Low impedance drive units with UCD400

[BOB LEWIS]

Jan-Peter,
I intend to upgrade my actively driven Apogee Duetta Sig speakers with foil only mid/treble ribbons which have a DC resistance of approx. 0.2 ohms,although they will have 1ohm foil padding resistors;will the UCD400 be happy driving a 1.2ohm load ?Crossover frequency is 350Hz so not too much power will be required as such.

Regards,
Bob Lewis

[Jan-Peter]

Originally posted by BOB LEWIS
Jan-Peter,
I intend to upgrade my actively driven Apogee Duetta Sig speakers with foil only mid/treble ribbons which have a DC resistance of approx. 0.2 ohms,although they will have 1ohm foil padding resistors;will the UCD400 be happy driving a 1.2ohm load ?Crossover frequency is 350Hz so not too much power will be required as such.

Regards,
Bob Lewis

Is NO problem. Our standard test is to use 1 ohm, to check if the current protection works. Even in this low impedance the THD stays below 0.05%.

Regards,

Jan-Peter

[BOB LEWIS]

Thankyou for reply Jan-Peter.

Bob Lewis

[vulejov]

Originally Posted by Jan-Peter

Is NO problem. Our standard test is to use 1 ohm, to check if the current protection works. Even in this low impedance the THD stays below 0.05%.

Regards,

Jan-Peter

I thinking to use UCD180 for driving speakers with Re-1.3 Ohm, any problem?

[Ray Weikel]

I have recently required a great pair of Apogee Duetta Signatures. I used them bi-amped through a DEQX digital front end/crossover. I have been using a Pass Aleph 30 to drive the ribbon midrange/tweeter, and a Parasound A23 to drive the bass ribbons. Both are underpowered for the job, but because the power robbing passive crossovers are bypassed and the modest size of the listening room they never sound stressed. I am sure that more power would sound cleaner.

So, since I also have two home built mono block UcD180 amps that were driving matched 18" subwoofers (not used with the apogee - and not need), I decided to swap them out to drive the lower ribbon panels on the Apogee and move the Parasound up to drive the Mid/tweeter ribbon.

I expected the mono blocks which each has it's own power toroid and produces +-48V, to produce at least as much power if not more than the A23 (rated at 225W/ch into 4 ohms). The Bass ribbons have about a 3.6 ohms DC resistance.

What I hear!! The bass sound clean and tight and sounds great up to the point where heavy low notes come along, and then the output cuts out momentarily and then comes back as the volume demand subsides. It does not come close to the levels of the Parasound A23 so I think it doesn't like the load. I don't know if it is overcurrent protection, over voltage protection, or subsonic material triggering something. Any thoughts?

If it is overcurrent protection, assuming that the power supply is not the limit (I don't think it is as each transformer much is larger than the single one on the A23), would replacing the UcDv180 with a UcD400 allow it to deliver more current into a this load using the same power supply?? I think the circuit is limiting the current, not the power supply.

I have thought about using the UcD for the Mid/tweeter ribbon, but I am afraid of any turn on or off offset voltage. The Pass Aleph has a 0.1V offset that bows the Mid/twt ribbon outward, and it's turn on/off is prohibitively excessive. I actually disconnect the ribbons before turning the Pass Aleph on or off. I am afraid to even see what the UcD turn on/off does to these mid/twt ribbons. Has anyone had any experience with UcD directly hooked up to any ribbon??

Thanks for any information.

[apogee lover]

Ray Weikel,
The UCD400 would be more suitable for driving the bass ribbon as these have twice the current output,20 amps, than the UCD180.
The UCD180 should be adequate for the MRT ribbon especially if you remove the half ohm series resistor.The increase in efficiency doing this is surprising!
Switch on surge with these modules is zero;but there is approx. 30 mv DC offset at switch on from standby which results in about 1mm of ribbon deflection.This amount of offset reduces after warm up to just a few mvs.
The offset is adjustable on later modules.
I would not recommend driving the MRT ribbons with DC offsets as high as the Alephs appear to have.

Bob Lewis

[Ray Weikel]

I just now noticed that you had responded. Thank you very much. I have since moved the Apogees to a smaller home, but one with open concept family room that opens into both a Kitchen and Dining Room and has 12 foot ceilings, so a much larger acoustic space than previous environment. I am using the UDC 180 for the MRT with no issues of turn on/off or cut put. They are a direct hookup - no resistor. I am using my Halo A23 for the bass panel - which is adequate when you have bypassed all the losses of the passive network. I may build a pair of UDC 400s for the bass. The environment is very reverberant which would totally smear any conventional driver source system sound with tons of early reflections, but the strong horizontal projection from the Apogees works pretty well. I have yet to work on improving the acoustics.

Again, thanks for your post and sorry it took me so long to discover it.

Cheers