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

5.1 channel preamp
5.1 channel preamp
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Old 30th August 2019, 05:55 AM   #1
stratus46 is offline stratus46  United States
diyAudio Member
Join Date: Nov 2009
Location: Los Angeles
Default 5.1 channel preamp

This 'preamp' is part of my home made 5.1 audio system. Volume control
uses 3 CS3310 (same as PGA2311) volume control chips, 3 New Japan Radio
NJW 1119A tone controls for Bass, Mid and Treble. 3 OPA2134 opamps are
buffers, summers and LP filter and impedance buffer for the analog feed to the Arduino controller.
This 'preamp' includes a 6 channel power amp based on the T.I. TPA3116
that delivers 20 Watts /channel into 8 ohms. The box is my 5.1 audio for an LG OLED TV.

This is not the exact encoder I'm using but it is functionally the same.

Rotary Encoder + Extras ID: 377 - $4.50 : Adafruit Industries, Unique & fun DIY electronics and kits

This display is exactly what I'm using. For volume only 1 unit can suffice.
With the tone controls it's better with 2 units. BTW I like blue better but
that's just me. They have several colors including white.

Quad Alphanumeric Display - Blue 0.54 Digits w/ I2C Backpack ID: 1912 - $13.95 : Adafruit Industries, Unique & fun DIY electronics and kits

The IR modules are these.

38 kHz Remote TSOP4838 DIP-3 IR Receiver Infrared Radiation Modules XZ | eBay

The 'interface' is nothing more than a blank Arduino shield to mount the connectors.
3 pin for IR, 4 pin for the rotary encoder, 5 pin for the displays and a 10 pin
to talk to the preamp board and get 5 Volt power. The pins just connect to
Arduino Uno pins with no extra semiconductors but a couple of capacitors.

I got a little silly with the controls. The 'mute' function has a 'dim' mode. If you hold
the mute button more than a user settable preset, it goes to a secondary volume.
I usually set it to -15dB. The hold time can be set in 10mS increments up to
500mS to trigger 'dim' mode. It can also do 'fade' as mute. You can select
10 to 100 dB / second in 10 dB steps. Selecting 11 is not 110 dB but plain old instant mute.

Volume DOWN in mute or dim mode will reduce the level to un mute to but stay in mute.
Volume UP in mute mode comes out of mute and increments 1 dB. Mute button while in mute
just ramps back up to the old value. All settings are stored in EEPROM (non volatile).
My version includes a mono mix for a center channel in stereo mode and also low pass filters
the center to feed to the sub woofer. The Arduino gets a buffered center channel feed so
when it finds audio on the center channel it switches back to 5.1 mode.

The shaft encode is not needed but gives local volume control without a remote.
The button portion triggers mute and holding will also enter 'dim' mode.

This 'preamp' includes a 6 channel power amp based on the T.I. TPA3116
that delivers 20 Watts /channel into 8 ohms. The box is my 5.1 audio for an LG OLED TV.

Operationally the 5.1 is active always and uses the cable box remote to changes channels,
volume and inputs exactly like TVs of old before they turned into something that sometimes
need an engineering degree to use.

I know you can buy these thing but it's DIY. It's fun.

The TXT file need its name changed to .INO

Attached Images
File Type: jpg 6 channel preamp bottom P1040085.jpg (65.0 KB, 120 views)
File Type: jpg 6 channel preamp top P1040086.jpg (67.7 KB, 124 views)
File Type: jpg 6 channel preamp P1040483.jpg (79.6 KB, 121 views)
File Type: jpg 6 channel preamp P1040484.jpg (70.9 KB, 120 views)
File Type: jpg 6 channel preamp mounted P1040528.jpg (76.4 KB, 120 views)
File Type: jpg 6 channel preamp P1040511.jpg (71.8 KB, 37 views)
Attached Files
File Type: pdf 6 channel schematic.pdf (186.6 KB, 31 views)
File Type: txt LG_remote51T7.txt (31.1 KB, 16 views)
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Old 30th August 2019, 02:16 PM   #2
rsavas is offline rsavas  Canada
diyAudio Member
Join Date: Aug 2012
Location: Ontario
Well done,

I know how much work it is, when I made my portable radio/media player, using the TPA3100, before the TPA3116 was out. I still have code to write, I am not so good at it Should be fun reading your code . I think I left it at the IR decoder code. I made a remote encoder too.
My Mom uses the radio all day, she likes the RDS decoding. If you want to add AM/FM radio, I have code to give you.

I'll take a further look at your design, thanks for sharing.
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Old 31st August 2019, 03:52 PM   #3
Shaz is offline Shaz  United States
diyAudio Member
Join Date: Jul 2003
Location: Colorado
This is great work! Thank you so much for sharing details.

Your feature set is quite extensive. You've inspired me to give this type of project a try. However, I'm interested in building only an 8-channel volume controller using four CS3310 ICs.

I looked into the parts you used and I think my best course of action will be to start with the power supply, Arduino, its peripherals and the software. I can work in parallel to design the volume controller board.

It appears that everything can be powered with a +5V and -5V power supply. It doesn't appear that you are using multiple voltage regulators for the various +5V devices. Are you using any components to help isolate those leads.

