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Offline Chuck

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Circuit help needed for battery line mixer
« on: November 15, 2006, 09:56:25 AM »
I want to build a nice, quiet, full bandwidth, 12v DC powered 4 input, 2 output line mixer. I've seen the passive designs, but there is a lot of signal loss there.
Does anyone have a good circuit for this? I know it's easy to do with op-amps, but op-amps need a bi-polar power supply, unless you do single supply biasing, which adds noise and complexity. A simple transistor circuit would be best, as long as it's 12v powered and very clean.

I saw this:
http://www.aaroncake.net/circuits/mixer1.htm

Parts:

R1, R3 2 10K Pot 
R2, R4 2 100K 1/4 W Resistor 
R5 1 6.8K 1/4 W Resistor 
C1, C2, C3 3 0.1uF Capacitor 
Q1 1 2N3819 Junction FET 
MISC 1 Wire, Shielded (Metal) Case, Phono Or Other Plug For Output
 
Is this a good circuit? Is the transistor the best one for the task?

Can anyone help?
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline Chuck

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Re: Circuit help needed for battery line mixer
« Reply #1 on: November 16, 2006, 12:21:10 PM »
I just found this one...
Does anyone see any problems with this one? Would this be a better choice?
I'd rather run it on 12v DC. Would that change anything?
Maybe use a different op-amp?
I could do without the pan-pot too.

Parts:
P1,___________100K   Linear Potentiometer
P2_____________10K   Linear Potentiometer

R1,R2,_________15K   1/4W Resistors
R3,R4,R11,R12_100K   1/4W Resistors
R5,R6__________22K   1/4W Resistors
R7,R8_________390K   1/4W Resistors
R9,R10________560R   1/4W Resistors
R13___________220R   1/4W Resistor

C1,C2_________330nF   63V Polyester Capacitors
C3,C8_________100µF   25V Electrolytic Capacitors
C4,C5__________10pF   63V Ceramic Capacitors
C6,C7___________4µ7   63V Electrolytic Capacitors

IC1___________TL062   Low current BIFET Dual Op-Amp





--------------------------------------------------------------------------------

Circuit description:

The schematic of this circuit is drawn as a stereo unit to better show the input Main Fader and Pan-Pot connections. The TL062 chip contains two TL061 op-amps into the same 8 pin case and is wired as two virtual-earth mixer amplifiers having a voltage gain of about 4, to compensate for losses introduced in the passive Pan-Pot circuitry. Therefore, total voltage-gain is 1.
Each channel added to the mixer must include the following additional parts:
P1, P2, R1, R2, R3, R4, C1 and C2.
These parts must be wired as shown in the above circuit diagram, connecting R3 and R4 to pin #2 and pin #6 of IC1 for Right and Left channel respectively. These IC1 pins are the "virtual-earth mixing points" and can sum together a great number of channels.

Notes:

Current drawing for one stereo Main Mixer Amplifier Module is 800µA.
Frequency response is 20Hz to 20KHz - 0.5dB.
Total Harmonic Distortion measured @ 2V RMS output = < 0.008% @ 1KHz; < 0.017% @ 10KHz.
THD is 0.005% @ 1V RMS output.
Maximum undistorted output voltage: 2.8V RMS.
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline Church-Audio

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Re: Circuit help needed for battery line mixer
« Reply #2 on: November 16, 2006, 12:47:54 PM »

Looks good, I would lose the pan pots and replace it with a 1% resistor metal film. As a mater of fact, I would replace all resistors with 1% metal film. The caps c6-7 I would replace with 10uf 3uf is too low for an output coupling cap. I would check out also c1-c2. So for P2, if that is the pan I would replace it with a 5k 1% resistor, and I would hand match all of the resistors used to substitute the pan control so they are even closer then 1%. That way your stereo image is 100% correct. The distortion measurements mean nothing to me, because they did not spec at what input voltage this distortion is at. This is a critical factor, its no good having a preamp or mixer with a distortion of 0.004% if its at a input signal of say -30db :) This is a common trick among circuit designers, I measure my distortion figures at the real input level the preamp in question is likely to face day to day. I then I add 6 db to that input and then I measure the distortion. Build the circuit first do you have a breadboard? just wondering.

