Active valve pre for a WAD 6550

I've dredged the archives and I am still none the wiser, so I seek your collective wisdom.

I recently replaced my Cyrus C8/Smart Power with a WAD 6550 power amp, currently being controlled by an old Cyrus C5 (as pre). Suffice to say that the improvements in soundsatge, imaging, precision, detail and bass control are uniformly huge. CD is once again a viable option! Treble is still a tad glary and I assume this is down to the C5 (although it's much more obvious on CD, but that's no surprise). So I want a pre-amp. Almost certainly active and probably valve. Croft look too DIY, WD have yet to launch the sucessor to the WAD PreII. I've looked at an Icon LA3 and am pretty tempted but I don't like the tiddly volume control. Remote would be nice too, if poss. There are no dealers around here so demo-ing is tricky without a considerable drive. Advice?

 

As a WADer myself Im not sure you really need an active pre. Alot of valve pre's offer a high gain which is too much for the sensitive WAD's. Id personally recommend one the TVC based pre's but if you jump across to the WD site, www.world-designs.co.uk you find plenty of ideas on shunt-based passives.

 

The guy I purchased it off was using a Cary SLP 98 and it sounded pretty impressive (driving Tannoy Kensingtons), their website claims 20db of gain so I'd assumed I'd need active rather than passive. I'd considered TVC as an option but haven't heard much in the way of long term opinions (after the initial flurry). I could afford to take a punt on a Promethius (even though the wood finish is meh) but I can't afford to take risks at present. I noticie the Icons have 2 outs depending on power amp sensitivity. Pity about the tiddly volume control and selector...

 

I can confirm that a Passive can be used with the WAD 6550.
I played vinyl through a Phono II, then the PAS II into a 6550 and onto 88dB/w/m 'speakers in an average room. Plenty loud enough. NB getting the loadings right with Passives can be a bit of a black-art though...

Also don't assume that the 'glare' is entirely down to the pre, the 6550 is the most SS sounding valve amplifier I've heard. To my ears it has a slight 'edge' on the upper frequencies, especially if it hasn't been tweaked with the usual boutique bits (e.g. BlackGate caps in the PSU).

 

It has the blackgate caps... BTW, if I'm using the pre-out from an integrated, is that likely to be passive or active?

 

johnfromnorwich,

you have PM.

 

There's a new transformer based kit about to be launched by 'glasshouse' (ex WAD manager). I'll be playing with the prototype this week, and will report back.

Early reports are promising, rrp something like 300-400.

 

Sounds interesting. Price sounds in my kind of league (don't really want to go above £5-600 if possible, unless it's a verifiable bargain) and if the styling matches their passive pre, it should ensure domestic harmony too. Pity there's nothing round here to demo cos I'm still unsure whether active / passive or TVC is the way to go = John

 

What is the actual input sensitivity of the WAD 6550 power amp?

If it's as sensitive as my Canary 301 power (0.33 Volts for full output) then you will DEFINITELY need a pre with low gain, regardless of whether it's active or passive. Otherwise, you may end up with too much noise. I recently tried my 301 with two different valve preamps, one with 15db maximum gain, the other 12db. Both were too hissy through the Canary despite being very quiet designs! My existing TVC is perfect, as I cannot hear any noise through the Canary whatsoever. That said, the next time I buy a power amp, I won't be buying one that is so sensitive, as it limits the choice of compatible preamps.

 

According to the manual, sensitivity is 500mV. I spoke to the guy at Icon and he confirmed that their pres are designed to couple either high or low sensitivity power amps dependiong which output you use. But it sounds like TVC should be compatible (limited knowledge alert).

= John

 

you can adjust the sensitivity of an active pre-amp with a well placed resistor.

John, it's more a case of whether you like what a passive does or not.

If you prefer passives, I think the transformer ones are probably a little better than a stepped attenuator.

If you're in Norwich (as your name suggests) Id try borrowing a Music First pre and a decent active pre from the emporium in Diss. They are stockists.

In your budget, I'd be borrowing...

transcendent grounded grid (£300 used)
EAR 802 (£600 used)
Goldpoint SA1 (£200 used passive)
art audio VP1 (£950 used, but I know where you can get it much cheaper)
and the music first pre too.

I know that Penance and Wadia Meister rate the grounded grid pre, and for £300 that has to be one to look at.

 

Alas I'm no longer in Norwich. I'm in NW Wales. We have lots of mountains but no HiFi shops so auditioning isn't really an option. I'll be up in York in a week or so so I may take a look in Vickers. If I can get something s/h I'd at least be able to recoup on a resale if I didn't like it. Anyway, I figure most things suggested so far are going to be an improvement on the pre in a mass market integrated

 

Is it not slightly more complexed with a valve amp, as you change the impedence?

 

I rate the grounded grid too, I've heard it used with the WAD6550 a few times, does good things. I think you probably will want to alter the sensitivity of the 6550.

 

A resistor anywhere alters impedance, whether valves are involved or not

 

Perhaps- but I heard that you have to be a bit more careful with a valve amp, as it isn't quite as simple as altering the sensitivity of a solid state amp.

If it is all so easy to change, why is the Canary power amp 0.33 Volts? Wouldn't Canary have been better off bringing it into line with other amps by simply altering a resistor and making it 0.50 at the very least or, better still, lower sensitivity?

 

The sensitivity is affeced by the amount of negative feedback in the circuit. Change the feedback and you change the seneitivity, buy you also change the sound of the amp as both damping factor and distortion will change.

You can 'slug' the input to lower sensitivtiy but this is far from ideal and again will degrade performance.

The WAD 6550 was available with a pot fitted - a 50k log pot which works well with the curcuit so I'd look a using a 50K stepped attenuator as a start.
Magnetic pre amps can sound good but the input impedance on the WAD power amp is over 1M Ohm IIRC which makes a passive pot a suitable choice and mitigates the usual passive resistive problems of slightly flat dynamics.
You don't need an activer pre with the 6550 for reasons of gain but you may prefer the sound - I do.

 

This is what I suspected. The Icon pres I was considering are compatible and active (although they make a passive too). The LA4 even has a remote (this isn't laziness, If I go active, I'll need to put it up where the cat can't jump on it). My gamble is whether to spend a couple of hundred quid on a TVC or rather more on an active pre. I'm leaning towards the latter purely because I've never heard a TVC in any system and a little coloration is unlikely to be an issue at this stage since my speakers are hardly the world's most neutral.

I just wish WD would get round to launching their own pre!

 

I wouldn't panic John or rush into anything.
The new WD units cannot be far off - they have allready got prototypes and some of the thinking going into the designs is up on the WD site.

Send a PM or email Peter Comeau at WD. Peter is a nice chap and I'm sure he will update you on progress.

 

Well, after lots of deliberation, I've just shelled out for a Glasshouse TVC passive. Should have it in 10 days. It's a bit of a gamble due to the lack of demo options in this neck of the woods - especially as it's the first piece of non-2nd hand gear I've bought in a long time but I've yet to hear any significantly negative views of the TVC approach. Now I can start selling off the last of my Cyrus kit....