I'm new at reading O-Scopes but it looks like the the audio signal is being compressed? What's the modulation at?
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Speech Processor??? Anyone Have Info
- Thread starter Mudfoot
- Start date
No modulation in this test. The input was simply a 1 kHz tone or voltage signal applied to the input of the circuit where a microphone would be plugged into. In the second part of the test, the blue trace is being limited from going beyond a certain point. It keeps the output signal at a more even level no matter how soft or loud a person would talk.
Sorry I can't explain it better. I guess it is a form of compression, dynamic range compression. Maybe sometime soon I'll do a test showing a demodulated signal and how it relates to an audio signal at the circuit input. Thanks so much again for posting that project.
I was thinking along those lines of compression. I was wondering how it operated last night and you answered my question. Cool!
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Waking up an old thread because I'm curious about the Top Gun SP-1A. It's about all that's available in this day and although I've read mixed reviews on them I wonder what you fellas might have to offer in terms of how well they do the job. If one were to install one into a rig of today, would it install between the mic jack and echo board or after the echo board? Not to stir the pot with the echo dislikers but just for educational purposes.
I am not a tech by any means, but if I remember correctly the SP-1A has an mic pre-amp circuit so it should go before the echo board. The echo board may also have a mic pre-amp also so you may need to watch that. 'Just applying the garage in garage out theory you want to make sure you have everything clean before applying echo effects. The Top Gun Tec website should have the install instructions.
Hold ON!
There is a numbering Error on the Schematic...
Radio Shack isn't around like they used to, so the Electret stated in the schematic isn't around either. So you'll have to take into consideration the Operational Voltage Range the Element is capable of operating in. R13 and R14 would have put too much emphasis (Working Voltages) on the higher end of many of the newer Condenser elements that would work, yet not in the Voltage Range the circuit biased the ORIGINAL part within.
(If I'm becoming a PITA - let me know...)
There is a numbering Error on the Schematic...
Original...
WHY?
Q1 and Q2 are not correctly
identified...
MK1 needs to be able to operate at
Voltage Range stated in Schematic...
REVISED
WHY?
Q1 and Q2 are not correctly
identified...
MK1 needs to be able to operate at
Voltage Range stated in Schematic...
REVISED
Radio Shack isn't around like they used to, so the Electret stated in the schematic isn't around either. So you'll have to take into consideration the Operational Voltage Range the Element is capable of operating in. R13 and R14 would have put too much emphasis (Working Voltages) on the higher end of many of the newer Condenser elements that would work, yet not in the Voltage Range the circuit biased the ORIGINAL part within.
(If I'm becoming a PITA - let me know...)
That's what I was assuming myself and you're correct about both echo and sp-1a having a preamp so that would be a critical part of setting up.
Andy, I'm lost my friend. I don't think that's the one I'm referring to.
This be the one
And you'd be correct - LOL - sorry about that...
I Went back a "page" to the start of the Thread and seen where a PDF of a circuit may be considered useful, but since no one spoke of it, I thought it would be wise to issue a correction to a potential problem - I see My Memo didn't get to your desk until after the fact - and of course. your Memo never getting back to my desk in time to stop the presses...
If you wonder where that schematic came from - look at Post #15.
It's a neat one to use - however, saw an obvious error no one spoke of, so felt it was kind of cool to see if anyone else in this thread could use such an Mic Audio Amplifier.
If anyone was curious, the use of the 2nd half of the chip was to develop a Negative-Going bias to the JFET which is set up as a current amplifier - so the NEGATIVE bias pulls down the apparent signal being sent to the 1st half op-amp - more downward in voltage that the Electret puts out - so there is less POWER present to amplify the voltage parameter of the signal - not it's current - so some symmetry is maintained - note the O-scope readings are symmetrical - no clipping - just audio level is adjusted to maximize to a level and stay there.
The phase difference is the propagation effect or "lag" due to the JFETs' purpose in the circuit is to Attenuate the input signal in relation to the output level selected by the user. If it had not been in there, the Op amp would have acted like an Voltage-Derived inverter amplifier - the amplified signal would be 180 out of phase - but due to the addition of the separate amplifier and Voltage-Multiplier - the effect is more 270 degrees out of phase.
What does this have to do with the SP-1 - not sure, the design for the SP-1 is a Quad Op amp with at least a clipper and feedback loop to handle the gain and leveling the two pots handle. The one in Post #15 - the Mic Audio compressor or "ALC" (Audio Level Control), is for those in the Radio world that need "Hot mics" to blare into the music or bass line for intros and yet not blast people off the Dance floor thinking someone's hitting the DJ.
It was fun...But sorry to interrupt...
Hi-Jack=Off.
.
The chip on the SP-1A is a Compander SA-571, I've built a few boards and they do work well. Although similar , the Cobra ST compander sucks and sounds like poop compared to the SP-1A IMO
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