Speakerplans.com Homepage
Forum Home Forum Home > General > 12v Powered Systems
  New Posts New Posts RSS Feed - TPA3116D amplifier board 2.1 modifications
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

TPA3116D amplifier board 2.1 modifications

 Post Reply Post Reply
Author
Message
superhans View Drop Down
New Member
New Member
Avatar

Joined: 07 December 2020
Location: UK
Status: Offline
Points: 6
Post Options Post Options   Thanks (0) Thanks(0)   Quote superhans Quote  Post ReplyReply Direct Link To This Post Topic: TPA3116D amplifier board 2.1 modifications
    Posted: 07 December 2020 at 11:15am
Hi,

I'm trying to put together a small system and have a TPA3116D board from ebay. It looks like the amplifier part is a reference design from the TI datasheet, but the board also has a low pass filter for .1 channel generation and a "tone control" which has a treble volume and treble frequency pot. The board is known as GHXAMP TPA3116 2.1 on others (not sure if I'm allowed to link to places that sell it).

Details below, but my questions are:

1. Does anyone have a schematic for a board like mine? 2xTPA3116, possibly a bluetooth module, and 5 pots (bass freq, bass vol, treble volume, treble freq, on/main vol)?
2. I'm thinking to mod the board so that it does a proper crossover (by removing the "tone" control) and possibly using a second pre-amp to do the high pass cut - is it possible to do variable gain and filtering with a single op-amp?

More info / what I've figured out so far:

1. I'm using a tapped horn for my "sub", so I need a high pass filter at least on the sub section. I was hoping the filter caps on the amp would do this for free, but there's no attenuation at the low end (measured with an oscilloscope).
2. The L/R channels aren't crossed over with the sub channel. The "treble freq" adjustment does seem to change the frequency but the frequencies it makes a difference at are really high (and I'm unable to tell what it actually does)
3. It has a switch between "Normal" and "All Freq" which I hoped would disable the treble tone control, but it seems to do nothing.

The tone control circuit has an RC4580 op amp pair feeding into 2 TL072C op amps. It's a single supply so the signals are all biased at 4.8V or so.

I've poked around at the thing with a multimeter and an oscilloscope and slowly reverse engineering the topology. My current guesses are:

The RC4580 is probably used to buffer the signal from the input, which is fed in through a 2gang pot.

The first TL072C is responsible for filtering and amplifying the stereo L/R channels and feeds each over to the first TPA3116

The second TL072C handles the bass channel, but I'm not totally sure how this works - I was hoping there'd be a spare channel to use but there are signals on both sides.

I'm out of my depth a bit with op amp circuits so it's slow work reverse engineering it.
Back to Top
studio45 View Drop Down
Old Croc
Old Croc
Avatar

Joined: 16 October 2007
Location: United Kingdom
Status: Offline
Points: 3843
Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2020 at 1:39pm
Look up some op-amp lowpass circuits and see if any of them match the component layouts you can see. 

Two amplifiers in the lowpass circuit indicates that it is probably an 18dB or 24dB slope - or it *could* be a 6 or 12dB slope followed or preceded by a flat buffer, but that would be a bit of a waste of an amp. 

It's probably not going to be possible to engineer another highpass on the amp board as it exists, but would be easy enough to make a fundamental highpass filter to put before the input. If you use capacitors on the input and output you don't necessarily need a dual-rail supply, just a 1/2Vcc divider to provide the bias voltage. 

Here is a website with various filter calculators, I would not be surprised to find out it was the exact one used by the designers of your board! https://www.changpuak.ch/electronics/calc_09.php


Studio45 - Box Builder Commotion Soundsystem -Mobile PA
Back to Top
slaz View Drop Down
Old Croc
Old Croc
Avatar

Joined: 27 November 2009
Location: London E2
Status: Offline
Points: 2627
Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2020 at 3:26pm
Well I congratulate you on being willing to do this kind of DIY/tinkering ... but I think you need to understand (if you don't already) the context of these kind of "2.1" amplifiers from China.

