321 lines
17 KiB
Markdown
321 lines
17 KiB
Markdown
# Conference Interpreter Unit
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[c3lingo.org](https://c3lingo.org) is doing the great job of translating many talks of the Chaos Communication Congress and other CCC-related events to multiple languages.
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But the required hardware for simultaneous translation is quite expensive to rent, even if it's "just" a specialized analog audio mixer.
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So the idea was born to design an easy to use hardware with the special requirements of our interpreters in mind.
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## Requirements
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The hardware unit should deliver the native audio (stage/ hall mix) to the interpreter's headset and provide a sum of all interpreter's microphone to the input of the video streaming/ recording chain.
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Mixing of the final translated audio (ducking the native audio with the translation) will be done as part of the streaming/ recording chain, so the interpreter unit should just provide the sum of all microphones.
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Normally just 2 interpreters will provide one translation, but demanding talks might require 3 people.
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So either 3 headphone inputs/ outputs should be provided or it must be possible to daisy-chain multiple units.
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The user interface of the unit should be as simple, as possible to decrease the risk of mis-configuration.
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This means, that no compressor and equalizer will be added in the input group.
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General requirements:
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- Line input of stage/ hall mix (native language) (XLR/ 6.3 mm balanced jack combo connector)
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- 3x Microphone input (XLR) (at first just dynamic microphones)
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* VU-Meter for each input channel. (Perhaps with special color scheme: too quiet, good, too loud, clipping)
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* Fader/ Potentiometer for gain control
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* On-Air switch (on/ off position, with state LED)
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* Temporary mute button (momentary switch)
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- 3x Headphone output (6.3 mm mono/ stereo (2x mono) jack)
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* Should output mix of native audio, own microphone and other translator's microphone
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* Potentiometer for output volume
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* Potentiometer for volume of own microphone in the mix
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* Potentiometer for volume of other two microphones in the mix
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- Outputs:
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* Sum of all translators (XLR/ 6.3 mm balanced jack combo connector)
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All inputs (besides the microphones) and outputs should:
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- expect/ deliver a nominal level of +6dBu (german TV broadcast standard, 0 dBu = 0,775 Veff)
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- be transformer balanced and galvanically isolated
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This results in a signal flow like this: 
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## Status
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### Tasks
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- [x] Requirements collection
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- [x] Electrical design draft/ proof of concept (breadboard)
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- [x] Proof of concept validation
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- [x] First PCB layout (prototyping modules)
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- [x] More testing/ validation
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- [ ] Second PCB layout + casing prototype
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- [ ] More testing/ validation
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Help is always appreciated!
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### Implemented Requirements
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- [x] Microphone input
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- [x] Line input
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- [x] Microphone summing and line output driver
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- [x] Adjustable headphone mix and output volume
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- [ ] ESD protection and galvanic isolation of line inputs and outputs
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- [x] VU meter (own PCB)
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- [ ] VU meter (integrated in front panel PCB)
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- [ ] Mute and On-Air buttons
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## Electrical Design
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This chapter contains some notes on the electrical design.
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Currently just the sources of the used circuit designs.
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### Microphone Input
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#### Preamplifier
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For the microphone preamp, we are using the NE5534 low-noise opamp with a circuit design from [circuitlib microphone pre-amp](https://www.circuitlib.com/index.php/schematics/product/29-balanced-microphone-preamplifier).
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#### Controllable Amplification
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In a normal mixer, you would be able to lower the microphone's volume to zero.
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But in our case we just need on/ off and some gain range to adjust for different microphones and loudness of different people.
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TODO: Integrate the On-Air button with it's LEDs
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### Line Input/ Input Module
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The line input must not be amplified at all, because loudness control of the headphones is done by the headphone amplifier section.
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But the differential line-level signal must be converted to a single-ended signal by the input stage.
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The current design uses a LM833N opamp to convert the balanced signal into a single ended signal and has a second LM833N to provide some degree (+- 6 dB) of "factory" adjustment.
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The second part of that circuit was taken from the [circuitlib audio mixer tutorial](https://www.circuitlib.com/index.php/tutorials/product/39-how-to-build-an-audio-mixer).
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TODO: How to achieve galvanic isolation?
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### Summing
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Summing is needed in two places: Creating the sum of all microphones (not adjustable, fixed output gain) and for the headphone mix (one input level adjustable).
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A simple summing circuit using one operational amplifier is enough for our application, like in [circuitlib audio mixer tutorial](https://www.circuitlib.com/index.php/tutorials/product/39-how-to-build-an-audio-mixer).
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The mixer design uses inverting op-amp circuits, because they require less components and signal routing.
