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    Attenuator vs. Potentiometer

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    TN Allen

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    Join date : 2013-01-01

    Attenuator vs. Potentiometer

    Post by TN Allen on Fri Feb 08, 2013 2:16 pm

    I've been looking through the posts regarding adding a way to control volume on an ST 70 amp. without using a preamp. I 'm curious about the advantage(s)of an attenuator rather than potentiometers. I'll probably order an attenuator from Mr. Latino, but it seems sensible to know the advantages before ordering.

    Bob Latino
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    Location : Massachusetts

    Re: Attenuator vs. Potentiometer

    Post by Bob Latino on Fri Feb 08, 2013 4:44 pm

    The fact of the matter is that stepped attenuators have two sets of fixed precision SMD resistors (one set for each channel) which typically give a tracking of much less than 1% difference from one channel to the other channel. Potentiometers on the other hand, unless they are expensive, usually do not track well from one channel to the other channel leading to a subtle volume imbalance between the two channels. The VTA potentiometers are quality units, have gold plated contacts and make no noise as you move from one step to the next. I use the stepped attenuator on my own VTA ST-120 amp. I had a good preamp for the system that my VTA ST-120 is in that I don't even use anymore. The amp sounds better with my Sony SACD player going directly into the amp with no preamp between.

    Bob







    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Attenuator vs. Potentiometer

    Post by TN Allen on Fri Feb 08, 2013 5:47 pm

    Sounds like the attenuator controls volume in discreet increments, uniformly L&R; the potentiometer along a continuum, and if it's a good potentiometer, also uniformly L&R.

    I'm also curious about the way either is reconciled with the input requirements of a particular power amp. Is there a website or forum post you may know of that explains this. I'm not looking for a way to do this myself, unless necessary, it seems more sensible to buy what you offer. However, I would like to try to understand the relevant details, and because I have ordered a DIY ST 35 board and parts from Triode and will want an attenuator for it as well. Perhaps the attenuator you sell will work with the ST 35 as well?

    Thank you, tna

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Attenuator vs. Potentiometer

    Post by Bob Latino on Fri Feb 08, 2013 6:06 pm

    Most CD players and other high level inputs have an output of about two volts. The newer CCS board on the VTA ST-70 and ST-120 only needs about 1 volt for full output. The stepped attenuator is a 100K unit and works well with the gain of the VTA ST-70 and 120 amps. On most systems you are getting pretty good volume somewhere around 2 O'clock on the attenuator knob. Of course this depends on the size of your room and the sensitivity of your speakers.

    Another note that has been mentioned before on this forum. You can also use the stepped attenuator WITH A PREAMP. If you turn the attenuator all the way to the right, the attenuator is basically out of the circuit. You will measure zero ohms from the input jack to the driver board. You do have one extra solder connection on the attenuator but I never heard a single solder connection alter the sound. You can also use the attenuator as a master level control with a preamp. If your preamp has the volume of the amp come on to quickly and the "range" of the preamp's volume control is very low - say at 10 o'clock the amp is already too loud, you can set the stepped attenuator at maybe 2 or 3 o'clock and now it will take more output from the preamp to get the amp pretty loud. You will have to turn the preamp's volume contol up much higher to get to a given volume level.

    Bob

    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Attenuator vs. Potentiometer

    Post by TN Allen on Fri Feb 08, 2013 6:21 pm

    Thank you for the rapid reply.

    Your suggestion regarding use of an attenuator with a preamp may well be an unsolicited solution to another problem I have with a recent PAS 3X preamp upgrade. It seems likely you have described a solution to the hum problem I have using this preamp with the ST 70. Perhaps it is not that the hum is excessive, so much as that the signal from the preamp to the ST 70 is excessive. The hum volume does not change with changes in the volume knob. With another preamp between the PAS 3X and ST 70, I can control the hum sufficiently for the present. Seems from what you write that the attenuator would do the same.

    How do I order your attenuator? Is it compatible with the DIYTube ST 35 upgrade?

    tna

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Attenuator vs. Potentiometer

    Post by Bob Latino on Fri Feb 08, 2013 6:30 pm

    I sent you an Email off the forum about the stepped attenuator ..

    Bob

    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Attenuator vs. Potentiometer

    Post by TN Allen on Fri Feb 08, 2013 6:35 pm

    Thank you, tna

    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Attenuator vs. Potentiometer

    Post by TN Allen on Sun Feb 17, 2013 12:47 pm

    I've connected the attenuator, it works very nicely.

    Additionally, although it does not solve the PAS 3X upgrade hum problem, it does make it possible to reduce it to an acceptable level, nonetheless, I'll continue to look for a solution to that problem.

    Thanks

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