connecting input directly to ucd, no input buffer - 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 4th July 2006, 03:11 PM   #1
mazurek is offline mazurek  United States
diyAudio Member
 
Join Date: Aug 2005
Default connecting input directly to ucd, no input buffer

If instructions for this exist, please point me to them, the only information I have seen has been regarding removing decoupling caps and changing the op amp power supply.

I am gearing up for fully active loudspeakers. Shortly, I will be posting crossover pcb, +/-12 v power supply pcb, project writeup, etc.

The next step will be to put the crossover circuit board and ucd amp in one box. I have a spot for adjustable gain on the crossover, so I can jack it up to 5, and hopefully connect the output directly to the UCD, bypassing the op amps. The OPA2134 in my board are low dc offset, I don't believe they will be a problem except for maybe the bass due to an LT circuit potentially amlifying any interstage DC emitted (in that case I'll use decoupling caps).

Any directions on connecting the circuit boards directly, bypassing the op amps. Without any further instruction, I may just try connecting the signal ground to amp ground and soldering input directly to the existing opamp output. I anticipate dealing correctly with the grounds will be a problem due to my unbalanced inputs.

I will report back in two to three weeks if everything goes well.

Lee
  Reply With Quote
Old 4th July 2006, 03:50 PM   #2
Account Disabled
 
Join Date: Feb 2004
Send a message via AIM to classd4sure Send a message via MSN to classd4sure
Hi Lee,

If it helps, the AC coupling caps are _after_ the op amp buffers. So if you remove them you can solder your inputs directly to the comparator, or output side, of the coupling cap via, and you're good to go.

Use the signal ground to connect your supply to, not the power/amp ground.

Trace the inputs back to the op amp and you'll then know which coupling cap was acting as inverting and non inverting, then you should know all you need to make a go of it.
  Reply With Quote
Old 9th July 2006, 05:10 PM   #3
mazurek is offline mazurek  United States
diyAudio Member
 
Join Date: Aug 2005
So I can just remove the ac coupling caps and connect the input to the non-inverting cap, and the ground to the the inverting cap, as shown in the picture? I located the caps, and circled their output pins.
Attached Images
File Type: jpg topost.jpg (90.6 KB, 520 views)
  Reply With Quote
Old 11th July 2006, 10:52 AM   #4
Account Disabled
 
Join Date: Feb 2004
Send a message via AIM to classd4sure Send a message via MSN to classd4sure
Yeap, I'm zombie brain at this hour but it looks right

You can also try being super slick and tweaky (....ahah..... sigh) and trace those pins over to the header pins of the daughter card, solder them direct to that, all for the sake of saving ~1cm of signal length and totally avoiding those wimpy lil traces.

I'd make a real effort to get them soldered fast though, and heatsink the header pins you're soldering to on the other side of the board (probably don't want too much heat getting into the daughter card!).

Whatever you feel most comfortable doing, but I think that will work.

Disclaimer time.... I haven't tried any of this myself

Let me know how it turns out.
  Reply With Quote
Old 11th July 2006, 11:55 AM   #5
mazurek is offline mazurek  United States
diyAudio Member
 
Join Date: Aug 2005
Thanks, sounds like a bit of a warning about the daughter card. I think I'll be safer soldering to the main pcb. The other option sounds pretty extreme, and I'm out of money.

I should get around to doing this early next week, my girlfriend is going on vacation with her family, and I will be playing electronics a lot. I've got circuit boards lined up for the day she leaves, and they have an adjustable gain so I'll be able to mod one channel only and compare. Though I hesitate to make any sweeping comments other than works/not works, good/bad, I'll see if I can get it done in time for the columbus diy meet so more experienced people can give their equally subjective but more reputable opinion.
  Reply With Quote
Old 11th July 2006, 08:31 PM   #6
Account Disabled
 
Join Date: Feb 2004
Send a message via AIM to classd4sure Send a message via MSN to classd4sure
Yeah it's a little bit of a warning, they never hurt. Proceed with caution and all. I don't think you'd want enough heat getting into the daughter card to reflow anything, or even create a poor joint with the header pins going into it. You can visually inspect that and touch up if need be though. Some forceps clamped to the pin on the top side of the board would make an excellent heatsink while you solder it.

