Date   
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

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: 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: 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

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: 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/

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: B40 LM386 and µB TDA2822 and that 470µF Cap

Gordon Gibby
 

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: full rig power control unit

Glenn
 

I'm thinking of doing a PCB for this but have a query about it's operation.

It seems to me that any detected fault turns on Q5, which in turn turns off Q1, which then has the effect of bringing up the 'Operate' LED D1 rather than the 'Fault' LED. ie they seem to be swapped over.

Has this Schematic actually been built and tested?

Glenn
vk3pe

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

Arvo W0VRA
 

On Thu, Mar 1, 2018 at 02:38 pm, Gordon Gibby wrote:
The opamp output transistor circuit can only move between zero and a positive voltage.  
Yes, but I'd think if someone was building an IC audio amp they'd go ahead and stick a cap inside it!

I suppose different applications would have different optimum caps.

Re: full rig power control unit

Glenn
 

There are some missing parts in the BOM also, C10 & C11. I assume 10nF (0.01uF)

glenn

For Sale - Raduino (from uBITX kit)

n5ib_2
 

I have a never-used Raduino/NANO (optionally, with LCD display) for sale.
$25 postpaid to a USA address for just the Raduino/NANO, $30 postpaid USA for the Raduino/NANO and display.
Shippping to a DX address would be around US $15 and require a customs declaration.

These are the ones that came with my uBITX. I have replaced them with my "RadI2Cino" and a 4x20 display.
The Raduino board has the handwritten annotation "547/1" and "not programmed"

I'll ship it as is, or if the buyer sends me a ".zip" file with their choice of Arduino firmware, I will program the NANO.

Reply --OFF LIST PLEASE-- to n5ib (at) juno (dot) com if you're interested.

Jim, N5IB

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

Jerry Gaffke
 

It would be really really tough to fabricate a 100uF cap as part of a silicon wafer.
Datasheet specs the quiescent output voltage to be around half of the supply voltage,
right where you would expect it given the totem pole output driver.
As per post 43200.

And as alluded to in previous posts, the size of the cap is dictated by the impedance
of the load (typically 8 ohms) and the lowest frequencies you need to be hearing.

If you don't like the cap you can use the bridge topology in the datasheet,
using the two halves of the amp at 180 degrees out of phase.. 
But then neither side of your speaker is a ground potential. 
It's either that or a big cap, your choice. 


On Thu, Mar 1, 2018 at 02:56 pm, Arvo KD9HLC wrote:
Yes, but I'd think if someone was building an IC audio amp they'd go ahead and stick a cap inside it!

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

Christopher Miller
 

One of the first replies suggested not wiring the ring, and using a mono to stereo adapter cable if stereo headphones are required. 

Chris
KF4FTR

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

Jerry Gaffke
 

And subsequent replies have suggested this may not be sufficient.

Some seem to fry when plugging something into the headphone jack even if there is no short to ground involved.
Or when powering up the rig.
Our best guess now is that there are significant currents involved when that 470uF cap suddenly has to charge up to Vcc/2
And that some clone TDA2822's may be weaker than mainline manufacturers.


On Thu, Mar 1, 2018 at 03:31 pm, Christopher Miller wrote:
One of the first replies suggested not wiring the ring, and using a mono to stereo adapter cable if stereo headphones are required. 
 

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

Jerry Gaffke
 

One observation that may or may not be relevant:
The datasheet from UTC spec's a supply voltage of 1.8 to 12v:  https://www.taydaelectronics.com/datasheets/A-1509.pdf
whereas the ST datasheet specs 1.8 to 15v:  https://www.taydaelectronics.com/datasheets/A-1003.pdf
Both spec an "Absolute Max" of 15v,
 


On Thu, Mar 1, 2018 at 03:39 pm, Jerry Gaffke wrote:
And that some clone TDA2822's may be weaker than mainline manufacturers.

Re: Designing Maritime Radio #bitx40

qonita.salimah@...
 

Thank you for all of your reply

In this picture below, the Band Pass Filter is using a tunable inductor. But in the schematic files in hfsignals.com using a fixed inductor and capacitor.
 

Is there any advantage and disadvantage for these two types of passive components?

Thank you so much :)

Re: Designing Maritime Radio #bitx40

qonita.salimah@...
 


Sorry this is the schematic picture

Where to from here?

davidaker@...
 

This afternoon, I drilled out my enclosure (one of the mailboxes from Lowes) and wired it up and made a contact on 30m and 40m (putting out 11 watts on 160, 8w on 80, 6w on 40m and about 3w on 20m).  How do I control output power and is there a way to jump to another band other than cranking the vfo?  Haven't wired up the mic yet.

Re: Where to from here?

Dave Bottom <ars.kd6az@...>
 

See Ian, KD8CECs blog and link to his firmware - turns it into a great radio 

Dave WI6R


On Mar 1, 2018, at 4:30 PM, davidaker@... wrote:

This afternoon, I drilled out my enclosure (one of the mailboxes from Lowes) and wired it up and made a contact on 30m and 40m (putting out 11 watts on 160, 8w on 80, 6w on 40m and about 3w on 20m).  How do I control output power and is there a way to jump to another band other than cranking the vfo?  Haven't wired up the mic yet.
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