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-   -   UcD modules - can the modules work without the input op-amp? (http://www.diyaudio.com/forums/class-d/88024-ucd-modules-can-modules-work-without-input-op-amp.html)

beppe61 10th October 2006 12:59 PM

UcD modules - can the modules work without the input op-amp?
 
Dear Sirs,

I understand, from what I have read here, that the dual input op-amps on the removable daughter boards of the UcD modules can be a limiting factor for the sound.
I have already what I deem a really nice single ended line stage that I would like to use in order to drive these modules without the input op-amp for better sound with the signal sourced by a CD player.
It has voltage gain=6 and can drive comfortably impedances as low as 5kohm.
Is this feasible? Is this op-amp inside any feedback loop?
Is a balanced input stage mandatory ?
Can the UcD modules actually work without the input op-amp?
I already looked at an Application Note but I have not been able to realize if all this is feasible.
Any info/advice would be extremely appreciated here.
Thank you very much and kind regards,

beppe

tbr 10th October 2006 05:05 PM

Yes, the modules do work without the op-amp. And they will sound better...

The op-amps are NOT on the daughter boards but the UCD circuit!

The op amp is an 8-pin smd-device on the bottom side of the (main) pcb. To get it out of the signal path find the coupling elkos from it to the UCD-board (2 of a bunch of 4 elkos close to the daughter board) and unsolder them. Then feed your signal in there.

Without the op-amp the gain in my system is just right, but I use a preamp. Played the module a few minutes with the op-amp, then I threw it out as the modules had ridiculous high gain with it. Works for nearly a year now, and that into a ~84dB 1R full range ribbon speaker...

It is posible that the input Z of the negative (inverted) input of the UCD is too low, but I would simply try it out. If you go single ended, connect hot and ground to the player, leave the inverted input open. Make a decision if you want to use a cap for DC-protection or not (I don't).


Thomas

beppe61 10th October 2006 06:28 PM

Quote:

Originally posted by tbr

Yes, the modules do work without the op-amp.
And they will sound better...
...
Thomas

Thanks a lot Mr Thomas for your very kind and valuable reply.
I thought about this solution after reading so many posts about the influence (not always for the better) on sound of the input op-amp.
There is also a 3D about replacing it with a higher quality discrete op-amp for better sound.
As I said my single ended line stage has already a voltage gain of 6 and a very low output impedance.
It is cap coupled at the output so another cap is unecessary.
Good to know that I can leave the phase (-) disconnected without any problem for the amp stage.
I did not know this sincerely.
Thank you very much indeed for your kind and precious help.
Kind regards,

beppe

P.S. in the meanwhile I also emailed hypex on the topic.
I will attach here after the possible reply. But now I know that it is possible (and recommendable as well !).

classd4sure 10th October 2006 07:36 PM

Beppe you haven't read the link I was kind enough to give you, have you?

Also, have you acquired these modules and actually heard them yet before planning all these "upgrades"?

Alfetta87 10th October 2006 07:55 PM

The UcD sound fantastic straight out of the box, if delivered with the AD8620 OpAmps.
Removing them might improve the sound, but there are simpler ways. Replace the coupling caps (22F) by better ones, or bypass them if you're sure about the offset of your preamp (there might be some coupling caps in the preamp already).
This is a huge improvement.
Some people suggest to bypass the caps, and put one or two (depends if driven in single ended or balanced) HQ cap at the input, for example betwenn the RCA sockets and the inputs of the board. For instance 6F Auricap would be an excellent choice.

Replacing the two large filtering caps (470F/100V) by some Panasonic FC's will also improve.

beppe61 10th October 2006 08:58 PM

Quote:

Originally posted by classd4sure

1) Beppe you haven't read the link I was kind enough to give you, have you?
2) Also, have you acquired these modules and actually heard them yet before planning all these "upgrades"?

1) Yes Mr Chris I read it. But honestly I did not fully understand it.
I am not an expert in electronics.
The proofs are that:
a) I thought that the input impedance of the modulator were 10K while a man said that is indeed about 2K
b) I did not understand if a balanced input driver were mandatory or not. Now I now that the inverting input of the modulator can be left open and it is possible to use the noninverting input and ground when the input is single ended.

