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@ -38,16 +38,13 @@ All inputs (besides the microphones) and outputs should:
This results in a signal flow like this: ![](docs/signal-flow.jpg)
## Status
### Tasks
- [x] Requirements collection
- [x] Electrical design draft/ proof of concept (breadboard)
- [x] Proof of concept validation
- [x] First PCB layout (prototyping modules)
- [x] More testing/ validation
- [ ] Second PCB layout + casing prototype
- [x] First PCB layout
- [ ] More testing/ validation
Help is always appreciated!
@ -59,28 +56,27 @@ Help is always appreciated!
- [x] Adjustable headphone mix and output volume
- [ ] ESD protection and galvanic isolation of line inputs and outputs
- [x] VU meter (own PCB)
- [ ] VU meter (integrated in front panel PCB)
- [ ] Mute and On-Air buttons
## Electrical Design
This chapter contains some notes on the electrical design.
Currently just the sources of the used circuit designs.
### Microphone Input
#### Preamplifier
### Sources and Design Considerations
#### Microphone Input
##### Preamplifier
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).
#### Controllable Amplification
##### Controllable Amplification
In a normal mixer, you would be able to lower the microphone's volume to zero.
But in our case we just need on/ off and some gain range to adjust for different microphones and loudness of different people.
TODO: Integrate the On-Air button with it's LEDs
### Line Input/ Input Module
#### Line Input/ Input Module
The line input must not be amplified at all, because loudness control of the headphones is done by the headphone amplifier section.
But the differential line-level signal must be converted to a single-ended signal by the input stage.
@ -89,8 +85,7 @@ The second part of that circuit was taken from the [circuitlib audio mixer tutor
TODO: How to achieve galvanic isolation?
### Summing
#### Summing
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).
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).
@ -100,151 +95,47 @@ In our case, there are just two types of summing: All microphones for the interp
Because the stage input is quite independent of the interpreter's microphones, no special phase/ inversion considerations are needed.
And the microphones connected to our unit will experience the same inversions anyways.
### Line Output Driver
#### Line Output Driver
Line Output conversion is done by the [DRV134](https://www.ti.com/product/DRV134) IC.
TODO: How to achieve galvanic isolation?
### Headphone Output Driver
#### Headphone Output Driver
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.
For the first draft, we're using one LM386 audio power amplifier even though it has a quite high minimal amplification of factor 20.
### VU Meter
#### VU Meter
When searching for VU meter circuits, many use the LM3916 LED bar graph driver, which already has the right scaling built in.
But this chip is obsolete and not produced any more, so we designed our own chain of comperators to drive a set of LEDs.
## User Interface
The user interface should enable the interpereters to adjust their microphone gain and headphone mix on their own.
Additionally, a (permanent) on/off switch, as well as a (temporary) mute button should be present.
A possible UI layout might look like this: ![](docs/ui-layout.jpg)
### Potentiometers
We need some single and dual channel logarithmic scale potentiometers, which are matching in size, for:
- top plate interface (all vertical style, threaded collar would be nice):
* 1 single channel for the input gain (resistance doesn't matter)
* 2 single and 1 stereo channel for the headphone mix (ideally 50K, b/c 3 will be in parallel)
- front plate next to the headset jacks (horizontal style, threaded collar not needed):
* 1 single channel for the headphone volume (ideally 50K, b/c that's already tested)
