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    Step Attenuator vs pre-amp

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    dacer38

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    Step Attenuator vs pre-amp

    Post by dacer38 on Fri Sep 11, 2015 10:17 am

    I know this is kind of an open ended question. What are the benefits and cost of each? Seems for my application the attenuator is the way to go. Have two sources, DAC and TT so it's and easy switch between sources.
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    Bob Latino
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    Re: Step Attenuator vs pre-amp

    Post by Bob Latino on Fri Sep 11, 2015 10:46 am

    dacer38 wrote:I know this is kind of an open ended question. What are the benefits and cost of each? Seems for my application the attenuator is the way to go. Have two sources, DAC and TT so it's and easy switch between sources.

    The stepped attenuator removes the preamp from the audio chain and some like the direct connection to the amp. If you are using and older Dynaco PAS-2/3 preamp in your system the sound quality will definitely be better without the preamp in the audio chain. With more modern high quality preamps such as the VTA SP preamps, any increase in sound quality will be neglible using the stepped attenuator. If you have two signal sources and are willing to swap cables and/or use some type of switch box for switching signal sources, the stepped attenuator may be a good choice.

    Just to be clear > You can also (at a later date) use the amp with a preamp with the attenuator still in place. If you turn the attenuator all the way to the right, there is a pass through of the audio signal directly from the input jacks to the driver board input eyelets and the stepped attenuator is "out of the circuit" with just one extra solder connection in the way.

    Bob
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    sKiZo

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    Re: Step Attenuator vs pre-amp

    Post by sKiZo on Fri Sep 11, 2015 2:49 pm

    Yup ... in my custom build, I added two high quality old school Mallory pots instead. That gives me adjustable balance as well.



    Be a bit difficult to shoehorn something that big into the stock chassis, but I'm sure there's room for two ... if you don't mind burning up a couple bits trying to drill stainless steel.

    And yes ... I also use a pre AND a DAC, both with their own level controls, not to mention software volume for digital files, in the signal path. Gives me multiple options for matching the signal through the components and feed them exactly what they're most happy with. You'd be surprised how much difference that can make after a bit of tweaking and listening.

    nmchiefsfan

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    Re: Step Attenuator vs pre-amp

    Post by nmchiefsfan on Fri Sep 11, 2015 5:43 pm

    If by TT you mean turntable you will need some kind of phono pre between the turntable and the amp.
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    Kentley

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    Re: Step Attenuator vs pre-amp

    Post by Kentley on Fri Sep 11, 2015 5:55 pm

    I'm with sKiZo on using BOTH a pre and the attenuator. The variations of tone available are subtle but real. In my case, adjusting the ST-120 attenuator so that my SP-14 pre can work pretty hard (at 2 to 4 o'clock) gives the best overall tone for all types of source material. In other words, I'm using the attenuator MORE for adjustments than the pre level control.
    Comparison between using the pre with the attenuator and using the attenuator alone in my system, with my ears, yielded a dramatically different result. When levels are just right, the pre+attenuator sounds much richer and punchier. And rounder.
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    pedrocols

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    Re: Step Attenuator vs pre-amp

    Post by pedrocols on Sat Sep 12, 2015 2:05 pm

    I literally sold my 4,000 BAT preamp after trying a passive preamp.  The BAT preamp will give sort of a greater 3D effect. However, for what I paid for the passive preamp the difference to my ears was not a very profound one.


    Last edited by pedrocols on Sun Sep 13, 2015 12:27 am; edited 1 time in total
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    Kentley

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    Re: Step Attenuator vs pre-amp

    Post by Kentley on Sat Sep 12, 2015 10:40 pm

    pedrocols wrote:I literally sold my 4,000 BAT preamp after trying a passive preamp.  The BAT preamp will give sort of a greater 3D effect but for what I pay for a passive preamp the difference to my ears was not a very profound one.

    I think I may be able to shed some light on why some folkses find little difference between an active pre and a passive one (which is essentially an attenuator plus some switching capability). In my experience, acoustically recorded music ("classical", older jazz, and any music recorded in a "real" acoustic space) will benefit far more from the use of a good pre - such as the SP-14 - than electric music recorded in a studio, where a great deal of the ambience, soundstage, and imaging is produced electronically or even digitally. In other words, if you prefer Pink Floyd to Beethoven, you might find it worthwhile to save some denari and use the attenuator alone, or an inexpensive passive pre. Studio music, especially in the Digital Age, is heavily processed in ways we sometimes are scarcely aware of - manipulated to the point where no elaborate signal path can ever enhance it. Vinyl - well, yer gonna need a pre no matter what.
    Of course, as always, system synergy, room setup and treatment, and good ol' personal taste is gonna matter more than anything else......
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    corndog71

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    Re: Step Attenuator vs pre-amp

    Post by corndog71 on Sun Sep 13, 2015 1:36 pm

    I've always found the trade-off to be a little better clarity from the attenuators vs. better dynamic swings and oomph from a good preamp. The latter wins for me.
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    Roy

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    Re: Step Attenuator vs pre-amp

    Post by Roy on Thu Jan 25, 2018 8:30 am

    Almost up to the point of placing my order for an ST-120 kit with the attenuator option but  I am left to wonder what kind of  range the 21 step attenuator would give me with our raspberry pi 3 with the Allo Boss DAC -a lovely little DAC with excellent sound quality  and that can handle most audio formats ( https://www.allo.com/sparky/boss-dac.html ) which has a max output of 2.1Vrms ;


    I have read some answers which conflict a little as to the inputs of the ST-120 - one stated that its max input voltage is 3/4ths of a Volt, the other mentioned 1 Volt. Which of these is the true input max voltage of the ST-120 and     if the Allo Boss is set to its max output level, how many steps would it take for the attenuator to get to the max of the input levels of the ST-120 ?
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    Peter W.

