Building a passive pre..

[bluegrass]

Hi,
A little while ago, i posted a thread on which quad amps were the best value. I subsequently bought a 405-2 and had it serviced by quad along with my 303..It was then suggested a passive pre would suit these well....Finally, after listening to cd directly connected to my power amps, it is time to listen to my records again. I have a separate phono stage, so now want the passive. I have checked out several sites, reviews etc and have decided to build one. Here is where i get stuck..I just need the one set of inputs. So, my question is, as a working musician, i need something cost effective, but that sounds good. Does silver wire really sound much better than copper, do silver plated RCA sockets sound better than the cheaper gold plated, and more significantly, does a stepped attenuator significantly out perform a good alps pot..
Thanks in advance for any input.

[honmanm]

I'm very new to the DIY side of audio and there are others out there who know a lot more... but here's my view on your question...

When you are building something for yourself, your upgrade path is at the point of a soldering iron rather than box-swapping. That means you can start with inexpensive components and each upgrade will cost you ?15-?20. The downside to DIY is that the product of your efforts will have less value that the components that went into it.

I've never had the money to play with golden-ears materials so can't comment on the question of silver vs. gold etc. Wires have electrical properties - resistance, capacitance, inductance and susceptibilty to RF pickup and resonance. Connectors have similar properties, however gold is useful on connectors because it does not oxidise when exposed to air.

The type of wire etc. can have an effect with passive preamps because they often present a less-than-ideal load to the source, and a greater-than-ideal source impedance to the load (so the cable characteristics become more significant). My really cheap passive pre suffers from this problem when used with a 303 and works better with some sources than others.

But it is better to start with a design that can shrug off weird sources, cables, and loads than it is to use component selection as a band-aid. If the design is sound, component selection is a way of getting a bit more out of it. To be honest, hearing that component X is "warm" or "dynamic" or whatever is worrying, I'd prefer the electronic components to have the least possible effect on the sound.

So at this point, don't worry about the golden-ears stuff because you can always add it later if you need it.

Regarding stepped attenuator vs. potentiometer, a cheap stepped attenuator is very much better than a cheap pot! Can't comment on attenuator vs ALPS blue pot (which I guess is what you are thinking of), as having found an attenuator for not much more than the cost of the ALPS pot I skipped the latter.

I used a ?10 stepped attenuator (from here (http://www.virtualvillage.co.uk/24-step-ladder-type-stereo-volume-attenuator-50k-001493-041.html)) - mechanically similar to the cheaper attenuators from the likes of hi-fi collective, but no precious metals were harmed in its making.

Hookup was via 50cm lengths of old interconnect, soldered to the attenuator. The resistor ladders were re-configured for shunt mode, still using the generic metal films that came with the attenuator.

Sound? Hard to say in a way as a passive device has a mostly subtractive effect on the sound. With a 303 and early HL-P3s the midrange was unblemished, really remarkable. Top-end rather rolled off, which turned out to be related to the choice of interconnect.

However changing the source also changed the presentation, so rather reluctantly I've come round to the idea of using a buffer stage in an otherwise passive pre. This is supposed to improve the impedance matching (well let's see...) I'll be trying the Pass B1 first, as it is simple enough to build on a bit of stripboard.

As a specific suggestion re wires and connectors, I'd go for gold-plated connectors (anti tarnish). While I have generally used silver or silver-plated wires, there is probably no difference from copper.

The internal hookup wire sold by Net Audio has worked well for me; for connection to a Quad power amp you might want to look at the Flashback cables (they're willing to make up cables to your requirements).

Mark

[bluegrass]

Well, thanks for your detailed reply, very useful. It seems like you have found a cheap stepped attenuator that i can try out without big expense. You lost me with the buffer stage, a step beyond my electrical understanding I'm afraid, but if it works well, maybe you can post about it again here. One question i have would be about the resistance. The Attenuator is 50k....is that OK for quad 303 or 405-2 , or is it close enough? (I was thinking 10k)
Regards.

[A.S.]

The QUAD has a 20k ohm input Z, so you really should use the 10k pot. That is, the top of the track is connected to the CD player, the wiper to the QUAD input and the earths (grounds) combined from the CD player audio and the input to the QUAD at the bottom end of the potentiometer's track.

[bluegrass]

Thanks for that Alan,
So i should look for a 10k version. You lost me with the second sentence, maybe i should just stick to playing my violin!

[Don Leman]

Thanks for that Alan,
So i should look for a 10k version. You lost me with the second sentence, maybe i should just stick to playing my violin!

In bluegrass that would be a fiddle :)

[bluegrass]

Your right Don, Bill Monroe will be turning in his grave!

[bluegrass]

Hi,
I Finally managed to put together a passive pre amp using an alps 10k 'black beauty' pot from ebay, and a box and other parts from maplins. I have found the sound through my Quad 405-2 and 303 is excellent , so thanks Alan for mentioning the idea..Total cost was around ?75.. There is also a stepped pot using dale vishay resistors on ebay which may be worth trying (see link). I may put that in another passive pre for my studio at a later date.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&Item=360138248175&Category=73369&_trkparms=algo=LVI&its=I&otn=2&afsrc=1