Do boosts act as a buffer?

[Gus]

Not for me I was just asking. 

[R.G.]

It's funny. Asking about starting up an effects company seems to happen coincident with learning to solder. 

[Paul Marossy]

It's funny. Asking about starting up an effects company seems to happen coincident with learning to solder. 

Yeah, until reality slaps you in the face. 

[liquids]

that is to say, while many boosts may not exactly be good buffers, my conclusions were that they are often a step up from just pickups on long cable runs/ big pedalboards, to my non-technical ears.

Your ears are right.
But then it's cookbook-simple to do a good buffer.

I realize I'm resurrecting an old thread for only semi-related reasons here....but humor me. Since I'm ever using Duncan's tone stack calculator when I don't have my workbench in front of me and a slew of time to do trial and error, for the sake of doing reasonable, accurate tone control experimenting, does anyone know the output impedance range of a 'standard' mini-booster?  R.G.'s written that the SRRP is about 5k, and that's been very helpful as a reference.  Similar info for mu-amps would help.   Likewise, for a Mosfet doing voltage gain.  

What I've found on jack's site is useful but minimal "The mini-booster has a high input impedance but a moderately high output Z, and is not a good buffer either."  Little more said.  Likewise for his mosfet boost in particular though I'm thinking more generally than that specific circuit...he says "the moderately low output Z is capable of driving almost any circuit that follows."   Anyone have numbers or ranges?

I guess it wouldn't matter for the most part if you just plug in a 'simple cookbook buffer' afterward, but thus far I've found, in my experiments on multiple occasions and scenarios, that putting a buffer after such stages often causes the buffer to clip, rather than simply improve the output impedance...even when using a LM833 (not rail-to-rail but very good op amp) as a buffer @ 24v, as I have lately, while the mu-amp types slamming into them only are running at times at down to 9v or so.  My only work around is placing the master voltage divider/volume control between them, but that's not realistic in some designs, so you often do have to 'work with' the poor output impedance.  'Working with' a known output impedance, if the case is as above, is useful for filtering calculations.  

I wish I had realized, let alone known the numbers earlier, but there's no time the present!  

[R.G.]

I realize I'm resurrecting an old thread for only semi-related reasons here....but humor me. Since I'm ever using Duncan's tone stack calculator when I don't have my workbench in front of me and a slew of time to do trial and error, for the sake of doing reasonable, accurate tone control experimenting, does anyone know the output impedance range of a 'standard' mini-booster?  R.G.'s written that the SRRP is about 5k, and that's been very helpful as a reference.  Similar info for mu-amps would help.   Likewise, for a Mosfet doing voltage gain.  

What I've found on jack's site is useful but minimal "The mini-booster has a high input impedance but a moderately high output Z, and is not a good buffer either."  Little more said.  Likewise for his mosfet boost in particular though I'm thinking more generally than that specific circuit...he says "the moderately low output Z is capable of driving almost any circuit that follows."   Anyone have numbers or ranges?

Good question - but complicated answer.
A Mu-amp has a high output impedance. The simple way to find out what it is is to measure it's output unloaded, then load it. The load which makes output half as big is equal to the output impedance. When I was writing about the SRPP, I did that, but I didn't keep the notes and exact data.

I did a quick sim run. I did a switchable SRPP/Mu amp from 2N5484 JFETs, which are available easily in my sim library. Stock setup with source resistor bypassed with a 100uF cap and a 5K isolation resistor in the middle gave 39db gain in mu-amp and 44db gain in SRPP, about five db more gain as an SRPP. That was with a many-megohm load. The Mu-amp dropped to half output with 39K loading (that will vary with JFET and isolation resistor) While the same parts run as an SRPP by un-shorting the isolation resistor gave half output with a 5K load.

The SRPP seems to have 5db more gain and 1/10 the output impedance of a mu-amp for apples-to-apples setups. I'd call the mu-amp about a 30K to 100K output impedance, depending on the devices and such, and a similar setup for SRPP about 3K to 10K and double the gain. The extra gain is almost certainly because the isolation resistor removes loading from the bottom JFET. Note that the bias resistor for the top JFET is also a load on the bottom JFET drain; changing that will also affect things. I used 3M in both case.

For a MOSFET in a simple amplifier setup, the output impedance at the drain will be the drain resistor to within a very close approximation. The MOSFET drain is a quite-high-impedance point.