Typically, you might see 50W + 50W +100W advertised. The 50W will be into 4R measured at 10% THD (!!) with absolute maximum supply rail voltage before the chip-amps/caps go bang. Also, the "100W sub" will be into a 2R load, half that into a 4R load etc.

Now the ones I've seen make no mention whatsoever of crossover point, slope etc.
I'm fairly sure there is no real crossover - just a crude LP filter on the bass output - and no HP on the 2 "mid-high" channels. IMHO, this is because they envisage use with a pair of small bookshelf/stack system speakers with 4" drivers or somesuch. They think its just for kids who want "loadsa bass" .... no actual control of it. Simlar to car amplifiers in a way.

To make something like a proper setup, just get a 2.0 amplifier for mid-top, another mono one for bass, and take care of crossover yourself - this could be with a mini-DSP or similar, or maybe an analogue board from the likes of KMTech (dunno what these are like in practice).
REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
Back to Top
superhans View Drop Down
New Member
New Member
Avatar

Joined: 07 December 2020
Location: UK
Status: Offline
Points: 6
Post Options Post Options   Thanks (0) Thanks(0)   Quote superhans Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2020 at 1:05pm
To be honest I was expecting some things to be crappy but I am disappointed that the board I have is worse than just a bare twin TPA3116D reference one. Ironically I picked this one over the other ones that lacked a frequency pot on the (silly) assumption that frequency control must mean crossover.

I was used to the useful output power being low on these amp boards, but yeah... Looks like for my 8R driver I can expect about 9W of usable power on 12V and 12W on 24V, so looks like I'll not really be able to use it for much. The runtime will be good on batteries at least :D.

I've got a crossover kit from KMTech coming which I'll either use to just send signals directly to the TPA3116s and scrap the filtering circuit on the board, or try to reuse bits of it to adjust the bass volume and implement a HPF for the bass channel. I guess then I can replace the amp with a proper amp easily without sinking time into making the input stage on the useless board work properly.

I've been able to figure out that the 2 TL072Cs are actually all concerned with the bass channel - I can see one side of the first TL072C buffers the full signal (maybe summed to mono) and sends it to the bass volume pot, then the second side of that same opamp sends it to the other TL072C, which at a total guess is implementing the LPF. I'll push on and try to at least produce a schematic for the input circuit, it'll be a week before the xover board arrives anyway.

Will start looking for a proper amp too in the mean time. Thanks for your inputs folks - you've saved me a fair bit of disappointment.

---

Edit: Parts Express sells this thing too - the switch apparently enables or disables a 6db/octave 150Hz high pass filter. I'm actually quite surprised it's reviewed so highly, but you're totally right about the application - bookshelf/boomboxes!

Edited by superhans - 08 December 2020 at 1:19pm
Back to Top
slaz View Drop Down
Old Croc
Old Croc
Avatar

Joined: 27 November 2009
Location: London E2
Status: Offline
Points: 2627
Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2020 at 2:53pm
Yeah you'll likely get as much SPL out of a PA-type bass driver given 12W as you would from a similar-size of 2R car sub driver with full watts :-) - but obviously with much better battery run-time.

Interested to hear how you get on with the KMTech thing (and how much current it uses if you get around to measuring that). Watch out for ground-loop hassles if powering it from the same rails as the amplifier.
REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
Back to Top
JoshR77 View Drop Down
New Member
New Member
Avatar

Joined: 08 December 2020
Location: United States,
Status: Offline
Points: 4
Post Options Post Options   Thanks (0) Thanks(0)   Quote JoshR77 Quote  Post ReplyReply Direct Link To This Post Posted: 11 December 2020 at 3:30am
Originally posted by studio45 studio45 wrote:

Look up some op-amp lowpass circuits and see if any of them match the component layouts you can see. 

