Preamp remotely turning on Monoblock PSUs - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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 9th July 2012, 02:03 PM   #1
elaar is offline elaar  United Kingdom
diyAudio Member
 
Join Date: Oct 2005
Default Preamp remotely turning on Monoblock PSUs

Hi Chaps,

I partially built a pair of gainclone monoblocks a while back and they have sat on the bench for a good year as at the time I could not work out the best way to "turn them on" through a seperate preamp.
The monoblocks have no power switch and each contains a 225VA (230v 2x 25v/4.5A ) toroidal transformer and 10000uF caps.

I was hoping I could run this by you guys and see what you thought, I am looking for the most simplistic (but safe) method as possible to start with.

The preamp will contain a PIC MCU (that controls an LCD among other things). I plan to use 6v 0.5VA transformers (I have these spare), regulated to 5vDC and feed this voltage to each monoblock using a 3.5mm-3.5mm cable, that will in turn power on a relay inside the monoblock with a protection diode. The preamp's PIC will turn on/off this 5v using appropriate transistor(s).
The idea of this being that space inside the monoblocks is extremely limited and I don't really have space for another transformer. So with this idea I could possibly just get away with a relay and a diode inside the amps, and the preamp can ensure the amps are last to turn on and first to turn off.

The relays I had in mind are 6A rated (15A peak), 5v control 125ohms (40mA) 250v (400V), which I assume are more than capable of handling the inrush current for this transformer.
Is it frowned upon to switch just the LIVE and should DPST be used? Lastly, everywhere I have read, people have stated that under 300VA a softstart isn't necessary, would you agree with that or would you use something relatively simple for 225VA such as NTC?

Any help would be gratefully received and might mean I actually end up finishing these one day!!

Cheers,
Andy
Attached Images
File Type: jpg SDC10461.JPG (100.4 KB, 65 views)
  Reply With Quote
Old 9th July 2012, 02:44 PM   #2
diyAudio Member
 
Join Date: May 2005
Location: toronto
A softstart circuit for the size of unit you isn't required, but a thermistor (Keystone CL series are good) on the AC primary would be a good idea as toroids draw high curents at turn on which is hard on your power switch. Size the thermistor for above your maximum AC draw at full load - also the thermistor will be warm when it's operating so keep some space and air around it. Also make sure your mains switch has a mains rated (specialy rated and labeled ceramic or film 0.1 uf ) cap across it's contacts to suppress arcing as well. Snubbing the relay contact(s) with the same 0.1 uf cap per pole would also be good. It will save pitted relay contacts over time and avoid early replacement.
Also do not turn the amp off and then on immediately - it takes time for the thermistor to re-set ( maybe a minute) to allow another start without stressing the power switch. A real soft start would reset instantly , but is more costly to build and takes up more space.

Last edited by ticknpop; 9th July 2012 at 02:51 PM.
  Reply With Quote
Old 9th July 2012, 04:01 PM   #3
diyAudio Member
 
Join Date: Mar 2012
Location: ISANDO GAUTENG
Quote:
Originally Posted by ticknpop View Post
A softstart circuit for the size of unit you isn't required, but a thermistor (Keystone CL series are good) on the AC primary would be a good idea as toroids draw high curents at turn on which is hard on your power switch. Size the thermistor for above your maximum AC draw at full load - also the thermistor will be warm when it's operating so keep some space and air around it. Also make sure your mains switch has a mains rated (specialy rated and labeled ceramic or film 0.1 uf ) cap across it's contacts to suppress arcing as well. Snubbing the relay contact(s) with the same 0.1 uf cap per pole would also be good. It will save pitted relay contacts over time and avoid early replacement.
Also do not turn the amp off and then on immediately - it takes time for the thermistor to re-set ( maybe a minute) to allow another start without stressing the power switch. A real soft start would reset instantly , but is more costly to build and takes up more space.
I used caps before and it did not help what I did then is to fit a transorb of 240 volts over the contacts and it still works fine after ten years on a freezer thermostat that failed which I replaced with one based on a 555 i.c.
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Remotely Controlled Motorized Volume Pot. fotios Analog Line Level 65 5th June 2013 10:19 AM
Building a circuit to remotely switch T1 amps on/off n8huntsman Parts 3 20th April 2012 05:27 PM
amp that allows for remotely located line level controls? thasp Solid State 0 27th December 2010 05:08 AM
Does turning down the "preamp" slider in the itunes equaliser destroy dynamic range? GregH2 PC Based 22 5th August 2010 10:56 PM
FS: complete UCD 700AD dual monoblock kit, PSUs, Cases, everything pburke Swap Meet 33 3rd March 2009 12:35 AM


New To Site? Need Help?

All times are GMT. The time now is 03:05 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2