Request for Guides/Explanation Regarding Audio Mixer Circuits - Page 2 - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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 9th December 2012, 01:30 PM   #11
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Hi indianajo,

Comparing opamps and seeing which is "best" is a hot topic generally.

The 741 is fine for experimenting and learning... its cheap, its tough, its stable and it has a low power consumption.

Everything has to be put in perspective. A 741 compared to say a current $10 "audio" opamp is a bit like comparing a $1000 CD player to a $10 portable CD player from the supermarket. There are differences for sure, but the cheapo one can be surprisingly good when slotted into a top flight system. Remember 741's were the industry standard for many years and were used in many hifi products/projects of the day.

If you fit a socket to any projects then you can try different opamps to see if you can hear the differences.

(I'm not trying to make a case for the 741 just that it is absolutely ideal as a starting point for learning and ultimately you might be surprised how "good" it still is when used correctly)
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 9th December 2012, 02:17 PM   #12
diyAudio Member
 
Join Date: Dec 2012
Quote:
Originally Posted by Mooly View Post
The split power refers to the opamp power supply. For that circuit to work (and it is the normal and correct method), it needs the opamp (assuming the device numbers mentioned) to have a positive supply on pin 7 with respect to "ground" (thats your zero volt line) and a minus supply on pin 4 with respect to ground.

To power the circuit from a single rail, for example from one battery, would require additional components to derive a "mid point" reference level.

Its a subtle thing to grasp. On a single supply the opamp output would have to be biased to half the supply voltage in oder that the output could go "equally high" and "equally low". ON a single 9 volt battery that means the opamp output would be arranged to sit midway at 4.5 volts and then it could go toward 9 volts or down toward zero volts.

The split supply is a recognised and standard way of powering opamps but for battery use single rail operation can be more convenient.

If your speakers go to 40 Hz then you need the reponse to go lower than that by some margin in order that the 40Hz level is un-attenuated. A typical figure would be around 5 Hz.
Quote:
Originally Posted by indianajo View Post
If you look at op amp datasheets (like on datasheetcatalog.com) you will find they have a drawing that shows how close you can get the input to the supply voltage before they stop working. Plotted against the supply voltage, usually. This means the ground symbol in your drawing post one, is 1/2 way in between the voltages you put on pins 4 (-v) and 8 (+v) of your DIP package op amp.
So the split supply doesn't use a lot of current in the middle, the ground place. Rather than monkey with replacing 9v batteries all the time (at $8 the pair, starting last week), I found a way with two 5 Watt 8v zener diodes and a couple of resistors to turn a DC wall transformer (18 VDC) into a split supply. With only one op amp you could probably get away with cheaper 3 W zener diodes. Schematic is in the last post of Improving a "Disco mixer" to mid-fi performance If you have a 24v wall supply from the charity resale shop, you can use 11v zeners, With a 32 V printer/fax/copier wall transformer you can use +-15 v zeners. The maximum input signal you can mix is roughly +V - (-V) - 4, so my +-8v mixer handles a 9 Vac radio output just fine.
Copying other people schematics is the easiest way to "calculate" the input and output capacitors. I've used .22 uf on the input with 10kohm input impedance, but .1 is cheaper if you have to buy them. 10 uf on the output is usual.
741 sounds vile, TL071 sound nice but latches up (stops working) if you get the input too close to the supply voltage even once. Note the power supply decoupling capacitors (+ to - to ground) are not on your schematic but are necessary for anything faster (slew rate) than a 741 or 4558. 4558 has mediocre sound, NE5532 is better with no latchup and no capacitor required around the feedback resistor. But 5532 comes in the wrong package a lot, have to carefully check you're getting 8 pin dip package.
If you're going to build something, 8 pin DIP package is nice, watch what package you order. In the US mcmelectronics has some nice cheap ($2) dip project boards, there is something similar in France but I lost the link when I had to reload the operating system. Vector board is $10 a slice.
A steel box is useful to keep hum from the transformer away from the op amp, and chokes on the power coming in keep lamp dimmer/switcher power supply/CB radio trash coming in the power lines. A 100 pf cap to ground on each input keeps radio trash from coming in that way.
Have fun.
Thanks a lot for the explaination.
So, basically what I need to do is to create a -6V and + 6V from a 12V DC supply?
  Reply With Quote
Old 9th December 2012, 04:33 PM   #13
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Quote:
Originally Posted by 2ndIdentity View Post
Thanks a lot for the explaination.
So, basically what I need to do is to create a -6V and + 6V from a 12V DC supply?
In some form yes. Here is your circuit re-arranged for a single supply. The two extra resistors are made equal in value and chosen to be high enough that they draw little current from the supply. Again 10K is suitable. The capacitor is recommended and would be around 10uf to 47uf. It ties the opamp input to ground at AC and stops any stray pickup.

