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AW

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Feb 15, 2021
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Great news It's compressing now, ran a bass track through it but sounds distorted and there are like sort of a popping sounds at high peaks, Is that because it's not calibrated?
 

Ilya

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There're no audio calibration for PYE, only meter calibration. This sounds like distortion, PYE is not very tolerant of high levels. What're your input and output levels? What's the threshold setting?
Also, the copmressor is very fast, so the peaks probably distort an input transformer.
 

AW

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Feb 15, 2021
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I see what you mean, brought done the level on the bass track, and distortion, and popping went away. Very different compressor compared to your LA2a, 1176 etc..
I just have to see where it belongs in a track.
Thanks IIya for your help, it's nice that you stuck with me to figure this out. I will be buying another PYE PCB, and face next month from you.
Tony
P.S.
I wonder why no one has chimed-in on this, This post has over 9k views, and only a few people have posted here including myself???
 

Ilya

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Glad we sorted everything out. Now you have a nice "patient" to play with your soon-to-appear scope :)
I wonder why no one has chimed-in on this, This post has over 9k views, and only a few people have posted here including myself???
No idea. Sometimes people like to find out what's wrong. Often it's like a detective book. But that's just my speculations.
 

AW

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One last question, If someone wanted to check there DC voltages against mine for trouble shooting they should be valid except the AC voltages after the SC transf will be different right?
 

Ilya

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They probably are. I started with AC readings and went right to the SC network, didn't pay much attention to DC. If your unit is behaving properly, then DC readings should be valid for the discrete oscillator version.
 

AW

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I guess I have another problem, when I apply the 1khz 0db(.775vrms) test tone to the input, and adjust R15 for 0db at output I can only get a max output of .353vrms(R15 fully clockwise)
Thresh=0, ratio=1:1, decay=1
 

Ilya

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Check the wiring of your output transformer. Make sure it’s wired as 1:3 step-up. From your AC chart it looks like it’s not 1:3.
 

AW

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I didn't have a output load on it when i took the measurement, I am getting .65vrms now with load connected at the output with R15 fully clockwise. I am pretty sure I have the output transf wired correctly, but I will double check.
 
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AW

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Output Transf is wired correctly
Ok I am a space, I took the output voltage in respect to ground when I should have taken it across the output molex connector,, getting 0db now with R15 around mid level.
 

AW

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I installed the compressor in my rack and ran some bass, guitar, and kick drum through it one at a time.
I think it's not working properly, I am getting pops, and the threshold led's peak whenever there is a slight peak increase in level of the track, like if the drummer hit the kick slightly harder it will pop. All my levels are fairly low when I track, so it's not that. I will send you an mp3 example tomorrow.
 
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AW

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Here are the samples
 

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  • bypass.mp3
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  • T=0 R=1_4 D=2.mp3
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Ilya

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Do you have C90 installed and not shorted out? If installed, try replacing it with a short and see what happens.
What's your chopper transistor?
Attached is what I get when I run your track through my unit. Compression LEDs show ~6-10dB of compression

As for calibration, you can check compression level by engaging either bypass or 1:1 ratio. You get the increase in level in bypass. The difference between this level and the level with compression engaged is your gain reduction. You need to adjust your generators so that you get 1dB for a first generator and 9dB for a second. This makes switching between signals easier and you can calibrate your meter faster.
 

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AW

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Feb 15, 2021
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I am using the BF824-215 for the chopper, I do have a pn3640 TO-92-3 package I got from EBAY, let me short out C90 and see what happens,,

 

AW

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Feb 15, 2021
Messages
116
Do you have C90 installed and not shorted out? If installed, try replacing it with a short and see what happens.
What's your chopper transistor?
Attached is what I get when I run your track through my unit. Compression LEDs show ~6-10dB of compression

As for calibration, you can check compression level by engaging either bypass or 1:1 ratio. You get the increase in level in bypass. The difference between this level and the level with compression engaged is your gain reduction. You need to adjust your generators so that you get 1dB for a first generator and 9dB for a second. This makes switching between signals easier and you can calibrate your meter faster.
I am still a little confused you say: Apply the 1kHz 0dBu test tone to the compressor input. Adjust the Threshold control so that the module compresses 9 dB?
What is the rms voltage for 1db, and 9db,, there are a lot of charts on this but want to make sure I get the input voltage correct.
 

Ilya

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1 and 9 dB readings are delta (ie difference). So the RMS voltage depends on the reference level. You can monitor your output signal level in the DAW and take a note of your reference bypassed level in dBFS. Then your goal is to set the threshold so that the output level is 9 dBFS less (adjust the threshold and ratio only, don't touch your signal gen!). For example, if you get -10 dBFS reading in bypass, you should get approximately -19 dBFS when compressing.
If you insist on AC volts RMS readings, I suggest setting your output level to a convenient reference (for example, 0 dBV), and work from there. You should be able to calculate V RMS for -9dBV easily.
 

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