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JimOfOakCreek 9th July 2007 01:10 PM

Passive Preamp With Class-D
I am in the planning stage of building a passive preamp. I am contemplating which amp project to build and have the Hypex class-d amp modiles on my short list.

Has anyone used a passive preamp with a class D amp? What do you think?

zacster 9th July 2007 03:04 PM

I built my Charlize with a blue velvet pot and use it without a pre. It's OK, but when I put a tube pre in front of it it just has more drive. In the end though it went to my kids without a pre as they're just plugging an iPod into it and are perfectly happy the way it is.

BWRX 9th July 2007 04:45 PM

A passive preamp will work just fine with most class d amps, but it does depend on the input impedance of the amp and the output impedance of the preamp. Normally you want an amp with a moderately high input impedance in order to work well with a passive preamp.

JimOfOakCreek 9th July 2007 04:49 PM

>>when I put a tube pre in front of it it just has more drive<<

I have a hybrid tube/ss int amp. Compared to my Panny XR50, the hybrid just doesnt quite have the detail. The hybrid doesn't put up as focussed of a soundstage as the Panny either.

That was my reason for experimenting with a passive. I want detail and a tight soundstage. I plan on building a Hypex class-d amp along with the passive preamp. My fear is that the passive might be too thin. The passive is cheap enough to build so I can accept failure if the resuslts are not to my liking.

Pano 9th July 2007 09:32 PM


Originally posted by JimOfOakCreek
The passive is cheap enough to build so I can accept failure if the resuslts are not to my liking.
And you might build with enough space to go to an active preamp later. Just a little rewire to turn passive into active.

I have such a preamp (it ain't pretty) that can be switched passive or active. In other words, the active circuity can be bypassed but all the connectors, volume pot and input selector remain the same.

Nanook 10th July 2007 05:11 AM

I use an alps blue based passive...
with my 41Hz amp6 Basic to good effect. The real limit is making sure your source can push 3V, and a little current. My old Pioneer Elite can:)

emperor 10th July 2007 11:33 PM

I have an NVA Pre Amp, driving a slightly modded Trends TA10.1 in power amp mode. I do have to push the volume up, but it works perfectly well, with the NVA. i am however lacking a little bit of power, so may buy an autocostruire t100hcl module and , get a transformer, etc, to get the extra oomph, from the klipsch speakers.:)

webchimp 11th July 2007 12:42 AM

I'm thinking of builing a Hypex based power amp and was also wondering what preamp to use with it.

I asked Hypex what they thought about it and they suggested that if I build passive preamp that I should use 10k pot or stepped attenuator. They also pointed me to the active preamp, with remote control, made by MM Audio, that also produce a range of Hypex based power amps:

CI Audio use a passive preamp with their Hypex based amps. There are two versions, one remote, one manual, but both use 10k Alps RK27 (Blue velvet) pots:

Personally, I like remote control and I came accross these remote control preamp kits while looking around:

JimOfOakCreek 11th July 2007 01:23 AM

>>10k Alps RK27 (Blue velvet) pots<<

The volume control I'm using is a 10K Ohm Goldpoint Stepped Attenuator. I can't wait until everything gets delivered and I can start my project.

webchimp 11th July 2007 03:34 PM


10K Ohm Goldpoint Stepped Attenuator
I've never actually tried a stepped attenuator, I've always wondered whether 24 steps will be enough. I'll be interested to read your views when you have it up and running.

Here's a nice remote controlled passive preamp with 60 steps: There is also a kit version, although they are both fairly pricey; it certainly looks the part though.

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