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Old 20th January 2010, 12:14 AM   #1
Zodiac is offline Zodiac  United States
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Default Improving my UCD180

Ok, I need your help team!

I built two amps using the bog standard UCD180 module about 3 years ago.

Each amp is comprised of a 500VA transformer, soft recovery diode bridge with snubber networx and a 10,000uF BHC Aerovox capacitor per rail. From that I'm running two UCD180 modules.

The application is in a bass amp for a pair of Linkwitz Orions. Each UCD180 module drives one Peerless XLS10 in an open baffle, with quite a lot of EQ applied. The Peerless is crossed over at 24db/oct at 100Hz. There are two XLS10s per side, hence one amp per side.

Cabling is Goertz Alpha Core 13AWG.

Now my problem is that as my system has improved I feel the bass performance not as good as the rest of the system. I run an acoustic tuning company so its not a room issue but an issue with the electronics, which isn't my strong side. The symptoms are that the bass is a little wooly, ill defined and does not seem to be 'of a piece' with the rest of the speaker.

The amps used on the speaker to drive the mid and tweets are Pass Labs Aleph 3, which are 30W p.c. pure class A.

I'm wondering if there are some recommended changes that I could make to the power supply or cabling to improve performance.

Any suggestions?
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Old 20th January 2010, 05:55 PM   #2
rha61 is offline rha61  France
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are the UCD near the speakers ?
with 200W/4R and 300W/2R i think the ucd is not the problem
maybe it 's a linearity issue or , if the midrange is smooth , the bass will appear "slow "
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Old 20th January 2010, 06:08 PM   #3
DcibeL is offline DcibeL  Canada
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I would also suspect the UcD amp is not the problem. I'm not sure what is recommended for the Orion, but one UcD180 per XLS10 should be plenty. Perhaps voltage gain is not matched between the UcD and your Pass amp, could be simple as a level difference. Perhaps the speaker location in the room is affecting it, however I think I read that the Orion is not very sensitive to room placement.
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Old 20th January 2010, 06:18 PM   #4
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I'd add another 10000uF per rail (or possibly 20000uF).

10000uF per rail is not much for a PSU supplying two amp modules.
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Old 20th January 2010, 07:35 PM   #5
Zodiac is offline Zodiac  United States
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80w per driver is sufficient to reach max excursion on the drivers.

The UCDs have been modded from 26dB gain down to 20dB gain to match the Pass Labs amps.

The measured response using an RTA is reasonably good at 1/24th octave, with no significant modal resonances or dips due to speaker boundary interference. And what I perceive isn't room related I feel, as I've now had the Orions and those amps in 4 different rooms with very different sizes and constructions.

The UCDs are approx 1m behind the speakers so cable runs are short.

What I hear is that with single drum hits alone have good clarity but multiple tend to run into each other and lose impact. Culprits I was considering: low ps capacitance, low quality coupling caps (there is one cheap electrolytic before UCD input stage and another before output stage), cables not sufficient AWG, cheap transformer.

Would be interested to hear from those who have done those types of changes and how it impacted the sound.

Last edited by Zodiac; 20th January 2010 at 07:40 PM.
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Old 22nd January 2010, 09:35 PM   #6
Zodiac is offline Zodiac  United States
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bump
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Old 25th January 2010, 12:01 PM   #7
EVO1340 is offline EVO1340  United Kingdom
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Hi Zodiac,
The most likely is the capacitance in your PS, I have 20000 uF per rail, and have no problems, my speakers are Klipsch La Scala (very high efficiency) and as such do not drain the power so much with high volume levels. The input coupling caps are there for a reason: if you are sure your preamp does not have any DC at the output, you can replace them witha short, as discussed in the Hypex thread elsewhere. Other mods I have done: replace the stock input dual opamp with a LM4562, better transparency and midrange.
Hope this helps

Arthur.
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Old 28th January 2010, 12:39 PM   #8
rha61 is offline rha61  France
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if i was you , i should rent a good conventionnal four channels pro amp ( crown , chevin , ram audio ...) , to be sure it's an electronic problem , not a mechanical one
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Old 28th January 2010, 04:06 PM   #9
Ltralus is offline Ltralus  Denmark
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Congratulations for having discovered that even lowly bass reproduction requires some degree of accuracy. You said you're using a bog standard UCD180, that means you're listening to electrolytic coupling caps that lack any bias across them which makes them even worse. As Arthur noted, you may not be at liberty to short them out, matter of fact, on the old 180 modules with the 5532 op amp you have to change the op amp first. You should go read those old threads, you'll find the answers sooner than waiting around for residual echos. In the very least you must address the electrolytic coupling cap problem somehow, it will clean up the sound and firm up the soundstage a great deal. Other than that obvious bit it is all but pointless commenting further when we're unable to see the potential nightmare in wiring and grounding you may be working with, which alone could cause the problems you described, but the coupling caps are always a necessary step.
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Old 28th January 2010, 08:12 PM   #10
jacq. is offline jacq.  Canada
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Hey, why not try a simple test, by switching amps in your set-up? UCD180's are suppose to be very nice for mids & highs and as for class A for bass, well it's one of there strong points.

As an Orion owner myself I would not hesitate to do so as to try it at least.

Jacq.
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