#### User Interface Hardware
After some long research to find single and dual channel, logarithmic scale potentiometers with the same dimensions, there are only a few options left:
1. Alps Alpine Series RK09K/D, 10 kOhm (log), 15 mm length, vertical mount: RK09K1130AJ3 (single) and RK09K12C0A19 (dual)
6 mm D-style (4.5 mm) shaft, 6 mm flattened + 2.2 mm (incl. 0.8 mm collar) = 8.2 mm from top
Notes: Knob might touch surface, assuming 2 mm front plate thickness
2. Alps Alpine Series RK09K/D, 10 kOhm (log), 30 mm length, vertical mount: RK09D117000C (single) and RK09K12C0A8K (dual)
6 mm D-style (4.5 mm) shaft, 12 mm flattened + 11.2 mm (incl. 5.0 mm collar) = 23.2 mm from top
Notes: Quite long shaft, matching knobs difficult to find
3. **Alps Alpine Series RK097**, 10 kOhm (log), 15 mm length, horizontal mount: RK097111080J (single) and RK09712200MC (dual)
6 mm D-style (4.5 mm) shaft, 7 mm flattened + 8 mm (incl. 5 mm threaded collar) = 15 mm from top
Notes: More expensive than RK09K; Thread should fix 2 mm front plate well
4. Alps Alpine Series RK097, 10 kOhm (log), 20 mm length, horizontal mount: RK097111080R (single) and RK09712200HA (dual)
6 mm D-style (4.5 mm) shaft, 12 mm flattened + 8 mm (incl. 7 mm threaded collar) = 20 mm from top
Notes: Quite long shaft, matching knobs difficult to find
Possible knobs may be:
- (A) Re'an F311/ F313 series (11/ 13 mm diameter) -- 0.40 €/ 0.55 €:
Boring: 9.0 mm D-style hole + 0.0 mm nut cover section = 9.0 mm
- (B) Re'an P670 series (12 mm diameter/ 16 mm at bottom) (alt. Davies Molding 1101) -- 0.78 €:
Boring: 7.5 mm D-style hole + 4.5 mm nut cover section = 12.0 mm
Nut cover: 12.9 mm diameter (M7 nut is 12.5 mm corner to corner)
- (C) Re'an P300 series (11 mm diameter/ 15 mm at bottom):
Boring: 9.0 mm D-style hole + 3.0 mm nut cover section = 12.0 mm
Nut cover: ? mm diameter (M7 nut is 12.5 mm corner to corner)
- ~~(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)~~
~~Notes: D-style boring has wrong size (5 mm instead of 4.5 mm flatted)~~
- Rean F311/ F313 series (11/ 13 mm diameter): 9 mm hole depth (no skirt/ flush with end of flatted axis section)
Notes: Will fit option 1 (and 2, if potentiometer placed accordingly)
- Rean P670 series (12 mm diameter/ 16 mm at bottom): 7.5 mm hole depth + 4.5 mm skirt = 12 mm
Notes: Should fit option 3
- 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)
Notes: Should fit option 3 (boring for potentiometer nut a bit tight); Size quite like Rean R670
- Rean P300 series (11 mm diameter/ 15 mm at bottom): 9 mm hole depth + 3 mm skirt
Notes: Might also fit option 3
Potentiometers from Alps Alpine seem to have a decent quality in a small package size and quite affordable price.
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):
- Alps Alpine Series RK09K/D (6 mm D-style (4.5 mm) shaft):
* vertical (top plate):
+ **single channel: 10K, 15 mm -- RK09K1130AJ3 -- 0.91 €**
actual shaft length (dwg. 2): 7.4 mm (6 mm flattened)
_matching knobs: A_
+ dual channel: 10K, 15 mm -- RK09K12C0A19 -- 1.23 €
actual shaft length (dwg. 10): 7.4 mm (6 mm flattened)
_matching knobs: A_
+ **dual channel: 50K, 20 mm -- RK09K12C0A2S -- 1.44 €**
actual shaft length (dwg. 10): 12.4 mm (7 mm flattened)
_matching knobs: C, B (depending on front plate thickness)_
* horizontal (front plate):
* single channel: 10K, 15 mm -- RK09K1110A2S -- 0.67 €
actual shaft length (dwg. 1): 7.4 mm (6 mm flattened)
_matching knobs: A_
* **single channel: 50K, 15 mm -- RK09K1110B1R -- 0.67 €**
actual shaft length (dwg. 6): 7.4 mm (6 mm flattened)
_matching knobs: A_
- Alps Alpine Series RK11K/12L/14K (6 mm D-style (4.5 mm) shaft):
* vertical (top plate):
+ single channel: none
+ dual channel: 10K, 20 mm -- RK14K12C0A1S -- 1.17 €
actual shaft length (dwg. 2): 11.8 mm (7 mm flattened)
_matching knobs: C, B (depending on front plate thickness)_
