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Old 19th July 2012, 12:22 PM   #31
Bonsai is offline Bonsai  Taiwan
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At 1 ms the device SOA capability is 7 A at 65 V. If you switch the device at 100 us the SOA capability is 70A.

Using photo diode to drive th gates does result in slower switching. I used 2 in parallel on the e-Amp control board. However, if you switch the speaker ground return line, you can direct drive the gates, and then turn on turn off times are less than 30 us.
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Old 21st August 2012, 06:24 PM   #32
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It is great to see, that more and more enthusiasts start to trust in the Back2Back arrangement of two MosFets for speaker relay applications and measurement applications as well.

Also thanks to David and Jan for getting the spelling of the title corrected.
It is the way like Jan guessed, in Germany we write 'Relais' and my ignorant brain simply mixed the languages
Stay tuned, more errors to come :
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Old 21st August 2012, 09:07 PM   #33
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Well Chocoholic your'e not alone in the desert.I'm busy with these things already for some time now and it works very well.But I think your control circuitry is too complex.
It can be done with a single photovoltaic coupler as already mentioned by DAI.
He mentions the old International Rectifier part PV1050N, but Toshiba has a few of them an newly also Panasonic Electric works :APV1121S cost arount 1.50 Euro at Mouser.These are simply optocouplers that DELIVER a voltage at the output.
Some people's reactions in this tread are about the off-switching time,but this is really a non-issue compared to the off switching time of a electro-mechanical relay.
And not to mention the danger of the contacts welding together.
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Old 21st August 2012, 09:24 PM   #34
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Quote:
Originally Posted by ChocoHolic View Post
Analog:
If the relay is high quality and in good condition, then I cannot measure and cannot hear any issue with a relay. Relays are fine, except old/defect/poor quality.
When I took one relay from my shelf I found an ugly high order spectrum with peaks in the range around -80db. Knocking a few times to its plastic cover 'repaired' it...

The above experiences are my motivation to move away from the relays.
Hi I experience a lot of defective relays in audio equipment especially in japanese quality amps. For some reason Sony engineers (amongst others) design their amps for years now with the same crappy quality relays with gold contacts for speaker switching. The used relays often can not switch more than 2 A which is a design error on itself. These relays burn in easily as gold is soft and then they fail eventually starting with channels fading or crackling. We know that current switching should be done with (hard) silver (or silver/nickel 90/10) contacts. Voltage switching i.e. input switching in amps should be done with gold contact signal relays. This of course counts for audio applications, for industrial use there are other materials. This gold/voltage and silver/current issue is common knowledge which is documented at relay manufacturers. So why Sony/Kenwood etc. guys still make the same mistake I don't understand....

I found that using simple pin compatible replacement industrial relays from Schrack that have high current switching capacity and silver/nickel 90/10 contacts is the most easy and convenient solution to repair such amps. They also use less current which is good for the driving transistor. Never had one that failed till now. The "welding" of contacts as described by others does not happen often with silver contacts in speaker switching applications. It does happen very often with gold contacts though. I can not hear a negative difference with these relays when they are in the speaker path.

IMO the replacement relays should have the following features:

- sealed (glued/molded) so moisture and dust/dirt can not creep in
- silver/nickel 90/10 contacts, preferably double contacts too !
- at least 8 or 10 A switching capability.

http://relays.te.com/appnotes/app_pdfs/13c3236.pdf
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Last edited by jean-paul; 21st August 2012 at 09:53 PM.
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Old 21st August 2012, 09:52 PM   #35
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Originally Posted by cowboy_film_fan View Post
It can be done with a single photovoltaic coupler as already mentioned by DAI.
These photovoltaic MosFet drivers are pretty nice.
The only downside is that it cannot drive large MosFets fast, this will lead to limitations for high power applications.
Turn OFF can be speed up with a simple PNP on the floating side. Speeding up the turn ON is also possible, but boosting complexity in a way, which would kill the charming simplicity of the photovoltaic MosFet drivers...
Nevertheless, for small power they seem to be the perfect fit.
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Old 21st August 2012, 10:16 PM   #36
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@jean-paul
Right. Relays look simple, but they are not all the same.

To bad. I cannot find a data sheet of the relay that showed distortion before knocking.
It was an unused relay, so it was definitely not a welding issue.
Type: Schrack, RP11006, 250VAC/10A, must have been waiting in my box for 15 years....
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Old 21st August 2012, 10:27 PM   #37
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Aha, that is easily explainable as unused relays after time (especially 15 years) develop a film over the contacts that needs a small switching arc to disappear. Non-sealed relays have this phenomenon much more then sealed relays which is why I recommend using sealed versions. You can read the arc explanation in the link I gave in my previous post. Simple matters tend to be overlooked. It seems our good reliable friend the relay has some secrets left to know for you.

So I think the relay is perfectly fine, it should have switched a current once and nothing would be wrong. Such relays are designed to switch currents anyway...which they do in speaker switching applications.

To me using MOSFETs instead of good relays has a similarity to the transformer/switched PSU dilemma. While many complain about weight. losses etc. of transformers I never had one failing. If I should count the defective switchers I had.... but they were power efficient and even more so after they died The landfill is full of them being very power efficient.

BTW I wonder what unused MOSFETs do after have been on the shelf for 15 years ?!

The data sheet of the RPII (an also obsolete later version of the RP I guess) can be found here:

http://relays.te.com/schrack/relays/pcb.asp
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Last edited by jean-paul; 21st August 2012 at 10:56 PM.
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Old 21st August 2012, 10:35 PM   #38
dai is offline dai  Wales
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Hi jean-paul
If you want to find out what unused mos-fets would do I have lots of SI
unmarked 2n7055 devices that I have had for more than 20 years still in
the bag I would be quite willing to let you have some to experiment with
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Old 21st August 2012, 10:53 PM   #39
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Thanks for the offer but I stick with relays for speaker switching purposes and although I would like to do the experiment I lack the time at the moment.

But that should not prevent you from letting the magic smoke come out these 2N7055's
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Old 22nd August 2012, 08:20 AM   #40
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Long tim to switch on?? Let's take the heaviest mosfet we can find :IPB025N10N3 from Infieon. 100V/180A 2.5mE it has a 14nF iput cap. 2 of them make 28nF An APV1121S charches this with 14uA in 20ms from 0 to 8V.I really don't see a problem here.
And let's be honest: you do not need a 2.5mE MOSFET.This is at least 10 times better than the contact resistance in your binding posts.
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