want passive pre ( volume control) for ss amp

soundfreak1 · December 2011

Does anyone know of a simple single input passive pre. Have a adcom slc505 in another sys. And that would work but really only need one input and volume control. Just want a quiet control like the adcom just don't need all the inputs. Any suggustions?

FTGV · December 2011

....

mhardy6647 · December 2011

it's not hard to build one (get a nice ALPS stereo log-taper pot, a pair of single audio taper pots, precision stepped attenuator(s), or see below*)... but going with a transformer (autoformer) volume control can give audibly better results - I'm a believer (FWIW).
http://www.intactaudio.com/

* It is claimed (I have no ears on experience) that the best way to do audio pots is to 'fudge' log taper with a linear taper pots. See, e.g., http://sound.westhost.com/pots.htm

EDIT: or go this route, with as cheap or fancy components as you choose:
http://www.audiokarma.org/forums/showthread.php?t=155993

soundfreak1 · December 2011

That cigar box looked cool! Can't be any simplier than that. Thanks for the idea.

mhardy6647 · December 2011

I have one built in a little teeny black plastic Hammond enclosure...

dudeinaroom · December 2011

what are you using for a source? does it possibly have variable outputs?

soundfreak1 · December 2011

Plan to use it for ( non -critical) listening in bebroom for going to sleep listining to streaming music, don't want to burn my tubes all night. I have a spare 2 ch. Amp just no extra pre.

soundfreak1 · December 2011

Have desired to build ( have built, my equip. Tech. Can build for less than the cost of buying a good sodderingi iron ) figure 30. 00 in parts, upgraded everything. Added a 2nd source with a a/b switch and silver wiring , gold rca's ect. Will post picts when done parts on order.

mhardy6647 · December 2011

Cool enuff. I'd (humbly) opine that you won't regret adding an input selector :-)

heiney9 · December 2011

Why passive? Especially since it's in a non-critical, secondary rig for streaming.

H9

soundfreak1 · December 2011

Hi h9: mainley cost and the amp I'm using sounds great without any coloring. And have been using it thru a adcom slc 505 passive and it sounds better than other Active pre I've used on this amp.

heiney9 · December 2011

As long as you realize every passive is different. It's can be real difficult to mate a passive pre to an amp. Just because the SLC 505 works well doesn't mean another type of passive will work easily as well.

Good luck and the DIY sounds like a fun project.

steveinaz · December 2011

The Creek OBH seems like a nice, relatively inexpensive passive. I looked at quite a bit, but decided on a Placette.

soundfreak1 · December 2011

H9- I'm a little confused by " diff sounding passives? By my deff. Of a passive is one that has no power and can not effect the sound in any way, hence my confussion as to your statement. Maybe I'm confussed as far as the function of a passive. It seems to me if it has no power plug, no tone controls, nothing but an in, a volume pot and an out how could it have any effect on the sound? Good or bad. My exp. With the sl505 is that it ( as I call it ) invisible in the sys. And has no impact on the sound at all. Maybe I'm wrong .

mhardy6647 · December 2011

The issue is basically source impedance/impedance matching. Fortunately, there's little or no black magic involved.

heiney9 · December 2011

First, nothing is absoultey invisible passive or not. The signal is still being altered as it passes through the electronic components.

Second, impedance matching is very, very important when dealing with a passive pre-amp. Since there is no gain if there is a mismatch then it's compounded.

Thirdly, all passive pre-amps use different quality and quantity of components so they will all sound different. Hell, the volume control alone can make or break a passive unit. Why do you think some very precise stepped resistor type vol controls cost so much more vs. a standard carbon wiper type volume control? They all sound different and will make or break a passive unit. The Adcom is fairly inexpensive so if you like the sound of it, then you'll probably be fine. Nothing fancy inside the SLC505 as far a parts, espeically the vol. pot.

I'm just pointing these things out so you are aware. Small tracking issues are exacerbated in a passive vs. active pre-amp unless precautions are taken. Also if you want more than one source using switching relays is better than a typical switcher type control. Incorporating relays for switching is costly. These are just some off the cuff examples. These all apply to active pre-amps as well, it's just they become more of an issue in a completely passive circuit.

soundfreak1 · December 2011

Ok, your getting a little deep for me. At least for today..(
Lol) I have a basic understanding ( I think) of what u r inferring. I can see how an active pre can place an effect on the impedence of a device or piece of eke. Where as a passive should have none and if that if the source dosent match correctly to what the amp see's it may not sound right, I think? Where as an active can have variables programed in ( so to speak ) to adjust for this or not. I have had many active pre's that I did not like at all on many diff. Amp combinations. I suppose due partially due to this and other factors. So I think I have an idea of what u speak.
However if I have this correct it would be right or not be right. As the passive has much less to effect the signal than an active. Do I have my head wrapped around this correctly or at least close.

heiney9 · December 2011

Maybe this article will help. Spelled out much better than I could ever write.

