NCD questions - Page 3 - 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 14th October 2006, 10:05 AM   #21
ghemink is offline ghemink  Netherlands
diyAudio Member
 
Join Date: Jun 2004
Location: Japan
Quote:
Originally posted by Bgt

Utter bs, if you look at the wiring diagramm you'll see the output from the preamp, input at poweramp, going directly to the + and - input of the opamp, so where is the difference in signal????? The groundlift resistor has nothing to do with purityy of sound

I think there is a lot of misunderstanding here. What Bgt says may work very well for his RCA input setup. Bgt avoids the GND loop while using the differential - input as his signal GND. Basically seperating the signal GND and the power GND. For RCA based systems that share the same power supply with multiple amps, probably that is the best solution as the power GND level maybe contaminated by the other amps, apparently that caused issues in Bgt`s setup.

What Classd4sure is talking about in my opinion is a setup where XLR input is used and where he wants to make sure that the signal GND is tightly connected (no GND lift) to the amps GND. Actually I have GNDed my mid and tweeter amp currently this way and I have a GND loop present as both amps share the same supply. Do not notice any issues at the moment with that GND loop, however, it is of course only a short loop, local in the amp and everything is balanced input so should not be very sentive to it anyway. Still, in the future I want to go to a setup where each amp has its own supply so that there are no loops anymore, waiting for the SPS30.

Best regards

Gertjan
  Reply With Quote
Old 14th October 2006, 10:16 AM   #22
diyAudio Member
 
Join Date: Oct 2003
Location: The Lab
Ghemik: thanks for these comments. Actually you are right, the GND scheme Bgt has proposed uses the minus input (which i didn't see at first glance).
This is not optimal. I can never recommend using the minus input in a RCA setup, unless it's for phase reversal. NEVER as any kind of GND. You can short it to the GND terminal next to it, but that's all.

I would recommend Bgt to use his setup, but replace the 'minus input' with GND input of his modules. The he doesn't require the 10 Ohms resistors. And simply short the minus inputs to the input GND terminal.
__________________
www.newclassd.com
  Reply With Quote
Old 14th October 2006, 10:35 AM   #23
ghemink is offline ghemink  Netherlands
diyAudio Member
 
Join Date: Jun 2004
Location: Japan
Quote:
Originally posted by Lars Clausen

I would recommend Bgt to use his setup, but replace the 'minus input' with GND input of his modules. The he doesn't require the 10 Ohms resistors. And simply short the minus inputs to the input GND terminal.
Hi Lars,

It seems Bert tried that in the past and then he got issues with channel seperation if I remember correctly. That`s why he ended up with the current setup.

The best and (always?) problem free way is one supply per amp with the supplies floating from the case. That`s why Hypex shows only dual mono setups on their site. Dual supplies does not automatically mean that the cost of the supply doubles, smaller transformers and caps can be used. So serious DIYers should probably consider this option seriously.

Gertjan
  Reply With Quote
Old 14th October 2006, 11:24 AM   #24
diyAudio Member
 
Join Date: Oct 2003
Location: The Lab
I couldn't agree more. Slightly more complicated to build though. At the moment more than half of the sets we are selling are Dual Mono sets. So i guess many have seen the light.
__________________
www.newclassd.com
  Reply With Quote
Old 14th October 2006, 11:39 AM   #25
ghemink is offline ghemink  Netherlands
diyAudio Member
 
Join Date: Jun 2004
Location: Japan
Quote:
Originally posted by Lars Clausen
I couldn't agree more. Slightly more complicated to build though. At the moment more than half of the sets we are selling are Dual Mono sets. So i guess many have seen the light.

Even if the cost of two supplies is the same as that of one supply and assuming one supply cost as much as one amp module, then a dual mono setup would cost only 33% more than a stereo setup with one supply. If I had to make a stereo amp, I knew what I would do, I would avoid a lot of potential problems for that additional 33% :-)

Would be really nice if someone would market an SMPS for stereo or multi channel use in which a PFC (power factor correction) module drives 2 or more independent SMPS, so that we could have regulated supplies (SMPS) independent for each amp, GNDs would be floating and seperated as each SMPS would have its own output transformer (hint to Hypex, Coldamp, NCD, ......).

