Regarding the AMZ Mosfet boost Buffer option...

[moritz]

Hi all,

Just started perfing the AMZ Mosfet boost, and i can't decide whether or not to add the buffer option in the "revised" schematic (see: http://www.muzique.com/schem/mosfet.htm -it's the 2nd schematic further down the page).

Basically, this would allow the pedal to also act as a mosfet buffer, like the one on http://www.muzique.com/lab/buffers.htm (being switchable between boost and buffer mode via a DPDT).

Anyway, what i'm wondering is how would this buffer compare to that of a Boss pedal on bypass mode? (what kind of buffering do boss use anyway... jfet? bipolar? opamp?) Is there any advantage of using this mosfet buffer over boss' bypass buffering? I mean, If I were to, say, use the mosfet buffer next to a boss pedal in my sigal chain, then all the pedals following these in the chain are going to receive a buffered signal input regardless of if the mosfet boost/buffer is there or not, right? This would kind of make the "buffer" option useless wouldn't it?... or is there something about the mosfet buffer that makes it a desirable addition?  

:?

[moritz]

boss' bypass buffering

Whoa... try saying that coherently after a few drinks!...  :|

[Alpha579]

boss' bypass buffering

Whoa... try saying that coherently after a few drinks!...  :|

lol!
i think im right in saying it would be a bad idea to have more than one buffer throughout your signal chain, it'll mess with your sound quite badly...so yu shouldnt need one, but its nice to have the option if you ever get rid of your non-tru-bypass pedals...

[OG]

My two cents:
first, i'm not technically competent enough to tell you about he advantage of mosfet versus jfet.
But for what i know, with the mos boost buffer circuit you have the advantage of a very high impedance, great for for instance if you plan to use an acoustic guitar, Otherwise, 1 meg is enough to avoid loading the signal down.
You may like it or not, because for me the point is do you hear a difference or not, and do you want to?
I have tried the 3 options : ic (tl071), jfet, and mosfet, even with a dpdt switch to "hear" the difference. Personally ( very subjective) the ic is the best one, totally transparent. Some say it sounds "sterile", (?) maybe. Broadshaw uses ic buffers in his racks, Cornish discretes...
jfet = possibly less parts, a very little but noticeable lost of gain (it is not really unity gain like with an op amp, and i find strange the idea of loosing signal first); and for my ears, mosfet in that configuration colours the sound to much. As a buffer, because the amz mosfet boost itself is really a wonderfull circuit, simple and brilliant.
Of course all this is in case you place the buffer fist in chain -some would put the booster last just before the amp-   and if you have a bunch of boss pedals after it, they will colour the sound. Will it be a problem, yes if you find it annoying ... ;-)  
If you admit there will always be some kind of signal degradation if, like the Boss, they are not true bypass (some would say even with Tr. BP but it's another debate like the "sound" of plugs) you could go with it.
Again, all this is very subjective, the important is what you hear.
Think i've been too long, sorry...
OG

[Ben N]

My untutored $.02, FWIW:
The Mosfet boost has much higher input impedance than any Boss (500k).  If you can hear the difference (and some insist that you can), the MFB first in the chain will give you a clearer, brighter, harder sound-more spank.  As to how many buffers you need/want, that depends.  A board full of Boss-type pedals in series is certainly too much, where you gain nothing but noise and distortion from all those extra devices in your signal chain.  But anyplace where a high output impedance is interfacing with a low input impedance is a good place for a buffer.  That is why I keep my CE-2 in front of my DanEcho--its output buffer keeps the relatively low-impedance input of the delay from sucking too much tone.  Also, if you have any kind of passive signal splitting going on, chances are you are halving the input impedance of something, and a buffer would be a good idea.  An example would be using the extra jack on an Electric Mistress.  That jack is just tied to the input in parallel, IIRC, so if you use to split off the uneffected signal, your effective input impedance is substantially reduced.  As someone pointed out, you may also want a buffer at the end of the pedalboard if you have a long cable to the amp, although I would think a bit of gain would be more useful there than simple buffering.
HTH,
Ben

[moritz]

Thanks guys! Once again, the helpful folks here have come to the aid of a stomper in need!

I've decided to leave out the buffer option, and keep it as a boost-only pedal -if I want to whack another buffer in my chain, i'll probably just make one of those nifty opamp buffers from AMZ...

Once again, thanks Alpha, OG, Ben for your input.  :wink:


...oh yeah, one more thing: while we're on the topic, does anyone know what kind of buffering boss pedals use when in bypass mode? Thanks.

[TheBigMan]

...oh yeah, one more thing: while we're on the topic, does anyone know what kind of buffering boss pedals use when in bypass mode? Thanks.

Depends on the pedal.  Older ones (E.g. SD-1, DS-1, DM-2 etc) use a pair of NPN emitter-followers as input and output buffers.  Some of the second series pedals (E.g. CS-2, DD-2, DM-3) used a FET buffer for a higher 1Mohm input impedance.  There are others (E.g. CH-1, CS-3, DC-2, RV-3, DD-5) which use opamp buffering.

[moritz]

Ok, thanks Big Man... my curiosity has been satisfied!