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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

MUSES 72320 electronic volume
MUSES 72320 electronic volume
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Old 15th March 2019, 12:51 PM   #421
mt490 is offline mt490
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Almost there with my project.

MUSES72320 volume control of course flanked with quad stereo inputs switched by ADG1439's, stereo peak level meters and RMS responding linear-in-log loudness meters with about 110dB response range.

Not shown is the micro doing the brainwork and the level display, still some work to go, it will eventually be integrated with the amplifier for power control and power metering. Also it can do stuff like live normalisation and limiting, but for most of my use that will be a play tool than anything useful.

Feature wise mostly overkill, just made to push the boundaries of technique. The business end of the level meter is made involving SOT-563 dual transistors which were a learning experience to handle without paste.

I will probably build a second one to use as a general purpose measurement interface.

Click the image to open in full size.


---

Q: Has anyone tried to omit the cap shown at the opamp inputs for bipolar operation?

I have the OPA1642 ready to go in now that all functional parts are tested though, so maybe not so important. Currently there's the bipolar opamp there but I'm wondering if the DC blocker at that position is really just the fruit of a perfecting engineer, or if it's genuinely a detail that will degrade performance.
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Old 15th March 2019, 03:28 PM   #422
CeeVee is offline CeeVee  Portugal
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MUSES 72320 electronic volume
Just in case anyone is interested there is a arduino libary for the MUSE chip now at : GitHub - qhris/Muses72320: Muses72320 library for Arduino
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Old 4th April 2019, 03:38 AM   #423
wayne325 is offline wayne325  United States
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Default caps in path ?

I'm having trouble finding a schematic for modules people are building with the Muses 72320, among the 42 pages or so.

The application diagrams on the data sheet show caps on the input and output for attenuation and boost mode. I assume these are DC blocking caps.

Are these caps necessary? Given the audio community hates caps in the signal path, I'm having trouble figuring out how everyone is so in love with this device if it requires 2 blocking caps and none of the posts make much mention of them that I can see. I therefore suspect those caps aren't required and rather the chip is being used without the caps.

Thanks for any replies.
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Old 4th April 2019, 12:22 PM   #424
alexcp is offline alexcp  United States
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MUSES 72320 electronic volume
I use DC blocking capacitors - Nichicon MUSE ES - and sleep well at night The caps, I understand, are mainly to prevent clicks when changing volume. You can probably leave them out if you can make sure (trim?) opamps have no DC offset.
Attached is the schematic for one channel. Full schematic and other documentation can be found here.
Attached Images
File Type: png bvc_gs_muses_one_channel_sch.png (468.1 KB, 297 views)
File Type: jpg hifiocean_-_19_1024x1024@2x.jpg (317.0 KB, 299 views)

Last edited by alexcp; 4th April 2019 at 12:29 PM.
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Old 4th April 2019, 01:04 PM   #425
wayne325 is offline wayne325  United States
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Hi Alex,

Thanks for that, I'll have a look later today. The good thing about a serial cap is, one could plan for it and try it out beforehand by merely shorting the connection. If it's giving trouble, remove the short and add the cap. I want to use it as a volume control for a tubed single-ended preamp, but I want to be able to put the same control later into balanced gear. And I have a nice shiny new BeagleBone Black for control and an LCD touchscreen. :-)

And now to throw more fuel on the fire, does anyone have good experience with the Maxim MAX5437 as an alternative to the Muses chip? I spotted it in some pics of a really top end piece of kit.

Cheers,
W/
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Old 4th April 2019, 05:21 PM   #426
alexcp is offline alexcp  United States
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MUSES 72320 electronic volume
Quote:
Originally Posted by wayne325 View Post
Maxim MAX5437 as an alternative to the Muses chip
No experience with MAX5437, but AFAIK it is a linear digital pot. For volume control, it should work well as a negative feedback element for, say, an opamp. To use it as attenuator, a log pot would be preferable. I've done some work with DS1882, a very nice digital pot that I believe was used in some PassLabs amplifiers. It seems it doesn't like to be loaded heavily, but otherwise works fine.
Attached Images
File Type: png ds1882 sch.png (168.8 KB, 284 views)
File Type: jpg DS1882 - 5.jpg (46.8 KB, 282 views)
File Type: jpg DS1882 - 19.jpg (317.5 KB, 99 views)
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Old 5th April 2019, 02:44 AM   #427
wayne325 is offline wayne325  United States
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Alex you've been a busy lad. Those are some very cool PCB projects you've made. Well done. Thanks for the replies. I think I'll try the Muses chip and see what happens. I can put a 0 ohm resistor in parallel with the series caps on the layouts and try both.
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Old 5th April 2019, 06:07 AM   #428
Theodosis O. is offline Theodosis O.  Greece
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Instead of an input capacitor, which destroys the sound, you can put a 500 ohm resistor.

When I had my Muses (Meldano boards) directly connected to my CD (Esoteric K-03) there was big problem.
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Old 5th April 2019, 03:17 PM   #429
alexcp is offline alexcp  United States
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MUSES 72320 electronic volume
Thank you Wayne!
Quote:
Originally Posted by Theodosis O. View Post
Instead of an input capacitor, which destroys the sound, you can put a 500 ohm resistor.
Very interesting. What the resistor is for? Couldn't you just short it instead?

Last edited by alexcp; 5th April 2019 at 03:24 PM.
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Old 6th April 2019, 07:15 AM   #430
Theodosis O. is offline Theodosis O.  Greece
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I guess it is for isolation.
When sorted there was no sound, only craks instead.
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