Date   
Re: B40 LM386 and µB TDA2822 and that 470µF Cap

Gordon Gibby <ggibby@...>
 

The capacitor is there because this are you amplifier is designed to be operated with one supply voltage, +V, and ground.

The opamp output transistor circuit can only move between zero and a positive voltage.  

To avoid keeping a physical offset displacenent on the speaker cone, at the cost of significant current through its very low DC resistance! One adds a large capacitor in series to allow the speaker cone to rest at neutral position.

In the datasheet I looked at, they were using a 1000 µF capacitor.   That’s probably give you a better low frequency response, and basically the value isn’t that critical.



On Mar 1, 2018, at 17:20, Arvo KD9HLC via Groups.Io <arvopl@...> wrote:

Someone said if you find a fence ask why it's there before you tear it down.

On the B40 there is a 470µF cap on the output, between the LM386 output and the speaker.  On the LM386's TI datasheet Figure 10 there is a 250µF cap in that spot.  It's not an unreasonable leap to surmise that someone thought, "Hmmm, a 470 would probably work there and I've got a bunch of them."  I can't find anything in the datasheet explaining the need for the capacitor.  It may be that there is some DC offset in the output that needs to be removed.

On the µB there is also a 470µF cap between the output of the TDA2822 and the speaker.  On the TDA2822's STMicroelectronics datasheet application circuits there are examples with both 100µF and 470µF capacitors.  Again, I can't find why those caps are there.

The presence of these caps in the manufacturer's guidelines makes the "too much capacitor in the µB" hypothesis much less probable.  Maximum input voltage rating of 15V in the TDA2822 datasheet imply that 12-14V supplies should not be a problem, either.

A dead short on the output should not be a catastrophic problem for the amps because the caps are blocking DC current, so any power to be dissipated is associated with how loud you've got the volume knob cranked.  So if you turn it up and don't hear anything, turn it back down!

All bets are off if we have parts of unknown provenance, ie, counterfeits.  Does HF Signals have a process in place to assure the supply of components that conform to the expected specifications?  Bad batches of parts shouldn't happen from reputable suppliers.

All that said, there should probably be a pretty plain heads up somewhere in the tribal knowledge that if you wire up the µB speaker jack per the website and plug a TS (tip-sleeve) as opposed to a TRS (tip-ring-sleeve) male connector into it, you will have a dead short across the jack and it won't work properly.

One way to avoid that trouble is to simply wire the output of the amp to the tip connector of the jack and leave the ring connector of the jack floating (unconnected).  If you plug in a mono speaker, or an old fashioned earphone, it will work.  If you plug in stereo headphones you'll only hear audio from one earpiece.

I'm leaving mine wired for stereo.

Re: U1 fried

G1KQH
 

Recently I found some TDA2822's on ebay from China, I got the GQRP club to purchase a batch ( I bought 50 too ). Tony Fishpool (G4WIF) setup up a test and found although they worked well at low Volts they got hot over 7V!:


His findings are made public here on his website here: http://www.fishpool.org.uk/audioamp.htm


Food for thought!

73 Steve

GQRP 11049

http://g1kqh.blogspot.co.uk/

Re: uBITX - U1 Getting Fried - possible cause #ubitx

G1KQH
 

Recently I found some TDA2822's on ebay from China, I got the GQRP club to purchase a batch ( I bought 50 too ). Tony Fishpool (G4WIF) setup up a test and found although they worked well at low Volts they got hot over 7V!:


His findings are made public here on his website here: http://www.fishpool.org.uk/audioamp.htm


Food for thought!

73 Steve

GQRP 11049

http://g1kqh.blogspot.co.uk/

B40 LM386 and µB TDA2822 and that 470µF Cap

Arvo W0VRA
 

Someone said if you find a fence ask why it's there before you tear it down.

On the B40 there is a 470µF cap on the output, between the LM386 output and the speaker.  On the LM386's TI datasheet Figure 10 there is a 250µF cap in that spot.  It's not an unreasonable leap to surmise that someone thought, "Hmmm, a 470 would probably work there and I've got a bunch of them."  I can't find anything in the datasheet explaining the need for the capacitor.  It may be that there is some DC offset in the output that needs to be removed.

