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Old 1st September 2010, 07:41 PM   #1
diyAudio Member
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Default Mute Circuit

Alright this is my first post at diyAudio!

I am designing an ABX comparator aka AB switch box with some extra features. I am in need of some assistance on creating a mute circuit using a FET. I am thinking that a JFET would be the best for this.

I can't use relays mainly because I already have 16 of them and space is an issue. The signal at max is going to be around 60A. If anyone has some past mute circuit designs that work with low noise, quickly, and no popping that I can reference that would be great. I can post up what I have here shortly once I get it on the computer.

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Old 2nd September 2010, 12:33 AM   #2
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60 amps peak is a lot of current. 1.8 kilowatts in a 4 ohm speaker, if you take it as 30A Pk-Pk (21.2 RMS) or a lot more depending how you slice it. Why would you want to run 1800 watts or more thru an ABX box?

Do you really mean 60A?

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Old 2nd September 2010, 01:00 AM   #3
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Kinda...60A is just overhead, the max I am going to be putting out of one amp is 3750W per channel into 2 ohm loads. I can potentially put out 9000 watts with a 4 ohm bridge mono but that won't be used. Probably going to just use a p-channel JFET and use amplified control from a 555 timer for delays and control.
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Old 2nd September 2010, 11:10 AM   #4
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
where is the mute going?
In the 60Apk output circuit? Surely not.

If the mute is going elsewhere then we don't need to know the peak current output capability.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 2nd September 2010, 03:24 PM   #5
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The mute is after the amplifier and before the speakers. I am not just muting the signal source. That would be EXTREMELY convenient but I have to mute the amplified signal. Basically the mute is a protection circuit so that way while the relays are switching from amp A to amp B there is no way that both amps are powering one set of speakers at the same time.

The other reason why it is needed is because I have to parallel mechanical relays and there needs to be a timed mute so that way the relays will be for sure on before signal is sent through.
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Old 2nd September 2010, 05:35 PM   #6
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So the mute will be in circuit with the amplifier while driving the speakers.

I wouldn't use a FET or FETs here, there'll be complications with AC or DC coupling, and the FET on resistance will not be negligible. Use a relay. The on resistance will be negligible. Arrange the timing with RC delays on some of the relays' coils, or better still a PIC with an internal oscillator.

It all sounds highly unlikely to me...

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Old 2nd September 2010, 08:30 PM   #7
nattawa is offline nattawa  Canada
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Location: Mississauga, Ontario
Originally Posted by dbbaker2007 View Post
.......I can't use relays ...... The signal at max is going to be around 60A........
I have 2 automotive relays of 60A/80A contact rating in my pimped Citation 16 amplifier working as speaker protection relays. These are DC rated contact capacities for automotive applications, should be ok for your application I guess? Picture of the relay in my amp could be found here

I pimped my Citation Sixteen! (or, resurrected?)

Another option I'd use would be power MOSFETs. They can have very low on-state resistence and you can always double/triple/Quardruple them up for even lower resistence. You must use at least two of them to make a switch, tie the souce of the two together, one drain used as input, the other drain as output, so that the parasitic diode between the drain and souce in one FET will block that in the other. Each such switch must have its own isolated control signal. The schematic could look like this...... inside the box of dotted line, and ignore the photo cell

Just a thought, never tried myself.

Last edited by nattawa; 2nd September 2010 at 08:40 PM.
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Old 2nd September 2010, 09:09 PM   #8
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What you are saying makes sense. Those relays are DC and won't work if I am trying to mute an AC signal. I don't know a WHOLE bunch about relays so you can correct me if I am wrong. I am still in school atm and trying to figure out all this audio stuff. I am a micro guy trying to learn audio.

I am gonna run a sim on that setup tomorrow and see what I come up with. Thanks for the info.
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