That1580 mini mixer

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mediatechnology
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Re: That1580/1510 mini mixer

Post by mediatechnology » Tue Apr 25, 2017 9:46 am

not sure I follow,,, do you mean virtual earth?
Yes.

I think I recall from the SSL discussions that broadcast/mono compatibility drove the compromise to -4.5 dB.
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Plandemic Series: "Pland3mic - Indoctornation" https://proaudiodesignforum.com/content ... nation.mp4
Plandemic Series: "Plandemic - Doctors In Black" https://proaudiodesignforum.com/content/Plandemic.mp4

CDC: "For 6% of the deaths, COVID-19 was the only cause mentioned. For deaths with conditions or causes in addition to COVID-19, on average, there were 2.6 additional conditions or causes per death." https://www.cdc.gov/nchs/nvss/vsrr/covi ... /index.htm

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mediatechnology
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Re: That1580/1510 mini mixer

Post by mediatechnology » Tue Apr 25, 2017 9:53 am

Looking at the 1286 LCR panner circuit I'm not so sure that the internal resistors' absolute tolerances do participated in the overall gain.
The first time I looked I didn't see that the reference terminal was looped back to the + input.
That puts the resistors in series with the noninverting input.
Though their absolute tolerance won't effect gain they will add noise.
I think it will work fine though.
I'm not sure why it's better than a dual op amp other than it saves 4 outboard gain resistors.

EDIT:

Wouldn't this be simpler and eliminate the 1286/pan buffer stages?

Image

I realize that it may not have the "offness" of the shunt configuration but it is a lot simpler.
or 4 resistors off of the sp3t switch, two center resistors adjusted to whatever pan law I want. The latter foregoes a buffer amp but I think I'd have to switch over to virtual earth summing from the current passive mix bus plus gain.
It's what I meant by current summation - combining the LCR "pan" switch circuit with virtual ground summing.
The preamp output feeds a single build-out R and 1 pole 3 pos rotary.
This eliminates all those 1286s and tons of resistors and lots of power.
It also gives you an optional third bus. (Break where C sums into L and R.)

You could get fancy and eliminate the mechanical switch, add DG41X switches and put LCR assignment under remote control.
You'll still come out ahead on power (compared to the 1286s) and with CMOS switches use a series/shunt configuration to improve offness if its needed.

Did I see a headphone amp in this gizmo?
If so add a 3.5mm stereo line input for playback or IFB.
https://ka-electronics.com

Plandemic Series: "Pland3mic - Indoctornation" https://proaudiodesignforum.com/content ... nation.mp4
Plandemic Series: "Plandemic - Doctors In Black" https://proaudiodesignforum.com/content/Plandemic.mp4

CDC: "For 6% of the deaths, COVID-19 was the only cause mentioned. For deaths with conditions or causes in addition to COVID-19, on average, there were 2.6 additional conditions or causes per death." https://www.cdc.gov/nchs/nvss/vsrr/covi ... /index.htm

weroflu
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Re: That1580/1510 mini mixer

Post by weroflu » Fri Apr 28, 2017 9:09 am

No headohone amp planned

re: cmos switches, I thought about those for phantom, pan and phase as was intended from the 5171 designers but I don't know what ground noise problems await so I went for analog. Plus, the intended use for this box is set and forget, set gain, pan, phantom and use it to record. There will be no gain riding or on the fly panning.

Metering maybe could be useful but the downsteam box will have meters so it's not really essential.

I'm still studying the panning you suggested. You were not the 1st, 5th or 10th person to tell me to use virtual ground. Initially my reason for staying with passive bus was my panning scheme was incorrect and I thought there would be 4 channels per bus which would be somewhat quieter with a noise gain of 4 vs. v.e. noise gain of 7. With 6 channels per bus I may as well go ahead with v.e. summing. JR, in some other posts I think brought up the point that it's not just a noise issue but phase errors as well from v.e. if I understood correctly. So that coupled with expected ground noise led me away from v.e. summing. Maybe it's possible to keep the summing topology modular/isolated to the summing card alone. I'll need an inverting stage before/after the v.e. summing.

There is one other issue. I actually wanted to burn a little power to increase efficiency on the ltm8049. Too low a current draw and I might be heating things up too much. Will check datasheet later. I really need to pick a number for the rails and stick with that, but it's going to require a new p/s board and parts since I used fixed voltages on the regulators. I wonder if I should put some mini trims on the ltm8049 fbx V output resistors and use TI matching TPS7A4700 and TPS7A33 regulators and mini trims there too.

On the subject of powering That preamps, do you think using the ltc3265 charge pumps would create any audible problems due to weak/slow current supply. I've heard various opinions on that topic. If I do wind up lowering the current draw I might switch over to using 2-3 ltc3265's for the rails, or one per preamp card.

I've been trying to learn basic measurements with the picoscope. Sweep and spectrum plot is working but the in-built signal generator is unbalanced 600ohm output. I didn't realize it would output down to 1mV, no pad needed. For now I'm just going to tie signal generator V+ to Mic input+, sig gen gnd to Mic input-, and float ground. I'm working on a test jig board that plugs into the backplane with a drv135 on it so i can just use a 3.5mm cable out from the test board into a preamp. It seems like there are a lot of very useful things I could put on this test board, any ideas? Maybe some resistors and a switch to simulate different microphone impedances.

