Increasing output channels of preamp. - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 15th January 2002, 12:05 PM   #1
diyAudio Member
 
Join Date: Jun 2001
Location: Flanders, Belgium
Question Increasing output channels of preamp.

Hi,

does anyone have a idea how to increase the amount of output channels of a preamp (or mixer)? I'm looking for something to connect on an excisting output, with four (or more) in volume adjustable outputs. I was thinking about placing a buffer after the output of the preamp to prevent too low impedances for that output. After that buffer I would connect the extra pre-amps with the gains adjustable by potmeters.

I could realise this with simple opamps, I know how they work and how to calculate the resistors etc... But I'm not very experienced with opamps practically speaking. Which types are usable for good audio performance?

I could also use transistor stages, it's a little more complicated than previous method, but I can handle this.


If you have any ideas or excisting schematics, please let me know.


Many thanks to this GREAT forum!!

Hugobross.
  Reply With Quote
Old 15th January 2002, 01:01 PM   #2
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
Good opamps.
  Reply With Quote
Old 15th January 2002, 02:03 PM   #3
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Hugobross

Do you wish to be able to increase the voltage level of individual outputs relative to the voltage output of the pre-amp or merely to reduce it? The optimum solution will depend on this.

Geoff
  Reply With Quote
Old 15th January 2002, 07:05 PM   #4
diyAudio Member
 
Join Date: Jun 2001
Location: Flanders, Belgium
The meaning is to be able to reduce the amplitude per channel.
So we will need per channel a potmeter to reduce amplitude.

regards,

HB.
  Reply With Quote
Old 15th January 2002, 08:16 PM   #5
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
HB

Any competant pre-amp should be able to drive its full rated output into a 600ohm load so it should be possible to use a completely passive arrangement. Four 10kohm pots in parallel should not overload the pre-amp but you would need to keep the connections between the pots and the following equipment reasonably short (< 500 to 750mm) to prevent high frequency roll off.

For longer cable lengths, or to be absolutely on the safe side, a buffer (eg OPA 634, BUF04) or an op-amp wired as a non-inverting unity gain buffer between each pot and output would be required. If there is any doubt about the pre-amp's drive capabilities then a further buffer between the pre-amp and the pots would be desirable. All this is very much as you indicated in your original post.

The buffer ics tend to be relatively expensive so it would probably be more economic to use op-amps. When wired as a unity gain buffer and with a limited (<2Vrms) output voltage swing there is probably very little audible difference between various op-amps once a certain quality standard has been reached. Any differences become far more apparent as the gain and output voltage swing become greater.

In view of the fact that you are going to need up to 10 of each device for your four stereo outputs, I do not think that the cost of something like an OPA627 would be justified unless you have some very high quality equipment in your system. Instead, I would suggest that you consider the NE5534 (or NE5532 dual), which has a very good performance for its price, or the OPA134 (or OPA2134 dual) which is a somewhat more expensive but has a good reputation. Another alternative would be the OPA604 (OPA2604 dual).

If you are interested in some comparison measurements of these devices, take a look at the 'elements of op-amp design' article at Doug Self's website:

http://www.dself.demon.co.uk/ampins.htm

Geoff
  Reply With Quote
Old 16th January 2002, 10:19 AM   #6
diyAudio Member
 
Join Date: Dec 2001
Location: Howick South Africa
HB

I have a DIY for guitarists book where they have designed a "spluffer" (splitter / buffer) the idea being to split and buffer a guitar signal into two so that you can drive two amps, or effects pedals etc. I have designed a board for it but doubled it so that I get four outputs for my son's PA system, but have not got around to building it.
I can send the schematic and board if you want.
The board was designed on "Eagle Lite" but if you want I can convert to a GIF or something.

Dieterd
  Reply With Quote
Old 16th January 2002, 01:49 PM   #7
diyAudio Member
 
Join Date: Jun 2001
Location: Flanders, Belgium
thanks,

Geoff, I will check out the types you've mentioned, but right now have to spend some time to study electronics for school - on highschools we've examinations here in Belgium at this time. I will start to design something in two weeks; I will post a reply then to say what I've done to realise that; thanks!

Dieter, can you please post the image in this thread? Then I can compare it in what I've in mind to build.


See you soon (after studying) ,

HB.
  Reply With Quote
Old 16th January 2002, 01:58 PM   #8
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
HB

Best of luck with your exams. When you get back to your project, please remember that the NE5534 will require additional compensation when used as a unity gain buffer. The other op-amps I mentioned are all unity gain stable and do not normally require a compensation capacitor.

Geoff
  Reply With Quote
Old 16th January 2002, 02:02 PM   #9
Warp Engineer
On Holiday
 
AudioFreak's Avatar
 
Join Date: Oct 2001
Location: Queensland, Australia
Geoff, is the LF411ACN unity gain stable? how can i tell from the data sheets if an opamp is or is not unity gain stable? Thanks again.
  Reply With Quote
Old 16th January 2002, 05:26 PM   #10
diyAudio Member
 
Join Date: Jun 2001
Location: Flanders, Belgium
Geoff,

Looking to the prices let's start with the cheap ones, the extra amount of outputs are only used in cases we're going to play on events or parties where more than three poweramps are needed.
So I, as the "technician (hmm)" of our group, have to create something in cases we'll need more outputs. So this whole schematic will not be used that frequently, and is only ment to drive heavy power amps playing some loud music. I just wonder if someone can hear in this case the difference in quality between those relative expensive opamps and the cheap ones such as the NE5532?

Do you mean that the ne5532 needs a capacitor (22 pF) between pins 5 and 8. I just looked at some page of rod's:
http://sound.westhost.com/project30a.htm

He uses 22pF between pins 5 and 8; is this what you mean with additional compensation??

What about the TL072 he also uses?

best regards,


HB.
  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
Optimus amps - Increasing output DCJuicer Car Audio 17 1st July 2008 05:18 PM
Increasing preamp caps Sony Parts 3 23rd January 2007 09:25 AM
increasing current output xplod1236 Solid State 7 27th March 2004 06:24 AM
increasing output/decreasing distortion amo Multi-Way 3 14th October 2003 10:07 PM
Increasing Power Output of a Car amplifier Dj BASS AMP Solid State 5 5th October 2002 11:37 PM


New To Site? Need Help?

All times are GMT. The time now is 02:06 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