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Normally an audio mixer should take care of adding signals in-phase, because otherwise two microphones might cancel each other out.
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In our case, there are just two types of summing: All microphones for the interpreter unit's line-out and the individual headphone mixes.
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Because the stage input is quite independent of the interpreter's microphones, no special phase/ inversion considerations are needed.
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And the microphones connected to our unit will experience the same inversions anyways.
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### Line Output Driver
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Line Output conversion is done by the [DRV134](https://www.ti.com/product/DRV134) IC.
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TODO: How to achieve galvanic isolation?
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### Headphone Output Driver
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The headphone output needs a maximum output power of about 0.1 W and should put the mono signal on both stereo channels of the TRS jack.
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For the first draft, we're using one LM386 audio power amplifier even though it has a quite high minimal amplification of factor 20.
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### VU Meter
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When searching for VU meter circuits, many use the LM3916 LED bar graph driver, which already has the right scaling built in.
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But this chip is obsolete and not produced any more, so we designed our own chain of comperators to drive a set of LEDs.
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## User Interface
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The user interface should enable the interpereters to adjust their microphone gain and headphone mix on their own.
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Additionally, a (permanent) on/off switch, as well as a (temporary) mute button should be present.
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A possible UI layout might look like this: 
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### Potentiometers
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We need some single and dual channel logarithmic scale potentiometers, which are matching in size, for:
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- top plate interface (all vertical style, threaded collar would be nice):
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* 1 single channel for the input gain (resistance doesn't matter)
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* 2 single and 1 stereo channel for the headphone mix (ideally 50K, b/c 3 will be in parallel)
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- front plate next to the headset jacks (horizontal style, threaded collar not needed):
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* 1 single channel for the headphone volume (ideally 50K, b/c that's already tested)
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Possible knobs may be:
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- (A) Re'an F311/ F313 series (11/ 13 mm diameter) -- 0.40 €/ 0.55 €:
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Boring: 9.0 mm D-style hole + 0.0 mm nut cover section = 9.0 mm
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- (B) Re'an P670 series (12 mm diameter/ 16 mm at bottom) (alt. Davies Molding 1101) -- 0.78 €:
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Boring: 7.5 mm D-style hole + 4.5 mm nut cover section = 12.0 mm
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Nut cover: 12.9 mm diameter (M7 nut is 12.5 mm corner to corner)
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- (C) Re'an P300 series (11 mm diameter/ 15 mm at bottom):
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Boring: 9.0 mm D-style hole + 3.0 mm nut cover section = 12.0 mm
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Nut cover: ? mm diameter (M7 nut is 12.5 mm corner to corner)
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- ~~(D) Cliff K87MAR series/ RS Pro 777-73xx: 7.5 mm hole depth + 4.5 mm skirt = 12 mm, inner size of skirt 12 mm (measured)~~
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~~Notes: D-style boring has wrong size (5 mm instead of 4.5 mm flatted)~~
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Potentiometers from Alps Alpine seem to have a decent quality in a small package size and quite affordable price.
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From their lineup, the RK09K/D, RK11/12/14, RK09L and RK097 series are left considering our requirements (mouser prices without VAT, shortlist marked bold):
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- Alps Alpine Series RK09K/D (6 mm D-style (4.5 mm) shaft):
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* vertical (top plate):
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+ **single channel: 10K, 15 mm -- RK09K1130AJ3 -- 0.91 €**
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actual shaft length (dwg. 2): 7.4 mm (6 mm flattened)
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_matching knobs: A_
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+ dual channel: 10K, 15 mm -- RK09K12C0A19 -- 1.23 €
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actual shaft length (dwg. 10): 7.4 mm (6 mm flattened)
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_matching knobs: A_
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+ **dual channel: 50K, 20 mm -- RK09K12C0A2S -- 1.44 €**
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actual shaft length (dwg. 10): 12.4 mm (7 mm flattened)
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_matching knobs: C, B (depending on front plate thickness)_
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* horizontal (front plate):
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* single channel: 10K, 15 mm -- RK09K1110A2S -- 0.67 €
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actual shaft length (dwg. 1): 7.4 mm (6 mm flattened)
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_matching knobs: A_
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* **single channel: 50K, 15 mm -- RK09K1110B1R -- 0.67 €**
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actual shaft length (dwg. 6): 7.4 mm (6 mm flattened)
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_matching knobs: A_
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- Alps Alpine Series RK09L (6 mm D-style (4.5 mm) shaft, collar with M7 thread):