On the µB there is also a 470µF cap between the output of the TDA2822 and the speaker.  On the TDA2822's STMicroelectronics datasheet application circuits there are examples with both 100µF and 470µF capacitors.  Again, I can't find why those caps are there.

The presence of these caps in the manufacturer's guidelines makes the "too much capacitor in the µB" hypothesis much less probable.  Maximum input voltage rating of 15V in the TDA2822 datasheet imply that 12-14V supplies should not be a problem, either.

A dead short on the output should not be a catastrophic problem for the amps because the caps are blocking DC current, so any power to be dissipated is associated with how loud you've got the volume knob cranked.  So if you turn it up and don't hear anything, turn it back down!

All bets are off if we have parts of unknown provenance, ie, counterfeits.  Does HF Signals have a process in place to assure the supply of components that conform to the expected specifications?  Bad batches of parts shouldn't happen from reputable suppliers.

All that said, there should probably be a pretty plain heads up somewhere in the tribal knowledge that if you wire up the µB speaker jack per the website and plug a TS (tip-sleeve) as opposed to a TRS (tip-ring-sleeve) male connector into it, you will have a dead short across the jack and it won't work properly.

One way to avoid that trouble is to simply wire the output of the amp to the tip connector of the jack and leave the ring connector of the jack floating (unconnected).  If you plug in a mono speaker, or an old fashioned earphone, it will work.  If you plug in stereo headphones you'll only hear audio from one earpiece.

I'm leaving mine wired for stereo.

Re: Escaping smoke #ubitx

Bill KC5SB
 

Installed the replacement parts today - back up and running.  Going to work on the case and a few mods now.  Thanks for the help everyone.

Bill

Re: U1 fried

Mike Woods
 

On 2/03/18 10:00 AM, Mvs Sarma wrote:
Whether it could be batch wise observation?
 I don't remember such cases reported earlier

I do say in the article:

"However, it could equally as well be a run of bad chips, or the fact that the device is running near its voltage maximum (it is rated for 15v maximum)."

I suspect you are correct Sarma in that this could be a batch issue with the TDA2822, in the same manner, there seems to be occassional runs of postings about K3 or K1 relay failures.  Yet most of us don't have problems with component failures.  Just user error!

Mike


--
Mike Woods
mhwoods@...

Re: U1 fried

MVS Sarma
 

Whether it could be batch wise observation?
 I don't remember such cases reported earlier


On 2 Mar 2018 02:25, "Mike Woods" <mhwoods@...> wrote:
Hi everybody

I have tried to summarise what we know about the TDA2822 problem, prevention and fixes in this article on ubitx.net:

http://ubitx.net/2018/03/01/tda2822-problems/

Let me know if you can suggest further improvements to my text.  We don't want 2000 µBITx owners to go through the same pain as some of you have experienced ...  I hope to insert a resistor in the output circuit today!

73 Mike ZL1AXG


On 2/03/18 9:50 AM, Claude-Alain Baumgartner via Groups.Io wrote:
Hi Howard,

Yes, both pins 2 and 4 of the LM386 go to pin 4 of the socket (ground).

Regards,
Claude


--
Mike Woods
mhwoods@...

Re: uBITX - U1 Getting Fried - possible cause #ubitx

Tim Gorman
 

I'm not sure even a 100uf cap is needed. For communications purposes
you should be able to get by with a 47uf capacitor. A 47uf cap in
series with an 8ohm speaker should give you a low freq 3db point of
about 500hz. I realize this is a kind of a paper napkin calculation
because a speaker doesn't exhibit true resistance but it should still
be close.

You can get an 8ohm, 4" CB replacement CB speaker for about $5 on
Amazon.

I personally like the idea of a fuse in the speaker lead. That's
probably what I will do. If it is a current spike of several amps that
is blowing the 2822 then a fuse should protect it. And you don't have
to worry about wasting half your audio power in a resistor.

tim ab0wr

On Thu, 01 Mar 2018 12:16:35 -0800
"Jerry Gaffke via Groups.Io" <jgaffke=yahoo.com@groups.io> wrote:

I think you're right.

The output pin has a quiescent DC voltage of around half the supply
voltage, or about 6v, so the 470uF cap will have a 6v charge on it
when operating.  A significant bit of energy for the TDA2822 to
provide, and it tries to do so almost instantaneously in the case of
a short. A series resistor seems prudent. 

