THAT - 1570 Pre for 500 Series

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bruce0

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Jan 24, 2010
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I am laying out a THAT-1570 preamp for the 500/51X series. 

I want to make a really inexpensive very quiet wire plus gain type amp. I can get really low noise out of the chip and a simple card can be put together at really low cost per channel.

But to get the best noise numbers out of those chips I have to either use the digital control or a reverse log dual gang pot or a dual gang rotary switch.

So my question is, is grayhill the only option?  Are there any other less expensive rotary switches with at least 10 positions?

(I don't want to use the digital control, and the reverse log pots are hard to find, and I like switches. But the way things are going the switch is the most expensive part in an otherwise very low cost module).
 
I've looked quite a lot for cheaper grayhill alternatives.

There is this:
http://uk.mouser.com/ProductDetail/Alpha-Taiwan/SR2921F-0112-19R0B-E9-S-W/?qs=sGAEpiMZZMvNbjZ2WlReYnqYHrQfuERsRcKE2i5WjfE%3d

But I have never seen it in stock.


You can get stackable wafers by lorlin, up to 5 wafers in a switch:
http://uk.rs-online.com/web/p/rotary-switches/0352317/

Not sure of the mechanics exactly. Plus, might be a little large for 500 series.

Another stackable one from lorlin:
http://uk.rs-online.com/web/p/rotary-switches/2047736/

Again, the shaft is maybe a bit wide...
 
ramshackles said:
You can get stackable wafers by lorlin, up to 5 wafers in a switch:
http://uk.rs-online.com/web/p/rotary-switches/0352317/

Not sure of the mechanics exactly. Plus, might be a little large for 500 series.

Those are cool.  Appear sealed, available in different contact material, not sure how available they are in the US.  I will look into it.

Datasheet here http://www.lorlin.co.uk/PDF/PT.pdf.

1.25" off the top of the PCB, which might actually work with low PCB standoffs (at least on the front of the card).

 
culteousness1 said:
The cheapest solution will still be a digital control.
So may I ask, why you do not want to go digital?

Best,
Carsten

Part of it is that I want to make a simple prototyping platform, and a rotary switch mounted would help there.
I want to make a "prototype" board that will in it's simplest form have a cheap quiet mic pre on it (the 1570 specs are quite good).  But I also want to be able to put other things on the card without doing point to point. If I don't install the 1570 chip and associated stuff I hope the card will have cutouts and mounts for output transformers, and Phase, Pad, Phantom and Line switches along with associated relays and control circuit.  The idea being to be able to build a 1/2 eurocard Mic Pre, and have an easy way to mount it in a 500 rack without doing all the measuring and panel cutting. 

Think of it like all the little doo-dad cards without the ribbon cables and capable of fitting in a 51x rack (JLM go between, stereo link etc).  I just want to enable easier 500/51x prototyping

I agree digital would be cheapest, but I would need to put some sort of micro-controller in to drive the 5171 chip it seems, and it is all new learning for me.  Then I would need a display to tell what level it was at, etc. And the gain control might not be as useful for other prototype projects.
 
bruce0 said:
ramshackles said:
You can get stackable wafers by lorlin, up to 5 wafers in a switch:
http://uk.rs-online.com/web/p/rotary-switches/0352317/

Not sure of the mechanics exactly. Plus, might be a little large for 500 series.

Those are cool.  Appear sealed, available in different contact material, not sure how available they are in the US.  I will look into it.

Datasheet here http://www.lorlin.co.uk/PDF/PT.pdf.

1.25" off the top of the PCB, which might actually work with low PCB standoffs (at least on the front of the card).

If you want me to get some, I'll probably be getting some for myself.
The 'switch' part:
http://uk.rs-online.com/web/p/rotary-switches/0665837/

They have them at farnell, so perhaps they have them in the US (newark):
http://uk.farnell.com/lorlin/pt6434-bmh/switch-1pole-12-pos-tht-0-5a-250v/dp/1123674
 
ramshackles...

Let us know what you find when you get them... There are stopless kinds and kinds with stops, and it is unclear (to me) how the part numbers break out.

It seems like there are three parts needed.  The switch part, the wafer part and the spacer kits

I guess I could make a 3 wafer with 1 switch, two wafers and a spacer kit (but I can't really tell).

I am very interested in your experiences with these.  The PCB layout is quite different from the Grayhill (6,5,4,3,2,1,pole,12,11,10,9,8,7), but if they are really available in different numbers of poles that would be a big plus, and they are not that much.

I can get the switches in the US at Newark, but let us know the quality
 
That's a good idea, but the application requires something close to 5K, and it needs to be a dual pot, and REV log.

I couldn't find one, do you know of one?

Maybe I should look at faking it with a resistor to the wiper though...I need to think about how that works in this application... (it doesn't need to be constant total resistance)
 
Hey Guys: Mouser stocks lorlins basic switches. In single quantity they are approx. $4.70 usd. I would give you a catalog page but my catalog is 2012. Type Lorlin switch in the search box on the web site, then choose a switch, pull it up & you will find the catalog page & the data sheet; just click them on for full info. For the price they are hard to beat.
 
the basic lorlins are a single wafer 12 throw switch with adjustable stops available mbb or bbm, and they are nice and cheap.

The switch required has 2 poles, and as it is used for gain I wanted a 10 throw switch or more.  The basic lorlins in 2 pole are 6 throws (1P/12T, 2P 6T,3P 4T, and 4Pole 3Throw).  For two poles I would need to do 12dB gain steps.

The lorlin that ramshackles came up with is a different animal entirely, (the LORLIN PT series specifically) carried by Newark but not Mouser. 
 
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