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Dirty-South Blues Harp forum: wail on! > cm element 1megaohm to only 500k input in pedal?
cm element 1megaohm to only 500k input in pedal?
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Udderkuz03
52 posts
Oct 14, 2014
12:42 PM
My bugera amp has 1 megaohm output Mic works fine-not so fine into rp355 pedal. Pedal I believe is 500k input 1/4"-100k output 1/4"... My question is can I put a modified cap or resistor in the input to raise it to 1 megaohm and then have the output raised to what I don't know but it seems like 1 megaohm from Mic to amp works so why not raise pedal output..Also who works on these rp355s, or where do I get a schematic diagram of the circuits? I was thinking if no one you fellas could turn me on to who could mod it, I would take it to a local electronics shop with a schematic diagram and let them handle it...so, anyone able to straighten me out?
Greg Heumann
2860 posts
Oct 15, 2014
7:55 AM
500K input impedance is more than high enough for a CM. Even 100K is OK. Changing the output impedance of the pedal? Probably can be done but it would not be trivial. You'd need access to the schematic and a good engineer to work it out for you. It is highly likely It will be more involved than just changing/adding a cap or resistor.
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***************************************************
/Greg

BlowsMeAway Productions
See my Customer Mics album on Facebook
Bluestate on iTunes
NathanLWBC
5 posts
Oct 15, 2014
10:31 AM
I looked, and I couldn't find a schematic, so I can't really answer the question. However, the work is probably way more trouble than it's worth, like Greg said. I'd suggest you just find another way to get your effects. You can probably sell it off to a guitar player and buy something that's either harp specific or easier to mod.
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--Nathan Heck
Lead Technician, Lone Wolf Blues Co.
customerservice@lonewolfblues.com
Udderkuz03
53 posts
Oct 16, 2014
8:43 AM
To greg heumann:
I was just thinking from what I had learned from you guys here at MBH is that following the impedance path from Mic. to pedal to amp should be 1 megaohm output (Mic.) to 7-10 megaohm input (pedal) to 1 megaohm input (amp)...trying to get top tone without it being overloaded with 1 megaohm microphone overloading a 500k ohm input in the pedal...
Edit:- I just remembered greg I got the controlled magnetic element from you and I talked to you on the phone or E-mail and you said the volume pot on my bullet Mic. (recent model) wouldn't have to be changed..so does the same 14k ohms come last from the pot or does the 1 megaohm cm element change that before it goes into the pedal?... before I go any further with this?...

Last Edited by Udderkuz03 on Oct 16, 2014 9:32 AM
Greg Heumann
2861 posts
Oct 16, 2014
10:04 AM
@Udder - sorry I'm not sure I understand where your 14K comes from but when it comes to impedance - within one circuit, such as an element to a volume control to a pedal - everything has impedance and can be thought of as resistors in parallel. Doesn't matter what order - every resistor added lowers the impedance. The formula is r1r2/r1+r2.

So, for example, if you have a 1M ohm volume control and you're plugged straight into an amp with 500K ohm input impedance - the formula is 500,000,000,000/1,500,000 = 333,333 = aka 333K ohms. Note the result of this formula is always lower than either of the input values.


When you have more than 2 resistors, take the 1st two and apply this formula - then use that number as R1 and apply it again with the third resistor as R2, etc. When talking about the load an element sees you don't include the element - only the stuff downstream - and THAT only to the first stage that re-amplifies the signal. That means for most pedals WHEN THEY ARE ACTIVE the pedal's input is the last thing the element sees. The signal is regenerated by the pedal before it heads to the amps so the impedance of pedal-to-amp is unrelated to the mic circuit.

In the end - you're way overthinking this. If you are using a CM don't worry. If you're using a crystal make sure you have the highest possible input impedance. That means your volume control if you have one, your pedal - and your amp if your pedal is in true bypass mode when it is off (or if you don't use a pedal).

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***************************************************
/Greg

BlowsMeAway Productions
See my Customer Mics album on Facebook
Bluestate on iTunes

Last Edited by Greg Heumann on Oct 16, 2014 10:05 AM


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