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Haselsh1
24-02-2009, 13:59
Has anyone out there any experience with a Creek Audio OBH-22 passive pre but with motorised volume pot...???

Filterlab
24-02-2009, 15:25
Not specifically, but there is a magic with passives.

Ali Tait
24-02-2009, 16:30
As long as impedance matching is not an issue.

Alan
24-02-2009, 16:33
It's best if the power amp is designed to work with a passive pre, the only negative comments I've heard are down to mis-matching gear. Which is Like what Ali said, but less eloquent. If it works for you, the pre will be utterly transparent. (make sure to use the shortest I/C you can, and that should be low capacitance).

Ali Tait
24-02-2009, 16:35
If there is a problem,it can be overcome with a buffer stage.

Ali Tait
24-02-2009, 16:37
This is a cheap one you can get from ebay-

http://cgi.ebay.co.uk/Valve-Buffer-Amp-6N11-6DJ8-6922-ECC88-Indeed-Hi-Fi-Lab_W0QQitemZ250374723531QQcmdZViewItemQQptZUK_Con sumer_VintageAudio_RL?hash=item250374723531&_trksid=p3286.c0.m14&_trkparms=72%3A1690%7C66%3A2%7C65%3A12%7C39%3A1%7C 240%3A1318

Filterlab
24-02-2009, 16:45
As long as impedance matching is not an issue.

Good point, a good ratio is 100:1 as a minimum (power amp:source).

Alex Nikitin
24-02-2009, 17:33
Good point, a good ratio is 100:1 as a minimum (power amp:source).

it is not so much the ratio as a linearity of the input impedance of a power amp that matters. There are amps that need to be connected to a low output impedance of an active preamp as their input impedance is unlinear and as a result a high(ish) source impedance of a passive preamp could seriously impact their sound quality.

Alex

Primalsea
24-02-2009, 20:55
Almost all valve amps with a volume pot are effectively a passive preamp connected to a power amp in one box.

Almost all solid state intergrated amps are a buffer stage followed by a passive volume pot followed by a buffer stage.

What this means is that a non transformer based passive preamp is best used on a power amp or a solid state intergrated.

Try to get the output impedance of the souce components buy looking at the spec sheets or phoning the manufacturers. If is low (sub 1K ohms) you should be OK.

Haselsh1
24-02-2009, 22:45
The only way I could guarantee the correct preamp output impedance is to use an NVA P50sa as they make it to your requirements. My amplifiers input impedance is 15K. All of this could be irrelevant if I go the route of a valve integrated and replace the Samson but I was considering two Samson's biamped with a passive pre.

Filterlab
24-02-2009, 23:10
I would personally avoid NVA, the requirements for usage in terms of cabling make it far too impractical - unless of course you want to buy an all NVA set-up.

Alan
24-02-2009, 23:52
:confused: There are no requirements for usage with a passive pre - NVA or otherwise. It's power amps & integrateds you need to be careful with - the Capacitance of I/Cs and speaker cable is important for these amps, which are designed for passive preamps.

Steve Toy
25-02-2009, 01:21
Alan,

Too true. I experimented with a Glasshouse TVC passive last summer and whilst it gave me a glorious midrange it seriously screwed dynamics given the i/c lengths I had to use between the different coponents on different stands and the i/c lengths (rather expensive too) at the time. We live with whatever constraints we work with at any given time...

I'm sure that with smaller boxes working in closer proximity, I might have derived better overall results but then I'd have compromised the microphonic-reducing stand configuration I was using and still use. On balance, I prefered the rather expensive Spectral solid state pre I had at the time. This was soon replaced by anthonyTD's rather excellent active grounded grid pre giving me the best compromise of the two worlds of midband lucidity and dynamic contrast.

The sheer geography of setup as well as synergistic matching never ceases to make this hobby no less than incredibly fascinating, certainly if holism in pursuit of (recorded) musical enjoyment really is your thing.

StanleyB
25-02-2009, 02:43
:confused: There are no requirements for usage with a passive pre - NVA or otherwise.
Once one starts messing about with words and calling a transformer an amplifier, we got a problem. Reactance comes into play, and a uniform phase relationship across the audible spectrum is then a prime candidate for signal misalignment.

Primalsea
25-02-2009, 08:36
I vaguely remeber that this question was asked a while ago but it looks like the posts were lost in the recent attack. I ran a few simulations on the PC and reported that bandwidth was OK unless you had a really high load. 7.5K was OK (2 x 15K i/p impedance amps as a load) but the phase started to change alarmingly after about 1 Khz would could be a real problem.

Note that a passive pre based on a volume pot is a totally different thing to a transformer based passive pre.

Haselsh1
25-02-2009, 09:08
Mmmm... for what it's worth... I would prefer to buy the Creek Audio OBH-22 as it has a remote volume control but I am unsure about cabling and I do know this can be problematical. For power amp duties I am using a Samson Servo 600 studio amp into Dali Suite 2.8 speakers but my interconnects are Van Den Hul 102 III Hybrids. These have a very restrained treble already but it suits my delicate ears (lol) however I spend a lot of time listening to techno music as well as folk.
At the moment I am using the Samson's inbuilt gain pots on the front panel but find that I need some form of input switching so a passive pre with a remote volume pot could be the answer.

Mike
25-02-2009, 10:17
Shaun,

I thought you were looking at replacing your amp set-up?

If so, I'd wait until you've done that before worrying about passive pre-amps. You may render it useless!

Haselsh1
25-02-2009, 10:26
I am indeed. There are so many variables though it's hard to keep track of them all. I like the Samson but it's not Hi-Fi is it...??? That is the main weakness. If I had around a grand behind me the choices would be so obvious but I am working to a 500 pound budget and that makes it much more difficult. I love valves but for techno...??? I am just not sure.

Mike
25-02-2009, 10:27
Does that mean I can offer my WD88XL on the 'open market' then? ;)

Haselsh1
25-02-2009, 10:30
I would dearly like to buy your amp. My last experience of WAD amps was stunning. As I have said though, at the moment I'm working to a budget of 500 pounds. You want 700 and I can't afford it right now. In a few months I will be able to. I simply need a bigger budget and that will come with time.

With the best of intentions I have so many people telling me so many things.

Alan
25-02-2009, 11:40
Once one starts messing about with words and calling a transformer an amplifier, we got a problem. Reactance comes into play, and a uniform phase relationship across the audible spectrum is then a prime candidate for signal misalignment.

I agree Stan - A passive pre-amp is not an amplifier at all. The one under discussion is a stepped attenuator resistor based unit, with no transformers at all.

WikiBoy
25-02-2009, 13:24
I would dearly like to buy your amp. My last experience of WAD amps was stunning. As I have said though, at the moment I'm working to a budget of 500 pounds. You want 700 and I can't afford it right now. In a few months I will be able to. I simply need a bigger budget and that will come with time.

With the best of intentions I have so many people telling me so many things.

So why ask and listen to other peoples opinion, they know nought more than you do, it is all ******* into the wind. Use your ears - get product either on loan or equipment where you can try and get refunded if you don't like. All you need is your system, your room, your music, your time. OR buy second hand and resell if you don't like. Be a Jerry :smoking:

Marco
25-02-2009, 13:29
Welcome back, Richard. Would you like the customised user title you had before? If so, remind me what it was and I shall attend to it. Meep meep! :)

Marco.

SteveW
25-02-2009, 19:15
Hurray...Richard's back.

The words breath and fresh air spring to mind.

Mike
25-02-2009, 20:31
Hi Richard,

Hope you're still, well, 'you'! ;)

Cheers...