Gertjan
  Reply With Quote
Old 14th October 2006, 03:27 PM   #26
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
Quote:
Originally posted by Lars Clausen
I would recommend Bgt to use his setup, but replace the 'minus input' with GND input of his modules. The he doesn't require the 10 Ohms resistors. And simply short the minus inputs to the input GND terminal.
Lars, if I do this my crosstalk figures go down more than 30Db and my input cable becomes very sensitive to EMI.
The 10 ohm resistor is just for separating the input ground from the power ground and keep all the EMI out.
In your amp. I wired it as you suggested but there is no issue here because you already separated the power ground from the input ground with a 2.5 ohm resistor which has the same effect as my 10 ohm resistor.
__________________
Kind regards,
Bert
  Reply With Quote
Old 14th October 2006, 11:57 PM   #27
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
Gertjan, see it this way, if you take the groundlift resistors out the speakers would take some signal from the other channels ground through the input grounds and that will give distortion/crosstalk. With the groundlift resistors the supply ground, 0V, for the speakers is always better at their own ground, 0V, terminals. They don't steal signal from the other ground, 0V. This is with a 1 transf. design. 2 separate supplies ofcourse don't have this problem. Thats what I noticed as being very different. Here you just connect the input grounds to chassis.
__________________
Kind regards,
Bert
  Reply With Quote
Old 15th October 2006, 12:25 PM   #28
ghemink is offline ghemink  Netherlands
diyAudio Member
 
Join Date: Jun 2004
Location: Japan
Quote:
Originally posted by Bgt
Gertjan, see it this way, if you take the groundlift resistors out the speakers would take some signal from the other channels ground through the input grounds and that will give distortion/crosstalk. With the groundlift resistors the supply ground, 0V, for the speakers is always better at their own ground, 0V, terminals. They don't steal signal from the other ground, 0V. This is with a 1 transf. design. 2 separate supplies ofcourse don't have this problem. Thats what I noticed as being very different. Here you just connect the input grounds to chassis.

Hi Bert,

I fully agree with your explanation. I had exactly the same thing in mind, and would basically try to avoid the same thing (currents running in those input GND cables). However, in my case, I use the modules only with a real balanced XLR input, so even if there are some currents flowing in those GND cables, my signal should not be influenced by that as the GND is not really used as a reference point for the signal.

Best regards

Gertjan
  Reply With Quote
Old 15th October 2006, 09:10 PM   #29
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
Gertjan, you got it. No problem in your setup
There is no way for me to do it differently and have all the goodies in crosstalk and distortion figures with a 1 transformer design and RCA input. Remember I also don't use a mains ground, is not obligatory in the Netherlands and I am happy for it. It saves a groundloop(NAD C272 usus also no mains ground). Furthermore my grounds are switched in my pass. preamp. So only the choosen source will pass its ground to the power amp.
__________________
Kind regards,
Bert
  Reply With Quote
Old 16th October 2006, 04:40 AM   #30
ghemink is offline ghemink  Netherlands
diyAudio Member
 
Join Date: Jun 2004
Location: Japan
Quote:
Originally posted by Bgt
Gertjan, you got it. No problem in your setup
There is no way for me to do it differently and have all the goodies in crosstalk and distortion figures with a 1 transformer design and RCA input. Remember I also don't use a mains ground, is not obligatory in the Netherlands and I am happy for it. It saves a groundloop(NAD C272 usus also no mains ground). Furthermore my grounds are switched in my pass. preamp. So only the choosen source will pass its ground to the power amp.

Yes, I like XLR, should be less critical than RCA although there is many articles everywhere on the infamous pin 1 problem and some equipment does not have the pin 1 connected correctly (to the chassis). I had to modify my own DEQX PDC XLR outputs to connect them to chassis (done in the newer models). This allowed me to remove the mains earth connection between all the equipment that was needed before to have a GND reference. Now everything is floating from mains GND and power supply GND and just connected via pin 1, I think it sounds better, however, can not easily do any AB testing so maybe I`m subjective :-)

Another remark, I assume your crosstalk problems would be less if you make a very solid (thick and short copper wire) between the signal GNDs of the two modules, in that way, most of the GND loop current would flow through that wire and GND loop induced voltages would be less. Would be interesting to see if it helps. I guess however that you do not want to experiment with this anymore as you have found a solution.

Best regards

Gertjan
  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
Some Quad els57 questions! - Novice Questions! Fanuc Planars & Exotics 13 5th December 2007 10:26 AM
PSU for QSC amp questions rkc7 Parts 5 10th November 2005 06:18 PM
Last questions about this Madmike2 Multi-Way 9 14th June 2005 12:12 AM
Questions, questions, from newb DIYer Phatman91624 Multi-Way 41 3rd August 2002 03:52 AM


New To Site? Need Help?

All times are GMT. The time now is 11:00 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