2) As I said previously I have been already exposed to them.
I heard an amp based on UcD 400 modules at a friend house.
Unfortunately I was not able to heard it full range, because it drove only the mid-high section of a biamplifed system.
In the next days I will bring my speakers (Dynaudio) to this friends in order to test them with the mentioned amp.
After this decisive test I will make my move.
I have done so many mistakes with power amp.
Presently I have four unused at home.
So you can understand a little hesitation.

Anyway I think I have gathered enough information about the hardware.
Thank you very much again to your and all the nice DIYers who have disclosed with me their valuable findings.

Kind regards,
beppe

classd4sure 10th October 2006 09:30 PM

Quote:

Originally posted by beppe61


1) Yes Mr Chris I read it. But honestly I did not fully understand it.
I am not an expert in electronics.
The proofs are that:
a) I thought that the input impedance of the modulator were 10K while a man said that is indeed about 2K
b) I did not understand if a balanced input driver were mandatory or not. Now I now that the inverting input of the modulator can be left open and it is possible to use the noninverting input and ground when the input is single ended.

2) As I said previously I have been already exposed to them.
I heard an amp based on UcD 400 modules at a friend house.
Unfortunately I was not able to heard it full range, because it drove only the mid-high section of a biamplifed system.
In the next days I will bring my speakers (Dynaudio) to this friends in order to test them with the mentioned amp.
After this decisive test I will make my move.
I have done so many mistakes with power amp.
Presently I have four unused at home.
So you can understand a little hesitation.

Anyway I think I have gathered enough information about the hardware.
Thank you very much again to your and all the nice DIYers who have disclosed with me their valuable findings.

Kind regards,
beppe


Not fully understanding OK. You can ask questions on what you dont' understand, and it's very much the kind of thing you can read 10X over or more.

I can't agree with leaving one of the inputs open, you may however neglect the ground if need be, but yes, you can drive it either single ended or balanced, again there is now a nice app note on the site that explains how and tells you what your options are.

My concern is actually not whether or not you've heard the modules, it is in fact if you actually have them yourself, and properly implemented.

You're going to make mistakes with these as you learn how to get them into your system in the best possible way. It's good because they're so rugged they can take some abuse as you learn, but at the same time it's bad because they're so rugged, alot of non optimal methods seem to work OK. You can't make the mistake of settling for that, you really do have to play around with it until you figure it out.

It's because of this that I don't see the sense in encouraging you to even be considering things like swapping out the input stage, when there's so many other areas of concern that are a sure bet to improve on. Mostly what Alfetta87 said, along with your PSU, layout, wiring...

Anything more exotic, which is very likely to not be an improvement, should be well out of your mind at this point in time. The goal here is exactly to keep you from making a big mistake, by keeping your perspective on both what works and what matters.

beppe61 10th October 2006 09:38 PM

Quote:

Originally posted by classd4sure

Not fully understanding OK.
...
Anything more exotic, which is very likely to not be an improvement, should be well out of your mind at this point in time. The goal here is exactly to keep you from making a big mistake, by keeping your perspective on both what works and what matters.

Let's say that modding them is not an option for an unexperienced diyer like me.
In any case I will use them as they come. Without any mod.
I will focus my attention on power supply execution without touching the modules.
I think it is the wiser approach after all.
Thanks again and kind regards.

beppe

RX5 11th October 2006 07:35 AM

Re: UcD modules - can the modules work without the input op-amp?
 
Quote:

Originally posted by beppe61
Dear Sirs,

I understand, from what I have read here, that the dual input op-amps on the removable daughter boards of the UcD modules can be a limiting factor for the sound.
I have already what I deem a really nice single ended line stage that I would like to use in order to drive these modules without the input op-amp for better sound with the signal sourced by a CD player.
It has voltage gain=6 and can drive comfortably impedances as low as 5kohm.
Is this feasible? Is this op-amp inside any feedback loop?
Is a balanced input stage mandatory ?
Can the UcD modules actually work without the input op-amp?
I already looked at an Application Note but I have not been able to realize if all this is feasible.
Any info/advice would be extremely appreciated here.
Thank you very much and kind regards,

beppe




beppe,

to put it simply...

>> op-amp buffer is underneath the main board and NOT
on the duaghterboard...

>> If you want to go single ended(RCA) , +IN and GND
to your CD player, the -IN is SHORTED//connected to
GND... not left open...

>> I you do NOT want to use op-amp, you can remove
the 22uF coupling caps, and tap from there onward...
but since you said your not at all good at
electronics, you probably might need someones help
doing THIS upgrade....

Regards,
Raff


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