I am rebuilding my pre-amp and I want to include more than one input. I am doing a steam punk motif and want to use 2 pole/2 throw knife switches which will give me 4 inputs. It will take 2 switches for each input so 8 switches in total which means I need to do some planning to design the right chassis.
I have a Pete Millet Low-Mu pre-amp and a Prometheus pre-amp TVC with only one input and remote control for the stepped attenuator in the Prometheus.
I plan on building an artsy-fartsy chassis to fit all this into. I would like the knife switches for input selection. Do you see any issues with doing that???
I have a Pete Millet Low-Mu pre-amp and a Prometheus pre-amp TVC with only one input and remote control for the stepped attenuator in the Prometheus.
I plan on building an artsy-fartsy chassis to fit all this into. I would like the knife switches for input selection. Do you see any issues with doing that???
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Here is the style I am using for the chassis. I'll make a box 22"L x 6"H x 6"W and line it with duct tape, then fill it with all different types of sticks crosswise, then fill it with black dyed epoxy. When it is fully cured, I take it out and cut 1" slabs off it lengthwise. I'll make the chassis from those slabs.
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Not an antenna, just one plate of a capacitor. The other plate is formed by something nearby which has 60Hz on it. This will feed hum current into your source so how much hum voltage is developed depends on the output impedance of the source. This effect always happens, but normally we don't need to worry about it for three reasons:
1. audio switches are normally small
2. audio switches are often inside a metal chassis
3. well-designed audio sources have low output impedance
You may be fine, but given a combination of large switch metal, unscreened and a high output impedance (e.g. some 'audiophile' designs) you could get some hum.
Just something to be aware of.
1. audio switches are normally small
2. audio switches are often inside a metal chassis
3. well-designed audio sources have low output impedance
You may be fine, but given a combination of large switch metal, unscreened and a high output impedance (e.g. some 'audiophile' designs) you could get some hum.
Just something to be aware of.
Just a thought. You could use the knife switches to operate relays. That way you could eliminate the issues caused by unscreened contacts and possible tarnishing of the contact surfaces of the exposed switch. Use something like very good quality reed relays with doubled contacts to do the real switching.
I used these in my valve preamp:
HE722A0500 Littelfuse Inc. | HE554-ND | DigiKey
For reliability, parallel the contacts.
HE722A0500 Littelfuse Inc. | HE554-ND | DigiKey
For reliability, parallel the contacts.
Use both contacts of a single relay per channel; ie. since a single relay has two contacts, use one relay for channel 1 left, another for channel 1 right, and so on. Also called doubling the contacts. This increases the reliability and halves the contact resistance.
For the absolute best signal relays, you should use the mercury wetted reed type, but these are nearly unobtainium these days, because of all the enviro-bovine-manure.
But since many respected manufacturers use even lesser relays than those ones I pointed out, I think you're quite well off with those ones. Should be slightly better than sufficient.
For the absolute best signal relays, you should use the mercury wetted reed type, but these are nearly unobtainium these days, because of all the enviro-bovine-manure.
But since many respected manufacturers use even lesser relays than those ones I pointed out, I think you're quite well off with those ones. Should be slightly better than sufficient.
By god, please tell me where I can get these? And how cheap are they? Shipping to the Soviet EU?
To be honest, obsessing about the "best ever part" never moves any project forward. Use parts that are known to be good enough, shun unnecessary exotica. 95% of the sound is determined by the circuit, the rest might be due to parts and layout, as long as parts used are good 'nuff.
if I use both channels of 1 relay (I am assuming you mean running the signal from channel one through both side of 1 relay) what do I do with the ground? Do I just connect all the grounds straight through without switching?
Good point J. I have found a lot of different looking single pole switches. No need to have them all look the same.
I found a bunch of them on eBay. I didn't look to see if they shipped to the SEU.
Also, when I look at relays, I see a coil that actuates the connections. Will the small voltage of the coil leak into the signal and cause hum or something?
These are the ones I would LIKE to use, but at 100 bucks a piece, I'll pass. They just look cool!!!!
These are the ones I would LIKE to use, but at 100 bucks a piece, I'll pass. They just look cool!!!!
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