I have an old velodyne vx-11 subwoofer which was recently fried. I took it apart and discovered the transformer and the crossover boards are working according to spec––I can put another class-D amp between the audio out of the crossover and the speaker and it plays as expected.
However, when I plug in the amplified board, I can smell that "smell", and also the standby/on LED on the crossover no longer lights up.
The board is pictured below with the TDA8920BTH analog amp IC:
I checked all the capacitors with a DMM and they seem fine. The board gets +/- 25.8VDC from the crossover board as shown below:
I'm a bit of a noob here, but Is it possible that by replacing TDA8920BTH IC, the board will be as good as new?
However, when I plug in the amplified board, I can smell that "smell", and also the standby/on LED on the crossover no longer lights up.
The board is pictured below with the TDA8920BTH analog amp IC:
I checked all the capacitors with a DMM and they seem fine. The board gets +/- 25.8VDC from the crossover board as shown below:
I'm a bit of a noob here, but Is it possible that by replacing TDA8920BTH IC, the board will be as good as new?
If you feel OK about soldering an surface mounted chip then try it.
On the other hand a new board can be bought quite cheaply: https://www.aliexpress.com/item/328...1;23.77;-1;-1@salePrice;GBP;search-mainSearch
Or a bit cheaper: https://www.aliexpress.com/item/100...1;18.52;-1;-1@salePrice;GBP;search-mainSearch
Cheers
On the other hand a new board can be bought quite cheaply: https://www.aliexpress.com/item/328...1;23.77;-1;-1@salePrice;GBP;search-mainSearch
Or a bit cheaper: https://www.aliexpress.com/item/100...1;18.52;-1;-1@salePrice;GBP;search-mainSearch
Cheers
Removing a SMD is quite likely to damage tracks, and some have a solder blob underneath to conduct heat. That is another headache.
Should not blow up, though.
Check the supply, and get two boards, on as spare, shipment will be cheaper.
Buy the more expensive one, simply because it may have netter parts.
Should not blow up, though.
Check the supply, and get two boards, on as spare, shipment will be cheaper.
Buy the more expensive one, simply because it may have netter parts.
I agree. I bought two of these: https://www.aliexpress.com/item/400...;12.57;-1;380@salePrice;GBP;search-mainSearch only ever used one, well over a year now and utterly superb. You may need to remove a couple of resistors to stop some hiss how to here: https://fh3classd.blogspot.com/p/class-d-xh-m590-tpa3116d2.html
Cheers
Thx for the comments, I'll bookmark it for reference.
But an unexpected development––when the VelodyneAcoustics service rep learned I was in Brussels, he said HQ could replace it if I paid for shipping. (None of the US authorized repair centers I contacted had parts for an item this old.) I'm waiting to confirm he meant the part and not the entire subwoofer. But in general, this is excellent service for a +10y product.
But an unexpected development––when the VelodyneAcoustics service rep learned I was in Brussels, he said HQ could replace it if I paid for shipping. (None of the US authorized repair centers I contacted had parts for an item this old.) I'm waiting to confirm he meant the part and not the entire subwoofer. But in general, this is excellent service for a +10y product.
What is going on with Pin 14 (VDDP1 - channel 1 power supply) in your pic? It looks dark for some reason, but I can't make out if it's burned or not
I noticed that as well. I scraped it off with an xacto knife and it cleaned up fine. I was also getting power to pin 14 when I put a battery to the DC power supply pins. But in the end, that didn't fix the problem.
I contacted Velodyne in Germany late January and they offered to send me a replacement board--for free. However, it's 9 months later and they still haven't received the part, and instead they offered a complete new back panel for €120.
In the meantime, I've been using a Dayton KAB-250 monkey-patched in place. It seems to work fine, all the other components on the back panel seem to operate correctly. Now I'd like to find something more permanent.
I looked at the above item, but it seems to only have AC in. I've got +/-25.8VDC from the internal power supply, and I'd like to connect it directly. Also, the TDA8920BTH is from 2010. Is there a better alternative or different chipset entirely that I should consider?
