Passive Preamp?

[OldiesButGoodies]

the volume pot looks bad ass

[RuralTom]

What do you think about your DIY passive, Rev?  Does it surpass the Schiit?  Mid range dynamics any better?

[Reverend]

Yes, it had more balance than the SYS but that little Schiit is pretty damn impressive for $50.  I used quality RCA's, a really nice pot donated by OBG, industrial gold plated toggle switches and 16 gauge litz copper wiring.  If any of you have ever messed with litz you'll know it is a pain in the ass but worth it.  Each strand is individually coated.  You have to torch off the coating then sand the ends to solder correctly.  16 gauge was overkill but I happened to have a small roll of it in-house.

The mid end does seem more prominent now and the imagining has also improved.  The dynamics are through the roof.  I haven't been able to spend more than an hour in my system so I still have some sit down time before I can comment further.  I did end up taking it to Tom's last week and we hooked it up to one of his carver baby tube amps, my ipad, and the large advents in the basement work area.  It sounded really damn good.  The imaging was crazy good.  Even Tom was surprised.

[ataudio]

I'm glad to hear of your positive results.  As mentioned earlier I've used them for many years.  They don't seem
to garner the respect they deserve.  Perhaps others had other issues that just complicated the use of a passive.
I've breadboarded my inexpensive ElectraPrint PVA and am extremely impressed.  Bass is tighter, faster.  Mids/highs
are extremely smooth and just damn good.  And..a bonus...it has GAIN.  Its a STEPUP transformer based passive.
Check out Jack' website for more details. Its a very worthwhile upgrade to an already good passive.
Just be aware of the input impedence.  Its on the low side...(mine is 150 ohms) which any decent CD, DAC can handle
with zero issues.  Haven't tested my tuner yet which gave me greif on an earlier tranny based passive.
You can pick the input Z And he winds the tranny to your specs.

[MacGeek]

OBG or Rev-what kind of pot is that and where did you get it?

This looks like a relatively simple project even I can do.  and, I suspect my amps have more than enough gain to work.  I'll need two sets of outputs; will splitting the volume out adversely affect the signal (other than maybe reducing it)?

[Jim Pittsburgh]

Heard the passive pre last night.... what a big upgrade over the Melos! Sound is fantastic. Not many times will a single component change make that big of a difference. Super job Rev.

[RuralTom]

OBG or Rev-what kind of pot is that and where did you get it?

This looks like a relatively simple project even I can do.  and, I suspect my amps have more than enough gain to work.  I'll need two sets of outputs; will splitting the volume out adversely affect the signal (other than maybe reducing it)?

I find myself inspired as well.  I've has the SYS back in over the last week and thought it sounded great, though it is decidedly less user friendly.  As MacGeek stated, I think this is a project I could do fairly easily assuming I can narrow it down to a good pot and find other quality parts.

[Reverend]

Klaus, adding a second output shouldn't be an issue.  Not including the chassis and/or knobs, it can be made for less than $100.  I recommend a wooden chassis as you're less likely to develop a ground hum of some kind but this can be gotten around with copper shielding, inline resisters in the ground path or even an external ground.

Here is the link to the pot that i'm using:  http://www.analogmetric.com/goods.php?id=1000  I went with the 100k Ohm version.

Wire that I used:  http://www.ebay.com/itm/50ft-New-England-Wire-Technologies-100-Strand-Type-2-Litz-wire-AWG15-5x20x38-/191165549170?pt=LH_DefaultDomain_0&hash=item2c825aca72  I believe for the ground path I used 20 or 22 gauge solid copper wire.

Toggle switches:  http://www.ebay.com/itm/2-Carling-80-000-Series-E60272-LR39145-2GK54-73-DPST-ON-NONE-OFF-Toggle-Switches-/191121798969?pt=LH_DefaultDomain_0&hash=item2c7fbf3739  I bought mine from Graingers and they were slightly better quality but the same brand.

RCA Jacks:  http://www.ebay.com/itm/10-pairs-Female-Amplifier-RCA-Jack-Chassis-Sockets-TOP-QUALITY-USA-SHIPPING-/141560208817?  Great seller, have used him for years.

From the photo I posted previously it should be pretty simple to use that as your guide.  I can answer any questions you have.  I used DPST switches but a rotary switch would work just as well.  I took the design from a modguy who used toggle switches for each input.  In his case he went even further overboard and had a dual mono design with 3 inputs = 6 switches.  The one thing that's hard to see, and I did slightly harder then it had to be, was the toggle switches.  DPST means double pole single toggle  (if you didn't already know).  This means that there are two channels/sides or left/right for a single switch.  The easiest thing to do is wire the positive of both left and right from the input to the bottom two terminals.  That leaves the top terminals open and easy to work with.  You then connect all 3 top left terminals together (if it's a 3 input design) and do the same thing with the right side.  The volume pot will then be connected to the top left and right terminals you daisy chained together.

[RuralTom]

Thanks for the info, seems like there might be a number of these rolling around in short order!

[Reverend]

Made it even easier for you guys. 

[RuralTom]

Fantastic! Good visuals are always helpful for a neophyte like myself.

Do you think the Litz wire is critical component?  I might well buy a spool, you just made it sound difficult to work with.

[ataudio]

Excellent components lead to excellent results as Rev has shown.

Another critical component are the interconnects.  High quality interconnects
quickly come into play with passives.  Everyone on this forum knows this but the key point
here is to avoid high capacitance cables....you'll lose all your high frequencies and then complain that your
passive sounds dull, lifeless, no dynamics, etc.   

Dispite their controversial design I'm going to build a DIY version of the "anti cable" interconnects using
magnet wire and clear packing tape.  Very low capacitance cable. 

Litz wire....that does sound like a shit load of work per connection.  Maybe someday.

[MacGeek]

Thanks for the parts list and schematic, Rev.  I have some shielded, tinned wire (used in the boat) I am going to try.  An old cigar box may serve as a cabinet.  I think have an old parts rotary switch I may use in place of the toggles; however, the toggles may provide better isolation.

[bmwr75]

I bought this amp from Kegger on AK.  He built it from scratch using an HP Oscillator cabinet.  Have always wished the large knob on front actually was a volume knob, instead of just to look at now.

[Jim Pittsburgh]

I would not recommend using tinned wire in any audio application.... I've never heard good results when using it in interconnects nor as speaker wire. The risk reward is just not there for the few cents in cost savings.... even low oxy copper with real silver coating has its own unique audio sound.