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do all Amps need dc-protection ?
do all Amps need dc-protection ?
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Old 19th October 2013, 11:01 PM   #21
Mark Johnson is online now Mark Johnson  United States
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do all Amps need dc-protection ?
indianajo: good news, you made a mistake. You read the photo voltaic isolator's part number incorrectly. The third character is the letter "capital I" and not the numeral "1". DigiKey has 152 of them in stock, (here is a link) and Mouser has 962 of them.

Both DK and Mouser stock the TLP190, in surface mount.
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Old 19th October 2013, 11:24 PM   #22
tiefbassuebertr is offline tiefbassuebertr  Germany
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Originally Posted by Bigun View Post
I've started to work with MOSFETs instead of BJT power devices. I've produced smoke from burned resistors, sparks from shorted outputs, blown fuses, crackling sounds even. But the MOSFETs keep on trucking.

Modern parts appear to be very robust.

If the outputs are over-rated and the amplifier is stable and used for domestic (read - not abused) use then what would cause the outputs to fail ?

And if they never fail why would I ever be concerned about dc on the output.

And so why bother with dc-protection ?

I notice that Hugh's latest NAKSA 80 is MOSFET output and he says no dc protection is needed.

Is the only reason left the old 'so I can sleep at night' argument ?
do all Amps need dc-protection ?
yes, all audio amps for speakers need DC protection. Otherwise the voice coils will burn in such cases, if there is a shorting between C-E or D-S at one of both power devices from the output stage.

But the best way for DC protect is the use of a serial capacitor between the amp output and the voice-coil of transducer so as an non symmetrical supply rail (bad solution are relais contacts and a TA7317 or similar discrete protector stuff).
In such cases you will get an additional benefit: Sound quality will be much more better in most cases than DC coupled voice-coils after adjust the capacity value suited to the unwanted, but always present high pass character of the speaker-chassis in vented or closed envelope (convert from 12db/oct resp. 24db/oct. to 18db/oct resp. 30db/oct).
But condition are high quality capacitors with low ESR values and foil cap (MKP) bypass.

The claim, dc coupled stages haven't capacitors in the signal pad is complete nonsense, because this isn't possible. The caps of the power supply are at all cases in the signal pad in any kind, even if the circuit diagram shows a DC coupling in cases of symmetrical DC power supply rails (+/GND/-).
The evidence therefore is very easy.
If it were otherwise, then the power supply capacitors in most amp topologies should have no influence to the sound quality.
But this is not true, as everyone knows.
Anywhere here on diyaudio I have upload a schematic with an explanation, how one can modify a present ordinary DC coupled amp by remove the center tap of the mains power transformer. The only disadvantage is the need to double the voltage strength by the power supply capacitors.

Last edited by tiefbassuebertr; 19th October 2013 at 11:35 PM.
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Old 19th October 2013, 11:29 PM   #23
Bigun is offline Bigun  Canada
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do all Amps need dc-protection ?
Wow, your Triac blew up the 18 gauge wire too. You are having fun !

Originally Posted by indianajo View Post
Thanks for the digitec tip. Maybe I could bend the TLP191 leads down or something to stick them through the holes. No pick & place machine, here.
The leads of the surface mount parts are definitely not suitable for bending and sticking through a pcb hole. They are way too short. One option is to bite the bullet, get one of those desk light-magnifiers and a fine tipped soldering iron (these parts aren't that bad) or have a friend mount them on a small piece of board which you can then solder onto with less precision.
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 20th October 2013, 03:03 AM   #24
Bonsai is offline Bonsai  Europe
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I wrote up an SSLR design here Solid State Relay with PCB Layout

It does use some SMD components, buts it's small. It's THD same design running in my e-Amp and I have had no problems.
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Old 20th October 2013, 04:36 AM   #25
indianajo is offline indianajo  United States
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Originally Posted by transistormarkj View Post
indianajo: good news, you made a mistake. You read the photo voltaic isolator's part number incorrectly. The third character is the letter "capital I" and not the numeral "1". DigiKey has 152 of them in stock, (here is a link) and Mouser has 962 of them.
Both DK and Mouser stock the TLP190, in surface mount.
Thanks transistormark, I got that incorrect number off a print. Sure enough, the original FET driver IC Michael Bean used was the international Rectifier PVI5013 (papa victor indigo 5013), which comes in a DIP package for $6 from mouser etc.
Surface mount converters from mouser are $6 each, plus the wedge tip of my WP25 iron is too big to do stuff that small without making bridges. To get a leg hot enough with a pointy tip I'd probably need a Weller WCTCI 60W workstation for $176, which is about 2 months entertainment budget. I know where Weller comes from, Mexico, which is okay by me, whereas any other brand it is a big secret, you find out which country it came from when you open the box, like Santa Claus.
Bonzai, thanks for your paper again. I've had it a year, had been ignoring it because I can't do SMC components, can't etch boards or print out the masks, and nothing in your thread announcing the paper, or the Toshiba datasheet, explained about photovoltaic optocouplers creating voltage into a NMOS gate without an external power supply. If it did, I didn't understand. I had to stumble across thread 191449 speaker relay that you started to find out about Michael Bean's 3 part DC speaker relay, and Panasonic APV1122 IC which does come in DIP package, and is in stock at Mouser. I can solder a DIP .3" spaced package on $1.50 prototype boards from mcmelectronics.com 21-4575 with a big 7/32" screwdriver tip on my Weller WP25 iron.
One thing nobody but chocoholic has discussed is a latch to remember there was a DC fault and keep the SS relay from turning on and off as the fault comes and goes again. He used a 4013 cmos flipflop, but I'm trying DiodeTransistor RS flip flop with discrete TO92 transistors, so I can slow down the Reset base drive with a capacitor to make sure it powers up reset (relay closed), and couple the optoisolator output from the Peavey DC detectors to Reset base drive. (Peavey driver ground flies around with the music, each channel differently if the amp is not bridged). I've got red and green LED's in the front panel in the emitter legs of the flip flop to 1. increase the noise resistance of the flop and 2. show what state the protection circuit is in out the vent hole.
So thanks everybody.
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

Last edited by indianajo; 20th October 2013 at 04:48 AM.
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Old 20th October 2013, 01:30 PM   #26
Mark Johnson is online now Mark Johnson  United States
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do all Amps need dc-protection ?
Indianajo, I used a Hakko FX888 ($91 from amazon) to solder THIS surface mount board. The board has 3 SMD ICs and 14 SMD passsives. Of the 8 copies of the board that I built, all 8 worked perfectly. All it takes is the willingness to try plus a Can-Do attitude.
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