Two amplifiers in the lowpass circuit indicates that it is probably an 18dB or 24dB slope - or it *could* be a 6 or 12dB slope followed or preceded by a flat buffer, but that would be a bit of a waste of an amp. 

It's probably not going to be possible to engineer another highpass on the amp board as it exists, but would be easy enough to make a fundamental highpass filter to put before the input. If you use capacitors on the input and output you don't necessarily need a dual-rail supply, just a 1/2Vcc divider to provide the bias voltage. 

Here is a website with various filter calculators, I would not be surprised to find out it was the exact one used by the designers of your board!  https://www.changpuak.ch/electronics/calc_09.php



I often use this one too, really useful thing


Edited by JoshR77 - 11 December 2020 at 3:30am
Back to Top
superhans View Drop Down
New Member
New Member
Avatar

Joined: 07 December 2020
Location: UK
Status: Offline
Points: 6
Post Options Post Options   Thanks (0) Thanks(0)   Quote superhans Quote  Post ReplyReply Direct Link To This Post Posted: 29 December 2020 at 11:04pm
I've just finished the cabinet (after breaking it and screwing up the paint) and while it dries I've got some updates:

* The board uses a linear regulator to get 10V from the input and also 5V from the input
* Some stuff happens to the 10V rail to drop it to 8.9V or so
* A 11K/13K divider is used from that 8.9V rail to produce a 4.82V virtual ground that supplies the opamps
* Each input channel is fed into the main volume pot via one or more capacitors
* The output from the volume pot is split - it goes into the treble volume pot and through a 27kR summing circuit that gets fed into the opamps that handle the bass
* The treble pot output is filtered via a parallel resistor and cap, another cap, into an opamp with what looks like a high-pass filter (parallel RC fed back into the input)
* The tone control pot is a ground on one leg and a capacitor to ground on the other leg, so it's a series RC network, which is connected after the RC on the input stage to the RC4580..

This would explain why the treble volume and tone controls change the signal on the subwoofer.

I haven't followed the rest of the circuit from there, but given the summing is done before any of the TL072Cs there's probably a 24db slope LR filter.

Putting more thought into the power handling side of things - my driver should be good for up to 400W and while I didn't previously intend to use the headroom I've since realised it'd be nice to have the capability to.

I've spent a bit more time clinging to the idea of being able to get something cheap and DC powered but it's clear that cutting corners (or costs) isn't really possible - the TPA311x boards are all too low powered, the IRS2092S looks great except it requires a dual rail high voltage DC supply, but high power dual rail boost converters/rail splitters aren't cheap. I'm happy to concede that stringing random boards together isn't going to be worth my time and buying an off the shelf amp is a good idea.

I'm now wondering if a mains amp and inverter would be a bad choice versus a car amp?

Edited to avoid necroposting:

Turns out the input to the subwoofer channel is actually a differential input - the last op-amp is used to invert the channel I believe.

Edited by superhans - 15 May 2021 at 9:56pm
Back to Top
I-shen Soundboy View Drop Down
Registered User
Registered User


Joined: 21 December 2016
Location: Big Smoke
Status: Offline
Points: 375
Post Options Post Options   Thanks (0) Thanks(0)   Quote I-shen Soundboy Quote  Post ReplyReply Direct Link To This Post Posted: 29 December 2020 at 11:16pm
Originally posted by superhans superhans wrote:

... happy to concede that stringing random boards together isn't going to be worth my time and buying an off the shelf amp is a good idea.

I'm now wondering if a mains amp and inverter would be a bad choice versus a car amp?