for warranty returns email me at
EMAIL Sales@church-audio.com

Offline Chuck

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Re: Circuit help needed for battery line mixer
« Reply #3 on: November 16, 2006, 01:23:49 PM »

Looks good, I would lose the pan pots and replace it with a 1% resistor metal film. As a mater of fact, I would replace all resistors with 1% metal film. The caps c6-7 I would replace with 10uf 3uf is too low for an output coupling cap. I would check out also c1-c2. So for P2, if that is the pan I would replace it with a 5k 1% resistor, and I would hand match all of the resistors used to substitute the pan control so they are even closer then 1%. That way your stereo image is 100% correct. The distortion measurements mean nothing to me, because they did not spec at what input voltage this distortion is at. This is a critical factor, its no good having a preamp or mixer with a distortion of 0.004% if its at a input signal of say -30db :) This is a common trick among circuit designers, I measure my distortion figures at the real input level the preamp in question is likely to face day to day. I then I add 6 db to that input and then I measure the distortion. Build the circuit first do you have a breadboard? just wondering.



Chris:

Thank you very much for your response.
Basically, what I want is two stereo inputs with one stereo output. Both inputs have gain control. Does the single supply biasing for this circuit comprimise it in any way? I just want the cleanest way to combine two line level sources. I'm not entirely sure how to remove the pan pot.
The designer also noted that the pan pot drops the gain, so there is gain added by the op-amp to compensate.
I do not have a bread board. I usually just use a perfboard, and twist the leads togther as needed before soldering to test.

Would using 12v DC make a difference in this circuit? Would I have to change any of the components?


Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline Church-Audio

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Re: Circuit help needed for battery line mixer
« Reply #4 on: November 16, 2006, 01:50:33 PM »

Looks good, I would lose the pan pots and replace it with a 1% resistor metal film. As a mater of fact, I would replace all resistors with 1% metal film. The caps c6-7 I would replace with 10uf 3uf is too low for an output coupling cap. I would check out also c1-c2. So for P2, if that is the pan I would replace it with a 5k 1% resistor, and I would hand match all of the resistors used to substitute the pan control so they are even closer then 1%. That way your stereo image is 100% correct. The distortion measurements mean nothing to me, because they did not spec at what input voltage this distortion is at. This is a critical factor, its no good having a preamp or mixer with a distortion of 0.004% if its at a input signal of say -30db :) This is a common trick among circuit designers, I measure my distortion figures at the real input level the preamp in question is likely to face day to day. I then I add 6 db to that input and then I measure the distortion. Build the circuit first do you have a breadboard? just wondering.



Chris:

Thank you very much for your response.
Basically, what I want is two stereo inputs with one stereo output. Both inputs have gain control. Does the single supply biasing for this circuit comprimise it in any way? I just want the cleanest way to combine two line level sources. I'm not entirely sure how to remove the pan pot.
The designer also noted that the pan pot drops the gain, so there is gain added by the op-amp to compensate.
I do not have a bread board. I usually just use a perfboard, and twist the leads togther as needed before soldering to test.

Would using 12v DC make a difference in this circuit? Would I have to change any of the components?



Disregard what I said about  the 5 k resistor, and simply cut the pan pot out of the circuit. put nothing between the two resistors after the input level pot. I should warn you that the gain on this mixer is all 100% all the time this might increase your noise floor. But if the design is good it should be OK. It would be simple to change the feedback loop resistor to change the gain. If more or less is needed. It all depends on the type of input level this mixer will see what are you feeding it? Last but not least GET A BREAD BOARD they only cost $10 to $50 for a good one and they will save hours of reworking with a soldering iron, besides you might burn your fingers :) Go out and get one dammit don't be a cheap skate.

for warranty returns email me at
EMAIL Sales@church-audio.com

Offline Chuck

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Re: Circuit help needed for battery line mixer
« Reply #5 on: November 16, 2006, 02:19:27 PM »

Looks good, I would lose the pan pots and replace it with a 1% resistor metal film. As a mater of fact, I would replace all resistors with 1% metal film. The caps c6-7 I would replace with 10uf 3uf is too low for an output coupling cap. I would check out also c1-c2. So for P2, if that is the pan I would replace it with a 5k 1% resistor, and I would hand match all of the resistors used to substitute the pan control so they are even closer then 1%. That way your stereo image is 100% correct. The distortion measurements mean nothing to me, because they did not spec at what input voltage this distortion is at. This is a critical factor, its no good having a preamp or mixer with a distortion of 0.004% if its at a input signal of say -30db :) This is a common trick among circuit designers, I measure my distortion figures at the real input level the preamp in question is likely to face day to day. I then I add 6 db to that input and then I measure the distortion. Build the circuit first do you have a breadboard? just wondering.



