How to bypass the Buffer stage on UcD180 modules? - 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 9th March 2010, 11:05 PM   #1
NicMac is offline NicMac  Italy
diyAudio Member
 
NicMac's Avatar
 
Join Date: Feb 2009
Default How to bypass the Buffer stage on UcD180 modules?

Sorry if I might have asked the same question in another thread some time ago.....
I would like to make an integrated amp using the Buffalo II DAC with IVY III I/V stage (balanced output, close to zero DC offset and very low output impedance). I would like to pair this with a set of Hypex UcD180ST modules that I have coming in.
Can anybody please tell me how to bypass the coupling caps and buffer stage on the UcD180ST module? I don't need the gain, I have no or little DC offset and no real impedance issues.
Thanks,
Nic
  Reply With Quote
Old 10th March 2010, 06:23 PM   #2
Koifarm is offline Koifarm  Netherlands
diyAudio Member
 
Koifarm's Avatar
 
Join Date: Aug 2005
Hai, just look here:

Hybrid Hypex UCD

I removed the decoppling caps of 22uf from the UCD pcb.
They were between the opampinputbuffer and the UCD powerstage. Then i connect the input sym.+ en sym - to the new points on the PCB according the picture below.

Click the image to open in full size.
  Reply With Quote
Old 10th March 2010, 10:28 PM   #3
NicMac is offline NicMac  Italy
diyAudio Member
 
NicMac's Avatar
 
Join Date: Feb 2009
Hi Koifarm,
Thanks!!! Just the kind of info I was looking for. So the coupling caps are between the buffer and power stages and not directly on the inputs..... Do you know if this is also the way it is connected on the UcD180HG modules?
As you have done it the, mod is really simple and and pretty reversible.
I will try it. How did it work for you (sonically)?
Thanks again,
Nic
  Reply With Quote
Old 11th March 2010, 11:41 AM   #4
Koifarm is offline Koifarm  Netherlands
diyAudio Member
 
Koifarm's Avatar
 
Join Date: Aug 2005
Nic, with the opampbuffer i had a little noise( hiss ) in the speaker. Without the opampbuffer there was no hiss. The sound improved in detail, staging and dynamics.

Important is that your preamp can deliver enough signal to drive the UCD.

I have no pictures of the UCD180HG, because if you bypass his opampbuffer then you can better buy the "ST" version. The biggest difference between "HG" and "ST" version is the opampbuffer you gonna bypass. Except for two powerrail capacitors.

Ronny

Last edited by Koifarm; 11th March 2010 at 11:45 AM.
  Reply With Quote
Old 11th March 2010, 01:48 PM   #5
NicMac is offline NicMac  Italy
diyAudio Member
 
NicMac's Avatar
 
Join Date: Feb 2009
Hi Ronny,
I have a set of the ST coming in and I will tweak these. I guess the difference of the power rail caps between the HG and ST are relatively irrelevant as I'm using a regulated supply.
I will drive the modules directly of a Buffalo II DAC that I believe to be a perfect match (balanced, low output impedance, low DC offset, 4VRMS if in dual mono, attenuation in the digital domain).
Can't wait
Nic
  Reply With Quote
Old 12th March 2010, 08:55 AM   #6
Koifarm is offline Koifarm  Netherlands
diyAudio Member
 
Koifarm's Avatar
 
Join Date: Aug 2005
Buffalo Dac's are great. So the combination will be great.

Ronny
  Reply With Quote
Old 24th March 2010, 11:34 PM   #7
NicMac is offline NicMac  Italy
diyAudio Member
 
NicMac's Avatar
 
Join Date: Feb 2009
What is the input impedance of a UcD180 with bypassed buffer stage? Searching the fora I find 1k8 but I think this refer to a SE connection configuration. What about balanced?
Thanks,
Nic
  Reply With Quote
Old 25th March 2010, 02:08 PM   #8
Koifarm is offline Koifarm  Netherlands
diyAudio Member
 
Koifarm's Avatar
 
Join Date: Aug 2005
The impedance is the same. 1k8 for the "-" signal to earth and 1k8 for the "+" signal to earth.

Ronny
  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
UcD180 modules placement JohanH Class D 6 21st December 2006 09:12 PM
Installing Motorized Volume Control with UCD180 Modules Spiritzly Parts 0 1st March 2006 12:45 AM
Will the UcD180 modules have enough juice for Dynaudio speakers? beppe61 Class D 4 10th December 2005 06:41 PM
Opamp + buffer, how to bypass buffer at HF for unity gain? Christer Solid State 10 29th October 2003 07:50 AM


New To Site? Need Help?

All times are GMT. The time now is 05:24 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