I gather that your power supply bridge rectifier, filter caps and voltage regulators reside on your custom board. I don't see a transformer inside your enclosure. What are you using for a transformer? I also assume you're providing a single voltage from an external power supply to your amplifier board.
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Old 31st August 2019, 06:19 PM   #4
stratus46 is offline stratus46  United States
diyAudio Member
Join Date: Nov 2009
Location: Los Angeles
The preamp power transformer is a 12 VCT but it would have a little more 'wiggle'
room with a 14 Volt transformer. These guys sell good toroids inexpensively.

AN-0107 - 10VA 7V Transformer - AnTek Products Corp

The power amp uses a 19 Volt 9.5 amp laptop supply.

The CS3310 and PGA2311 data sheets recommend a low source impedance.
In my case the analog signal is coming from an optical input DAC so the source
is already low. You might want to use input buffers like U3 to allow any source
impedance. I my case U3 is to isolate the 10k summing amp from the source
since the CS3310 is also 10 K. I like low impedance but 5K is a little low even
for me, hence U3. The input then is the resistor to ground at the buffer, in my
case 10K.

It isn't clear on the schematic that U3 is a triple 2:1 switch similar to a CD4053.
All analog switches show varying series resistance vs signal level. The 4053
maybe 120 to 180 ohms at 25C. In series with the 10K load would cause some
non-linearities (distortion). The Analog Devices chip shows the same series
resistance change but varies from 3.3 to 4.3 ohms at 25C so an order of
magnitude plus better than a 4053.

Because the center and sub channels have 2 different sources because of the
analog switch, it stores 2 sets of tone control and volume numbers for stereo
vs 5.1, only for center and sub.

At work I'm known as Mr or Dr capacitor for all the 'lytic caps I've replaced
(10,000 plus). On this board the only 'lytics are 2200uF 16 Volt and those are
Organic Polymer. All the 10uF and 100uF caps are SMD ceramics in addition to
the 100n bypass caps. The capacitors in the signal path are 2% film.

The 4 resistors on the regulators are 1% thick film 0805. The rest are 0.5% thin
film 0805 Susumu from Digikey. 11 cents in single lot, 10 cents in 10s but 3.76
cents in 100 lot. I have considerable 'left overs' that cost less than the 'right'

Some tricks for SMD. I use a Metcal soldering iron with an STTC0126 700 degree
fine bent tip. Flux on the board from a flux pen in addition to the 63/37 Multicore
solder. After the parts are soldered but likely a little crooked, a hot air tool set to
the lowest air flow will allow the surface tension of the solder to align the part
without blowing them away. It's neat to see them self align.

Search for "858 hot air" on eBay and you should find lots around $35.

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Old 31st August 2019, 09:02 PM   #5
Ken Newton is offline Ken Newton  United States
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Join Date: Apr 2003
Location: Eastern Pennsylvania
Originally Posted by stratus46 View Post
This 'preamp' is part of my home made 5.1 audio system.
Stratus, your schematic seems to indicate that you do not use an dedicated channel steering surround decoder of some kind. Instead, you have what looks to be non-steering purely analog surround generation. Your schematic shows inputs for front Left and Right channels, plus surround Left and Right channels. However, where do those surround channel inputs come from. Is it from some kind of external surround decoder?

I ask because the usual impediment to a DIY surround preamp or DAC is the need for a channel steering type surround decoder. I'm also wondering how your non-steering solution subjectively compares to an channel steering decoder based solution?

Last edited by Ken Newton; 31st August 2019 at 09:11 PM.
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Old 31st August 2019, 09:50 PM   #6
stratus46 is offline stratus46  United States
diyAudio Member
Join Date: Nov 2009
Location: Los Angeles
Originally Posted by Ken Newton View Post
Stratus, your schematic seems to indicate that you do not use an dedicated channel steering surround decoder of some kind. <snip>
I use one of these set to 'pass' mode though the one I have has a 3 position switch marked 2.0, 5.1, and 'pass'.

Search eBay for optical analog 5.1

5.1ch Digital Audio Decoder Optical Coaxial Toslink to Analog 6 output Converter 784099939143 | eBay

It works correctly with all the over the air networks, our cable service and streaming like Prime and Netflix,
HTPC and the BluRay player.

The TV optical out feeds the DAC. The inputs to the TV are cable box, Roku box, HTPC and Blu-ray. The PC
required a Dr HDMI in between. The TV EDID reports it has 2 channels of audio but it will pass through 5.1
if fed to it. The BluRay had to be set to pass it, also true for the Roku box. The Roku box quirk is the first
time you set it to 'auto' to pass DTS but does not pass 5.1. There is a 'night time' mode mode for earphones
that forces it to stereo. When you exit night time mode it then passes 5.1.

The Dr HDMI tells the PC (Win 7 pro) it can pass 5.1 out the HDMI connector. When go into sound setup you
get the options beyond stereo. It will NOT encode 5.1 from 6 channels but it WILL pass through pre-encoded
audio. VLC CLAIMS to be able to pass 5.1 but I have never gotten to work so I use MPC-HC which will pass
through the 5.1 and works correctly with the KeySpan RF remote.

Yes the LG TV is 'smart' and can do Amazon and Netflix but I don't like the user controls on the LG remote so
I use a Roku box.

IOW the DAC does the hard work for me and all I need to do is control volume and tone.


Last edited by stratus46; 31st August 2019 at 09:56 PM.
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