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* vertical (top plate):
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+ **single channel: 10K, 12.5 mm -- RK09L1140A5E -- 1.61 €**
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actual shaft length (dwg. 2): 7.5 mm (7 mm flattened) + 5 mm thread length
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_matching knobs: A_
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+ **dual channel: 10K, 15 mm -- RK09L12D0A1W -- 1.64 €**
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actual shaft length (dwg. 4): 10 mm (7 mm flattened) + 7 mm thread length
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_matching knobs: C, B (depending on front plate thickness)_
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+ dual channel: 10K, 20 mm -- RK09L12D0A1T -- 1.64 €
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actual shaft length (dwg. 4): 15 mm (12 mm flattened) + 7 mm thread length
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_matching knobs: Unknown, b/c of quite long shaft_
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* horizontal (front plate):
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+ **single channel: 10K, 15 mm -- RK09L1120A2S -- 1.62 €**
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actual shaft length (dwg. 1): 10 mm (7 mm flattened) + 5 mm thread length
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_matching knobs: C, B (depending on front plate thickness)_
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+ single channel: 10K, 20 mm -- RK09L1120A69 -- 1.30 €
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actual shaft length (dwg. 1): 15 mm (12 mm flattened) + 7 mm thread length
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_matching knobs: Unknown, b/c of quite long shaft_
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+ dual channel: 50K, 15 mm -- RK09L12B0A31 -- 1.78 €
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actual shaft length (dwg. 3): 10 mm (7 mm flattened) + 5 mm thread length
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_matching knobs: C, B (depending on front plate thickness)_
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- ~~Alps Alpine Series RK11K/12L/14K~~: no suitable options
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- ~~Alps Alpine Series RK097 (6 mm D-style (4.5 mm) shaft, collar with M7 thread)~~: Only horizontal style and quite expensive (2.16 €/ 2.96 €)
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**Selection**:
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- Input gain:
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* RK09K1130AJ3 (single, 10K, 15 mm) + Re'an F311/ F313 (diameter TBD)
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* or RK09K12C0A2S (dual, 50K, 20 mm) + Re'an P670 or similar
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- Headphone mix:
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* RK09K12C0A2S (dual, 50K, 20 mm) + Re'an P670
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- Headphone volume:
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* RK09K1110B1R (single, 50K, 15 mm) + Re'an F311/ F313 (diameter TBD)
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### Switches
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The **On-Air** button needs to be a latching DPDT switch, ideally with LED illumination and max. 8 mm height (PCB to front plate), like:
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- E-Switch TL2230EEF140, no illumination -- 0.60 €
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DPDT, PCB mount
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Height: 7.0 mm + 5.5 mm plunger (2x3 mm cap terminal)
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Cap: see APEM models
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- **APEM MHPS2273 (EU version: PHAP4673), no illumination, no audible click -- 0.41 €**
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DPDT, PCB mount
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Height: 7.0 mm + 5.5 mm plunger (2x3 mm cap terminal)
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Cap: U542x (11.5 mm square, 4 mm height), **U453x (9.4 mm dia., 6.65 mm height) -- 0.64 €**
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Cap color codes: **2 Black**, 4 Grey, 5 Yellow, 6 Red
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The **mute** button needs to be a momentary SPST (normally open) or SPDT push button, like:
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- E-Switch TL2230OAF140, no illumination -- 0.53 €
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DPDT, PCB mount
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Height: 7.0 mm + 5.5 mm plunger (2x3 mm cap terminal)
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Cap: see APEM models
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- **APEM 1413NC6/ 1415NC6 -- 3.72 €**
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SPST/ SPDT, front plate snap-in mount, solder lugs
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Button size: 12 mm square, Color: Red (color code 6)
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Cap: U542x (11.5 mm square, 4 mm height), **U453x (9.4 mm dia., 6.65 mm height) -- 0.64 €**
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Cap color codes: 2 Black, 4 Grey, 5 Yellow, 6 Red
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Depth: 13 mm + 6 mm for contacts = 19 mm
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- NKK Switches LP0115C{C,M}KW01-C -- 7.91 €
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SPDT, front plate bushing/ snap-in mount, solder lugs
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Button size: 13.6 mm dia., Color: Red (color code C)
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Depth: 22 mm
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### Casing
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The casing should be a desk console (angled surface), ideally with space at the front to mount the headset ports (XLR and 6.3 mm jack), like:
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- [Bopla ATPH 1865-0250](https://www.bopla.de/gehaeusetechnik/product/alu-topline/alu-topline-gehaeuse/atph-1865-0250.html) (front might not have enough space for the connectors)
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- Design our own casing to laser cut/ 3D print
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## Notes
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A dynamic microphone needs at least 50-60 dB gain in the pre-amp, because a typical signal is at about 1 - 100 uV (-118 to -78 dBu or -120 to -80 dBV).