The resistors being equal set a voltage of Vsupply/2 on the op amp non inverting input.

For opamps with negative feedback (such as this circuit) a golden rule is "that the opamp output will do whatever is neccessary to keep the difference between the two inputs at zero volts. So with the non inverting input now biased to 6 volts the output also goes to 6 volts to keep the difference at zero. For AC signals (audio) the opamp can now swing equally above and below this 6 volts level. The caps have to fitted with correct polarity. The output cap should technically have a high value resistor from its output to ground to tie and define the cap output end to ground. This resistor can be around 100k
Attached Images
File Type: jpg Capture.JPG (66.8 KB, 70 views)
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 9th December 2012, 04:41 PM   #14
diyAudio Member
 
indianajo's Avatar
 
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
Quote:
Originally Posted by 2ndIdentity View Post
Thanks a lot for the explanation.
So, basically what I need to do is to create a -6V and + 6V from a 12V DC supply?
If you have a 12 VDC supply from a wall plug transformer you can get about +5 & -5V out of it (buy 5.1 v zener diodes). 10v-4v=6v means you could handle signals up to about 6 v peak to peak with that. Okay for CD players but maybe a little bit marginal on computer signals. A 12 VDC rated naked e-form transformer, after you put a diode bridge on it and a capacitor you can get about 17 volt DC out of it at op amp currents. That you could go to +-7 v zener regulators.
I would say for experimentation go right to 4558D op amps, they are hard to s**** up and sound okay but hiss a bit. They don't latch up like TL071 if you hit the power supply rail, which I did I on my first op amp experiment and I would have never figured out about installing the input capacitors if the 4558 hadn't recovered automatically every cycle. I paid $.38 ea for my ST33078's which sound really good (hiss lower than the heater pilot light) but they require a 22 pf capacitor across the feedback resistor which might be one step too far for a newbie. Last time I looked at NE5532 they were about $.65 but my usual vendor only had the 14 pin DIP package which wouldn't fit my 8 pin DIP 4558 upgrade experiment. 5532 is supposed to really quiet and not require a feedback bypass capacitor. Oh, if you are only using one op amp of a dual DIP package, connect the inputs of the other to ground to prevent oscillation.
If you're in Europe I'll work harder to find the link to those cheap DIP package experimenter boards in France. In the US, mcm has the cheapest ones.
If you'll tell us if you're in Europe or western hemisphere, we can point out vendors that sell board op amp kits that have all the little parts already etched on them. Point to point soldering on a bare board by twisting the leads can be done, I have, but soldering to a pad on a kit board is easier to get right the first time.
Good luck.
__________________
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

Last edited by indianajo; 9th December 2012 at 05:00 PM.
  Reply With Quote
Old 9th December 2012, 06:42 PM   #15
diyAudio Member
 
Join Date: Sep 2004
Location: UK
This has veered off out of range a bit!

The OP was asking for help on listening to 'phone or laptop through his speakers and offered a MIXER circuit after searching.

Unless you WANT to listen to both signals at the same time you do not need a mixer, you need a switch! Somewhat simpler and lower tech!

But keep on asking - the only way to learn!
  Reply With Quote
Old 9th December 2012, 08:39 PM   #16
diyAudio Member
 
Join Date: Dec 2012
Quote:
Originally Posted by Mooly View Post
In some form yes. Here is your circuit re-arranged for a single supply. The two extra resistors are made equal in value and chosen to be high enough that they draw little current from the supply. Again 10K is suitable. The capacitor is recommended and would be around 10uf to 47uf. It ties the opamp input to ground at AC and stops any stray pickup.

The resistors being equal set a voltage of Vsupply/2 on the op amp non inverting input.

For opamps with negative feedback (such as this circuit) a golden rule is "that the opamp output will do whatever is neccessary to keep the difference between the two inputs at zero volts. So with the non inverting input now biased to 6 volts the output also goes to 6 volts to keep the difference at zero. For AC signals (audio) the opamp can now swing equally above and below this 6 volts level. The caps have to fitted with correct polarity. The output cap should technically have a high value resistor from its output to ground to tie and define the cap output end to ground. This resistor can be around 100k
This is so clear now.
I have saw so many different types of split supply circuit.
This is by far the simplest.
I guess this will do the job since I am not really amplifying (unity) the source?

