QA400 analysis of 1176 ratios

[Bo Deadly]

I needed a quick and dirty way to confirm my custom 1176 board was working.

If you happen to have a QuantAsylum QA400 it has a macro called THD vs Output Level. Here is a plot of that macro for each ratio:

You can see clearly the ratios are indeed working as expected. Very easy!

More specifically, I used the following macro parameters:

Level:
Start -20 dB
End 0 dB
Step 2 dB
Freq:
Start 200
End 2000
Per Oct 2

Attack and release we set full CW.

I saved each CSV file for each ratio (No gain reduction, 4:1, 8:1, 12:1, 20:1, SLAM) and then imported them into Excel.

I measured the exact level on the wiper of the input level control with the QA400 output set to -10 dBV. Turned out to be 2.0 Vpp or -0.8 dBu.

I created a new table with all of the 1.1kHz columns and adjusted to dBu using said measured value.

Then I just inserted a scatter plot.

Of course the THD values themselves are somewhat meaningless. But if we assume that THD reflects the amount of compression, then the curves can be compared to give a meaningful result. Visually it's quite clear that it's working.

Incidentally here's a pic of my 1176 board:

The preamp, GR, meter driver and controls fit in two stacked 4.7"x1.5" boards. The board to the left is a THAT1206/THAT1646 balanced IO board and the board in the background is the power board. Not a conventional build but it works.

 

[ruffrecords]

I really like the knobs you are using. The switches look like 1/8 inch shaft types. Do the knobs fit them directly? Where do you get them?

Cheers

Ian

 

[Bo Deadly]

I really like the knobs you are using. The switches look like 1/8 inch shaft types. Do the knobs fit them directly? Where do you get them?

Those are 0806D1 from smallbear electronics. Switches are Grayhill 1/8" 56DP30. I used TE Connectivity KR104 shaft adapters.

However, those particalar knobs are too small and they're not deep enough.

A larger knob that is pretty much identical but larger is 0806D. Also, another really nice knob that complements these is 0825C.

Here's a pic of all three:

The lower left is the 0825C. They're narrower than even 0806D1 but they're long and have a nice grip to them.

One word of caution though. The KR104 adapters have a slot that allows the set screw to grip the shaft and not the adapter. This sounds good but the set screw does not have a lot of teeth in contact with the knob. I got some of of the phenolic versions of the one knob and the set screw lost it's grip. Fortunately I also got the ABS version too and those worked fine but I don't crank on that set screw too much. I will probably get some longer set screws from McMaster Carr but another option would be to use the shaft adapters from capi-gear which are crimp style instead of slot. But I think KR104 with longer set screws would probably have a better grip.

As they are, Grayhill 56DP30 with KR104 and these knobs have a very solid professional feel. You might think a 1/8" shaft would have a crappy feel or the knob my not be seated properly but that is absolutely not the case. It might not survive a direct hit with the headstock of a guitar but there's a lot of modern consumer gear that will not.

 

[ruffrecords]

Those are 0806D1 from smallbear electronics. Switches are Grayhill 1/8" 56DP30. I used TE Connectivity KR104 shaft adapters.

However, those particalar knobs are too small and they're not deep enough.

A larger knob that is pretty much identical but larger is 0806D. Also, another really nice knob that complements these is 0825C.

Here's a pic of all three:


The lower left is the 0825C. They're narrower than even 0806D1 but they're long and have a nice grip to them.

Cool. I think these are identical to the ones I get from Thonk here in the UK:

https://www.thonk.co.uk/shop/1900h/

If you scroll down it says they are an ABS moulding Davies 1900H clone. I just love the huge range of colours they come in.

Good points about the KR104; noted.

Cheers

Ian