Passive pre with quad 303 (net audio)?

After advice from here and elsewhere I got my quad 303 upgraded by net audio.

Current system:
Cyrus CD8x, Quad 33 (Dada mods), Quad 303 (full net audio upgrade), Mission 773e speakers. Ixos cables.
Music:
I love a broad spectrum eclectic music, especially classical music(except classical era) and 70s rock but the grail for me is to have a system that does choral music well in big acoustics (I was a chorister in St Pauls).

I'm wondering whether I can get any improvements over the quad 33, and am thinking about the passive route. Does anyone have any experience of this, or give any advice?

I decided to try to simulate passive pre by using an inline attenuator by modding an IXOS cable with 20kOhm resistors. This was not nearly enough as the climax of the four last songs donated a decent dose of distortion. I hadn't realised it was so loud, perhaps because having missed out the quad 33 pre, the gained clarity, openness and feeling of presence, was extraordinary, it never felt harshly loud. I'm now at 160kOhmsish and that is appropriate for a sunday morning listening level in a block of flats, though Dieskau just had one small brief bit of distortion in a loud bit of the Dichterliebe.

Is a passive pre a viable option in my system? If it is, what max impedence is appropriate?! What are peoples thoughts about this upgrade route? I was thinking of net audio or glass house pres.

Cheers for any thoughts!

Jamie

 

I used a Promitheus TVC with a Quad 909 for a fair while and the combination works very well, but in retrospect:

My view is that the Quad 909 (which shouldn't be vastly different to a modded 303) is perhaps rather too straightforward. Some people would view this as honest and uncoloured, others as grey and uninvolving - two sides of the same coin to my mind.

The Promitheus (and other TVC passives) I've heard is notable for being clear, fast and precise but perhaps lacking in atmosphere.

Cyrus CDPs (I've heard several and own one) are generally on the clear/forward/clinical (depending how you view things) side as well.

Taking all of that together,and owning several versions of the Four Last songs as well as the Fischer-Dieskau Dichterliebe, I would hesitate to recommend a passive as an obvious improvement.

What I would say is that if the subtle colourations of the human voice are important to you, which I'm guessing they are, then an LDR passive will go a long way to revealing what is actually on the recording without the perhaps too forward nature of a TVC; but if you are after the scale, sonority and magnificence of choral works in large spaces (I only ever sang in the crypt at St. Pauls) then this on it's own won't provide the answer.

 

well said ......

thats exactly what I hear with passive preamps

yes should work with the 303 ...no reason to think it would not is more the case!

With the proviso already stated all styles of passive pre amps for me seem to give greater clarity but seem to loose some of the musicality on the way .....thats not wrong , just not my cup of tea !


....might be worth looking at a valve preamp as well to get the opposite presentation

 

have you had a play with an LDR based pre yet? to my ears they do much better on the musicality front

 

no ...but if they have not lost that extra something ..then they could be on to a winner

 

I used a Quad 303 with a passive pre for years and it was fine. I think it was a 20kohm pot made by QED. It was a long time ago, but I'm still using passive pres (albeit with different amps). If you stick with a resistive passive pre you might want to try it with a buffer (best of both worlds?). TVCs are also definitely worth a try.

Forgive me if the following is obvious, but it sounds as if you are using an in-line resistor to reduce volume. A passive pre acts as a voltage divider, so a 10kohm or 20kohm unit would be OK.

 

Cheers for the reply. Are LDR passives commercially available? What is their retail? If I was after the sonority and magnificence of choral works in large space, what kind of pre should I consider?

 

NB off topic, whats your favourite four? Mine is the Felicite Lott, but I only have Schwarzkopf and Kiri Ta Kanawa for comparison.

 

I kinda presumed that a valve pre was well out of my budget. I've gone down the modding route to get the sort of sound I want on the shoe string budget I have, but i'm prepared to sound anything out.

 

You might have to help an ignoramus here. Whats a buffer?

I am using some Kiwames as in line resistors. Is there anything wrong with that other than the limitations of having two cables with two different in line resistors, and thus a very limiting two volume system?! I hadn't appreciated that a passive pres works as a voltage divider, I was under the impression that the stepped attenuators merely selected a different in-line resistance....

 

Maybe you just need to make sure you pre-amp is up to spec with good caps etc... I notice you say 'data mods' but I don't know what that means. If all parts are running well it should be pretty decent I imagine.

Personally I think the best passive pre-amps in a system without a huge input impedance on the power amp (most don't have that) is a TVC (transformer) type. I use what is essentially a 'Music first' pre-amp and I think it is great. Extremely low distortion (I've measured it) so very open. Maybe you could keep an eye open for a second hand unit of that or a 'Django', which works by the same idea.

 

The dada mods to the 33 include updating all the electrolytic caps, a power supply mod and a few other things - i've also removed the tone controls. Missing out the 33 entirely with just a fixed inline resistance in my cables has given quite an improved sound. I'd love to try a music first, but it'd have to be throught the second route.

 

This is the one I use:Eva
works out to about GBP 160.00 delivered in the UK, only one input and only remote control - so no moving parts at all. You would need to keep an eye out as they go in and out of stock very quickly.

Using a passive puts more emphasis on the recording and less on the reproduction. If you want all of your music to be big and lush then some valve pres will do that for you. If you want to rely on the performance and the recording engineer then, in my view, an LDR does a good job of preserving what was intended (for better or worse) - if the acoustics of the space are on the recording then you may or may want an extra layer of gloss on top of that, as it will inevitably mask some of what was there in the first place.

I tend to alternate between Schwarzkopf and Jessye Norman. I've only listened to Kiri once - in fact I'm not sure I even got all the way through. Must look up Lott though, not heard hers.

 

A buffer provides a match between the output impedance of the "up-stream" unit and the input impedance of the "down-stream" unit. Ideally the input impedance of the down-stream unit should be much higher (eg 10x) than than the output impedance of the up-stream unit. This makes a resistive passive pre a bit of a compromise: it must not have too low an impedance for the source nor too high an impedance for the power amp. Typically people choose 10kohm or 20kohm depending on their equipment. A buffer sorts out potential mismatch. I found that even with the TVC I use (Music First) using a buffer (especially after the TVC) made an interesting difference - not suprisingly making the sound more like an active pre. (However I am bi-amping with a passive hi-pass filter)

I initially thought that, but that's not how they work.

I'll let others who are more technically competent comment, but a voltage divider presumably presents a fairly constant load to the source wheras a variable in-line resitor would not.


I'd just grab a cheapish pot and try. If you like the passive sound, you could move on to something more ambitious without having wasted much. If you can borrow a decent TVC you may find it is all you need.

 

Do commercial buffers exist?

I wonder if anyone can help me here? Is putting an inline resistor (as opposed to a voltage divider) a bad idea - a for the sound, and b because it might damage my kit??

I think thats an interesting idea. Would it be possible just to rewire the potentiometer on my quad 33? Presumably, making a very simple pot based passive with a switch isn't a hard project?!

 

Well I wired up my cables to the 50k pot from my quad 33 (in an ice cream tub)!! The sound is not as open and detailed as with the inline cables I was using before, it also appears slightly veiled, set back, sotto voce, which may be a characteristic of using an old pot? However it did prove to me that a passive pre is an approachable DIY project, and I may buy some bits to do that while I wait for an eva to become available.

One question I had is whether the ground on the pot needs to be earthed.

Also, I still would like to know if there is an inherent problem with using an inline resistor in my cables, as the sound was very good using that method, but I wouldn't want to damage my kit!

And does anyone know if commercial buffers are available.

Cheers.