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Post subject: Pop Stop Module
Posted: Tue Dec 01, 2015 12:14 pm
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It's a common problem with solid state amps.
There's a pop at turn on and turn off. Then there is the loud thump at power off.
I am showing these pics of a Fender Deluxe 112+, but it can be adapted to many amps.
The pop at turn on/off is from an arc in the power switch that is picked up by the audio circuits.
This symptom can be addressed with .01uF/250VAC capacitors across the Power switch. They quiet by supressing the arcing.
These are shown in the right side of the pic as blue disks.
The Pop Stop module is the little blonde board to the left. Now you can buy little modules for speaker protection on Ebay for a few bucks. They don't seem to have the AC detect for a fast dropout, So I built my own fast dropout module.
Image
The thump after turn off can only be alleviated by disconnecting the speaker. This module effectively mutes the turn on pop and the turn off thump. Occasionally the turn off still produces a ninor pop, but the loud thump is effectively muted.
Image
It is based on a UPC2137 speaker protection IC. I based my circuit off of one at http://diyfan.blogspot.com/2012/03/spea ... ction.html
The formulas he gives for resistor values are to customize the circuir for different voltage amplifiers. I found that I had to play with the values to get 24 volts across the coil of the relay. I settled on 820Ohms.
The chips Vcc should be low to reduce the size and cost of the tantalum timing capacitor. 3 Volts Vcc is fine. So R8 at 10K &R7 at 56K were fine.
The chip uses an AC detect on pin 4 to drop out the relay before the thump. Its a fast, simple and stable syatem I set R4 to 27K for this Deluxe.
I did not use the DC offset protection at pin 2. It detects DC faults on the speaker line. It is used to prevent damage to speakers in case of amplifier failure. But with a guitar amplifier, clipping is considered normal operation and false triggering at maximum volume is not acceptable.
I also did not use the LED driver circuit as it is unusable in this application.
The relay drive is a sink to ground and can support quite a bit of current. It can easily handle driving 2 relay coils directly. The diodes are important to protect the relay coil and still offer fast drop out response.
If you use the Direct Out to go to a soundboard, you need a second relay to mute that output as well.
Pin 3 is grounded for resettable operation.
Image
I mounted it on the heat sink for easy installation.
There are five connections to the board..
Two for the speaker to the relay contacts.,
Ground at the two jumpwires at W19,
AC detect at the.Cathode of CR25
DC supply at the Cathode of CR23.
With a 15uF timing capacitor at C$, it turns on in @three seconds. Turn off is immediate.
To protect the relay contacts, don't Power Off at high power output. It can arc across the contacts and damage them.
Now I just have to beef up the mounting a bit, upgrade U2 & U3 and we'll be good to go..


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Post subject: Re: Pop Stop Module
Posted: Tue Dec 01, 2015 1:07 pm
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That's a pretty ingenious solution, Tim.

Looks like there's plenty of room within to add that second module for the line-out jack too.

Hand salute!

8)

Arjay

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Post subject: Re: Pop Stop Module
Posted: Tue Dec 01, 2015 3:51 pm
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There is no need for a second module. You can easily drive two relays from one chip.
Conceivably, you could run a double pole relay and switch them both with only one relay, but I would be concerned about cross talk, so two relays is my choice.
While I'm using a relay with a 24VDC coil, two 12V relays in series would work fine. Then connect the supressor diodes across them both.
I put a 2 relay module in a SWR California Blonde a while back. Its line out would make some crazy sounds for almost five seconds, which is an eternity onstage. I used a discrete digital circuit for that one.
This dedicated IC is simpler to use and does more.


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Post subject: Re: Pop Stop Module
Posted: Tue Dec 01, 2015 3:55 pm
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You should patent the design......you might make some money off of it.

:mrgreen:

Arjay

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Post subject: Re: Pop Stop Module
Posted: Tue Dec 01, 2015 4:18 pm
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I'd rather share it with y'all. Besides, its not a one size fits all. Each one needs to be customized for the amps voltages.
It drives me nuts to do the same thing twice, let alone go into production. And by this time next week, some Chinese guy who read this will already be selling a module for less than I could buy the parts.


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Post subject: Re: Pop Stop Module
Posted: Tue Dec 01, 2015 4:42 pm
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TimsAudio wrote:
And by this time next week, some Chinese guy who read this will already be selling a module for less than I could buy the parts.


LMFAO!

:wink:

Arjay

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Post subject: Re: Pop Stop Module
Posted: Tue Dec 01, 2015 8:13 pm
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Nifty fix


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Post subject: Re: Pop Stop Module
Posted: Wed Dec 02, 2015 6:51 am
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TimsAudio wrote:
And by this time next week, some Chinese guy who read this will already be selling a module for less than I could buy the parts.

that's the sad truth, but if you owned the patent, wouldn't you still stand to make money on their sales? I don't know how that works, but I'm guessing that's the point of a patent? But either way, it's cool that you would share it here for free. 8)

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Post subject: Re: Pop Stop Module
Posted: Wed Dec 02, 2015 11:24 am
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Its difficult to patent electronic circuits. The standards are for originality, not novel applications.
But obtaining a patent is only the beginning and making money off it is hard.