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Re: That1580/1510 mini mixer

Post by JR. » Fri Apr 28, 2017 9:45 am

weroflu wrote:No headohone amp planned

re: cmos switches, I thought about those for phantom, pan and phase as was intended from the 5171 designers but I don't know what ground noise problems await so I went for analog. Plus, the intended use for this box is set and forget, set gain, pan, phantom and use it to record. There will be no gain riding or on the fly panning.

Metering maybe could be useful but the downsteam box will have meters so it's not really essential.

I'm still studying the panning you suggested. You were not the 1st, 5th or 10th person to tell me to use virtual ground. Initially my reason for staying with passive bus was my panning scheme was incorrect and I thought there would be 4 channels per bus which would be somewhat quieter with a noise gain of 4 vs. v.e. noise gain of 7. With 6 channels per bus I may as well go ahead with v.e. summing. JR, in some other posts I think brought up the point that it's not just a noise issue but phase errors as well from v.e. if I understood correctly.
Probably not... The phase shift which I alluded to (in addition to noise), is related to loop gain margin and with only 6 stems not a problem for modern SOTA op amps. Further, passive summing requires make up gain in the same ballpark as the VE noise gain, so same-same....My strategy of summing current sources, did not have the noise gain component so less noise and less phase shift.

For only 6 stems, don't worry about it... I've done consoles with over 100 stems feeding the L/R bus.

JR

So that coupled with expected ground noise led me away from v.e. summing. Maybe it's possible to keep the summing topology modular/isolated to the summing card alone. I'll need an inverting stage before/after the v.e. summing.

There is one other issue. I actually wanted to burn a little power to increase efficiency on the ltm8049. Too low a current draw and I might be heating things up too much. Will check datasheet later. I really need to pick a number for the rails and stick with that, but it's going to require a new p/s board and parts since I used fixed voltages on the regulators. I wonder if I should put some mini trims on the ltm8049 fbx V output resistors and use TI matching TPS7A4700 and TPS7A33 regulators and mini trims there too.

On the subject of powering That preamps, do you think using the ltc3265 charge pumps would create any audible problems due to weak/slow current supply. I've heard various opinions on that topic. If I do wind up lowering the current draw I might switch over to using 2-3 ltc3265's for the rails, or one per preamp card.

I've been trying to learn basic measurements with the picoscope. Sweep and spectrum plot is working but the in-built signal generator is unbalanced 600ohm output. I didn't realize it would output down to 1mV, no pad needed. For now I'm just going to tie signal generator V+ to Mic input+, sig gen gnd to Mic input-, and float ground. I'm working on a test jig board that plugs into the backplane with a drv135 on it so i can just use a 3.5mm cable out from the test board into a preamp. It seems like there are a lot of very useful things I could put on this test board, any ideas? Maybe some resistors and a switch to simulate different microphone impedances.
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

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mediatechnology
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Re: That1580/1510 mini mixer

Post by mediatechnology » Fri Apr 28, 2017 10:00 am

I'll need an inverting stage before/after the v.e. summing.
You may not.

By redefining your balanced inputs' (or outputs') polarity, e.g. making "tip" at the input connect to the preamp's "-" inputs, you can provide a free inversion.
Look at how I handle the final 1646 outputs on the MS matrix to overcome the 5532 inverting stage.
You could also reverse the polarity of the mic preamp's common mode stage.
With several sections fully balanced you have lots of opportunities to flip polarity.
No headphone amp planned
I actually wanted to burn a little power to increase efficiency on the ltm8049.
Well you do need to burn power.

You might consider four physical buses with the LCR assignment switching.
L, C, R and Mix 0V.
I have to remind myself that the console "frame" fits in an Altoids tin but with all those switchers keeping it quiet may be a challenge.
Extending Mix 0V may make it a better antenna and counter-productive.
I'm working on a test jig board that plugs into the backplane with a drv135 on it so i can just use a 3.5mm cable out from the test board into a preamp. It seems like there are a lot of very useful things I could put on this test board, any ideas? Maybe some resistors and a switch to simulate different microphone impedances.
For the balanced input Phono Preamp I use a balanced H-pad.
The inputs legs are 4K99 each.
An H-pad provides build-outs that increase the apparent source impedance to about 2K since its emulating a MM cart.
Though I could have used a 2K shunt the leg resistances would have been high.

If I drive my H-pad with an unbalanced source it's just about as quiet, if not the same, as using a THAT1646/DRV134 to drive it.
With the input U-pad having such large value resistors a ground-referred unbalanced source looks to the input to be impedance-balanced.

I've been thinking about the best way to provide a test and measurement interface that would have a switchable output pad, selectable source impedance etc. that would be universal.
Pete Millet has a test and measurement interface and I've seen the beginnings of one at GroupDIY.
The GroupDIY project is ambitious and uses a lot of multipole switches for the attenuators adding to the complexity.

