Jan-Peter:
I'm so pleased with my four channel UCD180 amp that I plan to build a pair of UCD400 monoblocks (HiEnd I hope) soon.
Just to clarify:
About DC offset, you said:
>>The new modules are AC coupled so you don't have to worry about DC<<. So there's no need for speaker relée protection...(?)
Somewhere I read that DC coupled amps had better low frequency response. Does this means that the new UCD400 is weaker in this aspect? I hope not.
The modules sound is dependant on the input buffer opamp but I didn't find any comparison between OPA2134 and AD8620 soundwise (that is what matters anyway).
Can anybody tell his experience with the above mentioned opamps?
What type of wire has the UCD400 signal cable?
Thanks
Mauricio
I'm so pleased with my four channel UCD180 amp that I plan to build a pair of UCD400 monoblocks (HiEnd I hope) soon.
Just to clarify:
About DC offset, you said:
>>The new modules are AC coupled so you don't have to worry about DC<<. So there's no need for speaker relée protection...(?)
Somewhere I read that DC coupled amps had better low frequency response. Does this means that the new UCD400 is weaker in this aspect? I hope not.
The modules sound is dependant on the input buffer opamp but I didn't find any comparison between OPA2134 and AD8620 soundwise (that is what matters anyway).
Can anybody tell his experience with the above mentioned opamps?
What type of wire has the UCD400 signal cable?
Thanks
Mauricio
IMHO this is about the input. Feeding DC in the input wont result in speakers on fire, this gets corrected. However, it won't help if your FETs have a problem and juice 40V DC into your beautiful speakers.
I'm not sure about this though, maybe Jan-Peter can comment on the danger of this happening?
Hi,
I think I can help somewhat here.
Yves I think you're mostly right, but the DC seen on the input will be amplified, not corrected, it's just a half bridge, and so it will also pump up the rails, the module has overvoltage protection which will kick in at 67Volts in this case.
If you have very low DC offset from your source (I think 10mV or less was said before) you can get away with no AC coupling, and so some have removed it so they wouldn't have to deal with the sound of the coupling caps. Changing from an opa2134 to an AD8620 might not have much of a difference if the sound is swamped by the coupling cap, most making that modification have likely removed them.
So something like relay protection is likely to help your speaker if you remove the coupling caps and have too much DC at the input, depending on your rail voltage, but you dont' want it tripping all the time, ideally it would only be (and is only reliably)used for a critical failure of the output stage, for which AC coupling at the input will be of no help whatsoever.
Mauricio, your'e ucd180's have AC coupling as well, it's only the first version of the 400 that didn't have it. I'm sure the 3db point of the AC coupling would be lower than 10Hz, probably something like 4 or 6Hz. It's only poorer in the effects.... coloration etc, that the cap itself has, not in frequency response. So you can experiment with adding better coupling caps (black gates or whatever) or paralleling a high quality bypass cap with the existing ones, or if your source has very very low DC offset possibly removing it altogether, that's an educated gamble for you to take. If you gamble poorly, the module will be well protected before any harms come to it or your power supply (if you chose those parts wisely) but it doesn't mean your speaker will make it.
Regards
I think I can help somewhat here.
Yves I think you're mostly right, but the DC seen on the input will be amplified, not corrected, it's just a half bridge, and so it will also pump up the rails, the module has overvoltage protection which will kick in at 67Volts in this case.
If you have very low DC offset from your source (I think 10mV or less was said before) you can get away with no AC coupling, and so some have removed it so they wouldn't have to deal with the sound of the coupling caps. Changing from an opa2134 to an AD8620 might not have much of a difference if the sound is swamped by the coupling cap, most making that modification have likely removed them.
So something like relay protection is likely to help your speaker if you remove the coupling caps and have too much DC at the input, depending on your rail voltage, but you dont' want it tripping all the time, ideally it would only be (and is only reliably)used for a critical failure of the output stage, for which AC coupling at the input will be of no help whatsoever.
