Mosfet SSRs

[eschertron]

I stumbled across the LH1500 family of SSRs on Mouser, which has the LH1500
LH1500AT Vishay Semiconductors | Mouser
and others, including the 1501, a normally-on contact version of the relay.

Has anybody used these? Any specific info on the N.O. versions? They sound pretty useful.

I am basing any designs I make on the info presented in Merlin's preamp book about these devices. I will have to spend more time to figure out more how to channel-switch without introducing sand into the signal path, though.

[exclamationmark]

I've made an amplifier (well probably about a quarter of an amplifier) out of about 100 of these things. I have no qualms about sticking them in the signal path as they're extremely linear - I've A/B tested this amplifier against identical hard-wired circuits and they test pretty much identically. Because tube amps often operate with impedances in the 100k+ range, and the variations in SSR 'on resistance' with load current is perhaps an ohm or less, they provide an infinitesimally small (but still present) distortion. It's still probably less than carbon comp resistors though!

Here's a link to a little site I whipped up that highlights some of the problems with SSRs: Solid State Relays

[eschertron]

At this point I'm in the technological basement - looking to incorporate the SSRs for channel switching. Your pages have given me a glimmer of hope. Very nice! I hope to see more of your project soon.

[Steve A.]

Interesting thread! I've only worked with regular relays. With an unregulated supply (derived from the filament voltage with a rectifier bridge) it was tricky to get even 3 relays working properly because of the voltage drops in the coils. With the lower voltage and current you could use SSR's with a regulated DC voltage derived from the filament voltage, and use as many as you wanted.

Keep us posted on whatever you come up with!

Steve Ahola

[eschertron]

@Steve - you are right about the current consumption. At 3ma (4ma tops) per 'switch', there's plenty of headroom on a filament supply. I plan to use a LH1502 which has a combination NO/NC SSR on it. Driving both LEDs in series I simply calculate the leakage resistor based on two voltage drops, and the 3ma load remains the same!

The 'offness' of the form B (N.O.) SSR is much less than that of the standard form. I'll have to take that in consideration with the circuit. Has anybody used these 'form B' mosfets?

[Alan0354]

That's sounds very good, I don't dare to use it and now I have to deal with the popping sound when switch and have to put in a muting circuit to make it work. Do you have popping problem with the SS relay when channel switching?

[exclamationmark]

Although the SSRs have a small leakage current, in my experience they don't charge the capacitors enough, so they still pop (of course if you changes voltages or something, it's always going to pop as things equalize). I personally had another tap on my transformer that I used to power the logic stuff, and the muting circuit was microcontroller controlled.