High Z And Low Z Mics

jurb6006 · 2015-02-06T01:23:53+00:00

Guy wants to use a powered speaker, I tbink a "Technical Pro" brand with a microphone. I couldn't get a print on it but I see there is nothing wrong w ith it. The boss thinks you should be able to do that but the fact is it SA YS LINE on it. Tht means it is meant to be fed by a mixer or something, rig ht ? Not a microphone or guitar pickup. There is no distortion and in the relatively simple circuitry there is almo st no way you would lose gain without some distortion. Does anyone really t hink the AC bypass cap for the feedback is bad ? I don't. Not when every ot her cap in the thing doesn't seem to be causing a problem. It has clean out put and nothing drastic in the frequency response. there it goes through a 33K resistor to the inverting input of an OP AMP ( one side of a 4558). I paralleled a 10K with that resistor, making it what, about 8K ? Arond in there. Technically this should just about triple the g ain or so but bring down the input impedance. Should be OK for a mic or eve n a guitar pickup. I can't reverse engineer this whole damn thing, but have a question. In case that the customer already has a low impedance mic and wants to use it, really I should be able to decrease the value of that restitor to like 200 ohms. I should get the required voltage gain but it will load the input a hell of alot more, probably to the point of having a problem with other sources. Not just the impedance but the gain, if someone was to plug a mixi ng board into it, it probably would not work correctly. (maybe to say the l east) However they would still have the line level XLR jack for that. If they had t ? Because it will have stock gain, I am not modifying that one. That is a little too much reverse engineering to do something wrong. Just use the da Anyway, I am just wondering if there are any unforseen ramifications to cra nking that value down to like 200 ohms. Another thing is protecting the OP AMP. If somneone plugs a powered mixer in there is it possible...

Feb 06, 2015 21 Replies

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rev.11d.meow 11 years ago

fy the >amp at all. D'OH "

AMPs.

lips just fine, no distortion. If there was a fault in the amp it would hav e to be rtow separate identical faults causing the same reduction in gain i n two separate OP AMPs.

You still haven't said anything about the microphone in use, but this is th e usual fix.

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Audio-Technica CP8201 In-Line Transformer

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ansformer

That answers your original question, which is in itself limiting the soluti on to Not include Volume control, which is essential for PA purposes.

I never said you are wrong or incorrect in your approach, just time-wasting and too costly in the long run.

$10 and you'd be done. minus Volume control, that is... :)

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rev.11d.meow 11 years ago

That red button is a locking mechanism, not a potentiometer.

If you want to pay $20 more, use it plugged into the XLR Line IN, and your balanced microphone cable into it.

But, you still don't have a Volume control.

You could Manually PWM the mic's On/Off switch Really Fast to get a Volume control in there. :)

Peace

Out

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