Hi, I'm in the process of building the Rod Elliot Pre Amp (P97) The construction page suggests using a 6 way rotary switch on an extension shaft so that the switch can be mounted near the back of the case so as to minimise the wiring length, I only require 3 way - 4 Max.
I have read though some of the posts regarding switching of input signals, but they tend to drift off into using relays, which is not really the way I want to go.
I was looking at the range of wafer switches by RS Components as they can also supply an extension shaft, but these are open type wafers so would probably be prone to contamination.
The other thing is, is a MBB or BBM really important?
I was wondering if anyone else has built this pre amp and could share what they used for switching and or any problems they had.
Thanks In Advance.
I have read though some of the posts regarding switching of input signals, but they tend to drift off into using relays, which is not really the way I want to go.
I was looking at the range of wafer switches by RS Components as they can also supply an extension shaft, but these are open type wafers so would probably be prone to contamination.
The other thing is, is a MBB or BBM really important?
I was wondering if anyone else has built this pre amp and could share what they used for switching and or any problems they had.
Thanks In Advance.
"Contamination"? Are you using it open-case in a rock quarry? Better seal it.
Open-wafer source switches have been used a LOT for many decades. OK, when old they do go scritchy. We get what we pay for. Often an affordable switch serves better than one we can not hope to afford.
Extension shaft can be added to about any rotary switch. Most are 1/4" shaft. If a bespoke adapter is not at hand, 1/4" (6mm ID) fuel line and hose clamps and a 1/4" rod will do. The rod may have to be real 1/4" so it fits neat in a panel bushing broken off a low-price potentiometer or extra switch.
I am opposed to shorting sources to each other and would use break before make. Others worry about not having any source connection and favor MBB. It is probably not a real issue; you may be limited by what you can buy.
Open-wafer source switches have been used a LOT for many decades. OK, when old they do go scritchy. We get what we pay for. Often an affordable switch serves better than one we can not hope to afford.
Extension shaft can be added to about any rotary switch. Most are 1/4" shaft. If a bespoke adapter is not at hand, 1/4" (6mm ID) fuel line and hose clamps and a 1/4" rod will do. The rod may have to be real 1/4" so it fits neat in a panel bushing broken off a low-price potentiometer or extra switch.
I am opposed to shorting sources to each other and would use break before make. Others worry about not having any source connection and favor MBB. It is probably not a real issue; you may be limited by what you can buy.
Some of the multi-way selector switches have a moveable stop. You can change from a 6way 2pole to a 5way 2pole, or a 4way 2pole, or etc.
Similarly the 11way single pole can be changed to any from 1way to 11way.
contamination and corrosion are issues. The only switches that avoid both effects are mercury wetted reed switches. But these are virtually relays in that a magnet or coil pulls in the contact.
Very important. You have to determine which type of switch is required for your duty.
Hi Andrew, These would be the same as the ones sold by RS Components? or are you referring to the enclosed type that places like maplin used to sell, I used a lot of those in the past, and seem to recall the "Stop" was by means of a washer with a lug on it, and simply placed or located through a hole in the switch to form the stop point.
The MBB or BBM is a bit of an unknown at the moment and will depend on how the pre amp reacts to an open input or vice versa, but if I remember, those switches were fairly cheap, so one of each for experimentation shouldn't be a problem.
Black contacts are not necessarily bad contacts. An advantage of Silver is that most of its corrosion products are conductive.
_I_ have had just as much trouble with very-expensive switches as with $2 switches. My inclination is to make the switch easily replaceable (no PCB!!) and replace when needed.
_I_ have had just as much trouble with very-expensive switches as with $2 switches. My inclination is to make the switch easily replaceable (no PCB!!) and replace when needed.
Sulphur/sulphide can contaminate your components.
I would refer to that contamination as corrosion.
Silver when exposed to sulphur becomes black. Would that be a silver sulphide compound?
There will be other trace gases in the air. Many will corrode your contacts.
There will be other volatiles in the air. Many will contaminate the surface of your contacts. Some will be capable of migrating through the plastic insulations used in our builds.
I would refer to that contamination as corrosion.
Silver when exposed to sulphur becomes black. Would that be a silver sulphide compound?
There will be other trace gases in the air. Many will corrode your contacts.
There will be other volatiles in the air. Many will contaminate the surface of your contacts. Some will be capable of migrating through the plastic insulations used in our builds.
Yes, Fairly cheap too, so have ordered one of each (MBB) and (BBM) to see if one works better than the other during switching.
I built the preamp and just stuck it in my 40-year old Dynaco PAT-5 preamp in place of the old LM301-based board. Works great!!
Which Op Amps did you use?
I went for the OPA2134 after reading some very good reviews, probably on here somewhere...
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