UCD180 questions

[Hans L]

Originally posted by richie00boy
Flood solder the row of pins then use desolder braid to soak up the excess from between the gaps -- just place it across the row of pins and run your iron along the braid. No need for a fine point tip.

Thanks! I'l try that.

[Hans L]

The word b_u_g_g_e_r had been automatically moderated in my post above. How uptight can you be to be offended by that particular word?!? That is simply rediculous...

And this is the same place where post this 'funny' smiley:
IMNSOHO, that's pretty *****ed up

Excuse the OT talk, just had to get it off my chest...

[Bruno Putzeys]

The trick is not so much thin solder tips but thin solder! I can solder a normal SO8 device with a 2mm tip and 0.5mm pitch parts with a 1mm tip.
For clean SMD work, get 0.4mm solder.
Desoldering an SOIC is a bit tricky. I'm presuming you don't have a controllable small hot air gun.

If you want to keep the part you're removing, use solder wick. The best type I've used so far is "soder" wick with "rosin" from chemtronics. Not the no-clean type. It's so good you can get virtually all of the solder from the pad. Sometimes you can pull off the IC cold after doing that but I don't recommend it as the chance of pulling off a pad is significant.
Then, gently wedge a thin screwdriver under the IC and apply some twist while reheating the pins (slide the iron along a row of pins repeatedly working away from the screwdriver side). Be careful you don't lift the part to far when the first row of pins comes off. Then reheat the other side.

If you don't want to keep the IC (e.g. it's broken) flood both pin rows in solder so it's got some thermal mass and all pins are connected. Then, alternatively heat both sides with the iron in quick succession. After 2 or 3 times the IC will come off. Clean off the solder from the board.

Once you've got the hang of it you can rework boards so you don't even see there's been any hand soldering going on (after cleaning off the flux that is).

[Hans L]

Thanks Bruno! That seems to be a very good recipe for succes. What a great tip to flood the rows in case you just want to remove a part. Makes perfect sense.

[tiki]

Hello all,

in the last days I built up a Linkwitz style dipole subwoofer using these woofers and tried to measure its frequency behaviour and its
impedance curve.

It is clearly to be seen, that the impedance maximum of 60 Ohms of the paralleled chassis will require a high voltage to drive them appropriately at low frequencies around 20Hz. The ~27Vrms out of the UcD180 will result in 12W @ 60Ohms - not quite much.

I think of driving the UcD in a bridged configuration to double the voltage and increasing power by a factor of 4.
I also want to experiment a bit: driving the speakers by a current instead of a voltage, coming out of the UcD. Does anybody know an appropriate way to realise this, especially, if the UcDs are bridged? I hope to flatten the frequency dependent output power curve by compensating the impedance effect.

Thanks in advance!
Regards, Timo

[richie00boy]

Driving with current source rather than voltage source will result in a frequency response that mirrors the impedance curve, i.e. massive peak at resonance.

I don't think it's even important to have constant power as efficiency will change through the band.

[ghemink]

Originally posted by tiki
Hello all,

in the last days I built up a Linkwitz style dipole subwoofer using these woofers and tried to measure its frequency behaviour and its
impedance curve.

It is clearly to be seen, that the impedance maximum of 60 Ohms of the paralleled chassis will require a high voltage to drive them appropriately at low frequencies around 20Hz. The ~27Vrms out of the UcD180 will result in 12W @ 60Ohms - not quite much.

I think of driving the UcD in a bridged configuration to double the voltage and increasing power by a factor of 4.
I also want to experiment a bit: driving the speakers by a current instead of a voltage, coming out of the UcD. Does anybody know an appropriate way to realise this, especially, if the UcDs are bridged? I hope to flatten the frequency dependent output power curve by compensating the impedance effect.

Thanks in advance!
Regards, Timo

Hello Timo,

Sound pressure is not directly related to the power you put in the woofers but it is related to the voltage you apply to them. Around the resonance frequency, the impedance is high, this mean you are lucky since you need not that much power, just voltage, to get a certain amount of sound pressure out of the woofers.

On the other hand, dipoles drop off with 6dB/Oct, so you need more voltage at lower frequencies to keep the same sound pressure level. Because of that, using bridged amps maybe beneficial. In fact I want to try to bridge two UcD400 modules for my dipole woofers.

Best regards

Gertjan

[ewildgoose]

Also consider a bigger amp and doing some EQ on the dipole. I have an Infinite Baffle sub which is also supposed to drop off at 6dB/octave, I am using a serious amount of digital EQ to even out the bottom end and it's staggeringly effective.

Check out the "Cult of the Infinitely Baffled" mailing list. These guys advocate EQ on the designs as a matter of course and you can seem some IB stuff discussed ocassionally.
http://f20.parsimony.net/forum36475/

I will be writing up more about my system here:
http://www.duffroomcorrection.com

By the way, do note that you don't necessarily need to go down the serious EQ route to improve performance. Linkwitz's transform circuit is a really good start. Or add on a Behringer "Feedback Destroyer".

However, if you want to see just how good room correction can get, check out the graphs from the DRC readme:
http://drc-fir.sourceforge.net/doc/drc.html#htoc190

For me DRC is a huge change with stereo imaging exploding out and filling the room. Bass boom disappears and small details suddenly become much more obvious.

[tiki]

Some stuff to learn for me, thank you for that!
Gertjan, I would like to hear from your experiences, bridging the 400s for the dipole.
Because this is my first subwoofer, it is easy to say, I like the sound of my audio equipment much more than before, irrespective of the non-optimum behaviour until now.

Regards, Timo

[ghemink]

Originally posted by tiki
Some stuff to learn for me, thank you for that!
Gertjan, I would like to hear from your experiences, bridging the 400s for the dipole.
Because this is my first subwoofer, it is easy to say, I like the sound of my audio equipment much more than before, irrespective of the non-optimum behaviour until now.

Regards, Timo

Hi Timo,

I'm quite sure you will like the dipoles. Maybe you need a bit of time to get used to them as you will have far less booming bass than with conventional closed systems or basreflex system. So initially you may think there is less bass. What is less are the resonances. This is because dipoles excite less room resonances, bass is much faster. I apply a 6dB/oct equalization in between the pre-amp and power amp to compensate for the roll-of. Besides that, I'm using a DEQX PDC unit as my active crossover and speaker correction system.

I don't know when I can have the first results with the bridged UcDs, I'm still working on optimizing the SMPS supplies and don't have that much free time. However, I'll keep updates related to that supply in the following thread:

A and T labs K6 SMPS for Class D amp use

Best regards and good luck with the dipoles, hope you like them

Gertjan