Perhaps the 470uF cap could be reduced to 100uF.
At 500hz the 100uF would have an impedance of 1/(2*pi*500*100e-6) =
3.18 ohms, which seems borderline for good sound quality when using
an 8 ohm speaker.

I vote for the resistor.  Something like 4 or 8 ohms, 1/2 Watt.
But worth experimenting if somebody has a stash of cheap TDA2822's on
hand.

Configuring the TDA2822 for Dex's  bridge configuration does away
with the cap charging problem, but now the headphone jack has to be
floating.  The bridge would be ideal for an internal speaker.

Jerry

On Thu, Mar 1, 2018 at 11:47 am, Jim Sheldon wrote:


My take is that huge 470 uF electrolytic in the output of the
TDA2822M and the speaker gets a huge surge at turn on and during
any loud noise or POP in the audio chain.

Re: U1 fried

Mike Woods
 

Hi everybody

I have tried to summarise what we know about the TDA2822 problem, prevention and fixes in this article on ubitx.net:

http://ubitx.net/2018/03/01/tda2822-problems/

Let me know if you can suggest further improvements to my text.  We don't want 2000 µBITx owners to go through the same pain as some of you have experienced ...  I hope to insert a resistor in the output circuit today!

73 Mike ZL1AXG


On 2/03/18 9:50 AM, Claude-Alain Baumgartner via Groups.Io wrote:
Hi Howard,

Yes, both pins 2 and 4 of the LM386 go to pin 4 of the socket (ground).

Regards,
Claude


--
Mike Woods
mhwoods@...

Re: U1 fried

Claude-Alain Baumgartner
 

Hi Howard,

Yes, both pins 2 and 4 of the LM386 go to pin 4 of the socket (ground).

Regards,
Claude

Re: Raduino Connections #bitx40

Jerry Gaffke
 

Here's up to date firmware for the Bitx40
    https://github.com/amunters/

The "bitx40" branch will work with a stock bitx40 with no hardware mods,
probably best to get things working with that sketch first.
There are some optional hardware mods that enable some significant new features.

The "bitx40-raduino-v2" branch requires some minor hardware mods
and adds the flexibility of being able to vary the BFO frequency in firmware.
I'd recommend eventually moving to this firmware. 

Jerry


On Thu, Mar 1, 2018 at 12:18 pm, James Wilson wrote:
Thanks,  Where do I get the sketch for the Bitx40?

Re: Raduino Connections #bitx40

James Wilson
 

Thanks,  Where do I get the sketch for the Bitx40?

Re: uBITX - U1 Getting Fried - possible cause #ubitx

Jerry Gaffke
 

I think you're right.

The output pin has a quiescent DC voltage of around half the supply voltage, or about 6v,
so the 470uF cap will have a 6v charge on it when operating.  A significant bit of energy
for the TDA2822 to provide, and it tries to do so almost instantaneously in the case of a short.
A series resistor seems prudent. 

Perhaps the 470uF cap could be reduced to 100uF.
At 500hz the 100uF would have an impedance of 1/(2*pi*500*100e-6) = 3.18 ohms,
which seems borderline for good sound quality when using an 8 ohm speaker.

I vote for the resistor.  Something like 4 or 8 ohms, 1/2 Watt.
But worth experimenting if somebody has a stash of cheap TDA2822's on hand.

Configuring the TDA2822 for Dex's  bridge configuration does away with the cap charging problem,
but now the headphone jack has to be floating.  The bridge would be ideal for an internal speaker.

Jerry


On Thu, Mar 1, 2018 at 11:47 am, Jim Sheldon wrote:
My take is that huge 470 uF electrolytic in the output of the TDA2822M and the speaker gets a huge surge at turn on and during any loud noise or POP in the audio chain. 

Re: U1 fried - LM38t works

DrZ <zehrhj2@...>
 

I've taken Claude's suggestion with Jerry's addition, and I'm happy to say it works - lots of gain, too.  I haven't checked it extensively yet, but it's very promising.  When the TDA burnt up, I replaced it with a socket.  Then I used two more sockets to make a plug-in adapter, with Claude's pin-to-in guide and adding Jerry's suggestion of a .1 cap across pins 1 and 8.  Now I can get back to trying to solve the BCI problem....
Howard K4LXY

uBITX - U1 Getting Fried - possible cause #ubitx

Jim Sheldon
 

Now that I've fried 2 of the TDA2822M's in my latest uBITX once while it was just sitting there and once when I plugged a speaker in, I took a good look at things.