+ dual channel: 10K, 25 mm -- RK12L12C0A0E -- 0.81 €
actual shaft length (dwg. 2): 16.4 mm (12 mm flattened)
_matching knobs: Unknown, b/c of quite long shaft_
+ dual channel: 50K, 25 mm -- RK14K12C0A0T -- 1.87 €
actual shaft length (dwg. 2): 16.8 mm (12 mm flattened)
_matching knobs: Unknown, b/c of quite long shaft_
+ dual channel: 10K, 30 mm -- RK12L12C0A0G (alt. RK12L1230C0T) -- 0.81 €
actual shaft length (dwg. 2): 21.4 mm (12 mm flattened)
_matching knobs: Unknown, b/c of very long shaft_
+ dual channel: 20K, 30 mm -- RK12L12C0A0A -- 0.81 €
actual shaft length (dwg. 2): 21.4 mm (12 mm flattened)
_matching knobs: Unknown, b/c of very long shaft_
* horizontal (front plate):
+ single channel: none
+ dual channel: 10K, 30 mm -- RK12L12A0C0R (alt. RK12L1210C0R) -- 0.81 / 0.79 €
actual shaft length (dwg. 1): 21.4 mm (12 mm flattened)
_matching knobs: Unknown, b/c of very long shaft_
- Alps Alpine Series RK11K/12L/14K (6 mm D-style (4.5 mm) shaft, collar with M7 thread):
* vertical (top plate):
+ dual channel: 10K, 27.5 mm -- RK14K12D0A1X -- 1.13 €
actual shaft length (dwg. 4): 15 mm (12 mm flattened) + 5 mm thread length
_matching knobs: Unknown, b/c of quite long shaft_
+ dual channel: 50K, 27.5 mm -- RK14K12D0A18 -- 1.13 €
actual shaft length (dwg. 4): 15 mm (12 mm flattened) + 5 mm thread length
_matching knobs: Unknown, b/c of quite long shaft_
* horizontal (front plate):
+ single channel: 20k, 27.5 mm -- RK11K1120A31 -- 1.07 €
actual shaft length (dwg. 3): 20 mm (12 mm flattened) + 5 mm thread length
_matching knobs: Unknown, b/c of very long shaft_
+ dual channel: 10K, 22.5 mm -- RK14K12B0A0E (alt. RK14K1220A0F) -- 1.13 €
actual shaft length (dwg. 3): 10 mm (7 mm flattened) + 5 mm thread length
_matching knobs: C, B (depending on front plate thickness)_
+ **dual channel: 50K, 22.5 mm -- RK14K12B0A0R -- 1.13 €**
actual shaft length (dwg. 3): 10 mm (7 mm flattened) + 5 mm thread length
_matching knobs: C, B (depending on front plate thickness)_
- Alps Alpine Series RK09L (6 mm D-style (4.5 mm) shaft, collar with M7 thread):
* vertical (top plate):
+ **single channel: 10K, 12.5 mm -- RK09L1140A5E -- 1.61 €**
actual shaft length (dwg. 2): 7.5 mm (7 mm flattened) + 5 mm thread length
_matching knobs: A_
+ **dual channel: 10K, 15 mm -- RK09L12D0A1W -- 1.64 €**
actual shaft length (dwg. 4): 10 mm (7 mm flattened) + 7 mm thread length
_matching knobs: C, B (depending on front plate thickness)_
+ dual channel: 10K, 20 mm -- RK09L12D0A1T -- 1.64 €
actual shaft length (dwg. 4): 15 mm (12 mm flattened) + 7 mm thread length
_matching knobs: Unknown, b/c of quite long shaft_
* horizontal (front plate):
+ **single channel: 10K, 15 mm -- RK09L1120A2S -- 1.62 €**
actual shaft length (dwg. 1): 10 mm (7 mm flattened) + 5 mm thread length
_matching knobs: C, B (depending on front plate thickness)_
+ single channel: 10K, 20 mm -- RK09L1120A69 -- 1.30 €
actual shaft length (dwg. 1): 15 mm (12 mm flattened) + 7 mm thread length
_matching knobs: Unknown, b/c of quite long shaft_
+ dual channel: 50K, 15 mm -- RK09L12B0A31 -- 1.78 €
actual shaft length (dwg. 3): 10 mm (7 mm flattened) + 5 mm thread length
_matching knobs: C, B (depending on front plate thickness)_
- 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 €)
Selection:
- Input gain:
* RK09K1130AJ3 (single, 10K, 15 mm) + Re'an F311/ F313 (diameter TBD)
* or RK09K12C0A2S (dual, 50K, 20 mm) + Re'an P670 or similar
- Headphone mix:
* RK09K12C0A2S (dual, 50K, 20 mm) + Re'an P670
- Headphone volume:
* RK09K1110B1R (single, 50K, 15 mm) + Re'an F311/ F313 (diameter TBD)
### Switches
The On-Air button needs to be a latching DPDT switch, ideally with LED illumination, like:
The On-Air button needs to be a latching SPST (or SPDT) switch with LED illumination, like:
- E-Switch LP11EE1NCSYG
- TODO: other, less expensive options highly appreciated! Separate LED might also be OK.
