Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Pass Labs This forum is dedicated to Pass Labs discussion.

A possible approach to adding a silent start/shutdown to the ACA
A possible approach to adding a silent start/shutdown to the ACA
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 23rd September 2018, 12:01 PM   #71
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
A possible approach to adding a silent start/shutdown to the ACA
No way of knowing without actually trying it or setting up a simulation.

If you leave the SMPS on all the time and ramp the rails up and down very slowly then I'm sure you would quieten things down, but it leaves the problem of the ACA producing grossly distorted output while the rails climb and fall.

You could probably minimise the on noise by adding an NPN transistor and RC delay on its base to supply the 10k (R7) with a slow ramping voltage. The off noise would still be an issue though.

Any solution should be fool proof and work under any conditions and it also shouldn't need special conditions to be present for it to work successfully (such as making sure no audio input was present at power on and power off).

To me the shorting relay is an ideal option, and its non invasive to add to the ACA. It also allows a very short settling time (so no long waiting) for the ACA to stabilise. The quality of the relay is of secondary concern... all it needs to do is present as a short circuit during mute.

The series relay (solid state for consistency and reliability) is a technically more challenging solution but it should work in practice although you have the drawback of needing to have a large initial delay for the cap to charge via a dedicated resistor.
  Reply With Quote
Old 23rd September 2018, 10:33 PM   #72
Old'n'Cranky is offline Old'n'Cranky  Australia
diyAudio Member
 
Join Date: Aug 2009
Oh I agree with you entirely.
When trying to find a solution to a problem I tend let my brain go wild.
Some things are doable, some are just pure stupidity
There are far greater minds here than I could even begin to speculate about.

Me, I was ready to throw in a simple speaker protector on mine.
Then I saw your musings and thought I'll wait a bit to see what happens

In the direction of the output shorting relay.
I'm sure using a transistor in place of the relay would make things simpler, faster, better. (edit, second thoughts, no it probably wouldn't)
Wait, didn't someone (you ?) already suggest that ?

Last edited by Old'n'Cranky; 23rd September 2018 at 10:35 PM.
  Reply With Quote
Old 23rd September 2018, 11:56 PM   #73
Mark Johnson is offline Mark Johnson  United States
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
A possible approach to adding a silent start/shutdown to the ACA
One tremendous advantage of using the NC contacts of a relay is: it's completely out of circuit, completely, when music is playing and the output is not muted.

A solid state switch would contribute capacitance and leakage current to the output, and worse yet, since the loudspeaker output swings from 8V below ground to 8V above ground, you'll have to figure out how to bias the solid state switch OFF when the voltage across it is +8V and also when the voltage across it is -8V. Bipolar transistor? Gotta generate yourself a -9V power rail. IGBT? even worse. SCR/Triac? fuggeddabouddit. MOSFET? don't forget that pesky VGS "Absolute Maximum Rating". Oh snap!
  Reply With Quote
Old 23rd September 2018, 11:58 PM   #74
PaulBysouth is offline PaulBysouth  Australia
diyAudio Member
 
Join Date: Feb 2008
Location: Melbourne
Default mosfet speaker `relay'

Relays suitable for amplifier outputs are large and expensive. Much better to use a pair of mosfets.

Attached is a scheme to:
- Short the output to ground with m1,m2 (via R2) to charge up the output capacitor, and
- Connect the output after a delay (via m3,m4).
In order that the output is shorted at power on, a pair of depletion mode mosfets are used for m1,m2.

The vom1271 photovoltaic generators create a floating 8v supply to turn m1,m2 off and m3,m4 on. vom1271 are in short supply at the moment, but APV1121 is equivalent. Note the opposite connection for the DN2540s. M3,M4 need to be low Rds on (<15 mOhm).

The size and cost of 4 mosfets and two vom1271 is about the same as a decent relay. Drive the vom1271's with 20mA after a 1..2 sec delay.

The small white box shows what you would use for a headphone amp.

Regards,
Paul Bysouth
Attached Images
File Type: jpg Output-Relay-Test-1.JPG (405.1 KB, 68 views)
  Reply With Quote
Old 24th September 2018, 07:08 AM   #75
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
A possible approach to adding a silent start/shutdown to the ACA
The MOSFET relays are very good indeed when used correctly, the only real drawback being the additional complexity, not just in the 'relays' but also in the drive circuitry.
  Reply With Quote
Old 25th September 2018, 03:53 PM   #76
Preamp is offline Preamp  Germany
diyAudio Member
 
Preamp's Avatar
 
Join Date: Jul 2008
Location: North Sea, 54.7N 8.5E
Quote:
Originally Posted by tomchr View Post
That might work in a tube preamp where the output current is limited. In a solid state power amp like the ACA, you'll end up with full signal across the cap if someone turned on the source while the relay was closed. I doubt either the cap or the amp would appreciate that.
I suppose you could add a mute relay on the amp input, but it may be worthwhile to take a step back and look at which problem you're trying to solve exactly.
Add a muting relay for the input then .


Quote:
Originally Posted by tomchr View Post
In that case, an AC coupled amp may just not be for you. Or you'll have to accept the turn-on/off thump.
I'm currently living with the thump, but I'd certainly appreciate a simple and reliable way to avoid it.
  Reply With Quote
Old 25th September 2018, 05:21 PM   #77
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
A possible approach to adding a silent start/shutdown to the ACA
The short on the output shouldn't be a problem, even if the amp was fed with a very high input signal.

This shows the current draw of the ACA delivering its maximum voltage swing into 8 ohms. You can see the current rise and fall from the nominal bias current value. Second image is the PSU current when the amp is shorted.

The circuit topology of the ACA means it is inherently 'safe' working into a short circuit, Definitely DO NOT use this approach on a class AB output stage.
Attached Images
File Type: jpg Capture1.JPG (246.1 KB, 33 views)
File Type: jpg Capture2.JPG (235.3 KB, 32 views)
  Reply With Quote

Reply


A possible approach to adding a silent start/shutdown to the ACAHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
P3A amp shutdown 'plop' jacques antoine Solid State 11 28th May 2015 07:23 AM
NTC thermal shutdown lazzer408 Power Supplies 36 14th March 2015 05:59 PM
Squeal on shutdown famousmockingbird Tubes / Valves 48 11th February 2014 06:55 AM
OPA548 and shutdown kafka Chip Amps 9 5th September 2004 04:26 PM
Shutdown noise energyandair Solid State 3 10th May 2003 10:52 AM


New To Site? Need Help?

All times are GMT. The time now is 03:47 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki