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    A stepped attenuator for your ST-70/ST-120

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    Bob Latino
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    Location : Massachusetts

    A stepped attenuator for your ST-70/ST-120

    Post by Bob Latino on Thu May 06, 2010 12:58 pm



    I've been looking for a stepped attenuator for the ST-70/ST-120 that was small enough to fit into STEREO/MONO switch area. I finally found, through one of my distributors, a 21 step attenuator that fits the space and works well. This is a 100 Kohm unit with sliding steps and no "click" or any noise at all between the steps. It works extremely well. The black knob compliments the black tube sockets on original Dynaco amps or my kit amps. This attenuator will be great if you only have a single high level input source like a CD player because now you don't need a preamp at all. Another nice feature is that you CAN also use this WITH a preamp. On the final 21st step there is a complete pass through of the signal with zero attenuation. If your preamp has a volume control that has the volume come on too quickly you can use the attenuator as a "master level" control for your amp.

    I will probably be offering the stepped attenuator as an option with the kits and wired amps that I sell in about 2 weeks but the attenuator may be used with any Dynaco ST-70 amp. Right now I only have one extra attenuator/knob set but I will be getting some more later next week.

    Bob


    Last edited by Bob Latino on Sat May 22, 2010 6:30 pm; edited 1 time in total

    wolverine

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    Join date : 2010-02-20

    Re: A stepped attenuator for your ST-70/ST-120

    Post by wolverine on Thu May 06, 2010 11:30 pm

    This looks interesting Bob. I may want to add one of those to the bedroom unit where I basically use an Ipod.

    wolverine

    Bugs

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    Join date : 2009-04-17

    Re: A stepped attenuator for your ST-70/ST-120

    Post by Bugs on Tue May 11, 2010 2:04 am

    Sounds interesting, keep us posted. Cost?

    vegaseddoc

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    Join date : 2009-11-21

    Re: A stepped attenuator for your ST-70/ST-120

    Post by vegaseddoc on Fri May 14, 2010 4:21 pm

    Can I purchase one of these from you? If so, then when?

    Bob Latino
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    Re: A stepped attenuator for your ST-70/ST-120

    Post by Bob Latino on Fri May 14, 2010 5:16 pm

    vegaseddoc wrote:Can I purchase one of these from you? If so, then when?

    Hi,

    I will getting some more of these from my distributor sometime next week. They ran out of them because they only got an initial order of 25 of these attenuators. I ordered 20 of them but they only gave me two. I *should* have 20 sometime next week. I will post on this thread the day they arrive if anyone is interested in adding a stepped attenuator to their ST-70. Pricing will be in the neighborhood of $50 + shipping. Below is a close up photo of the back of the attenuator showing the SMD (surface mounted devices) low inductance resistors.

    Bob




    NOTE - Above is one of the older original VTA stepped attenuators. Below is a photo of one of the newer models from that have been used since early 2011. The newer models now have the SMD resistors and gold plated contacts on the inside sealed against dust. All the newer models also have a "D" shaped shaft instead of a knurled shaft. The black knob that comes with the attenuator fits over the "D" shaped knob and is held in place with a set screw . The reason for going to the "D" shaft is that sometimes a knob on a knurled shaft which is placed on the shaft with a "press fit" will (in time) grab the shaft so tightly that it is difficult to remove. Did you ever try to pull the bass, treble, balance etc. knobs off a vintage amp/preamp and have them feel like they were "welded" on?