http://www.enjoythemusic.com/diy/0708/first_watt_b1_preamplifier.htm

actually this might be better

http://www.6moons.com/industryfeatures/passive2/1.html

H9

soundfreak1 · December 2011

Ok h9 your last coment makes more sence to me. Even thought the passive may have less in it to say interfere with the signal it dosent mean the " interrferance" may be less per say. Just less to interfere. I was equating less ele. With less interfereance. Say maybe less oppertunity but not less effect.

mhardy6647 · December 2011

H9's advice is very sage. The autoformer volume control scheme addresses most of the concerns (although the lack of gain and buffering can be a disadvantage depending on the precise application). I've gone to a DIY passive source selector with an AVC from Dave Slagle and it's wonderful in my application. The nice thing about the $10 passive I also mentioned is that it's cheap and easy to implement; the bar to try one is very low (and I am all about empiricism when it comes to hifi - and I encourage everyone to be always willing to listen, to listen to lots of different things, and to keep as open a mind as possible when doing so).

The AVC is just delightfully transparent in use.

The AVC (silver box with two black knobs) is visible under the CDP/above the amp in this photo of the living room hifi.

Evrythngmatters · December 2011

A simple low cost solution that covers everything you need.
http://luminousaudio.com/axiom/rca.html

Just click on 'here' at the top of the page and you can enter your specs and the pre will be configured to your equipment. Gl.

soundfreak1 · December 2011

The slc505 used with the amp I'm talking about seems as I say "invisable" as it seem to work very well without coloring the sound and I like that in this use however I also love my tube pre which changes my main amp's sound to a fantastic level. Just don't need this for this use on this 2nd sys. I will litterally only listen while I go to sleep. I find it much easlier to go to sleep to music, espicially accoustic or soft jazz. And I do not want to burn out the tubes I use in my main sys. So as long as this passive design is not irratating it would fit the bill without a lot of expence. If not , little money spent and there is always plan b.

FTGV · December 2011

mhardy has given some great advice but I'll add another very simple recipe since I gather your looking for a basic attenuator.I suggest finding a good 10k (log taper) conductive plastic pot such as Noble or Alps.The Noble will be harder to source but having tested pots from both I have found the Nobles showed tighter tracking tolerances between sections.The 10k value is readily available and offers a good compromise between output/input impedance.For the case you could use one of these attractive little Hammond's. http://www.hammondmfg.com/1455ptbla.htm Then all you'll need is two pairs of RCA' cons ,(unless you need source swicthing)and some hookup wire.
I built the little passive unit in the pic' using one of the Hammond cases and some nice RCA con's from Parts Connexion .It now has a stepped attenuator but it originally had one of the Alps 10K Blue velvet pots.I suspect the ALC505 used something very a similar if not the same Alps unit.

FTGV · December 2011

Ooops Forgot pic's.

soundfreak1 · December 2011

I am fortunately a friend and customer of a retired mac. And parasound field tech. That lives in my area and he is looking at building one for me. He willing to do parts + labor and the labor is less than I can buy a Cheep soldering iron ffor so I'm going to let him have a wack at it and see what he comes up with. He has done wonders for me in the past on my parasound hca 1200 by rebuilding the caps and output relays and upgrading it to a point that it is incredable. He has looked at the diograms in this thread and others he has seen and said he can make me something really nice. He knows my amp, he has cked it for me , also knows the rest of me sys. And he knows what I like, so I will what majic he weaves. He is very good. I'm very lucky to have access to him. I will post picts and review when its done.

FTGV · December 2011

soundfreak1 wrote: »

I am fortunately a friend and customer of a retired mac. And parasound field tech. That lives in my area and he is looking at building one for me. He willing to do parts + labor and the labor is less than I can buy a Cheep soldering iron ffor so I'm going to let him have a wack at it and see what he comes up with. He has done wonders for me in the past on my parasound hca 1200 by rebuilding the caps and output relays and upgrading it to a point that it is incredable. He has looked at the diograms in this thread and others he has seen and said he can make me something really nice. He knows my amp, he has cked it for me , also knows the rest of me sys. And he knows what I like, so I will what majic he weaves. He is very good. I'm very lucky to have access to him. I will post picts and review when its done.

Well in that case ignore everything I posted.He He.

soundfreak1 · December 2011

Here are some picts almost done.

soundfreak1 · December 2011

Can't get the picts to upload, will work on it.

FTGV · December 2011

soundfreak1 wrote: »

Can't get the picts to upload, will work on it.

Maybe resizing will work and check format.I known .jpg 's are uploadable.

soundfreak1 · December 2011

Attachment not found.Picked up my volume control today! Very happy!!! No color to the music at all. Allows the amp to come thru beautifully. We made a few mod's to the design above. Went with two alps attunators ( gives me a ballance control and we added an extra source (just in case). Sounds fantastic. Going to try to add the picts if this phone will let me. Thanks for the input it was most helpfull.

FTGV · December 2011

Cool.

want passive pre ( volume control) for ss amp

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