Anyone here havea MXR Micro amp to look at the insides, or know what's inside?
My layout has a 15uF output cap (from CJ's scematic), Francisco's has a 1.5uF output cap, which is in the original? No discussion needed about which will actually sound better, I just need to know the original value.
What's the deal with that 22M cap off the input?????
Anyone, let me know if you can help me out.
Thanks,
JD
Whoops! Sorry Doug, this thread is YACQ (Yet Another Clone Question)
:D
JD
It's definitely a 22 Meg resistor, and a 15uf.
From a dumbass
RDV
22M resistors are *definitely* available - most stores only stock upto 10M though.
It doesn't actually make sense to have 2.2M at the inpur because the resistor to Vcc/2 is 10M and 2.2M would swamp it. The whole idea of the large resistor values to to have a very high input impedance preamp - it's actually suitable for piezo's.
Looked through my stuff and can't find any microamp pics. All I can say is MXR have used 15uF caps before but I haven't seen any 1.5uF caps- that doesn't mean anything!
Quote from: RDVConsidering that I've never seen a 22 Meg resistor, you can almost bet that CJ left a few decimals out of his schematic. 2.2 Meg and 1.5uf are almost sure bets.
An Opinion
RDV
Just used two 22 meg resistors in the MXR envelope filter. So they are definitely used in some pedals.
Bill
Just for the record I'd never seen one either.
http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=458206&e_categoryid=5&e_pcodeid=01428
Regards
RDV
The 1.5uf cap is for the usual function: DC blocking. There is a whole lotta space in the spectrum between pure DC and those frequencies where the cap starts to affect audible low end. In many cases, you could easily triple or quadruple the value of the existing cap without hearing any difference whatsoever in bass content, so it should not surprise you that output caps can vary considerably in the same model. That is one of the saving graces of knowing a bit about these things. I can't begin to count the number of times where I look at the schem and my parts bin and realize I don't have one of those at the moment. Then I do the math and realize that using what I *do* have is going to shift the low end rolloff (which is only a shallow 6db/oct anyways) from something like 2hz to 20hz, which no one, except maybe earthworms, will ever notice.
FWIW, a 1.5uf cap and 10k resistor to ground (we'll ignore the 470R resistor for arguments sake) has a 6db/octave low end rolloff starting at around 10-11hz.
Hi JD, I'd love to see inside a real MXR Microamp myself, I hope somebody can open one up. But until then, I'm inclined to agree with the other guys, the 22M is a commonly used resistor (Jack Orman even suggested I use a 22M in a Mini-Booster I built on one of your pcbs to boost an acoustic guitar piezo), and I've never seen, heard of, or have been able to locate a 1.5uf cap. The more I look at the schematic on CJ's site, the more I believe the values are definitely 22M and 15uf.
FWIW, I built my Microamp (God bless you and Francisco for ready-to-solder boards) with the 22M and 15uf, and I think it sounds great, very clean boost. I think its less tone-coloring and gritty than my stock JOAM Mini-Booster.
Still yet, I'm happy to be proven wrong if somebody can actually open up a real MXR, and these AREN'T the correct values.
Thanks, Russ
Quote from: RussI think its less tone-coloring and gritty than my stock JOAM Mini-Booster.
I think the JOAM Mini-Booster is designed to be tone-coloring and gritty by popular demand. If you want clean and neutral, build the Mosfet boost (or the Microamp of course). It would be nice if a schematic noted if the parts values checked against an actual specimen (which I guess is what JD is trying to do).
Kerry M
Having built all three (Mosfet Booster, Mini-Booster, and Microamp), I'd be in total agreeance with you, Kerry.
Russ
Thanks guys for all the input. I really appreciate it. I wasn't really questioning the validity of the 22M input pulldown, just wondering why it was so high, now I know, thanks.
I built it with the 15uF and 22M pulldown too and it sounds great to me. As Mark said, the 15uF is probably not a "critical" value to use and they are somewhat hard to find. I'm guessing a 10uF, or whatever, would work fine.
I just posted somethng new, useful and very similar to this Microamp at my site, check it out. :D
http://www.generalguitargadgets.com
Thanks again!
JD