My take is that huge 470 uF electrolytic in the output of the TDA2822M and the speaker gets a huge surge at turn on and during any loud noise or POP in the audio chain.  It will sit there just fine with nothing connected but the instant you plug a speaker in you cause that cap to discharge and recharge again causing a huge current spike and the TDA2822M can't handle it.

The current crop of 2822's do not have a recognizable manufacturer's logo on them and I suspect they are Chinese knockoffs.  I bought a handful of them off eBay from a seller called Teufel Tronics in the US and when the original blew, I replaced it with one of these.  It ran fine until I was working on loading some test software and turned it on with no speaker plugged in.  It was sitting there fat, dumb and happy until I plugged the speaker in.  All of a sudden, BANG and the top blew off the 2822.  Fortunately I have 8 of my stock left so if it goes again, it will be an easy fix.  I got smart and put an 8 pin socket in when I changed it this last time. 

It was suggested putting a 4 or 8 ohm resistor in series with the hot lead of the speaker and I intend to do this as soon as some get here from Digi-Key in a couple days.  That may limit the surge current enough to keep it from happening again.

Jim Sheldon W0EB

Re: full rig power control unit

Jerry Gaffke
 

Jerry didn't write the check, but that's in the ballpark for a fully loaded license.

I was encouraging them to look at other tools like Eagle, and later Kicad.
I like cheap, and would also prefer to not use anything stuck with MsWindows.
But folks there have a history of using PadsPCB going back to the 1980's,
and inertia is one of the elemental properties of the universe.

Jerry


On Thu, Mar 1, 2018 at 10:49 am, Michael Hagen wrote:

Jerry didn't not mention what the cost of Pads was, I bet over $10K.  And maybe another couple K PER YEAR to keep the license up.

 

Re: U1 fried

DrZ <zehrhj2@...>
 

Thanks, Jerry.  I have an adapter made and will give it a try.
Howard 

Re: Second batch of uBITX shipping? #ubitx

Tim Young
 

Hi Jay:

This would be a great place to start

http://ubitx.net/ BITX Web Site of Mike ZL1AXG

Tim

WB7UVH



On 2018-03-01 12:08, Jay Davis wrote:

Mine was ordered around December 26th and I opened my door this morning to a DHL package .It has arrived,  I had not asked for DHL shipping but it came that way quite quickly.  I will send the 10$ shipping and am excited to go back over all the mods discussed and decide which ones to install.  Any one have suggestions on what mods to add since I am starting my build from scratch now. 
Thanks Jay .  N3QPW


Re: Second batch of uBITX shipping? #ubitx

Jay Davis
 

Mine was ordered around December 26th and I opened my door this morning to a DHL package .It has arrived,  I had not asked for DHL shipping but it came that way quite quickly.  I will send the 10$ shipping and am excited to go back over all the mods discussed and decide which ones to install.  Any one have suggestions on what mods to add since I am starting my build from scratch now. 
Thanks Jay .  N3QPW

Re: TDA2822 ill treatment test!

Jerry Gaffke
 

Hmm, the TDA2822 does have a "bridge" mode where it is wired up with the two amps
out of phase to drive a speaker without needing output caps.
Is that what you are referring to?

The uBitx does not use bridge mode, the second section of the TDA2822 is left unused.
So the output load is between the amp output pin and ground,
allows the headphone jack to have the return at ground potential.
A DC blocking cap (C77 in the uBitx) is required.

> Shorting the output keeps both legs of it above ground.
Perhaps you mean that if we were in bridge mode with a 0 ohm load,
both sides of the load would wind up at a voltage above ground?

Jerry


On Thu, Mar 1, 2018 at 10:29 am, Dexter N Muir wrote:
Read the thread/s thoroughly, Raj (and all). Shorting the output keeps both legs of it above ground. It would seem that taking either leg to ground (that 'ring' connection that is taken there by a mono plug in particular) does the damage. It's the 'cheapo' method of boosting audio output: bi-phase two amps: 4x the power from the same supply voltage. This package evidently does this internally. If the spec sheet shows the internal circuit, this becomes obvious. I await reports...