Switching Info

[Omar]

My next amp is a two channel, high gain switcher. Any tips on where I can read up about switching techniques? I've never built an amp with any kind of channel switching before. From the little research I have done, it looks like relays are better then optoisolator b/c of signal bleed. I'm open to any and all suggestions.

Thanks in advance,
Omar

[Bear]

Kevin O'Connor's TUT I has a huge chapter on switching technologies. Never looked very closely at it as I'm more of a one volume knob kinda guy.

Bear

[erigm]

If you can design your switching system to incorporate shunt switching (shunting to ground, thereby grounding the signal you don't want to hear) London Power's ERK (Electronic Relay Kit) is awesome. I think it is only $15?! You can get it at www.londonpower.com. I have used it and it works great. Uses bjt's to shunt the signal to ground. Fast, quiet and simple. Kevin O'Connor is always helpful too. Good luck!

[Omar]

I read the switching chapter in TUT1 and it didn't help too much. IIRC, it went from basic switching types to a complicated power suppy for j-fet switching. I was looking for something a little more simple.

Omar

[MSS]

I have to agree Omar. The TUT series of books has been very informative however they get quite involved and simplistic solutions are not easy to come by.

Can it not be as simple as wiring up a few relays with short internal chassis leads and low DC voltages sent to footswitches to activate them? LEDS would have to be activated with each footswitch as well.

Haven't checked but I am assuming DC relays are available as used in battery operated devices...

I figure a low power transformer with diodes and a cap would be enough to power relays and minimize additional AC in the chassis. Anyone know of decent relays available for this?

Does this approach make sense? Is there a safety hazard?


MSS

[rhinson]

hello, you can buy a nice 6.3v relay board already assembled ready to wire up from webervst ---- ted weber of weber speakers site. he also sells all kinds of amp building parts and kits along with his highly regarded speakers.
it runs off your 6.3v winding and has the rect. and filter cap on the board to convert to dc to run the relay. check it out. rh

[Omar]

I've seen the Weber switching stuff and I think it would work but part of me feels like that's cheating myself out of learning how to do switching. Any websites with info?

Omar

[erigm]

I know in TUT1 it gets pretty complicated fast, but the ERK kit that you can get from his site (www.londonpower.com) for $35 (looks like he bumped the price up). It has a layout and is rather easy to understand. It can be built on a seperate board so you don't have to compromise your layout either.

I think the webervst (www.webervst.com) is another good idea, althought I don't know if it includes everything you need to get going. Do you have to develope a powersupply for that one, or does it come included?

[Omar]

The Weber kit connects to the 6.3VAC filaments and creates it's own DC supply.

Omar

[MSS]

I have to agree with Omar that using a kit after building the whole amp seems to defeat the purpose of building them ourselves.

Besides, I think the TUT relay kit only does one A-B switching. Their quad relay kit at $85 gets quite expensive.

I would need to footswitch at least three functions 1) reverb 2) a gain boost and 3)TBD (Fast/Slow or Thin/Fat, etc...). This is mostly because there is no more room on the chassis front for all the switches! I also need to keep room for other pots to modify the sound.

Again, a simple solution that can be expanded would be best!


MSS

[erigm]

I think either is a great solution! But, you argue that you don't want to use a kit since you built the amp yourself. That doesn't make sense. The weber relay is more of a prebuilt kit than londonpower's kit. Al least with the LP kit you could integrate it into you own circuit board. It is expandable as much as the weber kit is (to my knowledge). You can use the same derived power supply to power multiple A/B switches, switching the functions you described. One big plus for the weber kit is that it is a relay, meaning you can use it in the signal path, not just shunting signal to ground.

I want to reiterate ... I think both are fine solutions, and I am basically arguing for arguments sake. I digress ... I sound like a jerk.

[MSS]

We revel in the animated discussion and enlightenment. Its only arguing if we become obstinent about our opinions...

I got around to looking at the Weber channel switch board and I was pleasantly suprised to see it at only $8! Thats hardly more that the cost of parts alone, let alone the effort to make and assemble the board.

Besides, we can think of it as more of an "assembly" than a kit, for those of us sensitive to that sort of thing. LOL

MSS

[mhuss]

I have had good success recently using NEC MOSFET opto switches. They're small, efficient, and have ratings up to 400v. I can do a writeup if anyone is interested.

--mark h

[mhuss]

http://mhuss.com/18watt/schematics/MosfetSwitch.gif

[ampdoc1]

Here's a simple circuit I think I got from a Boogie MK 1. I've used it in channel switching applications on Fenders, and it works pretty well. The relay indicated is 5Vdc, 167 Ohm coil, 150mW. If you can't find this specific item, you can probably use something close.

DEH