I'm currently building a DG300B and want to use relays to change between three output options: 4 ohm OPT secondary, 8 ohm OPT secondary to binding posts, 8 ohm OPT secondary to an XLR headphone jack.
The amp is rated at 10W. Would a 2A signal relay be sufficient, assuming the output would never be switched while the amp was outputting?
From what I've read, higher power relays have issues due to needing a minimum load current to keep the contacts clean, whereas signal relays avoid this issue?
The amp is rated at 10W. Would a 2A signal relay be sufficient, assuming the output would never be switched while the amp was outputting?
From what I've read, higher power relays have issues due to needing a minimum load current to keep the contacts clean, whereas signal relays avoid this issue?
Use the biggest that will fit.
Signal relays are typically 500 mA or less, intended for control applications, not for switching on load.
It is the arcing at make or break that determines relay life.
Mechanical failures or coil failures are rare, contact damage is the most common failure mode in relays.
Signal relays are typically 500 mA or less, intended for control applications, not for switching on load.
It is the arcing at make or break that determines relay life.
Mechanical failures or coil failures are rare, contact damage is the most common failure mode in relays.
The ones I was looking at are 2A. Is arcing a concern if they will never cycle while the amp is outputting?
What´s wrong with using a rotary switch?
You´ll need a switch anyway to control the relays.
Unless you are building a computer controlled tube amp that is.
You´ll need a switch anyway to control the relays.
Unless you are building a computer controlled tube amp that is.
The only rotary switches I found with sufficient current ratings were very expensive. The issue is that I need a three position, two deck switch. The output transformers have 4 and 8 ohm secondaries. The 8 ohm would be on one deck so that position one of the switch would be speaker, two for headphone, three for nothing. The 4 ohm would be on the second deck, and position three would connect to another set of speaker outputs, and the 8 ohm would be inactive.
Changing subject, i would advise not to connect headphones to a power amp, you only have one set of working ears. Any glitches/ problems with the amp could permanently destroy your ears.
Use a separate headphone amp that has limited power, it will also save time on expensive tubes.
10W = I^2 * 4 ohm -> I^2 = 10/4 = 2.5 -> I = 1.6A rms = 2.5A peak.
Most signal relays are specified for 2A. If I were you, I would use the Mouser website to select down to what you need. Done.
For instance, selection General purpose relays|3A and 3.5A gives the following in stock.
You can select a DPDT relay to switch between 4 and 8 saving a relay.
Select coil voltage and current to your liking.
Jan
Most signal relays are specified for 2A. If I were you, I would use the Mouser website to select down to what you need. Done.
For instance, selection General purpose relays|3A and 3.5A gives the following in stock.
You can select a DPDT relay to switch between 4 and 8 saving a relay.
Select coil voltage and current to your liking.
Jan
Attachments
My amplifiers have 5-way binding posts.
Some of them have Common, 4 Ohm, and 8 Ohm posts.
Simple and effective. Then I use a Sharpie pen to mark them, C, 4, 8.
Some prefer to use relay contacts and two 5-way binding posts.
Some of them have Common, 4 Ohm, and 8 Ohm posts.
Simple and effective. Then I use a Sharpie pen to mark them, C, 4, 8.
Some prefer to use relay contacts and two 5-way binding posts.
Studs to which you attach wires, and tighten using thumb or wing nuts are called binding posts.
The other (head) side of the stud is connected to the rest of the circuit.
Poles as in polarity are quite different from street lighting poles!
The other (head) side of the stud is connected to the rest of the circuit.
Poles as in polarity are quite different from street lighting poles!
In my main speaker switchbox, I use these relays:
https://www.mouser.ca/ProductDetail...zwU8tEEmIbqxbf17nJ6LGM%2B3kACsArkfYw0C1Ub2g==
In my second one, I use these
https://www.hongfa.com/Product/Item/HF115F-T/TH
Both work well. Previously, I tried others but the channels would drop out randomly.
https://www.mouser.ca/ProductDetail...zwU8tEEmIbqxbf17nJ6LGM%2B3kACsArkfYw0C1Ub2g==
In my second one, I use these
https://www.hongfa.com/Product/Item/HF115F-T/TH
Both work well. Previously, I tried others but the channels would drop out randomly.
That’s interesting.
I was considering these 5A rated ones for a similar job.
https://uk.farnell.com/te-connectivity/im06dgr/relay-signal-dpdt-250vac-220vdc/dp/1629012
Just wondering if these one of the ones that did now work!
I didn't try any that small but looking at the datasheet, I'd suggest this instead:
https://uk.farnell.com/schrack-te-connectivity/rt424f12/relay-dpdt-250vac-8a/dp/1175085
They are twice the money (and size), but they should work for the life of the amplifier.
I've used those in an input switch, too.
https://uk.farnell.com/schrack-te-connectivity/rt424f12/relay-dpdt-250vac-8a/dp/1175085
They are twice the money (and size), but they should work for the life of the amplifier.
I've used those in an input switch, too.
That’s a good trade, 8A rated for twice the price.
Anything else jump out of the data sheet?
The contacts were gold plated on the small one. The switching current is only 2A. I would use them for switching RCA inputs maybe but not for speakers. OTOH, my amps are more than 10W. One is capable of 600W into 4R but the relays hold up 🙂