    Last edited by Bob Latino on Fri Aug 31, 2012 5:13 pm; edited 3 times in total

    vegaseddoc

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    Re: A stepped attenuator for your ST-70/ST-120

    Post by vegaseddoc on Fri May 14, 2010 6:24 pm

    Thanks Bob. I will definitely purchase one of these as I like to tinker with different preamp designs. I have my own wiring ideas but will you have any recommended wiring schemes?

    risetony
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    Re: A stepped attenuator for your ST-70/ST-120

    Post by risetony on Sat May 15, 2010 11:11 am

    I am also interested in an attenuator. I have components purchased over the last couple of years to assemble a repro ST70, but have let it languish. This will make the amp a little more usable with things like a CD player. Let us know how it mounts, if any mods to the chassis are necessary.

    baddog1946

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    Location : Costa Rica

    stepped attenuator

    Post by baddog1946 on Sat May 15, 2010 11:54 am

    I noticed it looks like it has only one row of resistors is it a stereo control or is the photo just not showing both rows of resistors?

    Bob Latino
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    Re: A stepped attenuator for your ST-70/ST-120

    Post by Bob Latino on Sat May 15, 2010 12:28 pm

    risetony wrote:I am also interested in an attenuator. I have components purchased over the last couple of years to assemble a repro ST70, but have let it languish. This will make the amp a little more usable with things like a CD player. Let us know how it mounts, if any mods to the chassis are necessary.

    Hi,

    There will be no modifications to the chassis of your ST-70 other than the removal of the STEREO/MONO switch and the installation of the stepped attenuator in it's place. You will get a short two page installation manual.

    To baddog1946 > This is a stereo control - there are two banks of SMD low inductance resistors - see the photo below with the two sets of solder attachment holes - one for each channel ...

    Bob



    Last edited by Bob Latino on Mon May 17, 2010 11:22 am; edited 2 times in total

    kevinmi

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    Re: A stepped attenuator for your ST-70/ST-120

    Post by kevinmi on Sat May 15, 2010 1:53 pm

    Bob, put me on your list for one of these also! Thanks, Kevin

    baddog1946

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    Re: A stepped attenuator for your ST-70/ST-120

    Post by baddog1946 on Fri May 21, 2010 5:32 pm

    Hi Bob:
    I'm interested in one of those attenuators for my ST-120. Can you give me an idea of what's involved in the installation of one?
    Does it need any other parts? Obviously a little soldering will be necessary or maybe you can post a diagram or outline about what it takes to put one in my amp so I can see if I am up to the job myself. If it is simple please put me on a list and inform me of when you can supply them.
    Thanks
    Baddog1946

    Bob Latino
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    Re: A stepped attenuator for your ST-70/ST-120

    Post by Bob Latino on Fri May 21, 2010 9:06 pm

    Hi Baddog1946,

    I moved the stepped attenuator photos to the "For Sale" area. I have five attenuator kits left as of today. These are in short supply right now because they are new. If you want one send me an Email to my regular Email address > Bob01605@aol.com

    It is a very easy installation into a stock ST-70 or ST-70 with any other driver board. A short two page manual with a couple of illustrations is included. You don't need any electrical knowlege. Just a few solder joints to make ..

    Bob

    RockyAM

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    Re: A stepped attenuator for your ST-70/ST-120

    Post by RockyAM on Mon May 24, 2010 3:37 pm

    Hey Bob,

    Did you notice any audible improvements or any difference in the sound of your amp after you installed the attenuator? RockyAM

    Bob Latino
    Admin

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    Join date : 2008-11-26
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    Re: A stepped attenuator for your ST-70/ST-120

    Post by Bob Latino on Mon May 24, 2010 4:02 pm

    Hi Rocky,

    Every component in the audio chain adds some audio signature to the music that comes through your speakers. If you remove one component in the chain (preamp) then that is one less component to add something to the music.

    Disclaimer > You asked the question but everyone knows that I also sell these attenuators. All should consider that fact in regard to my next few statements in the paragraph below ...

    Without my BAT VK-3i preamp in the chain I honestly think I am now a little "closer to the music". Resolution and soundstaging seem somewhat better now. I think that everyone has their own "test" CD's or vinyl records and I have mine. These are the tracks that you play when you change a component in your stereo system and are interested in how this track that you are very familiar with sounds with the new component in the chain. I played my test CD's with the BAT preamp in the chain and then straight with just the attenuator. Resolution WAS slightly better WITHOUT the preamp in the chain. Soundstaging seemed a little wider and deeper probably due to the removal of any phase abnormalities in the BAT preamp. Phase irregularities in any component will reduce the size of your soundstage. Someone on one of the Audio Asylums once said "the best preamp is no preamp" and I think I agree with him.

