Shiino Vesta Fire Compressor (with schematic)

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Shiino Vesta Fire Compressor (with schematic)

Postby floris » 30 Dec 2017, 02:52

I got a Vesta Fire Compressor of eBay that was not working.
Replacing the 6552 dual opamp with a NE5532AP dual opamp fixed it.

DC jack did not have a wire for GND to the PCB, grounding of the DC power was done via the enclosure.

Here are some gutshots (as can't find anything on this compressor on FSB):

7.jpg


2017-12-29 16.37.12.jpg


2017-12-29 16.38.57.jpg


2017-12-29 18.49.07.jpg
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Re: Shiino Vesta Fire Compressor (with schematic)

Postby floris » 30 Dec 2017, 03:13

And here is a schematic that I traced (Version 1):

Vesta Fire Compressor Schematic V1 - 2017-12-30 by Flo.png


Basically it is a feed-backward compressor with:
- Q2 KSC1815 NPN transistor as a variable resistor, parallel to the 100k R6 resistor which makes up a voltage divider of the signal with the 47k R5 resistor.
- IC1 dual opamp (was a 6552 which I replaced with a 5532) with a full wave rectifier at it outputs.
- IC1A has a Sense pot that sets the gain of the opamp.
- IC1B is an inverting stage with -1 gain.
- Output of IC1A goes to the 20kA Level pot for controlling the output volume.

I have omitted the bypass/FX switching, flip-flop and LED.
2 points in the schematic are labeled to go to the bypass/FX switching:
- Out To Switching CLEAN.
- Out To Switching COMPRESSOR.

I think the the full wave rectifier C7 C8 D2 D3 Q3 Q4 makes sense.
But I'm not completely happy with the components connected to the base of variable resistor Q2: R19 R20 D5 C11 D4.
Perhaps someone can check my schematic to see if it makes sense like this?
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Re: Shiino Vesta Fire Compressor (with schematic)

Postby floris » 30 Dec 2017, 16:51

An extra gutshot with the pots and DC jack:
2017-12-30 16.47.47.jpg
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Re: Shiino Vesta Fire Compressor (with schematic)

Postby tube-exorcist » 02 Jan 2018, 02:43

R19-D5 form a voltage reference of 0,65V

R20-C11 acts as a noise-filter for the voltage reference even when the main purpose of R20 is for the release time. Attack is determined by R18+C11

D4 is there to reduce the voltage reference to zero without a (sufficient) signal.

Purpose of this arrangement is to lower the threshold of operation.
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Re: Shiino Vesta Fire Compressor (with schematic)

Postby floris » 02 Jan 2018, 16:01

To me, D4 seems to be not needed. I would expect the Base Emitter diode of Q2 to already have that function to "reduce the voltage reference to zero without a (sufficient) signal. ... to lower the threshold of operation."
D4, in series with the Base-Emitter diode of Q2, makes Q2 less sensitive as there is an extra 0,6V threshold to "overcome". Doesn't that defeat the purpose of using D5? I expected D5 to be there to compensate for the Base -Emitter diode of Q2... so why the extra D4?

Also Q3 is not clear for me. Q3 Q4 look like a sort of Darlington configuration with Q3 providing extra current amplification for Q4. I would expect that having only Q4 and not Q3, would be sufficient for buffering the full wave rectified signal. Would Q4, without Q3, be too much load on the rectified signal? I think not, because it is powered by the low impedance of the opamp outputs... :?:
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Re: Shiino Vesta Fire Compressor (with schematic)

Postby jonasx26 » 07 Apr 2018, 15:43

floris wrote:To me, D4 seems to be not needed. I would expect the Base Emitter diode of Q2 to already have that function to "reduce the voltage reference to zero without a (sufficient) signal. ... to lower the threshold of operation."
D4, in series with the Base-Emitter diode of Q2, makes Q2 less sensitive as there is an extra 0,6V threshold to "overcome". Doesn't that defeat the purpose of using D5? I expected D5 to be there to compensate for the Base -Emitter diode of Q2... so why the extra D4?


My guess (after very brief, cursory glance) is that D4 probably does two things;

1) It shifts the effective "threshold" level by influencing the quiescent bias of the shunting transistor Q2. As you say, it adds another ~0.6V to the voltage required to turn on Q2.
ALL diode drops, including base-emitter junctions, in the path from the cathodes of D2 and D3 leading up to the base of Q2 influence the "threshold". Maybe D4 was added to shift this somewhat, maybe to compensate for or shift the range of effective "threshold" and sensitivity that is made adjustable through the "SENS" potentiometer.

2) Makes the charging/discharging (approximately the attack/release) of C11 asymmetric.Charging through R19 and R20 takes twice as long as discharging through R20.

floris wrote:Also Q3 is not clear for me. Q3 Q4 look like a sort of Darlington configuration with Q3 providing extra current amplification for Q4. I would expect that having only Q4 and not Q3, would be sufficient for buffering the full wave rectified signal. Would Q4, without Q3, be too much load on the rectified signal? I think not, because it is powered by the low impedance of the opamp outputs... :?:


It might add some thresholding and current gain. But most importantly, Q4 would never turn on without Q3 because of D2 and D3,.


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Re: Shiino Vesta Fire Compressor (with schematic)

Postby jonasx26 » 07 Apr 2018, 15:51

I did not read the thread :oops: tube-exorcist is spot on.
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