Quote:
Originally Posted by indianajo View Post
If you have a 12 VDC supply from a wall plug transformer you can get about +5 & -5V out of it (buy 5.1 v zener diodes). 10v-4v=6v means you could handle signals up to about 6 v peak to peak with that. Okay for CD players but maybe a little bit marginal on computer signals. A 12 VDC rated naked e-form transformer, after you put a diode bridge on it and a capacitor you can get about 17 volt DC out of it at op amp currents. That you could go to +-7 v zener regulators.
I would say for experimentation go right to 4558D op amps, they are hard to s**** up and sound okay but hiss a bit. They don't latch up like TL071 if you hit the power supply rail, which I did I on my first op amp experiment and I would have never figured out about installing the input capacitors if the 4558 hadn't recovered automatically every cycle. I paid $.38 ea for my ST33078's which sound really good (hiss lower than the heater pilot light) but they require a 22 pf capacitor across the feedback resistor which might be one step too far for a newbie. Last time I looked at NE5532 they were about $.65 but my usual vendor only had the 14 pin DIP package which wouldn't fit my 8 pin DIP 4558 upgrade experiment. 5532 is supposed to really quiet and not require a feedback bypass capacitor. Oh, if you are only using one op amp of a dual DIP package, connect the inputs of the other to ground to prevent oscillation.
If you're in Europe I'll work harder to find the link to those cheap DIP package experimenter boards in France. In the US, mcm has the cheapest ones.
If you'll tell us if you're in Europe or western hemisphere, we can point out vendors that sell board op amp kits that have all the little parts already etched on them. Point to point soldering on a bare board by twisting the leads can be done, I have, but soldering to a pad on a kit board is easier to get right the first time.
Good luck.
Wow, those are some tips!
Do you mind attaching simple schematics so that I can understand them better?
Or just link me to somewhere so that I can study them.
I am from Singapore by the way.
Gonna update my location soon.

Quote:
Originally Posted by cliffforrest View Post
This has veered off out of range a bit!

The OP was asking for help on listening to 'phone or laptop through his speakers and offered a MIXER circuit after searching.

Unless you WANT to listen to both signals at the same time you do not need a mixer, you need a switch! Somewhat simpler and lower tech!

But keep on asking - the only way to learn!
I want to listen to both sources at the same time!
Yeah, I previously intended to do a switch but I thought,"hey, why not learn something new!"
So far the community here is great!

Last edited by 2ndIdentity; 9th December 2012 at 08:47 PM.
  Reply With Quote
Old 9th December 2012, 10:38 PM   #17
diyAudio Member
 
indianajo's Avatar
 
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
Well, the DIP project boards MCMelectronics is selling are made in Taiwan by Datek, so I imagine somebody can get them in Singapore. I find soldering to DIP legs at their 0.100" spacing extremely difficult on perforated board, whereas the ones with the pads make it kind of easy. I used 8 pin sockets, phosphor bronze sockets, so all the heat of soldering went into the socket and not the IC which I plugged in later.
The 2 IC board is Datek #12-611b and the 4 IC board is Datek 12-617b. There is no use giving you a listing on US or Netherlands kit builders, the shipping cost would be astronomical. My RA88a 4 input mixer was made in Japan by Herald Electronics, it used 4558's but there were a lot of mistakes. They had no input capacitors, they had the e-core transformer right next to the op amps, and the AC power switch right next to the op amps too. There was a lot of hum until I replaced the internal transformer with a wall transformer and the 2 zener diodes and resistors and capacitors for the split supply. I had to isolate the RCA jacks from the case ground, also. There were no .1 uf ceramic power supply bypass caps on the power supplies, which is okay for 741's and 4558's but not any op amp quieter or faster. The Herald kit had great slide potentiometers, though, for gain control.
__________________
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

Last edited by indianajo; 9th December 2012 at 10:40 PM.
  Reply With Quote
Old 9th December 2012, 10:48 PM   #18
diyAudio Member
 
Join Date: Dec 2012
I am going to head down to the stores here to have a look at what they have.
Will have a look at your suggestions if I find them.
And yeah, I figured it is best to use a socket for the amps to avoid the heat from soldering from destroying the chip besides being able to swap different amps.
  Reply With Quote
Old 10th December 2012, 07:23 PM   #19
diyAudio Member
 
Join Date: Dec 2012
Hi guys,

I just wanna thank both of you for being so patiently answering my questions.
I've gotten and put all the component together on the breadboard; and I shall say, the mixer worked great and sounded extremely awesome! No audible noise, humming and stuffs!
  Reply With Quote
Old 10th December 2012, 07:47 PM   #20
diyAudio Member
 
indianajo's Avatar
 
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
Congratulations.
__________________
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300
  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
mixer circuits (looking for simple, but very high quality)... dfeweer Analog Line Level 6 21st December 2011 09:58 PM
Explanation of superiority of Linux for audio? mr_push_pull PC Based 2 3rd December 2011 07:24 PM
Mixer Section explanation help needed. graygem Analog Line Level 1 12th May 2011 04:56 PM
mixer circuits jonathanmatenga Multi-Way 1 9th August 2007 07:01 PM
request for an explanation of "Q" jaygeorge1979 Multi-Way 11 19th January 2006 06:56 AM


New To Site? Need Help?

All times are GMT. The time now is 09:46 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