    Bob

    anbitet66

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    Re: A stepped attenuator for your ST-70/ST-120

    Post by anbitet66 on Tue May 25, 2010 1:12 pm

    Hi Bob,

    I tried to leave you an email, but it seems to be stalled-in-transit. Thank you for the fast shipping of the attenuator. Your picture belies the fact of how small this thing really is! I have never seen one so small so installation should be really easy. I need to get back to my project of building my ST70 and I'll let you know how it goes. Tony

    Bugs

    Posts : 91
    Join date : 2009-04-17

    Re: A stepped attenuator for your ST-70/ST-120

    Post by Bugs on Fri May 28, 2010 2:34 pm

    My attenuator arrived in the mail today, thanks Bob. That attenuator makes a slick little package. It has nice smooth actuation. The magnification of your picture is deceiving, I can barely read the numbers on the surface mount resistors, even with using reading glasses. I hope to have it installed today or tomorrow.

    RockyAM

    Posts : 26
    Join date : 2008-12-14

    Re: A stepped attenuator for your ST-70/ST-120

    Post by RockyAM on Fri May 28, 2010 4:04 pm

    Hey Bob, My attenuator arrived today also and I just installed it. It is a nice compact unit and it works great. No noise or clicks between each step just as you said. I measured the resistance from channel to channel on each step and could find virtually no difference. The channel tracking is near perfect. Nice instructions too. Easy to follow. Thanks, RockyAM

    kevinmi

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    Join date : 2009-11-17

    Re: A stepped attenuator for your ST-70/ST-120

    Post by kevinmi on Sat Jun 19, 2010 11:46 am

    Since I'm off of work recuperating from prostate surgery, I decided I would install my attenuator in my ST-120. It only took a few minutes to do after the soldering iron was fired up. I found it easier to solder the six lead wires to the switch before mounting it, since the switch is so small and my eyesight ain't what it used to be. Thanks Bob, for a well thought out improvement on an already great product!

    dyna70

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    Re: A stepped attenuator for your ST-70/ST-120

    Post by dyna70 on Sun Jun 20, 2010 5:56 pm

    Hi Bob.

    Very interested in one of these for my VTA ST70 (original high gain board).

    Do you know how many resistors the signal goes through on this pot please?

    How much would postage for one be to the UK please?

    Best,

    - John

    Bob Latino
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    Re: A stepped attenuator for your ST-70/ST-120

    Post by Bob Latino on Sun Jun 20, 2010 7:54 pm

    dyna70 wrote:Hi Bob.

    Very interested in one of these for my VTA ST70 (original high gain board).

    Do you know how many resistors the signal goes through on this pot please?

    How much would postage for one be to the UK please?

    Best,

    - John

    Hi John,

    I am not really sure how many resistors the signal goes through ? I can check with the manufacturer ... Needless to say, IMHO, the attenuator does give much less change to audio signal that if the signal were to pass through the various gain stages of a preamp. My BAT VK3i preamp has been sitting unused for the past 3 months that I have the attenuator kit on my personal ST-120.

    I can send the attenuator kit to the UK for $7.00 USD

    Bob

    janka

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    Join date : 2010-06-25

    Re: A stepped attenuator for your ST-70/ST-120

    Post by janka on Mon Jul 12, 2010 1:50 pm

    I ordered and installed one of these in my stock st-70. Thanks for finding this Bob!! I am currently running my phono pre directly into the st-70 and LOVE it!! Since I have high efficeny speakers the volume at full gain is perfectly sufficent. Though a high gain driver board may be in my future since sufficent doesn't always cut it.

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