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Pop/click free HW-based relay attenuator V3
Pop/click free HW-based relay attenuator V3
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Old 27th April 2018, 08:06 AM   #1
Neutrality is offline Neutrality  Denmark
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Join Date: Oct 2004
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Default Pop/click free HW-based relay attenuator V3

A little less than a year after I relased V2 of my attenuator, V3 is finally done and tested and it works absolutely perfect.

Description :

Fully HW-based pop and click free relay attenuator.

All done with some clever use of digital logic and accurate timing.

127 x 0.6dB steps for an attenuation range of 0 to -76.2dB.

High quality Omron G6K relays, high quality low noise, low distortion 0.1% Panasonic 1206 ERA Thin Film resistors.

Perfect channel balance, from max to min attenuation.

The attenuator needs a 10K termination resistor to maintain a 10K total attenuator impedance.

Use a 100K Linear potentiometer to adjust the ADC input voltage.

150mm x 40mm 4 Layer ENIG PCB.

Changes from V2 :

1. A few Bugfixes : No board level modifications are needed on V3. Q1 is now a Mosfet instead of a BJT.

2. Improvements : The board is now uisng an external on-board clock source instead of the built in oscillator in ADC0804. The built in oscillator circuit just isn't good enough.

3. Simplification : The detent function that stabilizes the circuit by using the LSB has been made simpler but it still works as intended.

4. Expandability : Stackable expander board(s), there is now an extra output header that can be used to stack additional boards on top of the main attenuator board.

Build tips :

The supply voltage to the board should be between 14-18VDC for the attenuator board alone and 1 expander board. This is enough to control a balanced/differential signal.

If using 2 or 3 expander board I would personally keep the supply voltage to 14-15VDC to keep the dissipation in U12 to a reasonable level(below 800-900mW.

When ordering componenets the majority of them can be supplied from Mouser but 4 of the Thin Film resistors should be oredered from Digikey. However, everyone is free to use whatever resistors they like, as long as they fit on a 1206 footprint.

It is not needed to order the 14 Pin Male Header if you are only using the attenuator for SE stereo signals.

2. Selecting Potentiometer : Almost any 100K Linear potentiometer will work, but I personally use this one from Bourns :

Mouser : 53RAA-R25-A20L Bourns | Mouser Denmark

Digikey : 53RAA-R25-A20L Bourns Inc. | Potentiometers, Variable Resistors | DigiKey

Ordering: The price is 20$ per PCB and I only have a small batch available

Shipping is 5$ anywhere in the world. Additional shipping charges may apply if the number of PCB's ordered exceed the weight limit for 5$ shipping.

Send me an E-mail with your DiyA username, real name, adress and E-mail adress and I will send you a PayPal request. Since this is a hobby it might take me a day or two to reply and a few more days to ship. I hope people can live with that.

EDIT : The component placement drawing is not 100% correct, the CON1/CON2 connectors are actually 5mm more to the left than what is shown.
Attached Images
File Type: png Complete.png (840.9 KB, 743 views)
Attached Files
File Type: pdf Relay Attenuator V3_Schematic_Digital Logic.pdf (30.3 KB, 256 views)
File Type: pdf Relay Attenuator V3_Schematic_Supply-Relays.pdf (29.0 KB, 197 views)
File Type: pdf Relay Attenuator V3_Component Placement.pdf (36.1 KB, 121 views)
File Type: pdf Relay Attenuator V3_BOM_Simple.pdf (31.6 KB, 90 views)
File Type: txt Relay Attenuator V3_BOM_Mouser_Partial.txt (759 Bytes, 75 views)
File Type: txt Relay Attenuator V3_BOM_Digikey_Partial.txt (65 Bytes, 40 views)

Last edited by Neutrality; 30th April 2018 at 08:11 AM.
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Old 27th April 2018, 10:27 AM   #2
454Casull is offline 454Casull  Canada
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Excellent!

Do you have expander boards available?
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Old 27th April 2018, 10:46 AM   #3
Neutrality is offline Neutrality  Denmark
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Quote:
Originally Posted by 454Casull View Post
Excellent!

Do you have expander boards available?
I am sorry to inform you that I have no expander boards.

They are not a high priority since I have a feeling that there is limited interest in those.

But I will se what happens, if it turns out that there is a decent interest in them I might make them available anyway.
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Old 27th April 2018, 01:02 PM   #4
454Casull is offline 454Casull  Canada
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If we need to make the expander boards ourselves, will you make the Gerbers/BOMs/other documents freely available?
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Old 27th April 2018, 01:53 PM   #5
diyralf is offline diyralf
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Very nice project made with Eagle. Congratulations!

I had previously thought of a potentiometer with ADC. How do you prevent the 1-bit jitter?
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Old 27th April 2018, 02:12 PM   #6
Neutrality is offline Neutrality  Denmark
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Quote:
Originally Posted by diyralf View Post
Very nice project made with Eagle. Congratulations!

I had previously thought of a potentiometer with ADC. How do you prevent the 1-bit jitter?
U6/R32/R33 prevents 1-bit jitter.

Last edited by Neutrality; 27th April 2018 at 02:17 PM.
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Old 27th April 2018, 02:29 PM   #7
diyralf is offline diyralf
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I see. Great! Would be interesting to add a balance control.
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Old 27th April 2018, 03:18 PM   #8
thuanth43 is offline thuanth43  Viet Nam
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Quote:
Originally Posted by 454Casull View Post
If we need to make the expander boards ourselves, will you make the Gerbers/BOMs/other documents freely available?
Same question.
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Old 27th April 2018, 05:31 PM   #9
Neutrality is offline Neutrality  Denmark
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With regards to the expander boards, if there is enough interest, enough interest being a minimum of 5 pcs of them, I will make small a batch.

The size is 86mm x 40 mm and the price would be 15$, not that much cheaper than the larger main attenuator board but that is what you get with smaller batches.

Last edited by Neutrality; 27th April 2018 at 05:41 PM. Reason: Board length was wrong
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Old 27th April 2018, 05:38 PM   #10
454Casull is offline 454Casull  Canada
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Join Date: Jan 2004
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Quote:
Originally Posted by Neutrality View Post
With regards to the expander boards, if there is enough interest, enough interest being a minimum of 5 pcs of them, I will make small a batch.

The size is 88mm x 40 mm and the price would be 15$, not that much cheaper than the larger main attenuator board but that is what you get with smaller batches.
I would be interested in a main board and two expander boards.
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