Chris:

Thank you very much for your response.
Basically, what I want is two stereo inputs with one stereo output. Both inputs have gain control. Does the single supply biasing for this circuit comprimise it in any way? I just want the cleanest way to combine two line level sources. I'm not entirely sure how to remove the pan pot.
The designer also noted that the pan pot drops the gain, so there is gain added by the op-amp to compensate.
I do not have a bread board. I usually just use a perfboard, and twist the leads togther as needed before soldering to test.

Would using 12v DC make a difference in this circuit? Would I have to change any of the components?



Disregard what I said about  the 5 k resistor, and simply cut the pan pot out of the circuit. put nothing between the two resistors after the input level pot. I should warn you that the gain on this mixer is all 100% all the time this might increase your noise floor. But if the design is good it should be OK. It would be simple to change the feedback loop resistor to change the gain. If more or less is needed. It all depends on the type of input level this mixer will see what are you feeding it? Last but not least GET A BREAD BOARD they only cost $10 to $50 for a good one and they will save hours of reworking with a soldering iron, besides you might burn your fingers :) Go out and get one dammit don't be a cheap skate.



Thanks again Chris,

No, money isn't why I don't have a breadboard. It just never occured to me that it would be useful...
I will take your advice and get one. 

Yes, I realized that the circuit has a fix gain. I will probably lower it some. So, if I remove the pan pot, then I can connect the other stereo input essentially at the same place the pan-pot is now, right? I'm going to re-draw it and re-post later, to make sure I have it all figured out correctly...

As for the capacitors, should I replace the ceramics with something else? Tantalum maybe? This part of it is like the "black magic", I'm a bit lost as to what substitutions to make for the very best sound/ performance.
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline Chuck

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Re: Circuit help needed for battery line mixer
« Reply #6 on: November 16, 2006, 05:02:52 PM »
Isn't 100k a little high for the input pot? and 100k for R3  ???

Is this passive input section going to be OK? It seems like a brute force way to combine the inputs.

I wish there was just an easy to follow (already thought out) schematic for this. It can't be that difficult right?

I guess I just don't understand the part of the circuit that makes the op-amp single supply rather than bi-polar supply. I wonder if it compromises the circuit in some way?
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline Chuck

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Re: Circuit help needed for battery line mixer
« Reply #7 on: November 16, 2006, 08:02:51 PM »
Circuit reworked to remove the pan pots and simplify a bit. I removed the coupling capacitors in an attempt to avoid the distortions generated from them. I also lowered the input pots value from 100k to 10k.

Any help, advice is appreciated.
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline ghellquist

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Re: Circuit help needed for battery line mixer
« Reply #8 on: November 18, 2006, 05:34:43 AM »
You have to insert the coupling capacitors again (C1 and C2) in original circuit. These are necessary to remove any DC bias you get from the inputs. And no need to worry, they do not add any significant amount of distortion.

Gunnar

Offline Chuck

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Re: Circuit help needed for battery line mixer
« Reply #9 on: November 18, 2006, 09:51:11 AM »
Yeah, I realized that. I'll post the revised circuit soon.
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline Church-Audio

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Re: Circuit help needed for battery line mixer
« Reply #10 on: November 18, 2006, 09:56:59 AM »
Yeah, I realized that. I'll post the revised circuit soon.
Use 10uf 63 volt Poly caps in the input section.
for warranty returns email me at
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Offline Chuck

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Re: Circuit help needed for battery line mixer
« Reply #11 on: November 21, 2006, 04:06:20 PM »
Chris, is there a brand and model number that you prefer? Also, wat are the best caps for bypassing at the + and - side of the op-amps? I also know that people bypass around those DC blocking caps too.
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline kuuan

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Re: Circuit help needed for battery line mixer
« Reply #12 on: November 21, 2006, 04:41:56 PM »
sorry for plunging in.
I want to build a mic mixer and wonder if I could use Chuck's circuit.

