UCD180 questions

tim pattinson · 2004-12-01 10:59 pm

lack of bass ad8620

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 · 2004-12-02 10:14 am

Re: lack of bass ad8620

tim pattinson said:
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 · 2004-12-02 1:41 pm

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

alain

classd4sure · 2004-12-02 1:56 pm

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 · 2004-12-02 2:20 pm

This is probably the thread classD4sure talks about:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=32036&highlight=

Other good reading:

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

Koldby

jam · 2004-12-02 2:57 pm

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

classd4sure · 2004-12-02 5:15 pm

koldby said:
This is probably the thread classD4sure talks about:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=32036&highlight=

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

jam said:
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 · 2004-12-02 6:29 pm

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 · 2004-12-02 8:35 pm

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 · 2004-12-02 8:49 pm

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

IVX · 2004-12-02 10:09 pm

Hi all,
I hope that tube buffer for UcD would be great. I'll try to check this out soon.

IVX · 2004-12-03 9:58 am

BTW, simple discrete opamp from here http://www.diyaudio.com/forums/attachment.php?s=&postid=369533&stamp=1081722163 have ~0.03% THD at 2kohm load@4Vp-p output@gain=4, just by adding a current mirror ([bc857+bc857+220ohm+220ohm]=cost is nothing), THD will be less then 3 times (0.008%@20-20000hz flat).😎

Jan-Peter · 2004-12-03 7:00 pm

IVX,

Intersting!!

Who is making the schematic complete and creates a SMD PCB????

Or starts a new thread, I will offer to make the PCB design, I will put the gerberfiles for free to everybody on the Internet.

Regards,

Jan-Peter

stef1777 · 2004-12-03 8:08 pm

Small PCB please. I don't have any space left in my boxes. 😉

classd4sure · 2004-12-03 9:05 pm

Jan-Peter said:
IVX,

Intersting!!

Who is making the schematic complete and creates a SMD PCB????

Or starts a new thread, I will offer to make the PCB design, I will put the gerberfiles for free to everybody on the Internet.

Regards,

Jan-Peter

Impressive! Nice offer, very admirable indeed.

Koldby was right on too, that is the exact thread I had in mind, I guess I didn't read far enough into it for it to seem familiar at the time.

Thanks Koldby for that other link too, I had it saved for some rainy day reading but then I lost my hard drive. Another thing I'd missed is where they said this discrete amp works in class A..

What I didn't miss was Peranders questioning the need for an output buffer stage, and that the design as it currently stands is for loads >5K. Have we got work to do on this?

Regards

maxlorenz · 2004-12-05 11:37 pm

Jan-Peter:

At last, I got all the parts an I built my amp 😎

I'm the living proof that anyone can build an UCD based amp 😀

Of course, I have some dignity left not to show picture's of it yet 😉 , after those "chef d'oeuvres" that were posted recently in both threads.

Preamp is mi excellent DIY transformer based volume control(Stevens&Billington's TX 102 MK III-copper). I made an unbal to bal adaptor cable. I built first a stereo amp with: Ampslab's Inrush Current Limiter (works OK and is cheap!); Piltron 300VA (35-0-35 VAC); common bridge rectifier; cheap 4700uF*2 PS Ecaps. I got a healthy 47.6V DC.

I only had the time to listen a couple of CDs (Bossa Nova and Bartok's string quartets) and I'm amazed about how soft and effortless the amp sounds! Also the frequency extension is great, specially the bass, though I listened through monitor speakers. Someone asked for a comparison with class A amps long ago. Well, my main amps are Monarchy Audio's SE100 delux class A amps (mosfet) and of course I will compare them. First impressions: UCDamp has the coherence and "continuity"of my class A amp, notably in voices. I'm amazed that bass seams deeper and fuller considering 9400 uF versus 120000 uF of PS capacitance!
I got a little buzz that I plan to eliminate soon.

I will add two more channels next. I hope my TX can cope with the burden: it didn't even got warm after the listening.

Now, has someone a pair of Epcos Sikorel caps to sell?? 🙂

Thanks to Jan-Peter and Bruno for such nice products!

Mauricio

pa · 2004-12-06 10:24 pm

Hi, thanks for the comparison with the class A, it's the only type of amp wich could be better on quality, i'have 3 ucd modules at home, but i'm wating some 10000uF low esr philips 114 series fro the initial test... 🙂
35v isn't it to much ? i was thinking 32v was a maximum value...

OA51 · 2004-12-06 10:43 pm

Some pics of my finnished UcD180's

3 cabinets for UcD180's