I saw this TPA3255 unit on ebay and it takes DC48V:
https://www.ebay.com/itm/225107974290
https://www.ebay.com/itm/363464496325
I'm looking for something that is as clean a drop in as possible. The original VX-11 was rated 100W RMS to a 10" cone.
In the meantime, I've been using a Dayton KAB-250 monkey-patched in place. It seems to work fine, all the other components on the back panel seem to operate correctly. Now I'd like to find something more permanent.
I looked at the above item, but it seems to only have AC in. I've got +/-25.8VDC from the internal power supply, and I'd like to connect it directly. Also, the TDA8920BTH is from 2010. Is there a better alternative or different chipset entirely that I should consider?
I saw this TPA3255 unit on ebay and it takes DC48V:
https://www.ebay.com/itm/225107974290
https://www.ebay.com/itm/363464496325
I'm looking for something that is as clean a drop in as possible. The original VX-11 was rated 100W RMS to a 10" cone.
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We get transistor based populated boards here, good for 30-0-30 supply, with power in, signal in, and speaker out terminations.
That would be best, or you can try a 7294 based unit, power may be less.
Unless you have a large area to cover, most people are content with amps capable of 20W / channel or so.
I am not into Class D amps, see that forum also here, may be better for your needs.
That would be best, or you can try a 7294 based unit, power may be less.
Unless you have a large area to cover, most people are content with amps capable of 20W / channel or so.
I am not into Class D amps, see that forum also here, may be better for your needs.
Can you send me a link for reference? The problem with the VX-11 is they they didn’t add a power switch. But it wouldn’t be too hard to add a toggle somewhere just for the amp. I’m not super concerned about audiophile, it’s for a prototype digital piano. Once I figure out the basics, I can enhance the electronics.
Do a search, some issue prevents us in India from connecting to Chinese sites. So no links.
Or try Indian suppliers.
Or try Indian suppliers.
The boards sold in India are mostly with AC in, the transformer is connected to the PCB.
Rectifier, smoothing caps, and 7805 (for FM/USB/Bluetooth module), are all on the board.
The transistor boards are sometimes only the power amp, the 7805 part is on the separate pre amp section.
Do a search for assembled power amp board with 30-0-30 supply, and go from there.
Work out the need for heat sink, if the old one can be used, fine...or buy a PCB that comes with a heat sink, the sinks can be difficult to source at times.
Rectifier, smoothing caps, and 7805 (for FM/USB/Bluetooth module), are all on the board.
The transistor boards are sometimes only the power amp, the 7805 part is on the separate pre amp section.
Do a search for assembled power amp board with 30-0-30 supply, and go from there.
Work out the need for heat sink, if the old one can be used, fine...or buy a PCB that comes with a heat sink, the sinks can be difficult to source at times.
Try to get another bridged out Class D module or replace that chipamp if you can.
Downgrading to a non bridged Class AB amp (such as 7294) will reduce power to about 20% of what you have now 😱
I know you said "no need for HIGH power, it´s for an experiment" but power loss will be GROSS and your presumably biamplified system will be completely unbalanced.
Downgrading to a non bridged Class AB amp (such as 7294) will reduce power to about 20% of what you have now 😱
I know you said "no need for HIGH power, it´s for an experiment" but power loss will be GROSS and your presumably biamplified system will be completely unbalanced.
My soldering skills suck, so I'm gonna skip the latter.
How do I find the former? I understand the concept of bridging the output of a 2 channel amp. And I just recently learned the term "split rail" describes the 25.8-0-25.8VDC power supply I can draw from. But when I search '"split rail" class D power amp module' I find boards with TPA3255 chips that call for a single rail/switching power supply. (e.g. https://www.aliexpress.com/item/4000614590516.html) Am I missing a keyword in my search? or am I searching for the wrong thing?
Those need a bridge rectifier, connect 0 (center tap) to amp earth.
Add filter caps, 3300 to 6800 as recommended, if needed.
If you have +/- 25.8V DC, those are all that the amp needs.
See the photos close up, and schematics if available, or download the data sheets, such details are normally provided by chip maker.
Go from there.
Add filter caps, 3300 to 6800 as recommended, if needed.
