That1580 mini mixer

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weroflu
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Re: That1580 mini mixer

Post by weroflu »

Yes I looked at the 626x a few times. Most recently I didn't like the low-ish gain, no servo and, worse distortion figures on the preamp than the 1580. Thinking about it now, I could fit 2 470uF 10v cg's on a preamp card since I would only need 2 or 3 cards, 39/34 db gain is probably ok, but maybe with some dynamics mics maybe not. Distortion figures, not sure if that's audible, but I do really like the lme49720 op amps and probably because of their low distortion.

I was almost going to post a few weeks ago and ask you about how to do a differential servo for it.
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mediatechnology
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Re: That1580 mini mixer

Post by mediatechnology »

It looks like you'd have to servo into the input bases since one emitter has Rg in series.
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mediatechnology
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Re: That1580 mini mixer

Post by mediatechnology »

I think this may be relevant:

"Analog And Digital Gain In Microphone Preamplifier Design," Fink And Bortoni, THAT Corporation, Presented at the 153rd Convention
2022 October.

https://proaudiodesignforum.com/images/ ... T_Corp.pdf
weroflu
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Joined: Wed Apr 19, 2017 9:19 am

Re: That1580 mini mixer

Post by weroflu »

thanks for the link. read it and thinking on it.

for now it's not high priority as i'm still working on getting signal digitized.

just sent board order for revised adc, clock and mcu

fingers crossed things will start to work after this.

future versions might involve 626x to simplify things
weroflu
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Joined: Wed Apr 19, 2017 9:19 am

Re: That1580 mini mixer

Post by weroflu »

signal recorded. distorted and too quiet but it's sorta working.

got a few questions about the 6261 with 2 wire lav inputs

is there a better idea than balancing signal ended output from lavs to feed the 6261?

since there's no phantom feed, can i leave out the 220u's in fig 17 ?

tantalum ok for the 4 x 10u coupling from preamp section to adc?

cs53xx recommends 91 and 634r in the anti alias filter on the adc. 6261 uses 90r9(ok) and 796/893/1002.

cirrus wants the 2n7 caps right at the adc pins, is it ok to have them a few inches away from the 6261
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mediatechnology
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Re: That1580 mini mixer

Post by mediatechnology »

weroflu wrote: Sun Nov 12, 2023 6:29 am signal recorded. distorted and too quiet but it's sorta working.

got a few questions about the 6261 with 2 wire lav inputs

1) is there a better idea than balancing signal ended output from lavs to feed the 6261?

2) since there's no phantom feed, can i leave out the 220u's in fig 17 ?

3) tantalum ok for the 4 x 10u coupling from preamp section to adc?

4) cs53xx recommends 91 and 634r in the anti alias filter on the adc. 6261 uses 90r9(ok) and 796/893/1002.

5) cirrus wants the 2n7 caps right at the adc pins, is it ok to have them a few inches away from the 6261
I haven't used a 6261 so take my advice with a grain of salt...

1) Maybe use an identical value impedance-balancing resistor? Not sure about the 6261 but the 151X family likes to see some source resistance in both inputs so if you use it single-ended add some source R (maybe 10Ω?) in the inverting input.

2) I suppose you could leave out the 220uF at the inputs but you'd have to be certain it would never see phantom and, with imbalanced source R at DC, the resistive imbalance at the inputs could introduce a large Ib * Rsource offset.

3) Tantalum would be OK if you don't hear them.

4) I noticed that Cirrus also uses 470 pF vs 680 pF for the 6261. I think you'd need to sim it and scale C12/C13 (Cfb). My quick calc using Rfb of 893Ω nominal puts C12/C13 at 330 pF roughly equal the Cirrus CS53XX modulator.

5) I think having the 2n7 modulator capacitor right at the CS53XX's pins is a very good idea.
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