How to bypass the Buffer stage on UcD180 modules?

NicMac · 9th March 2010, 11:05 PM

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

Koifarm · 10th March 2010, 06:23 PM

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.

NicMac · 10th March 2010, 10:28 PM

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

Koifarm · 11:45 AM

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

NicMac · 11th March 2010, 01:48 PM

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

Koifarm · 12th March 2010, 08:55 AM

Buffalo Dac's are great. So the combination will be great.

Ronny

NicMac · 24th March 2010, 11:34 PM

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

Koifarm · 25th March 2010, 02:08 PM

The impedance is the same. 1k8 for the "-" signal to earth and 1k8 for the "+" signal to earth.

Ronny

9th March 2010, 11:05 PM	#1
NicMac diyAudio Member Join Date: Feb 2009	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

11th March 2010, 11:41 AM	#4
Koifarm diyAudio Member 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.

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10th March 2010, 06:23 PM	#2
Koifarm diyAudio Member 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.

10th March 2010, 10:28 PM	#3
NicMac diyAudio Member 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

11th March 2010, 01:48 PM	#5
NicMac diyAudio Member 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

12th March 2010, 08:55 AM	#6
Koifarm diyAudio Member Join Date: Aug 2005	Buffalo Dac's are great. So the combination will be great. Ronny

24th March 2010, 11:34 PM	#7
NicMac diyAudio Member 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

25th March 2010, 02:08 PM	#8
Koifarm diyAudio Member Join Date: Aug 2005	The impedance is the same. 1k8 for the "-" signal to earth and 1k8 for the "+" signal to earth. Ronny

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