Mauricio, your'e ucd180's have AC coupling as well, it's only the first version of the 400 that didn't have it. I'm sure the 3db point of the AC coupling would be lower than 10Hz, probably something like 4 or 6Hz. It's only poorer in the effects.... coloration etc, that the cap itself has, not in frequency response. So you can experiment with adding better coupling caps (black gates or whatever) or paralleling a high quality bypass cap with the existing ones, or if your source has very very low DC offset possibly removing it altogether, that's an educated gamble for you to take. If you gamble poorly, the module will be well protected before any harms come to it or your power supply (if you chose those parts wisely) but it doesn't mean your speaker will make it.
Regards
thanx, classD:
I'll have to re-read your answer with a textbook by my side
But I think I catch your points.
Currently a feed the UCD amp with a TVC (transformer based volume control). It will prevent DC arriving from the source to the input, I think.
I thought of building a "passive-integrated UCD amp": I mean installing the attenuating transformer in the amp box and connecting the secondaries directly to UCD's signal input connectors, saving one interconnect pair ($$). I'm affraid bypassing opamp is out of my skills ( appart the impedance issue )
What do you think?
Thanks
Mauricio
I'll have to re-read your answer with a textbook by my side
But I think I catch your points.
Currently a feed the UCD amp with a TVC (transformer based volume control). It will prevent DC arriving from the source to the input, I think.
I thought of building a "passive-integrated UCD amp": I mean installing the attenuating transformer in the amp box and connecting the secondaries directly to UCD's signal input connectors, saving one interconnect pair ($$). I'm affraid bypassing opamp is out of my skills ( appart the impedance issue )
What do you think?
Thanks
Mauricio
DC OFFSET
Hi All,
Anyone any ideas about the best way to null the DCoffset on the UCD400AD modules as I intend to actively drive APOGEE ribbon speakers with these? The MRT ribbons are very sensitive to DC,suffering displacement in the magnet structure plus premature aging and stretching.
Bob Lewis
Hi All,
Anyone any ideas about the best way to null the DCoffset on the UCD400AD modules as I intend to actively drive APOGEE ribbon speakers with these? The MRT ribbons are very sensitive to DC,suffering displacement in the magnet structure plus premature aging and stretching.
Bob Lewis
Jan-Peter said:
Also slightly off-topic:
Jan-Peter,
I'm dying here. I have attempted to order from your website on 3 different occasions (twice from home, once from work) and no confirmation. I have also sent private e-mails...I'm beginning to think I'm not really connected to the internet.
Mike
Mikela,
We just have had email contact, problem is solved
Actually strange problem, from 2 orders we get this complaint, the rest of the orders were no problem at all!
It's very importend the customer use the correct email adres, when there is an error in the emailadres you will never receive the confirmation.
We are busy with a new webshop, hopefully this will solve this problem.
Regards,
Jan-Peter
We just have had email contact, problem is solved
Actually strange problem, from 2 orders we get this complaint, the rest of the orders were no problem at all!
It's very importend the customer use the correct email adres, when there is an error in the emailadres you will never receive the confirmation.
We are busy with a new webshop, hopefully this will solve this problem.
Regards,
Jan-Peter
When you make the symmetrical connection asymmetrical at the source end, you pick up the symmetrical signal as close as possible by the source end. So you have most advantage of a symmerical connection. This is much better as making symmetrical connection asymmetrical by the input. In this way you have none advantage of the symmetrical input of the UcD module.
Regards,
Jan-Peter
classd4sure said:
Jan-Peter,
OK Everyone is allowed one silly question a day - and here's mine:
What is then the limit? Or more precisely - can I use my 2 x 50 VAC toroids (±69 V rails)?
I guess the answer also depends on what you load the modules with 8, 4 or 2 ohms (an 8 ohm answer is all I need!)
If the answer is yes - I'll order right away
Rgds
Henrik
Henrik Juhl said:
Jan-Peter,
OK Everyone is allowed one silly question a day - and here's mine:
What is then the limit? Or more precisely - can I use my 2 x 50 VAC toroids (±69 V rails)?
I guess the answer also depends on what you load the modules with 8, 4 or 2 ohms (an 8 ohm answer is all I need!)
If the answer is yes - I'll order right away
Rgds
Henrik
Hi,
See post #440
69V will trip the protection, it should not go higher than 67V when at a 10% mains overvoltage condition while unloaded.