THAT Compressor - help needed

[dtrax]

In an effort to learn more about electronics, I decided to take some simple schematics and prototype them. Going through the THAT Design Notes, I started with DN00A; a basic hard knee compressor/limiter (controls for Threshold, Ratio, Makeup Gain) and is a fairly simple schematic. HOWEVER, I'm stuck on one area. Here's the schematic in pdf for reference: http://www.thatcorp.com/datashts/dn00A.pdf

In the above linked schematic, I'm following Figure 1. I'm confused about one symbol on the schematic. It appears 2x, once running parallel to ground from the negative side of CT, and again on the negative side of C4. The symbol is a triangle with a "1" inside. Can anyone help clarify what that is? Initially I thought it was ground, but it doesn't make sense in regard to CT...

So far, it's been easy to proto on veroboard. If all goes well and I like the sound, I may elaborate on the schematic by adding balancing circuits to the input and outputs, soft knee control, switchable time constants, etc.... I don't expect it to sound like a $1000 compressor, but if it's something like a dbx160A I'd be stoked. But, I just want to get this sucker working before I get ahead of myself.  8)

Thanks for any help!

 

[abechap024]

That symbol is usually used to denote a ground of some sort, whether its "analog ground" or "power ground" I wouldn't worry about it too much, because whatever it means those 2 places are supposed to be connected to ground.

Let us know how it sounds! I have some old SSM compressors based on more or less the same type of topology and I think they sound great.

 

[dtrax]

That symbol is usually used to denote a ground of some sort, whether its "analog ground" or "power ground" I wouldn't worry about it too much, because whatever it means those 2 places are supposed to be connected to ground.

Let us know how it sounds! I have some old SSM compressors based on more or less the same type of topology and I think they sound great.

Thanks for clarifying for me! I'm pretty close to wiring it up; I should have her done by tomorrow. I'll post some clips, assuming all goes well....

 

[andrejs]

I suggest to try soft knee circuit in threshold amplifier. In my opinion it sounds cleaner than hard knee. Adaptive release time ability also gives improvement.

 

[abbey road d enfer]

In the above linked schematic, I'm following Figure 1. I'm confused about one symbol on the schematic. It appears 2x, once running parallel to ground from the negative side of CT, and again on the negative side of C4. The symbol is a triangle with a "1" inside. Can anyone help clarify what that is? Initially I thought it was ground, but it doesn't make sense in regard to CT...

That means that these two points must be connected as close as possible, and to a stiff ground, typically via a dedicated track going to the regulators reference. Although they are both grounds indeed, they carry relatively large current peaks and must be prevented to pollute the rest of the ground. I don't subscribe to "I wouldn't worry about it too much". Failure to take proper care of this leads to unnecessary distortion. I believe this is explained in other app notes.

 

[JohnRoberts]

+1 layout advice...  Many schematics include multiple ground designations to advise routing.

JR

 

[surfkat]

That means that these two points must be connected as close as possible, and to a stiff ground, typically via a dedicated track going to the regulators reference. Although they are both grounds indeed, they carry relatively large current peaks and must be prevented to pollute the rest of the ground.
[/quote]

Please explain "dedicated track going to the regulators reference". I assume that means you would NOT connect it to the ground plane on your circuit board. Does it go direct to a chassis ground?

 

[abbey road d enfer]

That means that these two points must be connected as close as possible, and to a stiff ground, typically via a dedicated track going to the regulators reference. Although they are both grounds indeed, they carry relatively large current peaks and must be prevented to pollute the rest of the ground.

Please explain "dedicated track going to the regulators reference". I assume that means you would NOT connect it to the ground plane on your circuit board. Does it go direct to a chassis ground?
[/quote] It shouldn't go to the ground plane, you're right. It should go directly to the point where the regulators reference and the smoothing caps get together.