UCD180 questions

[tim pattinson]

Lack of bass?? How much do you want? I can't believe how much my 400's [and for that matter 180's] produce. Most people I've read are abandoning their subwoofers due to the amps' ability to drive controlled extended LF.

A friend and I did measurements on the 400 with 8620's on a Neutrik test unit, and found that the LF response was ruler flat to below 10Hz, and beyond 26KHz.

I think the 8620's add a further level of clarity to the modules, but the difference is not night and day, as the standard input amps are already good.

[FuriousD]

Originally posted by tim pattinson
Lack of bass?? How much do you want? I can't believe how much my 400's [and for that matter 180's] produce. Most people I've read are abandoning their subwoofers due to the amps' ability to drive controlled extended LF.

A friend and I did measurements on the 400 with 8620's on a Neutrik test unit, and found that the LF response was ruler flat to below 10Hz, and beyond 26KHz.

I think the 8620's add a further level of clarity to the modules, but the difference is not night and day, as the standard input amps are already good.

The lack of bass comment is not mine but is bourne of the recent review by the Swede's on previous pages.

I'm not talking about a frequency response here, I'm talking about the individual performance of the AD8610/AD8620 and in particular the LF noise corner at 1.5kHz that gives you 75nV/rtHz noise at 10Hz (See datasheet P7) compared to 15nV/rtHz for the OPA627. This is massive amounts of noise and does a good job of pulling the bass to pieces in any system. The amount of feedback in the design may in some way compensate for this noise corner, but it doesn't point to a well designed op-amp. It looks a bit more like a bodge to keep the thing stable.

My point is that the UCD can probably sound better. The fact that the AD8620 makes a significant difference to the sound means that the input stage is limiting the UCD design. A decently design discrete stage would soon sort this problem. The fact that the AD8620 is a pile pants in the bass region is not up for debate here, its a simple fact!

F.

[rha61]

effectively i found that AD826 with an external PSU was better than AD8620

alain

[classd4sure]

Hi F.

I recall seeing a project or two in the Solide State forum regarding discrete input stages that sound like what you're after, you'll have to dig em up or maybe someone else can get you the link, not much help but I have a bit of a computer problem to sort out today. I do recall they were all raving about the sound of it and JFET inputs ring a bell as well.

Maybe a new thread/project could be started for a nice class A input stage....

Best Regards

[koldby]

This is probably the thread classD4sure talks about:
Dual discrete opamp PCB in DIP8


Other good reading:

http://www.passdiy.com/pdf/diyopamp.pdf

Koldby

[jam]

I wonder if Jan-Peter and Bruno had considered a discrete circuit to replacs the op-amp........

[classd4sure]

Originally posted by koldby
This is probably the thread classD4sure talks about:
Dual discrete opamp PCB in DIP8

I think there's another one out there too, fairly recent from a month or so ago? I did a google search for it but that's the only relevant link I found as well, it didn't seem familiar, I think there's more out there if anyone knows?

Other good reading:

http://www.passdiy.com/pdf/diyopamp.pdf

Koldby

Originally posted by jam
I wonder if Jan-Peter and Bruno had considered a discrete circuit to replacs the op-amp........

It's all about cost, DIY should be a little more than "plug and play" anyway yes? We're just spoiled

[Jan-Peter]

Originally posted by Jam:
I wonder if Jan-Peter and Bruno had considered a discrete circuit to replacs the op-amp........

There is listen to a very good designed discrete op amp, but the AD8620 do sounds also VERY good........

We have still to make a good A / B comparison between this two different preamps, but I already know the difference will not be very big!

Regards,

Jan-Peter

[jam]

You are correct that cost woul be an issue and the differences might be small..........but when you are waiting for the ultimate UCD700 (UCD1000?) I would pay the extra cost on probably what is the world's finest class D amplifier.

[Jan-Peter]

Jam,

Please do have patience the UcD700 or something about 1.2KW in 2 ohm , will be available.

Don't ask me about a timetable!!! But within a few months this must be possible. In a way the design is ready for testing......


Regards,

Jan-Peter