# BFD / Behringer DSP1124p Power Thump Eliminator



## spytech (May 22, 2012)

About 10 years too late........ Better late than never.lddude:

I, like the rest of the members here, have a lot of hard earned funds, invested in my HT and Hi-Fi.:spend:
I use the DSP1124P, better known as the BFD, for Eq'ing my subs. I got real tired of slapping my amps and drivers in the face, every time I would power up, or down for that matter. 
Here is my solution to the power on/off thump you may experience with the BFD / DSP1124P. (and maybe others)
It is completely powered by the BFD and draws approximately 50ma from the on-board bridge rectification circuit. It cost about $30.00 to build. and takes about an hour or less to install. It is comprised of the ELK960 time delay relay and an additional DPDT relay. 

How it works. 

It is based on the ELK960 which is an adjustable time delay relay, which activates a secondary DPDT relay for the two channels.The device holds the outputs at ground potential while the BFD powers up, and then, very quickly when at power down, pulls the outputs to ground once again, which eliminates the current from reaching the sub amps input.
I have been using it for about 3 weeks with no ill effects. It effectively eliminates the thump. (my amps and drivers like it a lot)

I am posting a png picture of the drawing, Maybe someone else can benefit!. 

If you are worried about the idea of shorting the OP amps on the unit to ground potential, I am pretty sure they are short circuit protected. If they were not, I would have had to replace them after the first power up!:neener:


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## spytech (May 22, 2012)

If you are not able to locate the Omron G6N relay specified, there is a new number for this relay. Also the pin configuration is different as well, so look at the data sheet here 
http://www.omron.com/ecb/products/pdf/en-g6a.pdf 

The 12VDC unit operates at 16ma. 

The part number is:
G6A-274P-ST-US-12DC


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## spytech (May 22, 2012)

spytech said:


> If you are not able to locate the Omron G6N relay specified, there is a new number for this relay. Also the pin configuration is different as well, so look at the data sheet here
> http://www.omron.com/ecb/products/pdf/en-g6a.pdf
> 
> The 12VDC unit operates at 16ma.
> ...


Correction on that replacement relay. The part number would be G6A-274P-ST-US-(DC12):dizzy:


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## dachness (Feb 17, 2009)

Thank you for sharing. Don't know if I would actually do it but I may consider it. About the only time I hear the BFD thump is when the power goes and and comes back on, other then that its always on.

Regarding to cost, did you look into using cheaper components?


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## spytech (May 22, 2012)

dachness said:


> Thank you for sharing. Don't know if I would actually do it but I may consider it. About the only time I hear the BFD thump is when the power goes and and comes back on, other then that its always on.
> 
> Regarding to cost, did you look into using cheaper components?


It may appear odd, to use the components that I did, it just happen to be goods, I had on hand. The same could be accomplished, with the use of a 555 timer, two MOSFET's and the resistor capacitor combination, for the delay time required. I have to say, it would use less power by far and when turning off, would shunt even faster. I have had my setup running, for quite a long time without issues. The only noise I hear, is a (very faint) pluck when turning the unit off, the MOSFET's would be a thousand times faster, therefor, no noise. In a nutshell, it is far cry from the original design.


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## dachness (Feb 17, 2009)

Thank you for the clarification. How much delay is needed and is it only required for power down?


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## spytech (May 22, 2012)

dachness said:


> Thank you for the clarification. How much delay is needed and is it only required for power down?


I have my unit setup for for approximately 2-3 sec, which gives everything the time to get up and going. The circuit in it's normal state shunts the outputs, after the delay it is released. Since the circuit I used has not caused any problems, I never went any further to refine if you will, the design. Also I mentioned using MOSFET, I think it might even better to use a form of opticoupler as the shunting device, as opposed to the or MOSFET, which will provide isolation.


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## savroo (Aug 16, 2008)

Hi Spytech

I was just searching on how to get rid of the on/off thump on my dsp1124p and found this thread. Its perfect but I need to exactly understand where to connect this. Do you have anymore pictures??? So I can see where u connected it all.

On ebay I've found digital delay timers so I will be using these unit they come in 5v , 12v or 24v format.

Regards

Sav


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## savroo (Aug 16, 2008)

Actually i understand the diagram abit better now, below is how i understand it.

5v voltage regulator is used to power the 1st relay
Secondary relay used as it has 2 channels
Secondary relay is connected to the XLR or Jack outputs

Instead of having 2x relays could this unit do the job of the 2 above relays.

See link - sorry i tried to add link but it never let me, but if you type on ebay 'Blue 2 Channel DC 5V Power Supply Adjustable Trigger Delay Time Relay Module ' you will find it.

It is a 2 Channel DC 5V Power Supply Adjustable Trigger Delay Time Relay Module, but i'm not sure how much power it would draw???

