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PostPosted: 11 Feb 2015, 01:28 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
Suncalc wrote:
allenb wrote:
I had read where the lower cost stepped attenuators were quite difficult to turn and were more switch-like. Does anyone have any experience with them and can tell me if I'll need a larger than typical control knob to turn it?
Yup; they take some torque to turn. If you look here (http://diyaudioprojects.com/Misc/DIY-Stepped-Attenuator/) you'll see that the one I used is fairly large (≈2-1/4"). The other thing that I have learned is to use some Loctite® on the set screw in the knob. Otherwise, the switch action tends to work the set screw loose over time (a relatively short time).

Good tip.

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PostPosted: 11 Feb 2015, 13:39 
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Joined: 09 Oct 2012, 19:43
Posts: 363
Location: Vancouver Canada
Good advice about the Loctite. Also, I have many times, modified sw's to lessen the amount of torque needed to turn the sw. Each sw is a little different in how it is made but, the method is usually a ball-bearing held in place with spring or spring steel plate to tension the ball. The plastic enclosed types are a bit trickier as they employ 2 balls one at each end of a spring which ejects the balls the moment it is opened. :eek: I open these in a plastic bag now due to experience, but they all can be moded a bit and it does not take much to make a big change in torque. In most sw's the torque to turn from one position to the next is "independent" of the torque between contacts. Therefore moding the turning torque does not effect the contact resistance. There are exceptions however so one should be observant.


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PostPosted: 11 Feb 2015, 20:26 
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Joined: 07 Sep 2011, 20:55
Posts: 24
Location: Longmont, Colorado
Thanks Matt for the loctite tip and Laurie54 for the torque reducing tip. I'll pick up a 100k unit http://www.analogmetric.com/goods.php?id=1000 (thanks Soundbrigade) and go for modding the spring tension. This sounds like a great idea and especially if the only thing causing the higher turning torque is the ball detents mechanisms high spring tension.
8audio are out of the 100k stereo stepped attenuators and don't expect to stock them anytime soon unfortunately.

Allen


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PostPosted: 28 Apr 2015, 08:03 
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Joined: 26 Dec 2013, 13:26
Posts: 18
I started with this project and i don´t know how to remove those unused leads from 369 EX power transformer.
Asking to Hammond (gently Gary Gray ) they reply:

´´ ...…as for the remaining unused leads, they need to be isolated from ground and each other so carefully apply a small wire connector to the end of each of the un-used leads and tuck them safely out of the way..``

but is there any way to remove those leads ?

TIA


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PostPosted: 28 Apr 2015, 09:00 
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Joined: 14 Feb 2010, 13:13
Posts: 711
Location: Lisbon, Portugal
Why would you like to remove unused leads from a transformer?

It makes no sense...


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PostPosted: 28 Apr 2015, 16:27 
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Joined: 04 Jun 2008, 20:59
Posts: 4285
Location: Arizona, USA
Hi I agree. Leave them alone. I put heat shrink on any like that in my projects and depending on the type of transformer just stuff them back inside it. Most trannies with "bells" have lots of room inside. For ones that don't I still use the heat shrink, but then bundle them together and use either a nylon fastener or a lug strip to fasten them in place so they don't flop around.


Good listening
Bruce

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PostPosted: 15 Jun 2015, 08:32 
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Joined: 29 Oct 2014, 12:32
Posts: 95
Location: Russia Komi republic
Good day!
Quick question - can I use this scheme, the volume potentiometer 100K? And if so, what changes should I make to the rest of the scheme?

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PostPosted: 15 Jun 2015, 17:55 
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Location: US Pacific Northwest
No. You can however put a single 250kΩ resistor in place of the back end potentiometer and put a 100kΩ potentiometer on the input. This is a perfectly acceptable substitution.

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PostPosted: 16 Jun 2015, 14:23 
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Joined: 29 Oct 2014, 12:32
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Location: Russia Komi republic
thanks!!!

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PostPosted: 02 Sep 2015, 22:48 
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Joined: 20 Feb 2014, 10:35
Posts: 59
Location: NZ
Hi, first post here but been following this thread. Finally got around to building a 4S, a very nice little preamp.
Straightforward build, I just used a Hammond box, transformer & choke. Most of the other bits from my parts bin.
A really fun project, & should be very useful for testing various 12A*7 tubes.
Thanks to Matt for his work on this & for sharing his ideas.

Chris.


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