mosfet due to high voltage at the gate. I usually burn them with high currents!

I'm not going to comment the results, they seem quite obvious to me.

All the best.

P.S.

Dubbed "Budgie Booster"

[bool]

I knew that "2" variants were biased high. It's unmistakable once you are familiar with "that" sound. Also the choice of drain and source resistors can play some role in the overall tone. With the voltage you used, I'd go a bit higher, a 510R/51R combo. (Perhaps 3W wirewounds for extra mojo if you manage without oscillations ... who cares for carbon, mëtäl is where it's at).

How hot did your IRF get? Did you push the voltage any higher, 24 volts or so? Heatsink or no?

You could also try IRF7xx's. They can be a slight bit grungier. But Nelson Pass loves the 6xx series so go figure.

[tca]

How hot did your IRF get? Did you push the voltage any higher, 24 volts or so? Heatsink or no?

With 18V and a 470 Ohm drain resistor, it is just a 10 to 20mA current (depending on bias), so no heatsink needed. You could do some higher current versions (remove the tone control completely, C3, C4, and pot) and go up to 100mA with a 100 Ohm resistor and a 10 Ohm source resistor. But as you know, there is *always* a sweet bias point for any given current, and it also depends on the next stage.

You can not go to higher gains (>= x10) with this kind of biasing without a lot of treble cut (due to the input capacitance of the mosfet), one way to do it is to buffer the mosfet stage. I tend to prefer the buffered version for voltage gain stages and unbuffered for current and voltage gain (to drive a low output impedance, a speaker).

This circuit will work nicely with an SS amplifier, because it colors, in the good way, the guitar signal. It adds some what more low end and thickness, and the mids and highs seem more polished and less ear shredding.

I will try the IRF7* series soon.

Cheers.

P.S.

... Pass loves the 6xx series so go figure.

You can get/learn a lot from his projects, but take them with a pinch of salt