Regards

Sav


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## spytech (May 22, 2012)

Sav,
The only critical parameter involved would be the current draw from the existing 5V regulator and of course it is a typical 1 amp TO220 package. There is not going to be more than 100ma available without adding at least a basic heatsink, Other than that, you could use whatever you like. A better layout would involve using a 555 timer and incorporating some optocouplers for the signal path switching. This was constructed 2 years ago, with parts I had on hand, for a quick solution. It still woks very well, so no need to update it!....lol. The picture in the first post shows the connections. You may need to full screen it, to be able to see the connections.
The original circuit I posted, is not the best approach at solving the issue. It was just an example of a quick solution.


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## savroo (Aug 16, 2008)

Perfect thk u, I opened my unit up and can easily tap into the 5 v regulator but finding it difficult to see how to connect to the XLR connectors without unsoldering them, but don't want to do that as too many electrical components nearby. 


By the way what do you mean by 'The device holds the outputs at ground potential while the BFD powers up'

Does this mean you are short circuiting the signal pin2 (hot on unbalanced) to ground pin 1 on start up???

If this is the case then this would be easy to wire up to the delay timed relay. 

Regards

Sav


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## spytech (May 22, 2012)

savroo said:


> Perfect thk u, I opened my unit up and can easily tap into the 5 v regulator but finding it difficult to see how to connect to the XLR connectors without unsoldering them, but don't want to do that as too many electrical components nearby.
> 
> 
> By the way what do you mean by 'The device holds the outputs at ground potential while the BFD powers up'
> ...


Sav,
Yes, essentially you will be creating a crowbar across the signal output. Prepare your wires, by tinning them and just solder right to the xlr pins on the cba. They really don't need to be very large. 22ga should be more then sufficient. a little flux is your friend when performing this action. I initially had second thoughts about shorting the outputs with regard to the effect on the outputs drivers. After 2 years it has proved to be a non-issue. Just remember, your not shorting to earth ground, it would be considered signal ground. I find around 15 seconds give or take, was enough for my system requirements. Your requirements my be different. Someday, I intend to revamp my unit with a 555 timer and the optocouplers. Much less current draw, isolation and a lot faster switching.

Oh, and remember, this is a signal path alteration, so keep leads as short as possible and completely away from the transformer. If you have to use longer than a couple of inches, consider using 75 ohm coaxial conductors like belden 1855A or similar for all the wiring, even the power.


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## savroo (Aug 16, 2008)

Hi spytech

Thks for ur help I just fitted the unit I bought from eBay. Works really well it's one of those multifunction self-lock relay with cycle timer which you can program. Works really well and no thump. Not sure how you upload a pic on this but looks good.


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## spytech (May 22, 2012)

savroo said:


> Hi spytech
> 
> Thks for ur help I just fitted the unit I bought from eBay. Works really well it's one of those multifunction self-lock relay with cycle timer which you can program. Works really well and no thump. Not sure how you upload a pic on this but looks good.


Good to hear, the concept helped someone achieve the desired operation of their unit. 
Enjoy your now quiet DSP1124.


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## savroo (Aug 16, 2008)

See attached pic


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## spytech (May 22, 2012)

Nice... Looks like you used the coax as well. What did your timing base end up being? Did you measure a current draw? and does it crowbar the output fast enough to eliminate the thump when you power down? Now you have me thinking about an upgrade....lol


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## savroo (Aug 16, 2008)

I had some spare Van damme - balanced coax cable, it only costs roughly £1 per metre.

I started the start up timing at 5 secs delay and reduced down to 1 second and still no thump.

On power down I also get no thump.

I never measured the current but the spec sheet states working current less than 180ma (less than 15ma before the relay is open , less than 3ma when it is closed).

The whole kit cost me less than £10, just had to wait 2-3 weeks for the module to arrive from China.

The hardest part was to programme the module as it has various functions you can use, the module did not come with instructions but managed to find a simliar unit with instructions (link as follows - https://www.google.co.uk/url?sa=t&r...=5oM9BRd4Xtxg0KWrIkZMkg&bvm=bv.64125504,d.ZGU)


Well worth the mod and lots of space within the unit so nice and easy to do.


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## spytech (May 22, 2012)

savroo said:


> I had some spare Van damme - balanced coax cable, it only costs roughly £1 per metre.
> 
> I started the start up timing at 5 secs delay and reduced down to 1 second and still no thump.
> 
> ...


The module functions like the ELK unit I used, the elk is hardware programed. I checked mine and the delay is set to 5 seconds, as I have it in conjunction with a Matrix switched, Sansui G9000 and an Onkyo TX-NR809 and the two units have an output delay of about 3-4 seconds before switching their respective outputs. Thanks for sharing your project. 
Regards,


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