Would it work mic level, or would I have go mic > preamp > mixer?
To mix mics I'd again need the pan pots, but should I keep the other mods of Chris?

Is my drawing correct?
If coming from my preamps could it be a good idea to omit the 100k input pots? Chuck, in your drawing you had made them 10k, but according to the original circuit the input pots are 100k, the pan pots are 10k. Was this on purpose, also that you omited R 9 and 10 and C 6 and 7 at the output section?

Are pan pots regular pots?


« Last Edit: November 21, 2006, 04:44:15 PM by kuuan »
Everything you do through out the day, every thought and every feeling leaves an impression stored inside you.
These impressions create tendencies, their sum total is your character.
gear: SP-CMC8+AT853 cards+omnis, AT822>DIY preamp>iRiverH120rockboxed

Offline Chuck

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Re: Circuit help needed for battery line mixer
« Reply #13 on: November 21, 2006, 07:25:25 PM »
I'm still working this. I'm debating now, whether to add two more channels for microphone inputs. I have been looking at the INA217 and the microphone pre-amp circuit TI has in the literature for it. I am going to do more research, before I build this. I want to get it right and use good layout and probably point to point wiring, as those home-made circuit boards are not for me.

That circuit you re-drew is for a line mixer.
I figured the 100k input pots were a bit high, and may cause exsesive noise. 10k log pots should work. I'm looking at the Panasonic EVJ-Y10F03A14, dual 10k log pot, that the headphone amp builders use. It's relatively inexpensive and easily bought at Digi-Key. As far as the pan pots, you can buy some that have the center nesting, which may be useful. Again Panasonic makes some. I didn't want to include the panning, so I omitted it. Unfortunately, you really do need the output capacitor, as with the single supply biasing there will be DC offset at the output.

If I go with making this a microphone pre-amp too, I may power it with those small SLA's, so I can get clean phantom power. Some of those 6v cells can be split off and used to power pre-amp/ mixer section.
Reality is merely an illusion, albeit a very persistent one.

Microphones: AKG C 480 B comb-ULS/ CK 61/ CK 63, Sennheiser MKE 2 elements,  Audix M1290-o, Micro capsule active cables w/ Naiant PFA's, Naiant MSH-1O, Naiant AKG Active cables, Church CA-11 (cardioid), (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlebox, Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Sound Devices MixPre-6, iRiver iHP-120 (Rockboxed & RTC mod)

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline kuuan

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Re: Circuit help needed for battery line mixer
« Reply #14 on: November 22, 2006, 07:07:05 AM »
I shall observe with interest how your final project will look like.
Would it work as a mic mixer though if each channel gets amplified by my DIY preamps? ( http://taperssection.com/index.php?topic=71782.0;all )

I have problems finding good pots here in austria. ( Digi-Key runs seperate sites for different countries but at their austria site the panasonic pot you mentioned is not sold, though it is at their US site, even though the order will be sent from the US and a charge of 31 Euros, over 40 US!! is added for the service. )
Found some at a conrad site which has shops in austria and will be much cheaper for me to buy from, but did not find any metal film rotary switch as recommended by Chris for my preamp.

pots, probably the best I found are:

'Vishay' branded socalled 'Drahtpotentiometer' in german, translated 'wire-potentiometer' with 10 steps, can be had in mono only, costing 8 euro each
stereo pots branded 'Alps', e.g. model number: RK27112 50KBX2CC, costing 14 Euro each.

Do you know these brands? Are they recommendable? They are expensive...wonder if I can find chaeper pots which do a good enough job ( specially for me, a beginner )
« Last Edit: November 22, 2006, 07:09:15 AM by kuuan »
Everything you do through out the day, every thought and every feeling leaves an impression stored inside you.
These impressions create tendencies, their sum total is your character.
gear: SP-CMC8+AT853 cards+omnis, AT822>DIY preamp>iRiverH120rockboxed

 

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