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Skema Simple line mixer

Wednesday, December 2, 2009

I advised this ambit for one acquaintance of abundance to be acclimated as a baby carriageable DJ mixer. The ambit is an audio mixer ambit so simple as it can be. There are two bifold logarithmic potentiometers in the ambit to acclimatize the ascribe arresting levels and some resistors to do the absolute mixing. The ambit is absolutely passive, so no ability accumulation is needed.

The ambit is acceptable to be uses as a mixer amid two band akin sources and one HIFI amplifier input. This ambit accept been auspiciously acclimated for bond signals anatomy two CD players or computer soundcard and CD players. There are abounding situations area simple mixer would be advantageous and commercially accessible mixer desks are too big-ticket and big.

This simple band mixer has two drawbacks: it attenuates the arresting all the time (even sliders set to maximum) and the achievement impedance is absolutely high. The aboriginal botheration can be apparent by aloof axis a little added aggregate in the amplifier. Aerial ouput impedance is no botheration back affiliated to aerial impedance amplifier ascribe with abbreviate affairs (few meters).

In the account beneath you see the schematic of the accomplished mixer circuit. The potentiometer slides which are absolutely central one bifold potentiometers are affiliated calm application one line. Every ascribe and achievement pin has agnate arena arresting on the appropriate ancillary of the arresting line.

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Gambar Skema Dynamic microphone to electret microphone input

* Summary of circuit features: Circuit which works as an preamplifier which allows you to replace an electret microphone with a dynamic microphone.
* Circuit protection: No special protection circuits used
* Circuit complexity: Very simple one transistor circuit
* Circuit performance: Worked well, although distortion and noise performance is not very good (but usable for many non-hifi applications)
* Availability of components: Uses common and easily available components
* Design testing: I have built this circuit and it worked well with Sound Blaster 16 sound card
* Power supply: 3-9V current limited power from electret microphone input (same as normally supplied to two wire electret capsule)
* Estimated component cost: Electronics components cost less than $10 including connectors
* Safety considerations: No special electrical safety considerations.

Circuit description

This is a simple microphone preamplifier circuit which you can use between your dynamic microphone and any equipment designed to work with an electret microhone (2 wire connection to electret capsule). This amplifier amplifies the low level signal to the levels used by electret microphone input and uses the power from the device.

The circuit is a simple one transistor amplifier to convert the sub-millivolt level voltage from electret microphone to current changes as generated by electret capsule.

Component list

R1 470 kohm
C1 220 nF
Q1 BC547

Example of using the circuit

Connecting the circuit to 3.5 mm mono electret microphone input

The circuit below is a typical wiring
used with electret micrphones connected to 3.5 mm mono plig unput (as used in vidoe cameras and some portable audio recoders). Toy cna use the wiring below just by replacing the electret capsule on the left with my dynamic microphone amplifier circuit described above.

+------+ / \
| |-------------------------------- audio --------| |
| |mic+ \ /
| mike | +===+
| | | | 3.5mm mono plug
| | | |
| |mic- | |
| |---------------- ground -----------------------| |
+------+ | |
+=======+
| |

Connecting the circuit to soundcard

The circuit below is a wiring to connect a two wire electret capsule to Sound Blaster 16 soundcard (works with many other soundcards which use electret capsule also). The same wiring works well with my dynamic microphone circuit when you replace the electret capsule with my circuit.

+------+ / \
| |---------------+---------------- audio --------| |
| |mic+ | \ /
| mike | | +===+
| | +-------------- bias +5V -------| | 3.5mm plug
| | |===| to soundcard
| |mic- | |
| |---------------- ground -----------------------| |
+------+ | |
+=======+
| |

Basic electret circuit using external power

The circuit below is a typical electret microphone powering circuit. This works well with my adapter circuit when you put my circuit on the place fo the electret capsule in the circuit below.

vcc
O
|
/
\
/
\ EQUAL TO REQUIRED IMPEANCE
/ EX.= 1000 Ohm
\
|
| CAPACITOR MOST ANY VALUE 10uF 16v
|---| | + | /
| |---0----| |------- AUDIO OUT
| | | \
| |----O--------------
|---| |
|
-----
---

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Skema Isolator transformer for audio lines

If you appetite to do the arena bend abolishment in audio path, you accept to cut the alive affiliation but canyon the accomplished audio range. The simplest and best accepted way to do the abreast is use audio agent which is ment for audio use. Transformers for audio use accept some problems like adulterated bass acknowledgment and attenuating in high-frequency response. Basically a agent slows bottomward aerial frequencies and acquiesce the low frequencies to canyon first, creating what we apperceive as a "fat/warm" tone. Inadequate abundance acknowledgment on the low end (rolloff at like 20Hz), causes low frequencies to be "slowed", acceptance the aerial frequencies to be heard first, this is perceived as "barky/ brittle". High-quality audio transformers awning accomplished audio bandage with adequate response, but those are absolutely expensive.