If you have +/- 25.8V DC, those are all that the amp needs.
See the photos close up, and schematics if available, or download the data sheets, such details are normally provided by chip maker.
Go from there.
Ok.
Your problem comes from the fact that "most" modern bridged Class D amplifiers try to use single supply rails for simplicity (what you found in your search), the problem being that each output stands at 1/2 supply rail voltage, they get out with it because speaker goes from one output to the other so it does not "see" that huge DC voltage.
While conventional Class AB amps used split rails so speaker out stays at ground voltage , 0V DC.
Even if used bridged (like most high power PA amps did) they still kept the split supply, which in any case was "the standard".
I GUESS Philips/NXP designed TDA8920 for split supplies (again, which is not common TODAY) for commercial reasons: it allowed manufacturers to use these newfangled amps with their current supplies, for which they would probably have large stocks of transformers and boards plus still valid OEM supply contracts, notice this amp uses a normal 50/60Hz "iron" transformer and NOT an SMPS.
Notice it´s a 2003 design.
Problem is you need a TDA8920 based split supply amplifier to replace it (I am not aware of others).
Thanks God there is at least one with such specs, I would buy it and adapt it to your current active speaker.
https://www.aliexpress.com/item/328...db!64612906734!sea&curPageLogUid=QjGq9hKK3Prx
Notice it has all the required connections:+/-V supply, BTL speaker outs.
Can´t vouch for their quality but hey, it´s the only game in town.
Not sure about input signal connection, not shown in your pictures either, but guess that´s manageable.
TDA datasheet explains stereo and bridged connections so worst case it can be deduced from there.
Thanks for your reply. I see that board and it looks like it will work as you described.
However, I managed to find a few other boards built on the TDA8954TH chip which take a dual-rail input voltage spec'd as VAC. Are these also compatible? I'm just trying to understand the underlying electronics and what to pay attention to when I choose a board.
https://www.aliexpress.com/item/1005001841234090.html
- mono amp (this is a mono subwoofer application)
- Input voltage: Recommended dual AC 24V( range: AC12-28V)
https://www.aliexpress.com/item/4000484519703.html
- dual channel amp with Input voltage: AC 12-28V
Now that I have learned more about power supplies, it seems the existing power supply is pushing dual-rail 18.8VAC through a bridge rectifier to get dual-rail 25.8VDC. But I would have to hack the VAC connector, while the VDC is easily accessible and ready to go.
Be clear, your supply is 25.8 + to -, or 25.8+ to 0, and 25.8 - to 0, for a total of 53.6 V, between + and -?
The 8920 is rated with supply between +/-12.5 to +/- 32V, at which point it locks up.
At 24V, many Class D boards are available, and will take 26V safely, so you have more choice.
The 8920 is rated with supply between +/-12.5 to +/- 32V, at which point it locks up.
At 24V, many Class D boards are available, and will take 26V safely, so you have more choice.
I have STRONG doubts about those BOARDS, specially the first one.
You sure those are populated boards and not bare PCBs?
* Price
NO WAY 1 TDA8954 + 6 supply caps + 2 filter toroids + 1 heatsink + 1 board and assorted hardware cost just U$9.96
*weight : NO WAY 1 TDA8954 + 6 supply caps + 2 filter toroids + 1 heatsink + 1 board and assorted hardware weigh just 120 grams.
The second one asks $30 for about twice the hardware so still dubious.
If "too good to be true" then they are probably not true.
.
Just stick to the TDA8920 based split supply amplifier I found (or any other with exact same specs) and call it a day.
You sure those are populated boards and not bare PCBs?
* Price
NO WAY 1 TDA8954 + 6 supply caps + 2 filter toroids + 1 heatsink + 1 board and assorted hardware cost just U$9.96
*weight : NO WAY 1 TDA8954 + 6 supply caps + 2 filter toroids + 1 heatsink + 1 board and assorted hardware weigh just 120 grams.
The second one asks $30 for about twice the hardware so still dubious.
If "too good to be true" then they are probably not true.
.
Just stick to the TDA8920 based split supply amplifier I found (or any other with exact same specs) and call it a day.