500 series Level-Loc project

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JMan

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Oct 26, 2019
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366
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@Bobby Baird wow, thank you for all that info! Very helpful indeed!

Okay, so to sum up, it would look like this, right?

Bypass - DPDT on-none-on
Threshold - DPDT on-off-on
Release - SPDT on-off-on
Pad - ""

IC1 - THAT1246

C17-C20 - 0.1uF electrolytic caps

Out of curiosity, you show a picture above that appears to show several ceramic caps connected between Input and Chassis ground. Would you mind elaborating on what that is? Is that also to do with the 1246, or unrelated?
 

Bobby Baird

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Joined
Jun 15, 2013
Messages
195
Location
Austin, TX
@Bobby Baird wow, thank you for all that info! Very helpful indeed!

Okay, so to sum up, it would look like this, right?

Bypass - DPDT on-none-on
Threshold - DPDT on-off-on
Release - SPDT on-off-on
Pad - SPDT on-off-on
YES
IC1 - THAT1246
Yes
C17-C20 - 0.1uF electrolytic caps
Yes
Out of curiosity, you show a picture above that appears to show several ceramic caps connected between Input and Chassis ground. Would you mind elaborating on what that is? Is that also to do with the 1246, or unrelated?
From THAT 1240 series datasheet

To reduce risk of damage from ESD, and to
prevent RF from reaching the devices, THAT recommends
the circuit of Figure 4. C3 through C5 should
be located close to the point where the input signal
comes into the chassis, preferably directly on the
connector. The unusual circuit design is intended to
minimize the unbalancing impact of differences in
the values of C4 and C5 by forcing the capacitance
from each input to chassis ground to depend primarily
on the value of C3. The circuit shown is approximately
ten times less sensitive to mismatches
between C4 and C5 than the more conventional
approach, in which the junction of C4 and C5 is
grounded directly.
 

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JMan

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Joined
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Messages
366
Location
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Very cool! I had seen that on the datasheet but had been totally obtuse as to its application. Presumably you feel that this is worth doing in this circuit, since you in fact did it, and so I think I will too. Do I understand correctly that this modification is independent of the rest of the components on the board? (i.e. it doesn't require changes elsewhere)
 

JMan

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Joined
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Messages
366
Location
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Hey @Bobby Baird , first of all, thanks for your help so far on this! I've taken your suggestions, and I'm nearly done with the build, although I had to reorder some switches because the SPDTs that I got ended up being momentary in one position (info which was so deeply buried in one of those million-mile-long cover-all-variants data sheets that I totally missed it).

Anyway, I was thinking of using your .fpd for the front panel. However, I noticed that the indications on the panel are a bit different from the .dxf provided by @Eliani (specifically the release and threshold controls, which on Eliani's are pretty much linear from left to right), and I'm wondering if this represented further modifications that you made to the connections. The pad values are different as well -- wondering if this is to do with the 1246 vs 1250?
 

Bobby Baird

Well-known member
Joined
Jun 15, 2013
Messages
195
Location
Austin, TX
Hey @Bobby Baird , first of all, thanks for your help so far on this! I've taken your suggestions, and I'm nearly done with the build, although I had to reorder some switches because the SPDTs that I got ended up being momentary in one position (info which was so deeply buried in one of those million-mile-long cover-all-variants data sheets that I totally missed it).

Anyway, I was thinking of using your .fpd for the front panel. However, I noticed that the indications on the panel are a bit different from the .dxf provided by @Eliani (specifically the release and threshold controls, which on Eliani's are pretty much linear from left to right), and I'm wondering if this represented further modifications that you made to the connections. The pad values are different as well -- wondering if this is to do with the 1246 vs 1250?
Yeah his panel design to my knowledge was incorrect in the layout. Threshold controls by switch position can easily be determined by voltage divider. More resistance to ground more signal. Switch center I found to be normal. Throw to the left was more or crunch, throw to the right was most or crush.
Just use your continuity meter to trace the circuit voltage divider to the switch pad. This will tell you the relationship to the switch. Same with the release. Bigger cap longer release. The values are in parallel with the center posistion 1uF cap c14 so they add up. 1uF fast 2uF medium 5.7uF slow. So, if 1uF is the center of the switch there is no way Eliani's panel layout is correct. Pad, I determind by just pasing a sine wave through at unity center switch position is your default, so why even give it a reference? I saw a -20db drop on my cubase meter when switched to the left and -10 to the right. Just get yours built up and confirm for yourself. Fill free to use the panel or change anything. Eliani's panel mounting holes to secure the panel to the rack were not even centered correctly. I fixed that in my fpd file.
 
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