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

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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.
 
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?
 
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.
 
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.
 

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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 :cool: ! 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
 
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