About Attenuators

[leiade]

I would try some good slide potentiometers Penny & Giles, one advantage is if you mount them side by side you have a instant balance control I must admitt that the balance controls where not on my schedule but I have realized that one have to use a balance control of some type, it's most convenient if you don't want to move speakers.
One idea is to use reed relays, just the switch element, and build a sliding type of attenuator device these elements is rather cheap and I think very good switches say that one use 24 x 2 it is about 48 $ plus the resistors.

[leiade]

I found a rotary P&G with very good specs check this link http://www.pgcontrols.com RF 15 maybe it is very expensive but I think it will do the job much better then a stepped attenuator much because of the infinity resolution.

[Brett]

P&G = expensive for the performance. These attenuators are designed for studio mixing consoles and the like where repeatable precision in level is required. Because of all the open area, they're also a dog to keep clean. Remeber studios have a maintenance tech to do it all the time.

Reed relay = best relay for audio, especially the shielded types. If you build a shunt attenuator like the Aleph pre's, you will only need 8 to 12 a channel and you can get a 70dB range in 1 dB steps if you use high precision resistors (0.1%).

Even simpler is a shunt using an Alps or Noble motorised pot as the shunt element. They track within a dB or 2 over a 60dB range and are really cheap and easy to implement.

[mrfeedback]

leiade,
Alps make (made ?) a volume control with detented 1dB steps.
The range is 0dB down to -20dB then mute.
You could add a 20 or 40 dB pad before or after to give lower level control.
I had a system where 0dB from the cd player would drive the amp to momentary clip with the pots at max.
The detented level steps made repeatable level setting a piece of cake.

Eric.

[leiade]

Hi,

This is my idea, no fancy digital electronics that controls the attenuating device, just simple mechanics with cheap parts this results in a very precise audio attenuator.
You can make this at home with ordinary tools of course the resluts will be better if you have an mech workshop.
Use aluminium, brass and steel of some quality use ready sprocket wheels the pro type with sprocket belts fine for exact function.

Look at the coarse drawings it is NOT to scale I don't claim that this is the final solution but it is something to begin with here it is.

[kevin gilmore]

The lecson preamp of the late 70's did this for all input
switching. Works great (till the magnet falls off)

remember to space the reed relays enough apart such that
the magnet only triggers one at a time.

[leiade]

Yes I remember their obscure products I have tried to repair one of their power amp it was very hard to take apart, well I have done this drawing with this product in mind but nowaday we have better parts for doing this mechatronic attenuator I think no parts have to fell apart, with som extra care when assembling this device it would work for many years without any service.
It would also be very simple to make the adjustments for different kind of switchings.
Well, Dears Sirs come on let's make it who will begin.

I repeat the cost of this will almost be nothing and the resluts will be outstanding no Hallco, DACT or any have a fair chance.

[Havoc]

Have tought about that myself, but the space it takes held me back. It will create a very large loop that can pick up interference. Be careful with your layout.

Infinite resolution from a pot? Just try it! Use a very stable supply and a 6 digit voltmeter HP quality (Agilent now, but on those it will still be HP, they are that old). See if you can set it on whatever voltage you want and if you can repeat it.

[leiade]

Ok!
If you draw everthing to it's end there is nothing that being what one think, nothing that we can create is perfect but some will be near, for example a high precision wirewound potentiometer from any good manufacturer but it is not cheap about 100 $ or more and it's linear so it makes something easier.I have seen some with 0.25% linearity or better over its whole length it was a 10 turn device, it may be used as a volume pot.
Remember not even a SKF ball is not exactly round.
BTW the small reeds they are about 1.8 mm so the total lenght may be about 65 mm depending on the space between the elements if you use 23 pcs.You also have possibilities to make a stepped click indicator option using the sprocket belt as template.
65 mm and good shielding practise may be worth a try I will build one prototype just to se if it is good enough for high end, I think so.If you have a good mech workshop you may even make this reed device look like a ordinary round switch.