Pre-amp Input Switching

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little eddy
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#1 Pre-amp Input Switching

Post by little eddy »

Similar to Phil's thread on volume controls, what's the latest and greatest in terms of pre-amp input selector switches/relays?

I know WD had an option (sent an e-mail) but anyone used any Eastern-pre-assembled relay boards?

If I only had 2 inputs and no wish for phono or rec outputs, does this open up other simpler options such as a high quality double pole switch (toggle or rotary) that would do the trick (admirably rather than adequately)?

Or perhaps preferably, is there a good DIY switch/relay solution with off the shelf relays?

Sounds like it could be one of them pcb thingy projects!
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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colin.hepburn
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#2

Post by colin.hepburn »

This is also something I am looking in to as well so will be interested on what options there are to I have at the moment a double set of the WAD input switcher PCBs Boards just need to get all the relays I have the schematic for the WAD one if you want a copy PM me your Email as far as other kits go this eBay chap has some possible that you may be interested in
got http://cgi.ebay.co.uk/MV04-Motorized-Re ... 1c14b96dd6

And
http://cgi.ebay.co.uk/Audio-Input-Selec ... 1c15767d95
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Mike H
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#3

Post by Mike H »

Dare I mention my switcher box topic in Everyone's Projects? :D


Just to broaden the horizon


A work in progress at the mo but I'm using Meder sealed reed relays from Rapid.

I did have these working like this before for a while and seemed very good, but unfortunately the rest of the pre-amp was shite so was dismantled, but I had the presence of mind to hang onto the relays :D



 
 
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#4

Post by Graeme »

For just 2 inputs i may be tempted to splash out on mercury whetted relay/s.

Or, just use mercury tilts. Thats one of the things ive been thinking of.

Other option is to use LDR's as on/off switches, then you have no contacts at all, just solderd joints.
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#5

Post by Mike H »

Trouble with LDR's is you'll probably never get less than a few hundred Ohms when 'on', and still a high resistance when 'off', e.g. a NORPS12 could go to > 15 Megs if you're prepared to wait a minute. Literally.

And I'm still suspicious about what an LDR might do to a signal passing through it.


I did have an idea of a virtual earth input mixer type of thing (like inverting summing op-amp function), that way you can have any number of inputs you like all coming into the same point, the only proviso being that they all have to be quiet except the one you actually want to listen to. That way no switches are involved, 'just' resistors and things



 
 
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#6

Post by Graeme »

Yeah, i know in theory LDR's should be bad.

but in volume controls they dont seem to have any negative effects.

I was under the impression you could get on/off LDR's, i take it thats not completely true then.


Still fancy mercury tilts myself but mercury isnt the greatest conductor is it?

I do believe that removing switch contacts is a good idea even though they are no different really to all the other conectors in the signal path.
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#7

Post by Mike H »

Graeme wrote:For just 2 inputs i may be tempted to splash out on mercury whetted relay/s.

Or, just use mercury tilts. Thats one of the things ive been thinking of.
Consider for a brief moment the humble reed switch, sealed in glass in a vacuum. Or at least an inert gas possibly. No oxygen, no dust, no dirt, no moisture, no germs even, no contact problems. Other than wear of course, whatever that amounts to, must be some.

Just my four penn'orth :D



 
 
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Mike H
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#8

Post by Mike H »

Graeme wrote:I was under the impression you could get on/off LDR's, i take it thats not completely true then.

I could be wrong, I frequently am :lol: may well be and I just ain't heard of 'em



 
 
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#9

Post by Graeme »

Mike H wrote:
Graeme wrote:For just 2 inputs i may be tempted to splash out on mercury whetted relay/s.

Or, just use mercury tilts. Thats one of the things ive been thinking of.
Consider for a brief moment the humble reed switch, sealed in glass in a vacuum. Or at least an inert gas possibly. No oxygen, no dust, no dirt, no moisture, no germs even, no contact problems. Other than wear of course, whatever that amounts to, must be some.

Just my four penn'orth :D




Except vibrating contacts (in theory) hence the use of mercury.

Im just not sure if mercury is a good enough conductor on its own, without also having the gold plated contacts its wetting.

If it is then mercury tilts would be a far cheaper alternative to mercury relays.

Just a little bit of hassle to use. Anything over 2 positions will require some fancy mechanics or more than one switch.
Then you need to remember to turn sources off before selecting the next one.


If micro vibrations of the contacts arent an issue in reality (that is whats reputed to be the issue with having contacts) then yes, reed switches would be fine i guess.


I havent looked for the on/off ldr's as i think ive had my fill of LDR's, as good as they are, they are too much hassle for me.
Ive no proof they exist, only things ive read.
I know the 'build an amp' guy who does LDR attenuator kits is building LDR source selectors.

Doesnt mean there any good though :lol:
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pre65
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#10

Post by pre65 »

You won't get any problems with the input switch on my DIY preamp.

It ain't got one. :wink: :lol:
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Mike H
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#11

Post by Mike H »

Graeme wrote:Except vibrating contacts (in theory) hence the use of mercury.
I'm not going to be jumping up and down on it so I don't think the problem will arise :lol:

Unless you mean when closing, well in my previous iteration I did not notice anything like that



 
 
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#12

Post by Graeme »

No, ive read a few theories that say the passing signal can cause micro vibrations in the switch contacts, creating a less than perfect signal transfer.
Unless there very tight, then they wear too quick.


Sounds a little far fetched to me but i do think the less friction contacts the better.
Phono plugs etc arent such an issue as they can be very tight.
Im sure we all admit loose phono contacts arent great, take that down to a smaller level, and MAYBE switch contacts could vibrate in a bad way?

I dunno.
What i do know is when you cant afford to spend out on building new amps, paying stupidly obsesive attention to detail can also pay dividends :lol:
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#13

Post by Mike H »

Well I dunno the people who made them oscilloscopes I got from Hampshire month before last seemed to think using reed switches in them for the input signal switching would be OK. :D



 
 
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#14

Post by Graeme »

That just about sums it up really doesnt it :lol:

I have no input switching at the moment, i hard wired it and just swap leads over to change source.

Doesnt get any better than that and i cant say i noticed any difference between that and any of the other switching ive used.

It will stay like that untill i make my mind up what to do.

Since ive been looking at attenuators i am starting to wonder whats wrong with a good old fashioned high quality switch.

If there good enough for high quality stepped attenuators why not just use one for input to and forget about it!
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#15

Post by Mike H »

Could do that, HFC have (or I did see one once) like a Lorlin type with gold plated contacts.

My problem is I want 8 inputs and a 12-pin Lorlin type won't do it.

Will if it switches relays, as will work in like "mono"

Meanwhile same as you I swap phonos around, like old fashioned telephone switchboard, only thing is they're starting to take a beating constantly being plugged / unplugged



 
 
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