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Line level in professional audio gear is at +4 dBu, which is 1.228 V (RMS).
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Because 0 dBu is defined as 1 mW at a load of 600 Ohm, which needs a voltage of 0.77 V.
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Increasing the voltage by a factor of 10 is an amplification of 20 dB.
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## BoM
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Approximate prices in Euro.
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Connectors and Buttons (User Interface)
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| Count | Manufacturer + Art. No. | Description | €/ pc.|
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|-------|--------------------------|----------------------------------|-------|
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| 1 | Neutrik NAC3 MPA-1 | Mains Power Input | 3.33 |
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| 1 | Neutrik NCJ 6 FAH | Line Input | 1.27 |
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| 1 | Neutrik NC3 MAAH | Line Output | 0.92 |
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| 3x1 | Neutrik NCJ 6 FAH | Headset Microphone Input | 1.27 |
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| 3x1 | Rean NYS 216 G | Headphone Output | 0.93 |
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| 3x1 | APEM 1415NC6 | Mute Button (red cap, snap-in) | 3.72 |
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| 3x1 | APEM MHPS2273 | On-Air Button | 0.41 |
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| 3x1 | APEM U4532 | On-Air Button black cap | 0.64 |
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| 3x1 | Alps RK09K1130AJ3 | 10K log Mono Pot. (Gain) | 0.91 |
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| 3x1 | Re'an F311 | Potentiometer Knob | 0.40 |
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| 3x3 | Alps RK09K12C0A2S | 50K log Dual Pot. (Headset Mix) | 1.44 |
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| 3x3 | Re'an P670 | Potentiometer Knob | 0.78 |
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| 3x1 | Alps RK09K1110B1R | 50K log Mono Pot. (Headset Vol.) | 0.67 |
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| 3x1 | Re'an F311 | Potentiometer Knob | 0.40 |
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| 1 | Vishay M64{Y,Z}104 | 100K Trim Pot. | 0.95 |
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| | | **SUM** | 54.50 |
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Sub-Components
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| Count | Manufacturer + Art. No. | Description | €/ pc.|
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|-------|--------------------------|----------------------------------|-------|
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| 1 | Traco Power TXL 035-1515D or TOP 60533 | Power Supply | ~48.00 |
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PCB Components: TODO when schematic is finished
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| Count | Manufacturer + Art. No. | Description | €/ pc.|
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|-------|--------------------------|----------------------------------|-------|
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| 3 | NE5534 | Low-noise Op-Amp | 0.54 |
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| 8 | LM833 | Generic Op-Amp | 0.88 |
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| 3 | LM386N-4 | Audio Power Amp | 0.83 |
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| 1 | DRV143 | Line Driver | 4.50 |
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| TODO | TODO | El. Capacitor | TODO |
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| TODO | TODO | Cer. Capacitor | TODO |
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| TODO | TODO | Resistor | TODO |
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| | | **SUM** | TODO |
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VU Meter Components
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| Count | Art. No. | Description | €/ pc.|
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|-------|---------------------|---------------------|-------|
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| 1 | Vishay M64{Y,Z}503 | 50K Trim Pot. | 0.95 |
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| 1 | LM833 | Generic Op-Amp | 0.88 |
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| 2 | 1N4148 | Signal Diode | 0.02 |
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| 1 | 1k Metal Film | Resistor | TODO |
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| 1 | 3.9k Metal Film | Resistor | TODO |
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| 1 | 47 uF | El. Capacitor | TODO |
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| 1 | 100k Metal Film | Resistor | TODO |
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| 3 | LM339 | Quad-Ch. Comperator | 0.29 |
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| 5 | 100 nF | Cer. Capacitor | TODO |
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| 1 | 1 uF | El. Capacitor | TODO |
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| 5 | Vishay TLHR 5404 | LED red | 0.18 |
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| 4 | Vishay TLHY 5404 | LED yellow | 0.14 |
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| 3 | Vishay TLHG 5404 | LED green | 0.17 |
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| 12 | 390R | Resistor | TODO |
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| 1 | 39R | Resistor | TODO |
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| 2 | 68R | Resistor | TODO |
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| 1 | 100R | Resistor | TODO |
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| 1 | 150R | Resistor | TODO |
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| 1 | 270R | Resistor | TODO |
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| 1 | 390R | Resistor | TODO |
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| 1 | 680R | Resistor | TODO |
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| 1 | 1K | Resistor | TODO |
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| 1 | 1.5K | Resistor | TODO |
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| 2 | 2.7K | Resistor | TODO |
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| 1 | 3.9K | Resistor | TODO |
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| | | **SUM** | TODO |
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