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    User report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp

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    GP49

    Posts : 733
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    User report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp

    Post by GP49 on Thu Jan 28, 2016 6:52 pm

    This is an inexpensive ($12 plus $8 shipping) stepped attenuator made in China and offered on EBay by a Hong Kong seller.  I ordered two, one to install in a mildly upgraded Dynaco PAS-3x, one for "future needs."  The seller shipped quickly and the item arrived on the West Coast of the USA in five days.  

    *Note that this isn't a genuine DACT attenuator, hence the seller's calling it a "DACT Type." It is a Chinese clone.

    The attenuator is physically smaller than the stock Dynaco volume pot.  Its mounting boss is also smaller than the hole in the Dynaco front panel.  This is no problem except that you may wish to carefully align it in the hole before tightening the nut that secures it.  You may want to get a proper-size lockwasher, to prevent the new attenuator from rotating or shifting in use, even if you tighten the nut firmly; only a flat washer is supplied.  The shaft is splined, which matches the PAS-2 and PAS-3 knobs; factory-built PAS-2x and PAS-3x have nonsplined shafts and setscrew knobs, but their knobs work on the splined shaft, just fine.  The length of the shaft is correct for the Dynaco PAS; no need to hacksaw it to length, as on the Radio Shack ALPS control, which is of the wrong resistance anyway (100kΩ vs the correct 250kΩ).

    A locator lug on the attenuator must be broken off, as there is no matching hole for it in the Dynaco PAS front panel.

    Note that the attenuator does not have a loudness tap.  The loudness control on the stock Dynaco will not work; its wiring should be removed and the loudness switch bypassed.

    The attenuator being smaller may cause some minor issues if the existing wiring is too short, as it's a longer "reach" for the wiring to the solder pads than it was to the lugs on the old volume control.  I had to remove and replace the existing wires; they either didn't reach or were marginal.

    It helps to prewire the attenuator before physically installing it to the front panel, as it is easier to wire up to the mode switch and circuit boards than to solder to the attenuator once it is in position.  Be aware that you are soldering to printed circuit board material, not to solder lugs as on the stock volume control.  When I prewired it, I took care to solder the wires to the REAR of the connection board so that the wires would not foul the front panel. as the spacing is close.  Also you must make sure that the soldered wires do not short to the front panel due to being too long.  Use nothing larger than AWG20 solid wire; larger wire won't fit in the holes in the solder pads, and stranded wire is a pain to get through those little holes.  

    On completion, the installation was a complete success.  Its channel-to-channel tracking is very much superior to that of the stock Dynaco potentiometer and audio played through it is noticeably more "transparent" than through the admittedly old stock Dynaco part.  The internal switches are "make-before-break" which eliminates popping sounds as the volume knob is turned.  

    Suggestion: while you have the preamp opened up, clean the rest of the controls and switches, too, using an appropriate product.

    EBay photo:


    tubes4hifi
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    Re: User report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp

    Post by tubes4hifi on Sat Jan 30, 2016 9:28 pm

    as "cheap" in price as these things are, they are actually really decent quality, and this is what I've been using as standard equipment
    for my SP12 & SP14 preamps for the past two years, much better quality than the older ones that used to cost me twice as much.
    They are surprising small, and look cheap, but don't let that fool you, they are well made, and tracking is better than 1% channel to channel.
    FAR superior to any other control I've seen for under $90.

    hogzilla

    Posts : 14
    Join date : 2015-09-04

    Re: User report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp

    Post by hogzilla on Mon Feb 01, 2016 2:11 pm

    I picked this same one to replace a broken ALPS (total pain in the arse to install due to the post threading being very tight). This is FAR better than the ALPS. Nice smooth action with light "clicks" for each step. This is an excellent solution and for under $20 delivered, very cost effective as well.

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: User report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp

    Post by peterh on Mon Feb 01, 2016 4:16 pm

    I did buy a couple of the "alps" 250k pots from hongkong, and succeeded mounting one of them in a pas3. The pots were intended for board mounts, thus there was no eyelets, one had to
    turn the wire around carefully.
    Of course it was tight, but i managed it. And it works very well, thanks.

    Gregg R.

    Posts : 78
    Join date : 2014-02-20
    Age : 72
    Location : Land of 11,842 Lakes

    Re: User report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp

    Post by Gregg R. on Tue Feb 02, 2016 1:03 am

    I recently purchased a used passive mini-preamp made by Tisbury Audio in the UK. Tisbury Audio is somewhat coy about the origin of their 10K attenuator, but it sure looks like the Chinese model cited in this post:

    Tisbury 10K stepped attenuator

    Click on the far right photo. I haven't hooked up the Mini-Pre, but it has gotten good reviews. The wallofsound.ca review shows the unit broken down. An enterprising person could probably build a comparable device for a fraction of the price.

    UPDATE: I hooked up the Tisbury mini-pre above, but ran into problems with a buzz/hum, probably caused by my use of unshielded Kimber Hero into the VTA-70. I had the same issue with a Burson Conductor SL DAC/pre. I have no problems with my Grace M920 or two Emotiva DAC/pre. (2-24-16)


    Last edited by Gregg R. on Thu Feb 25, 2016 2:51 am; edited 1 time in total

    tubenutr

    Posts : 62
    Join date : 2015-01-25
    Age : 59
    Location : Northern Ontario

    BasketUser report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp.

    Post by tubenutr on Thu Feb 25, 2016 12:17 am

    The Chinese DACT type is quite good. It sure beats their knock off Alps pots. Good channel balance and transparency.

    evoroadster

    Posts : 39
    Join date : 2015-06-16
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    Re: User report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp

    Post by evoroadster on Thu Feb 25, 2016 12:37 am

    I also used a Chinese ALPS 250K knockoff to replace the volume control in a SCA-35. No complaints here.

    tubenutr

    Posts : 62
    Join date : 2015-01-25
    Age : 59
    Location : Northern Ontario

    BasketUser report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp.

    Post by tubenutr on Thu Feb 25, 2016 12:41 am

    If you're are using a balance you may not notice, but if you eliminate the bal. you will hear the difference.

    deepee99

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    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: User report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp

    Post by deepee99 on Thu Feb 25, 2016 1:09 pm

    Khozmo http://www.khozmo.com/products_dale_shunt.html
    Makes a great 48-step 10k pot for $180, with a remote option with LED display for another $200.
    I have one in my Sachs SP-14 (non-remote) and love it. Contacts are gold and it's good for 50,000 spins. There are only two resistors in the signal path regardless of setting.

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    Re: User report: DACT Type* 21 Stepped Attenuator 250K for Tube Amp

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