Complexity got me to thinking about specialized interfaces for each task such as MM phono, Mic, direct Line-level and +20dBu generator outputs.
That avoids a lot of switching.
I was actually eyeing using some Altoids and candied ginger tins I've been collecting to provide shielding. :lol:
https://ka-electronics.com

Plandemic Series: "Pland3mic - Indoctornation" https://proaudiodesignforum.com/content ... nation.mp4
Plandemic Series: "Plandemic - Doctors In Black" https://proaudiodesignforum.com/content/Plandemic.mp4

CDC: "For 6% of the deaths, COVID-19 was the only cause mentioned. For deaths with conditions or causes in addition to COVID-19, on average, there were 2.6 additional conditions or causes per death." https://www.cdc.gov/nchs/nvss/vsrr/covi ... /index.htm

weroflu
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Re: That1580/1510 mini mixer

Post by weroflu » Sat Apr 29, 2017 12:32 am

frequency.jpg
frequency.jpg (238.59 KiB) Viewed 6768 times
Android phone stereo signal generator out, right channel phase inverted, in to preamp card, usb adc interface/audacity, 20hz -20khz sweep

https://instaud.io/Urp

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mediatechnology
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Re: That1580/1510 mini mixer

Post by mediatechnology » Sat Apr 29, 2017 8:08 am

Where's all that comb filtering coming from?

Try these: http://www.audiotester.de/mainE.htm or this http://www.sillanumsoft.org/

AudioTester has a nice swept function.

I've never been able to figure out how to do a sweep in Visual Analyzer but its FFT is easy to use.
Setiing up VA's generator for a sweep is easy; plotting is not well documented.
https://ka-electronics.com

Plandemic Series: "Pland3mic - Indoctornation" https://proaudiodesignforum.com/content ... nation.mp4
Plandemic Series: "Plandemic - Doctors In Black" https://proaudiodesignforum.com/content/Plandemic.mp4

CDC: "For 6% of the deaths, COVID-19 was the only cause mentioned. For deaths with conditions or causes in addition to COVID-19, on average, there were 2.6 additional conditions or causes per death." https://www.cdc.gov/nchs/nvss/vsrr/covi ... /index.htm

weroflu
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Re: That1580/1510 mini mixer

Post by weroflu » Sat Apr 29, 2017 2:13 pm

I'm on a linux box.

Trying to come up with the easiest way to diagnose the mic preamp signal. Then I can get to the fun stuff like meters and proper panning.

At my disposal are android phone
picoscope with 600ohm bnc unbalanced signal generator, two 1x/10x probes, two scope input channels, no bnc cable for the signal generator yet
dynamic, phantom mics

I ordered some drv135's to balance the picoscope sig gen and feed it into the preamp. mid week should have results.

I'm taking the signal now post panning, before the summing card. I would like to bypass the line receiver and pan just to eliminate that signal path as a problem.

Stuck on this problem at the moment. At least phantom power is working, tested a phantom mic and it works as well as a dynamic, passes a weak, too easily distorted signal.

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mediatechnology
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Re: That1580/1510 mini mixer

Post by mediatechnology » Sat Apr 29, 2017 3:39 pm

I'm on a linux box.
Was thinking you might say that.
Wine?
I have Linux Mint and Zorin .iso files that I've been playing with in live boot.

Can you use Audacity or a media player to generate tones using either the PicoScope output or the internal Soundcard?

No telling what your phone is doing to the audio on the way out.
I saw that comb filtering on the Android output and thought some kind of width enhancement was going on.
https://ka-electronics.com

Plandemic Series: "Pland3mic - Indoctornation" https://proaudiodesignforum.com/content ... nation.mp4
Plandemic Series: "Plandemic - Doctors In Black" https://proaudiodesignforum.com/content/Plandemic.mp4

CDC: "For 6% of the deaths, COVID-19 was the only cause mentioned. For deaths with conditions or causes in addition to COVID-19, on average, there were 2.6 additional conditions or causes per death." https://www.cdc.gov/nchs/nvss/vsrr/covi ... /index.htm

weroflu
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Re: That1580/1510 mini mixer

Post by weroflu » Sat Apr 29, 2017 5:01 pm

Sure I can generate tones. Do they need to be fed balanced into the 1580 though?

There are plenty of linux soundcard/scope apps. I should probably learn how to use the pico though.
Tuesday I can dead bug a drv134. I'll have a bnc adapter/cable by then as well. I mistakenly bought the wrong coax today, the bnc world is new to me. The pico sig gen goes down to 1mv, so I won't need to pad it, and should be able to at least feed a balanced mic level tone into the preamp. drv134 output impedance is 100ohms? (just about perfect if that's correct). If thedrv134 is a fail for whatever reason I have a preamp box that will balance a signal but the output is 600ohms, not terrible i guess.

In that audacity screenshot, on the bottom there is a box called size. If I pick a much lower value what you're calling comb filtering goes away.

Reflowing another card presently, just in case there was some sort of unsolvable joint/trace issue. One of my backplane boards was not fabricated properly, just switching to a new board solved it.

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