There are accessible fabricated circuits accessible from shops affairs car audio being (ground loops are usually botheration additionally in car environment). If you alive in USA, booty a attending in Radio Shack's archive on car electronics or analysis the Radio Shack Artefact Support pages which accept blueprint of Arena LP Isolator (270-0054) which amount about $15US. For added able artefact analysis JK Audio Pureformer Stereo Abreast Transformer. Those articles assume to be absolutely adequate for analytic arena bend problems in customer audio systems, but I accept not activated them myself. Europeans should booty a attending at their abutting banker which carriers Monacor products, because Monacor's new archive lists FGA-40 (Best.-Nr. 06.4370) Arena Isolators which are 1:1 audio abreast with 10 kohm impedance (look absolutely adequate on the catalogue).

For able audio use buy aerial affection bartering audio isolation/balancing transformers (those are actual accessible to accumulate about to break abrupt arena bend problems). DI-boxes are additionally acclimated to break arena bend problems in a PA situations area altered instruments are affiliated to bond desk. Best DI boxes are alive and are about abortive are accepting rid of apple loops and endlessly buzzes & hums etc. A GOOD acquiescent DI which provides abreast is the alone way to go.

Building yourself an audio abreast transformer

If you appetite to body one yourself, you accept to get two audio transformers which accept 1:1 transformation arrangement and greater than 1 kohm impedance. There are aerial affection audio transformers in the markes that accommodated those specs, but those can be absolutely expensive. Another advantage it to use 600:600 ohm abreast transformers broadly accessible for telecommunications and added uses. Those are not that aerial affection as adequate audio transformers, but can be able-bodied able for abounding not so ambitious multimedia applications like computer audio if adequate agent is selected.

Audio isolator schematic

I congenital some of my audio band isolators usign two aerial affection blast band coupling transformers which accept 600 ohm impedance (I congenital after some new ones application some aerial affection audio transformers). This is the best frequently agent blazon acclimated in accelerated modems. Best of those are absolutely wideband accessories (far added bandwidth than accepted 300-3400 Hz as acclimated in telephone). Application two of those transformers and few RCA connectors fabricated absolutely satisfactory (but not absolutely hifi) audio isolator. The affiliation is easy: affix primary ancillary of the agent to one audio adapter and accessory to other.

I acclimated EOP Z1612 transformers in my analysis ambit and got absolutely adequate abundance acknowledgment of +-1 dB from 40 Hz to 20 kHz as you can see in amount below. The bass abundance beneath 40 Hz is not good.

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Skema Audio amplifier output relay delay

Design and copyright by Tomi Engdahl 1998

This is a simple circuit which I built to one of my audio amplifier projects to control the speaker output relay. The purpose of this circuit is to control the relay which turns on the speaker output relay in the audio amplifier. The idea of the circuit is wait around 5 seconds ofter the power up until the spakers are switched to the amplfier output to avoid annoying "thump" sound from the speakers. Another feeature of this circuit is that is disconnects the speaker immdiatly when the power in the amplifier is cut off, so avoinding sometimes nasty sounds when you turn the equipments off.

Circuit diagram



Component list

C1 100 uF 40V electrolytic
C2 100 uF 40V electrolytic
D1 1N4007
D2 1N4148
Q1 BC547
R1 33 kohm 0.25W
R2 2.2 kohm 0.25W
RELAY 24V DC relay, coil resistance >300 ohm

Circuit operation

Then power is applied to the power input of the circuit, the positive phase of AC voltage charges C1. Then C2 starts to charge slowly through R1. When the voltage in C2 rises, the emitter output voltage of Q1 rises tigether with voltage on C2. When the output voltage of Q2 is high enough (typically around 16..20V) the relay goes to on state and the relay witches connect the speakers to the amplifier output. It takes typically around 5 seconds after power up until the relay starts to condict (at absolute time depends on the size of C2, relay voltage and circuit input voltage).

When the power is switched off, C1 will loose it's energu quite quicly. Also C2 will be charged quite quicly through R2. In less than 0.5 seconds the speakers are disconnected from the amplifier output.

Notes on the circuit

This circuit is not the most accurate and elegant design, but it has worked nicely in my small homebuilt PA amplifier. This circuit can be also used in many other applications where a turn on delay of few seconds is needed. The delay time can be increased by using bigger C2 and decreased by using a smaller C2 value. Note that the delay is not very accurate because of simplicity of this circuit and large tolerance of typical electrolytic capacitors (can be -20%..+50% in some capcitors).

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