The mute button needs to be a momentary SPST (normally open) or SPDT push button, like:
- NKK Switches UB15NBKW01N-C
@ -252,13 +143,11 @@ The mute button needs to be a momentary SPST (normally open) or SPDT push button
- TE Connectivity PB6B2FM3M2CAL00
- TODO: other, less expensive options highly appreciated!
### Casing
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:
- [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)
- TODO: other options appreciated
- Or laser cut/ 3D print something
A possible UI layout for the Bopla ATPH 1865-0250 might look like this: ![](docs/ui-layout.jpg)
## Notes
@ -275,33 +164,32 @@ Approximate prices in Euro.
Connectors and Buttons (User Interface)
| Count | Manufacturer + Art. No. | Description | €/ pc.|
| Count | Manufacturer + Art. No. | Description | Price |
|-------|--------------------------|----------------------------------|-------|
| 1 | Neutrik NAC3 MPA-1 | Mains Power Input | 3.33 |
| 1 | Neutrik NCJ 6 FAH | Line Input | 1.27 |
| 1 | Neutrik NC3 MD-LX | Line Output | 3.22 |
| 3x1 | Neutrik NCJ 6 FAH | Headset Microphone Input | 1.27 |
| 3x1 | Rean NYS 216 G | Headphone Output | 0.93 |
| 3x1 | TODO | Headphone Output | TODO |
| 3x1 | NKK UB15NBKW01N-C | Mute Button | 7.50 |
| 3x1 | E-Switch LP11EE1NCSYG | On-Air Button | 5.00 |
| 3x1 | Alps RK09K1130AJ3 | 10K log Mono Pot. (Gain) | 0.91 |
| 3x1 | Re'an F311 | Potentiometer Knob | 0.40 |
| 3x3 | Alps RK09K12C0A2S | 50K log Dual Pot. (Headset Mix) | 1.44 |
| 3x3 | Re'an P670 | Potentiometer Knob | 0.78 |
| 3x1 | Alps RK09K1110B1R | 50K log Mono Pot. (Headset Vol.) | 0.67 |
| 3x1 | Re'an F311 | Potentiometer Knob | 0.40 |
| 3x1 | Alps RK097111080J | 10K log Mono Pot. (Gain) | 2.16 |
| 3x1 | Alps RK097111080J | 10K log Mono Pot. (Headset Vol.) | 2.16 |
| 3x2 | Alps RK097111080J | 10K log Mono Pot. (Headset Mix) | 2.16 |
| 3x1 | Alps RK09712200MC | 10K log Dual Pot. (Headset Mix) | 2.96 |
| 3x5 | TODO | Potentiometer Knob | TODO |
| 1 | Vishay M64{Y,Z}104 | 100K Trim Pot. | 0.95 |
| | | **SUM** | 79.99 |
| | | **SUM** | 84.88 |
Sub-Components
| Count | Manufacturer + Art. No. | Description | €/ pc.|
| Count | Manufacturer + Art. No. | Description | Price |
|-------|--------------------------|----------------------------------|-------|
| 1 | Traco Power TXL 035-1515D or TOP 60533 | Power Supply | ~48.00 |
PCB Components: TODO when schematic is finished
| Count | Manufacturer + Art. No. | Description | €/ pc.|
| Count | Manufacturer + Art. No. | Description | Price |
|-------|--------------------------|----------------------------------|-------|
| 3 | NE5534 | Low-noise Op-Amp | 0.54 |
| 8 | LM833 | Generic Op-Amp | 0.88 |
@ -314,7 +202,7 @@ PCB Components: TODO when schematic is finished
VU Meter Components
| Count | Art. No. | Description | €/ pc.|
| Count | Art. No. | Description | Price |
|-------|---------------------|---------------------|-------|
| 1 | Vishay M64{Y,Z}503 | 50K Trim Pot. | 0.95 |
| 1 | LM833 | Generic Op-Amp | 0.88 |