Would like to try and build a Tube pre/Hypex UcD 400 power unit for Light weight bass

[rim basses]

Hi All,

Names Robbie from RIM Custom Basses in the UK, Im a custom Bass guitar builder. Ive been looking at the amps coming out for bass guitars and at the moment everyone seems to be going into Class D stuff. I would like to try and build a 400/700w bass amp using a 6SN7 Tube preamp/Hypex Ucd 400/700 Power module with SMPS from Hypex also to keep it light. I would like to maybe have a Volume and tone control on the front end to keep it simple.

Any info or help on this would be great, as im a newbee to building amps. It looks doable and could be fun

Cheers,

Robbie.

[raintalk]

You're on the right track.
If you go to Hypex.nl and pick the UCD 400 there will be a manual.
Read the other thread in this forum about availability of SMPS for it.

You will end up with a high power, reliable, lightweight, super low distortion amp.

What's the tube for?

[rim basses]

I was thinking the valve front end would give it some extra warmth, this company makes there own tube preamp

http://www.lowenddistribution.com/lowendpreamp.htm

If not valve could you help me with any other types of preamps with maybe just Volume and tone controls.

Cheers,

Robbie.

[raintalk]

I'm sure that since you hand build custom basses they already have whatever you're looking for in "warmth"

There's an excellent book here:
http://www.thatraymond.com/downloads...ttala_v1.0.pdf

The author can often be found at:
http://www.ssguitar.com/

For bass, I would suggest 6.42
Change the cap values for bass.
You could be unique and use a strat type switch.

Best of luck,

[rim basses]

Im thinking this London Power bass preamp kit could work well,

http://www.londonpower.com/catalog/p...products_id=76

Cheers,

Robbie.

[stroy05]

Hey Robbie,

I have been working on the same thing for a couple of years. I have got something working for the past few years now and it actually great. I just posted a pic over in the Epifani club on talkbass.

[revintage]

Hi Robbie,

You are absolutely on the right track. For some reason there are no better interfaces for guitar and bass than tubes. The input of the old Vox AC-50 with 12AU7 is one my favourites for bass. But maybe some more Eq-controls are needed.

I build guitar-amps(check my profile) but have had the thoughts of this concept for bass.

I would then take it on step further with a tube driving the Hypex via an input transformer instead of the OP-amp buffer.

[Koifarm]

Lars, how would you design or buy this transformer for the UCD because the + input has 8k2 impedance and the - input has 1k8 impedance? This is a big difference to overcome.

[revintage]

Hi Koifarm,

You have to search(google) the basics of differential amps. I am no pro but this is elementary.

Even if it sounds strange the UcD has a Zin of 2*1,8k=3,6k when connected differential.

Differential connection is also the best as you should get a better CMRR and no risk of ground loops.

So a transformer with lets say 4,5:1 gets a reflected input impedance of over 70kohm at the primaryin the midband. But a 90 H transformer(as in the example below) has an impedance of just above 10kohm at 20Hz

There are plenty of transformer out there but I can highly recommend Lundahl.

One advantage is that you also get galvanic isolation between Hypex and driver/preamp with a transformer.

Below is a theoretical example of a combination that would work with low distortion without tendencies of clipping before a Hypex UcD400 does. The secondary L1 should read 4.4 when connected 4,5:1, though.

One could also use a parafeed or balanced configuration.

[revintage]

Robbie,
Kevins O´Connors preamp should be good company to the Hypex.

Still bypassing the input opamp and adding a tubedriver would be nice. Mail me if you want some help with the design.

With a SMPS supply you could travel really light ! The Redrocks supply looks promising.

I also use a DC/DC 12V/(up to)210V SMPS for the tube pre. 12V for this and the heaters is available from the Redrocks PSU