Probably the real advantage of doing it this way, far more so than avoiding that little bit of trace length, is that you can keep your wires tightly twisted right up to where you're soldering. If you do it the other way, at the cap solder pads, you're going to have a nice little loop of greatly increased area, be a great way to pick up noise.

If you trace it out, you'll see the pins you need are the top 2. I think that's how I'll do it when I try it.. eventually.
  Reply With Quote
Old 11th July 2006, 10:13 PM   #7
mazurek is offline mazurek  United States
diyAudio Member
 
Join Date: Aug 2005
I see you've given this some thought, I suppose I'll try the daughter board. It will be my payment for free advise, which I will inevitably nag for again in the future.

You think radiated noise is more important as the connection is closer to the switching components? If you think so I may go get some proper shielded microphone cable, I was just going to try twisted pair for experimentation and sub in better stuff if necessary.

At least if my goal is to remove the op amp, and I break it, I can buy one of the cheaper versions with no worries about op amp flavor.
  Reply With Quote
Old 11th July 2006, 10:29 PM   #8
Account Disabled
 
Join Date: Feb 2004
Send a message via AIM to classd4sure Send a message via MSN to classd4sure
Hm, I think experimenting with normal twisted pair first would be the best idea, why complicate it if you don't need to?

The HF carriere wave will appear at these inputs since you're skipping the buffer stage, that's likely to be more of a concern than proximaty to the switching node.

What good a shield would be since you're driving it single ended I'm uncertain of, probably twisting will do the job nicely.

Another thing you could try would be a ferrite choke or clamp on the twisted pair, close to the module, I'd probably opt for that before trying to add a shield.

If you do decide to try it with a shield, I think you'll also conveniantly find the signal ground maybe just one pin down

Pop the coupling caps off, like you were going to do anyway, and you should be able to leave the op amps in place for all your testing, can't break em that way! It might be a good idea to tie both their inputs to ground though (at the usual connector) to ensure they don't their outputs flying all over the place.
  Reply With Quote
Old 17th July 2006, 02:37 PM   #9
mazurek is offline mazurek  United States
diyAudio Member
 
Join Date: Aug 2005
I'm going to try this tonight, or tomorrow night. Does the ucd need to be connected to a low impedence output.

i.e, my crossover has a 200 ohm output resistor. Is it better to remove this or leave it in? There is approx 1.5 feet of cabling between crossover and amp boxes.
  Reply With Quote
Old 17th July 2006, 08:18 PM   #10
lucpes is offline lucpes  Europe
diyAudio Member
 
Join Date: Dec 2003
Location: Iasi
Send a message via Yahoo to lucpes
Quote:
Originally posted by mazurek
I'm going to try this tonight, or tomorrow night. Does the ucd need to be connected to a low impedence output.

i.e, my crossover has a 200 ohm output resistor. Is it better to remove this or leave it in? There is approx 1.5 feet of cabling between crossover and amp boxes.
I'd replace the 200 ohm with a lower value, say 22R or 47R.

The direct input impedance on the + input is 8.2k afaik, so it's a safe bet to have an as low as possible impedance on the source side.
__________________
Deep down inside.
  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
50M input impedance buffer? takodabut Solid State 12 5th December 2008 09:42 PM
TPA6120 without input buffer mr.duck Chip Amps 11 12th January 2007 10:46 AM
UCD 180 input buffer rotation Class D 63 12th October 2006 05:21 PM
Connecting Electret to Dynamic Input turbodude Solid State 2 11th September 2006 12:23 AM
How do I connecting speaker signals to line level input ? ANALOG GUY Car Audio 1 17th April 2006 07:42 AM


New To Site? Need Help?

All times are GMT. The time now is 03:57 PM.


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