UcD Showdown - diyAudio
Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st June 2005, 08:36 AM   #1
diyAudio Member
 
Join Date: Jun 2004
Location: Perth
Default UcD Showdown

Hey guys,

I have been reading, but the sheer quantity of stuff on here makes it nigh on impossible to get just the info I'm after.

I plan in the nearish future to spend a day at my friends audiophile shop and do some listening comparisons between a few different amps. Basically, I plan to line up my Gainclone amp (which didn't fare so well last time), a much "better" Gainclone of my friends, a nice N.E.W. amp, a Bel Canto which is favoured by the store owner, a Zappulse 2.2, and this small Tripath-based amp they've not long had in...oh and the new UcD180 based amp I'm looking to make soon.

Last time, the Gainclone got owned convincingly by the N.E.W. lacking the detail level it could produce. I'd half expected this given that the Gainclone was my first amp, it was a tad dodgy and it cost me only about AU$350 to make.

Of course, one does not take this lying down, so I hope to surprise them with the UcD180 based amp. I bought two UcD180AD modules this morning, so we have a good base to work with and I really hope to produce something that performs a bit better, to the level, or exceeding the level of the other amplifiers mentioned.

If it could just stay on topic, and not turn into a conversation as some of the other threads have, which led me to create this thread as it was too hard to pick though. Input from Bruno in particular would be GREATLY appreciated.

-What size (VA) transformers are recommended, I'm planning to run two as per my Gainclone setup as this was what was recommended to me. That said, if anyone thinks that this is not the right path to be taking, I'm open for suggestions. Also, what output voltage transformers are required?

-What level of capacitance is recommended?

-What simple tweaks or ways of setting it up will yield the best results?

Remembering this is a UcD180, I'm just struggling to find useful stuff through the rest of it now the UcD400 is available.

Apologies for the longish thread, any assistance will be most appreciated.

Cheers,
Nathan
  Reply With Quote
Old 21st June 2005, 09:40 AM   #2
diyAudio Member
 
Join Date: Jun 2004
Location: Perth
While I'm waiting for a response, I've been doing some more reading. Would a pair of 30V 160VA transformers be fine to use?
  Reply With Quote
Old 21st June 2005, 02:08 PM   #3
diyAudio Member
 
Join Date: Jun 2004
Location: Perth
Still looking around. I was thinking of using 8 Nichicon KG 63V 4700uF caps for the power supply. Does this seem like overkill? Does anyone in Australia know where I can purchase these?
  Reply With Quote
Old 21st June 2005, 02:17 PM   #4
diyAudio Member
 
Join Date: Mar 2005
Location: Sao Paulo
Nathan,

I think the 30VAC 160VA transformer is excelent for one UCD180. Many people would think that it would hold even two of those, but for a great amp, one-to-one VA-Watts rating is a great start.(My UCD400 monoblocks use 800VA transformers, because size and pricing was not very different from the 400-600 VA ones...) I personally favor the monoblock aproach, to be completelly sure cross-talk is almost inexistent.

About the capacitors, I guess the values are good enough, althoug I am not sure if you are considering 8 caps per UCD module. If it is, then you are certanly over-dimensioning, unless those caps have less than reasonable ripple current ratings... Not a problem though...


Look at the hotrodding topic for modifications. The one people seems to agree that have a big impact are the signal dc-coupling caps...
  Reply With Quote
Old 21st June 2005, 02:19 PM   #5
diyAudio Member
 
Join Date: Apr 2004
Location: BE/NL/RW/ZA
Apologies. I don't always look at the main page of diyaudio. One should contact me directly if one needs a certain reply.

160VA, 30 or 35V is OK. Use "slit foil" caps (available only as 10000uF so that answers that question). Soft-recovery rectifiers with 47nF caps across them. If your transformer has 2 separate secondaries, consider using 2 separate bridge rectifiers, so you get two single 45VDC supplies that you then place in series. If you want, this allows you to use schottky diodes for the rectifiers (half the voltage). In that case, substitute 1nF+10R for the 47nF caps.

Short the infamous input coupling electrolytics on the modules. If you expect a DC problem, use better caps that you place at the inputs of the modules (higher impedance than where the standard coupling caps are).

Let me know when you've gotten this far.
  Reply With Quote
Old 21st June 2005, 02:19 PM   #6
diyAudio Member
 
Join Date: Jun 2004
Location: Perth
I was planning on using 4 per UcD, for 18800uF per UcD180, having two monoblocks yes. Does this sound like overkill, i.e. should I just go a pair of 4700uF caps per UcD?
  Reply With Quote
Old 21st June 2005, 02:25 PM   #7
diyAudio Member
 
Join Date: Jun 2004
Location: Perth
Ahh, thanks will do in future

I'll do some digging around about these "slit foil" caps, I'm still kind of new to all this terminology.

"Soft-recovery rectifiers with 47nF caps across them." - This bit went kind of over my head, is it possible for you to elaborate slightly? I have part of an old Gainclone power supply that I was planning to utilise which has 8 rectifier diodes a channel which I'm assuming what you meant by two separate bridge rectifiers?
  Reply With Quote
Old 21st June 2005, 02:37 PM   #8
diyAudio Member
 
Join Date: Jun 2004
Location: Perth
Also, when you say that the transformer is OK, is that a good thing, or would you recommend something with say a higher VA?
  Reply With Quote
Old 21st June 2005, 02:42 PM   #9
diyAudio Member
 
Join Date: Apr 2004
Location: BE/NL/RW/ZA
Quote:
Originally posted by justcallmefrank
I'll do some digging around about these "slit foil" caps, I'm still kind of new to all this terminology.

"Soft-recovery rectifiers with 47nF caps across them." - This bit went kind of over my head, is it possible for you to elaborate slightly? I have part of an old Gainclone power supply that I was planning to utilise which has 8 rectifier diodes a channel which I'm assuming what you meant by two separate bridge rectifiers?
"Slit foil" is a particular kind of electrolytic capacitor for audio, see http://www.dnm.co.uk/capacitors.html .
I don't buy the eddy current story, but I like the way they sound.

Diodes take some time to come out of conduction when they have been forward-biased for a while. They will actually pass current the wrong way round for some time. When they finally do stop conducting, this often happens very abruptly. This produces high-frequency noise. A soft-recovery rectifier is a diode optimised to come out of conduction in a more controlled manner after a shorter period of time. This greatly reduces the switching noise. Adding 47nF capacitors directly across the rectifiers reduces this further.
  Reply With Quote
Old 21st June 2005, 02:43 PM   #10
diyAudio Member
 
Join Date: Apr 2004
Location: BE/NL/RW/ZA
Quote:
Originally posted by justcallmefrank
Also, when you say that the transformer is OK, is that a good thing, or would you recommend something with say a higher VA?
Normally one uses a transformer rated between 0.5 and 1 times the amplifier rating. 160VA is perfect.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Feastrex vs. Fostex Ultimate Showdown rjbond3rd Full Range 17 21st January 2009 12:26 AM
Troels VS. Zaph - 2 Way Bookshelf Showdown harrisni Multi-Way 24 2nd April 2008 04:40 PM
Tripath amp1 vs 300B vs AlephX,Gainclone.Showdown of the diy favourites. protos Chip Amps 7 30th October 2005 04:05 PM


New To Site? Need Help?

All times are GMT. The time now is 07:06 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2