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    Re: Step Attenuator vs pre-amp

    Post by Peter W. on Thu Jan 25, 2018 5:35 pm

    Mpffff... (that is an internal 'grunt', not a disparagement).

    I have several pre-amps, including:

    Dynaco PAS3x, PAT4, PAT5 BiFet.
    HK Citation 17
    Revox A720 ("preceiver")  

    All of which are capable of making ~5+V into 10,000 ohms, some much higher.

    Most line-level outputs are 'governed' to something between 1.5 and 2V into the same load.
    Most amplifiers (not all), have their RMS ratings taken at 2V. Most vintage SS Dynaco use 1.5V.

    A passive attenuator will allow something-less-than the line-level output. Which may, or may not be what is required to meet the output rating of the amplifier-in-question.
    An active pre-amp will allow you to exceed the 'rating input load'.

    EITHER is another link in the chain.
    Most good pre-amps allow themselves to be used as a straight-wire device as well.

    I see no downside to a decent pre-amp.
    I see no upside to a passive attenuator.
    The latter is a bit more emphatic than the former.
    My opinion, not offered as anything else.
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    Roy

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    Re: Step Attenuator vs pre-amp

    Post by Roy on Fri Jan 26, 2018 12:43 pm

    We got a fairly good solid state set now, power and pre but  my wife seriously disagrees with the gui so to speak.   pre amp vol down  - switch on -  switch on power amp   -     when done switch off power amp   - then wait  - then switch off pre..   Just having the  ST-120 with an attenuator and her main musical source  the raspberry pi with the nice dac and a remote would be nice. The Dual CS 721 and other stuff has me as a switch board operator -  I'd be fine just swapping rca cables for the while.. Just wondering what the actual input max V is on the ST-120 since I read  one of Bob's replies to someone blasting a cd player on step 21 saying the ST-120 had 3/4th of a volt as max and he was lucky he did not burn stuff out, and another he said that said 1v was the max.
    If the stepped attenuator is  linear that would make it round step 7 (around 0.75v) or step 10 (round 1v) going from near silence to full blast on the 2.1V coming from the dac wouldnt it
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    Bob Latino
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    Re: Step Attenuator vs pre-amp

    Post by Bob Latino on Fri Jan 26, 2018 9:50 pm

    Peter W. wrote:
    I see no downside to a decent pre-amp.
    I see no upside to a passive attenuator.
    The latter is a bit more emphatic than the former.
    My opinion, not offered as anything else.

    The VTA ST-70 and ST-120 require about 1.1 to 1.2 volts IN for full output. The 100K VTA stepped attenuator offered as an option allows the user to plug in any high level signal source directly into the amp. Since most high level signal sources have a pretty much standard level output of about 2 volts out, the 2 volts into the amp is more than enough input for the amp to reach full output. The stepped attenuator allows the user to pad down the incoming voltage to achieve a suitable sound level in his music system. The stepped attenuator has the following advantages ..

    1. It doesn't cost that much
    2. It allows the user to direct input any SINGLE high level signal source without the use of a preamp.
    3. Later if you do get a preamp, you can turn the attenuator all the way to the right and you get a pass through of the audio signal. In other words, it is like the attenuator is not even in the circuit.
    4. You can use the attenuator WITH a preamp as a "master level control". Years ago I had a Conrad Johnson preamp that would give full volume with most amps when the volume control was at about 9 to 10 o'clock. That preamp had way too much gain. If I had the attenuator years ago, I could have set the attenuator at about 12 to 1 o'clock. This would have required the preamp to be turned much higher to get full output from the amp. The judicious use of the attenuator will allow your preamp to have more "range" on the volume control.

    The attenuator is not helpful

    1. If you need tone controls
    2. If you have/need multiple input sources
    3. It you need tape in/outs, loudness controls, scratch filters etc
    4. If your primary input sources is a turntable which does not have an onboard phono preamp.

    Bob
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    Roy

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    Re: Step Attenuator vs pre-amp

    Post by Roy on Sat Jan 27, 2018 2:38 am

    That clarifies things for me - thank you!

    So basically I could either set the attenuator to dial in to either the max input voltage ( around half way I gather ) to step down a 2 Volt input signal to aorund 1.1 Volt so the inputs of the VTA are not overdriven and control volume from the playback device with max volume control range ( 0-100% giving minimum to maxium ear splitting volume)  ór I could attenuate somewhat tighter to less than 1.1V max input voltage to a assure soundlevels never exceed a maximum given when the volume on the remote of the dac is set to 100%   ..which would be handy with a little one running around with quick grabby hands and a definate prediliction for  L O U D


    ..or am I missing something with regards to the 270k ohm impedance of the vta inputs and the 100k ohm impedance of the attenuator?

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