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

My new preamp design: Arduino, 6 input selector, MDAC attenuator, IR etc
My new preamp design: Arduino, 6 input selector, MDAC attenuator, IR etc
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Old 1st October 2019, 01:56 AM   #71
stocktrader200 is offline stocktrader200  Canada
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that chip looks really good. Arduino control is great. My setup is not well suited as I am using a twin triode 6922 setup with the first stage driving the 100k pot with loudness function. The second 6922 drives the tone stack which then drives the SS amp.
Great looking preamp!!
input LEDS or LCD in the centre of wheel would indicate which input is selected and volume level expressed as -Db

Last edited by stocktrader200; 1st October 2019 at 02:06 AM.
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Old 8th November 2019, 03:20 PM   #72
zgtc is offline zgtc  Europe
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My new preamp design: Arduino, 6 input selector, MDAC attenuator, IR etc
Hi Max, again pretty nice project. I'm about to request the BOM to complete the input selector board, and have a (stupid) question.

I understand the MCP23S17 serves as a SPI expander, so we can use the SPI line between an Arduino and more than one sensor or IC.

What I'm not so clear about is the ULN2003V12DR relay load drivers. Since these support 3.3V to 5V CMOS logic input interface, wouldn't it be possible to send those signals from the MCP23S17 or Arduino directly? I mean, the latching relays just need a pulse, right?

Sorry, I know these are stupid questions, but would love to learn more.

Thank you
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Old 8th November 2019, 03:45 PM   #73
maxw is offline maxw  United Kingdom
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My new preamp design: Arduino, 6 input selector, MDAC attenuator, IR etc
Quote:
Originally Posted by zgtc View Post
Sorry, I know these are stupid questions, but would love to learn more.
No such thing

Quote:
Originally Posted by zgtc View Post
I understand the MCP23S17 serves as a SPI expander, so we can use the SPI line between an Arduino and more than one sensor or IC.
Correct.

Quote:
Originally Posted by zgtc View Post
What I'm not so clear about is the ULN2003V12DR relay load drivers. Since these support 3.3V to 5V CMOS logic input interface, wouldn't it be possible to send those signals from the MCP23S17
To quote the datasheet:

> Internal Free-Wheeling Diodes for Inductive Kick-Back Protection

If you don't have these then you will need a diode across each relay coil.

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Originally Posted by zgtc View Post
or Arduino directly? I mean, the latching relays just need a pulse, right?
Sure but then you need many free pins on the micro controller. 2 per relay. And depending on what controller you are using, you might not have that many free pins. That's why IMO it's nicer to use SPI.
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Old 8th November 2019, 03:57 PM   #74
zgtc is offline zgtc  Europe
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My new preamp design: Arduino, 6 input selector, MDAC attenuator, IR etc
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No such thing
cool


Quote:
Originally Posted by maxw View Post
Correct.



To quote the datasheet:

> Internal Free-Wheeling Diodes for Inductive Kick-Back Protection

If you don't have these then you will need a diode across each relay coil.



Sure but then you need many free pins on the micro controller. 2 per relay. And depending on what controller you are using, you might not have that many free pins. That's why IMO it's nicer to use SPI.
OK, I wasn't conceptually far, then!

Now, a not-stupid, just maybe weird scenario/question. Would it be possible to use the input selector to switch audio signals and also close/open power circuits? Changing the arduino code, maybe even changing the pcb design, that is. Example situation: relay 1 for phono audio, relay 2 for phono amp power circuit, relay 3 for dac audio, relay 4 for dac power circuit, relay 5 for aux audio. If this is conceptually possible, i would be able to only power the phone amp or the dac when i select those specific audio signals
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Old 8th November 2019, 07:06 PM   #75
zgtc is offline zgtc  Europe
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My new preamp design: Arduino, 6 input selector, MDAC attenuator, IR etc
As for the last question, maybe if switching power circuits is not supported by this design (even if modified), then I need to look into "triggers", i.e. Signal Detecting Auto Power-On Unit (project 38) by Rod Elliott (ESP), but will obviously do some more research.
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Old 11th November 2019, 02:13 PM   #76
maxw is offline maxw  United Kingdom
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My new preamp design: Arduino, 6 input selector, MDAC attenuator, IR etc
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Would it be possible to use the input selector to switch audio signals and also close/open power circuits?
It won't work as it's designed as (6 input, 1 output) x2. Perhaps you could have voltage going in and then you can connect 6 devices to this bus. It might work for low voltage things but definitely not safe for mains voltage.

Personally I would look for another solution. You can get cheap relays that you can control with an Arduino from Aliexpess.
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Old 11th November 2019, 05:20 PM   #77
zgtc is offline zgtc  Europe
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My new preamp design: Arduino, 6 input selector, MDAC attenuator, IR etc
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It won't work as it's designed as (6 input, 1 output) x2. Perhaps you could have voltage going in and then you can connect 6 devices to this bus. It might work for low voltage things but definitely not safe for mains voltage.
I think I'll keep the original use for the relays. Is it safe to leave 2 or 3 relays unpopulated?

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Personally I would look for another solution. You can get cheap relays that you can control with an Arduino from Aliexpess.
Hadn't thought of cheap relays, it's a nice idea. Thank you
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Old 12th November 2019, 12:35 PM   #78
maxw is offline maxw  United Kingdom
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My new preamp design: Arduino, 6 input selector, MDAC attenuator, IR etc
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Is it safe to leave 2 or 3 relays unpopulated?
Sure
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