mhuss

Re: Hairball Audio: 1176 Stereo Linking PCBs Support Thread
« Reply #200 on: July 08, 2016, 11:40:01 PM »
Just (finally!) finished my dual mnats 1176 with the Hairball red link cards . Both channels seem to work fine in dual mode. When in linked mode, sufficient input on channel 1 causes both channel meters to indicate GR as I would expect. However, the same input on channel 2 causes that channel to show /more/ GR while the channel 1 meter doesn't move.

All the connections and voltages on the red cards look good. However, I noticed that when I put in in dual mode, the input to the link switch (coming from pad 15 on the ch. 1 ratio board) goes flat - the signal stops. This happens even when the wire is disconnected at the red board (loop) end!  :o

I checked the DPDT switch and wires carefully with an ohmmeter and the switch seems to be working fine, and nothing is shorted to ground.

Any ideas what I should look at next?


joaofar

Re: Hairball Audio: 1176 Stereo Linking PCBs Support Thread
« Reply #201 on: May 28, 2018, 09:23:28 AM »
Hey guys,

I hope there is still someone out there since this looks like a stalled post, but anyways...

I need your help, I'm stuck.
I built a stereo version of Mnats rev. J boards with Hairball's stereo link (the stereo link was home etched).
Like some here, it works perfectly in dual mode, but when I switch into stereo mode the 2 channels are around 3-5db off (I did ricothetroll's wiring)

I read all the posts I could find about stereo linking 1176 but nothing there has helped me fix it so far.

The stereo link boards were home etched, so the first thing I thought was that there was something wrong with them. I measured the input (loop) on both boards while feeding a sine wave into both channels and they were feeding very different values, something like ~0.3V vs ~1.1V. The value was the same at the XLR inputs, around 0.775V, which I used to calibrate them. The input knobs on both channels were matched for the purpose of this test.

I then connected the XLR inputs directly to the boards (via the loop input) to be able to test them without the rest of the circuitry and there everything appeared to work normally, the summing worked as advertised.
So I'm assuming the stereo link boards are fine.
If this test methodology is wrong would someone suggest a better way for me to test them?

Since the mono channels are working fine, and tracking quite close in dual mode, I really don't know what to do next. The closest thing I found was germoju's post about matching other transistors in the main boards, but it was for a version D which seems to use different ones. Is this something I should investigate? I really don't feel like unsoldering transistors for no reason...

So, any suggestions?



P.S.The fets were matched, and I think they are really close, I'll leave the numbers below:

Device   VGS (V)   VDS (V)   ID (mA)
1   0.00   0.358   0.96
1   -0.25   0.50   0.95
1   -0.50   1.50   0.85
1   -0.75   5.87   0.41
1   -1.00   9.02   0.10
1   -2.00   9.94   0.01
1   -3.00   9.94   0.01
Device   VGS (V)   VDS (V)   ID (mA)
8   0.00   0.37   0.96
8   -0.25   0.49   0.95
8   -0.50   1.45   0.86
8   -0.75   5.87   0.41
8   -1.00   9.04   0.10
8   -2.00   9.94   0.01
8   -3.00   9.94   0.01
Device   VGS (V)   VDS (V)   ID (mA)
6   0.00   0.37   0.96
6   -0.25   0.50   0.95
6   -0.50   1.59   0.84
6   -0.75   6   0.85
6   -1.00   9.08   0.09
6   -2.00   9.94   0.01
6   -3.00   9.94   0.01
Device   VGS (V)   VDS (V)   ID (mA)
12   0.00   0.37   0.96
12   -0.25   0.50   0.95
12   -0.50   1.55   0.85
12   -0.75   6.00   0.40
12   -1.00   9.09   0.09
12   -2.00   9.94   0.01
12   -3.00   9.94   0.01


 

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