A patent takes an investment of $5-10K to obtain. The expectation is to get a return on that investment. You can either manufacture it yourself or license it to a manufacturer or sell the patent.
Making it yourself means additional investment for manufacturing, selling, and storing the product, Patent protection costs are yours alone. Its a career
Licensing to another company relieves you of production costs, but you lose control to another entity who may or may not pay you.
Patent protection should be shared with the licencee. Its an investment.
Selling your patent will relieve you of future investment or patent preotection, but it may be difficult to sell an unproven product. Its cut n run

In the real world, patent protection goes to the strong who can afford a lot of lawyers. The inventor of the electron tube, Lee DeForest, was broken by repeated lawsuits. The 20th century history of electronics is full of stories of ripped off inventors. It's one of the things that sets Bill Gates and HP and Apple apart. They are little guys that bucked the trend and managed to hold onto what they built.

You can get copyright protection for a circuit board layout and other designs. Copyrights need to be registered to receive legal damages.

My Dad told me if I want to get into business, to stay aa small as you can or go as big as you can. Everything in between will eat you up.
I'm happy to stay small. I sleep at night.
I did my stint in manufacturing and factory service. Now I don't like working on the same thing twice.
So if anyone wants to build this module and sell it, go ahead. Maybe you can make a few bucks on Ebay.. : I'm busy I've got amps to fix from here to eternity. :lol:


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Post subject: Re: Pop Stop Module
Posted: Wed Dec 02, 2015 5:56 pm
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Why do you suppose that the designers of these circuits don't add things like this. I know cost is an issue, but how much more could the cost be $1 or so. I guess you have to draw the line somewhere but you would think that on the high end products they would try to solve all the small issues. Someone spending a few k on a amp would happily pay a few hundred more (its not like Fender customers aren't willing to pay). A corporation has to make the decision are we "mcdonald's" or the four seasons" . In my small business people paid more because my product was better, I just couldn't cut corners. Fenders image is that they have the highest quality products available to musicians, its a bit perplexing that they don't smooth off the edges.


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Post subject: Re: Pop Stop Module
Posted: Wed Dec 02, 2015 6:07 pm
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Eroot64 wrote:
Fenders image is that they have the highest quality products available to musicians...


That's the perception, and it's based solely on a reputation from the distant past. I know the reality though and the truth is, contemporary products share very little with the Fenders of yore.

:(

Arjay

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Post subject: Re: Pop Stop Module
Posted: Wed Dec 02, 2015 9:13 pm
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Just today I was working on a 1995 Dual Professional.
I look inside and see Zinky '94 on the custom shop eyelet board. A nice ground buss down the length of it. Finally, I'm seein a really nice handwired piece from Fender.
But then, I spot a wire to the tremolo control that was soldered but didn't flow to the wire. It wiggled and pulled out. I guess it can happen anywhere...

Speaker protection relays have been used for decades on HiFi amps. Even more complex protection circuits are common in PA amps. But its an industry wide practice not to use them in SS guitar amps. The only place I see them is in Fishman acoustic amps and the like. I don't know why. I'd guess price points.


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Post subject: Re: Pop Stop Module
Posted: Thu Dec 31, 2015 9:51 am
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Well the jokes on me. :o
That was a fine little module that I built. The caps across the switch were some high quality snubbers. 8)
The customer picked up the amp after Christmas, and called back next day to say it wasn't fixed. :shock:
Electronics is such a humbling business. :oops:
Upon return, once in a while it would pop like clapping bricks together as soon as the switch opened.
i replaced the double pole AC switch. No pop. :!:
I examined the original. The contacts measure evenly at .4 ohms and look to be in perfect condition. No blackening. No pitting. Actuator springs strong and even. A nice Carling switch. ???? :?:
So when I install another pop stop and cap mod, it will include a new AC switch; regardless of apparent condition :)
Happy New Year y'all


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Post subject: Re: Pop Stop Module
Posted: Thu Dec 31, 2015 11:30 am
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Happy New Year TimsAudio


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Post subject: Re: Pop Stop Module
Posted: Sat Jan 16, 2016 12:38 pm
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Update on this amp when it came back in a month later.
The turn on pop is gone. the thump after turn off is gone
The pop at turn off is still there once in 5 tries. Sometimes weak, but sometimes very loud. I tried quenching magnets against the switch to supress arcs magnetically. No real effect.
So I took a different tack and decided to go after the receiver and not the transmitter of the pop.
To hear the pop, there needs to be a plug into the input to unmute the preamp.
I also tried putting a blind plug into the Power Amp In jack to isolate the preamp from the main stage.
This eliminated the pop entirely.
So the pop from the switch is radiating into the preamp.
On a scope, I can see a little ripple on the low voltage supplies, but replacing the caps didn't help. The source of the pop went all the way back to the input stage.
So I built a shield out of a 9 volt battery case over the input circuitry U2 and the input jacks. I soldered it to the frame of the volume pot and siliconed the other end to the board.
The shield covers the most sensitive circuits in the amp and it seems to have lowered the pop by about 1/2 . There also seems to be less hiss in the drive channel as a side benefit.
But it looks like popless isn't gonna happen with this amp. I sent it home with my apologies and no charge.


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