diy stepped attenuator under 10$

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K

kaushik

Member
Joined 2008
i started the building of DIY attenuator ,mechanism with
available parts at home
i always knew that the attenuator can be made with some
rotary arrangement.

But the roadblocks were ,

1) how to ensure durable contacts
2)how to make the rotary slider stay at a position
3) protecting from dust /impurities
4)how to exactly give contacts to moving rotary contact
5)keeping costs very low and avoiding machinery

i after a little thinking i have done little progress
adding plans and then pics


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
K

kaushik

Member
Joined 2008
first pic depicts the back side of the assembly, here i have
added 23 IC socket pins taken out by breaking the socket.

each pin has 2 sides
1)sharp pin side
2)flat contact side

How to build the circular contacts:

Put pin side thru holes ,and solder on the other side,contact side is bent .
The pads (socket pins)are laid on a circular fashion to so that slider touches 1 contact at each stable position.



second pic shows the rotary click mechanism
although it looks complicated ,it is NOT.
click mechanism works with a sprocket wheel designed from a toothpaste cap(i am sure there are many cheap robotics wheels,tape mechanism wheels that can be used).

spring + piston
Here I house 1 tiny spring taken from DPDT switch,piston is a tiny plastic cube,outer shell is a piece of refill.All attached with super glue.

I will add picture to make it clear .
piston is
 
S

suds

Banned
Joined 2006
When it comes to stepped attenuators, when changing volume, the contact breaks from one point and makes at another point during this break and make there will be "Glitch" or switching noise. how to avoid this and make a smooth transition.
One method would be using make before break mechanism, but these kind of switches are difficult to find, besides cost.

Any other ideas ?
 
S

suds

Banned
Joined 2006
Thanks for the info.. ! its not about $10 , I posted here cause I did feel like creating another thread.

I have some idea about stepped Attenuators, But the issue is,
when there one changes volume, there will be disconnection and re-connection when switch contacts move from one point to another point, during this transition, there will be unwanted response in form of distortion, glitch, undesired effects .. what ever one may call..
It is possible to prevent this ???
 
K

kaushik

Member
Joined 2008
MaxS
thank you , it is very helpful . The PCB in india is very cheap approx 2$, including all the whole device will be
near 10$.

suds read the translated page

http://translate.google.com/transla...projets&Itemid=34&sl=fr&tl=en&history_state0=

the resistor pattern is cleverly laid to avoid that "glitch"

so floating contact while shifting is totally avoided .
I am poor at mechanical design, my tested sproket is
not durable enough.

Please suggest some reliable locking mechanism(mechanical part)
 
K

kaushik

Member
Joined 2008
found a mechanical part for steps

Ok after searcing and even building one teethed wheel
I decided to go with some already available spares,
I have found the 'mouse encoder'..see the small blue spare...will cost just 10 cents max, can be had from damaged mouse for free!

http://www.eehomepage.com/reports/20080214_teardown_pics/wheel_insitu_mid.jpg

to be a suitable device , highly reliable and smooth.However the encoder is just a stepping device..its electrical operation will not be used.

more pics:
An externally hosted image should be here but it was not working when we last tested it.


attaching an wiper pcb contact will do i hope..
 
K

kaushik

Member
Joined 2008
quadtech said:
Here's an interesting implementation -

DACT Type 21 Stepped Attenuator Potentiometer 100K 2A3 - eBay (item 120474000457 end time Oct-26-09 11:06:39 PDT)
Click to expand...
I have seen that before also i have seen light speed attenuator ,
i will use smd resistors and finally try to make a low cost.
In many countries ebay + shipping+ customs =2x price
Glowbug,
the encoder is a mechanical part,well tested for very reliable mouse scrolling,so steps are very reliable,
main cream of this DIY is... the rotary contact arrangement

2 PCBS one with slider,and one with static contacts,both wil be spring loaded to remain rock steady in contact..
I need ideas for this..
early stages may give some problems but i hope finally
will do well... :cool:
 
star882

star882

Member
Joined 2007
What about just use a row of switches, each one switching in twice the attenuation factor of the last?

I think it would be much easier to use a good digital potentiometer and a rotary encoder. The HP signal generators I use in my ECEN classes use that method to vary the amplitude and the signal shows up nice and clean on the oscilloscope even at its top limit of 15MHz, regardless of the output amplitude.
 
K

kaushik

Member
Joined 2008
Audio purists say any digital processing add coloration to sound,thatz why the stepped pots sell at 200$ .

else i have 1000 digital designs,some chips are even dedicated
vol- controllers made by reputed Mfrs...

row of switches no one will like unless it is some recording preamp
smooth rotating volume with steps is desirable in all hi-end equipments.

i would like to know more of your ideas ..do post some pics/description detail..

I need ideas for making rotary contacts,i can use wiper from a pot,
what material should i use for contacts?
make-before-break layout? etc
 
Q

quadtech

Member
Joined 2007
at that price, $10 each + $5 postage, I'd recommend you buy two and test them.
Click to expand...

Don't need it now, else would have bought/tested. :)
Wouldn't have believed a few years ago, that one could get a $10 stepped
attenuator.

This part was recommended by someone a few
months ago, in the class D forum.
Hope whoever it was is reading this and can post the
step/resistor details.

The approach looks to be DIYable, using the pot shaft/wiper which
Kaushik is looking at.
Perhaps remove the part having the carbon track of the pot
and replace with your thin PCB with contacts pads arrange in a circle.
Use SMT resistors to keep it small, like the ebay chinese one.
 
Last edited:
rhing

rhing

Member
Joined 2007
Glowbug said:
I'd be a little wary of the reliability of something like that, unless a bunch of people had good results with it for a while.
Click to expand...

I've been using the 50k version of this SMD stepped attenuator, and it's been working very well in my integrated amplifier. It was a significant improvement over my amplifier's stock volume pot. I recommended this to a friend who installed one himself, and he agrees that the improvements were great. This is a nice stepped attenuator at this price. I'm sure DACT and Goldpoint SMD stepped attenuators are better, but at a much higher cost.
 
K

kaushik

Member
Joined 2008
An externally hosted image should be here but it was not working when we last tested it.


Plan is like this ( as in picture.)
I have refined the design and decided to use silver/tin rivets. The silver rivets will give better sonic perfomence.

There will be 2 PCBS , one carries wiper lever,one has riveted contacts and smd resistors.
The rivets will be close enough and wiper will do 'make-before-break'.
The encoder will help make the stepped rotation ,
the click click mechanical motion..

Q.What is the name of a riveted point if i give the PCB
for fabrication?
Q.can any one point to small silver/tin rivets that we can put in a home made pcb and solder with the smd resistors
 
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