Car amps every time.  The four channel ones can bridge.to 
give you L, R and bridged sub, and they throw in a crossover too.  When that's not loud enough bridge L&R and add.a monobloc for the sub.  I've got 1.2k on the back of a bicycle using just that.  It's all class D but still eats batteries.
Back to Top
infrasound View Drop Down
Old Croc
Old Croc


Joined: 13 May 2011
Location: Brizzle
Status: Offline
Points: 2252
Post Options Post Options   Thanks (1) Thanks(1)   Quote infrasound Quote  Post ReplyReply Direct Link To This Post Posted: 30 December 2020 at 12:09am
You can get amps with single voltage power supply for the most efficient solution- something like a TAS5630 would give you a ton of power at 40v+

Please don't use an inverter!
Back to Top
superhans View Drop Down
New Member
New Member
Avatar

Joined: 07 December 2020
Location: UK
Status: Offline
Points: 6
Post Options Post Options   Thanks (0) Thanks(0)   Quote superhans Quote  Post ReplyReply Direct Link To This Post Posted: 26 June 2021 at 11:00pm
It's been a while, but I owe you all thanks for your replies and guidance. I've just about finished the signal and amplifier stage for the project now.

Unfortunately, I killed the 2.1 board I was hoping to repurpose while trying to remove the input stage from it to bypass the tone controls (I'm sure I can fix it if I really need 2 TPA3116 chips on a board). I ended up replacing it with separate amp boards (both TPA3116) - one is built into a little mono boombox acting as a midtop and the other is stuck in a case with one of the tiny Sure/Wondom ADAU1701 boards and a really tiny boost converter to step up the input voltage to get a tiny bit more unclipped output into the 8R driver.

Since I've got DSP now I've been able to use it to put a HPF on at 25Hz to protect the drive, but testing with an old Peavey M4000 showed what the TPA3116 datasheets already told me - it distorts way before the power is high enough for that to be a concern.

All that's left is batteries - I've gone for salvaged 18650s as an experiment. (No inverter :))

The "rig" hasn't even left the house yet and I've already got plans - a beefier TDA7498E board is on its way plus a more powerful DC-DC converter which should hopefully get me some more headroom before I need to build more cabinets (though I'm tempted to build another THAM10 so it looks cooler).
Back to Top
slaz View Drop Down
Old Croc
Old Croc
Avatar

Joined: 27 November 2009
Location: London E2
Status: Offline
Points: 2627
Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 28 June 2021 at 12:56pm
Originally posted by superhans superhans wrote:


All that's left is batteries - I've gone for salvaged 18650s as an experiment. (No inverter :))


You want some salvaged 18650's ? Got a whole bunch here you can FOC if you can collect from London E2. There must be a few dozen of em ... from laptop battery packs. Some I've tested/charged, others are still in the laptop packs. Most seem to able to deliver current (esp in the context of intermittent curent draw like from class D amplifiers).

Lemme know if you want em .... in fact I was gonna put em up in the "free stuff" section.

REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
Back to Top
superhans View Drop Down
New Member
New Member
Avatar

Joined: 07 December 2020
Location: UK
Status: Offline
Points: 6
Post Options Post Options   Thanks (0) Thanks(0)   Quote superhans Quote  Post ReplyReply Direct Link To This Post Posted: 29 June 2021 at 9:51am
Originally posted by slaz slaz wrote:

Originally posted by superhans superhans wrote:


All that's left is batteries - I've gone for salvaged 18650s as an experiment. (No inverter :))


You want some salvaged 18650's ? Got a whole bunch here you can FOC if you can collect from London E2. There must be a few dozen of em ... from laptop battery packs. Some I've tested/charged, others are still in the laptop packs. Most seem to able to deliver current (esp in the context of intermittent curent draw like from class D amplifiers).

Lemme know if you want em .... in fact I was gonna put em up in the "free stuff" section.



Ah that's really kind but I'm based up in Sheffield so wouldn't be able to collect them. I did manage to buy some from ebay (but got rinsed on shipping since they can't get sent in the regular post anymore) so have a few to play with for now.

I'm sure someone will be interested but, if you can't shift them after a while I might be interested in buying a few (if you can be bothered to deal with shipping that is).
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.094 seconds.