SSL 4K channel dynamics. (And more in future). PCB's/kits: Available!

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Electrobumps

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jasonallenh said:
I do have a couple questions though-

1) what do you do if you don't have VR2?? I used the THAT chip instead and the schematic references the other chip in the notes you're referring to.

2) I was able to set the same reference level, but I cannot reduce VR'2 to  get -5VDC at TP2. Instead, I just set my reference level per your instructions, and then used the SSL procedure to set 0DB (Create a 4db decrease when switching in). The THAT portion of Igor's schematic does refer to this point as "set 0db, so I am assuming this is still ok even though this ended up giving me about 4.8VDC at TP2 instead of -5VDC. I thought maybe the PCB was arranged so that either option you choose uses one half of an opamp, but the schematic says that's not the case. It's behaving like a compressor though! and you're right, the comp does behave better.

Just had a look a the Schematic.  You should have VR2.  I think you are referring to VR1

The THAT chip has a fixed resistor (R1) instead of a trimmer (VR1) data sheets might show the THAT chip is fixed and can not be adjusted.  I do not have time to compare data sheets at the moment, but if DC can be adjusted on the THAT I would have expected Igor to put a trimmer at position R1 as it is on the the AD536.


jasonallenh said:
I was able to set the same reference level, but I cannot reduce VR'2 to  get -5VDC at TP2. Instead, I just set my reference level per your instructions, and then used the SSL procedure to set 0DB (Create a 4db decrease when switching in).

This is my thoughts, but could be wrong and do not have the THAT version to experiment!

What DC measurement do you get at TP1 at 1.55VRMS. I presume this will 0.2VDC

This ideally would be 0VDC.  However as you are fixed  you probably will not be get exactly 0VDC.  I think you want to get -5v difference.  So if TP1 reads 0.2VDC set TP 2 to -4.8VDC to achieve the the -5VDC. 

I think this will then create the 4db difference as per the SSL manual? 








 

HerbertR

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Hi, does anybody know how to solve the issue to use a nowadays more common INA 137 instead of the "hard come by" That 1246  Input Reveiver? The That 1246 does -6dB and the INA 137 does 0dB what I know. Is it possible to doubble a Resistor Value to half the Voltage? I have read for unity gain you need -6dB with the output Reveiver That 1646. My idea was to doubble the Resistorvalue of ONE of that ones:

-R115 after the Ina137 Output from 68 Ohms to 130 Ohm, or..

-R102 before of the That 2181C from 20K Ohm to about 40K Ohm, or...

-...or like Igor mentioned in the BOM - R3 which goes parallel in front of the AD536-In to the Ground from 10K Ohm to 22KOhm
What do you think Guys..? i would appreciate for some help! BR Herbert
 

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HerbertR

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I ve finished my builds. They are working pefectly.
Some things to mention:

-do not use IC Sockets for the two LM3914 VU ICs, it is to high at the end

-Calibration was not 100 Percent clear, so I did set the Thresholdset similar to a 1176 Calibration -> 0,86 V 1kHz SineSignal +1dBU on the Input, Max Ratio, Thresholdpot to 0dB, and set the Pot near the AD536 till on the Output was reached a 1dB Drop to 0,78V. Thats it. GR shows exactly halving the I/O Voltage 6dB GR on the Meter.

-Symmetry Pot - I did the adjustment with the the DAW Analyser, I matched the Spectrum between my two Units as similar and low Noise/Harmonics as possible by using also a 1kHz 0.78V Sinesignal. This Pot has a big impact on the sound in my Units. I also could lower the Outputlevel by to achieve nearly Unitygain between my replacement INA137 Input-Receiver (Instead of the That1246) and the original That 1646 Outputreceiver. The Window where this Symmetry Pot works perfectly is very narrow and can give enormously Stereoids to the Soundimage

Excellent Build, the Compressor sounds nice, the Gate is excellent - awesome musically....
 

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Electrobumps

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HerbertR said:
I ve finished my builds. They are working pefectly.
Some things to mention:


-Symmetry Pot - I did the adjustment with the the DAW Analyser, I matched the Spectrum between my two Units as similar and low Noise/Harmonics as possible by using also a 1kHz 0.78V Sinesignal. This Pot has a big impact on the sound in my Units. I also could lower the Outputlevel by to achieve nearly Unitygain between my replacement INA137 Input-Receiver (Instead of the That1246) and the original That 1646 Outputreceiver. The Window where this Symmetry Pot works perfectly is very narrow and can give enormously Stereoids to the Soundimage

I'm surprised you found this setting as sonically dramatic.  Not the case in my builds. 
 

Blondino

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Sep 4, 2019
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Hi guys, is this build still available somewhere? I trying to access Igor website or other links in here but seems everything has been wiped out from the web :(
Thanks
 

JMan

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Oct 26, 2019
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295
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Chicago
Hi guys, is this build still available somewhere? I trying to access Igor website or other links in here but seems everything has been wiped out from the web :(
Thanks
It has bounced around a bit, but is currently available from Frank at frontpanels.de
 

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