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PostPosted: 07 Oct 2011, 18:33 
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Location: WI, USA
I am new here and am planning on building the TDA2050 amp. I have a xformer with a single secondary of 19VAC @5500ma. Will this work for this project using a layout as shown on pg 8 of this topic? I am having trouble reading the resistor values on that drawing if someone could help me out with them.
What kind of power could I expect with the 19VAC xformer?


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PostPosted: 09 Oct 2011, 14:45 
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Hi marv,

you can use the first of the PSU circuits from page 8 (from the dtsup1 post).
The divider resistors are 4K7 / 2W (4700Ohm) each. The resistors for the snubber network are 2R7 / 2W (2.7 Ohm).

Your transformer will do the job, but you'll only have half of the rectified voltage at the V+ and V- rail. That will be 13.5VDC per rail.
(The best way to go still is a dual 18VAC secondary transformer or a 36Volt centre tapped one.)

An other option is the single supply circuit from the original ST datasheet. It will make the power supply more easy to build, but the amplifier circuit will cause more work.

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 09 Oct 2011, 19:22 
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Thanks for the reply. I am (now) resigned to buying a new xformer. I guess I knew that was the best way to go. I am planning on using the TDA2050 with my PC to drive two front speakers (my old 5.1 developed problem). I hope I don't get into trouble here but I would like to ask if you can direct me to a layout that I could use the two obsolete TDA8947J chips that were in my old 5.1 system to drive my sub. The PS with my old system is good and regulated at 12V. I've looked at the TDA8947J data sheet but am not sure how to go about this, especially the "mute" business. Would I be better off to use a different approach? Please be kind as I am now in my 7th decade. :)


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PostPosted: 10 Oct 2011, 17:09 
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Hi marv - no problem ;-).

Please let me ask a question: Do you have any specifications / power ratings for the 5.1 speaker set?
I would really like to help you with your speaker system and i'm sure there will be a way (or two).

Phillips provides a very good and detailed datasheet (with layout) for the TDA8947J.
Did you try this one? Phillips datasheet. The mute circuit is not a big problem. The modes are only voltage controlled.
By applying the correct voltage to the pins #mode1 and / or #mode2, the IC is #standby, #mute or #on. I know - sounds simple...

I don't know any official or public DIY design or PCBs for the TDA8947J but the one from the datasheet.

BTW - i think that it is not easy to unsolder the ICs from the circuit board. The solder joints are surely lead free (Pb-free) and very difficult to unsolder.
PB-free solder needs a temperature of about 380°C. The temperature is manageable, but what about apply it to 17 pins the same time?.
You'll cook the boards - imho. Pin-by-Pin desoldering could work, but you'll need a "solder sucker" and solder with much Pb (i.e. Sn60Pb40).
Also a lot of patience and time...

What about fixing the old 5.1 system?

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 11 Oct 2011, 19:25 
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I don't have much info on the old 5.1 system except to say it is/was a Dell unit. I don't know anything about the 2 (small) center speakers or the 4 front L/R and rear L/R. The sub driver is a 5" Samsung 13W67KA 6 ohm 40W unit that was housed in a vented box along with the amps under my desk.

As far a fixing the old 5.1 I have pretty much given up on that idea. The problem I was having is that it would play normally for some period of time and then the volume would shoot up and I was not able to adjust the volume down to zero (with pot). I assumed it was a temperature related issue so I tried to isolate the problem component using a can of Freeze spray. I think it might be the TFA 9843J chip (2 channel stereo amp) that is also used in this system along with 2 TDA 8947J chips. Of course with a bunch of other stuff. Regardless I figured none of the chips are avaiable for purchase anymore so what I had hoped to do is come up with something for a 2.1 system. Thats when I discovered your 2050 amp write up with plenty of detail and PC board layout. :up:

What I was shooting for is an amp that will drive a pair of drivers from my home theater system that I no longer use. The are from Audio Concepts Inc. and each are dipolar units (actually 2 drivers in each enclosure) where sound radiates forward and rearward. Frequency response 50-20k +/- 3db, sensitivity 86db 1w/1meter. Recomended RMS power 30-100 watts/channel. Do you think the 2050 amp is beefy enough?

I think for my sub I will use a 200w powered sub that I no longer use from my home theater system. (Still have one in use there). I don't see why I couldn't connect the powered sub to my sub-out jack on my PC do you?

BTW, I figured I could easily snip the leads off of the TDA8947J chips on top of the board and still have enough lead length to re-use.

Thanks for your help.
marv


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PostPosted: 13 Oct 2011, 14:04 
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Quote:
Do you think the 2050 amp is beefy enough?
Hi marv, yes - i think so. I'll never get it why some companies "recommend" a RMS (what is this good for?) power rating. 30 to 100Watt...
86db @ 1W @ 1m is enough to damage your ears when you drive it with 1 Watt @ 1m (1Watt power - not RMS). That's like living 10 meters away from a highway all the day.
30db plus and you'll have a starting jet in your listening area. 20Watts (20 real Watts) should be more than suffiecient for everyone under normal listening conditions :2c: .

It's actually a good idea to use the ACIs and the sub :2c:.

Yes, you can setup a 2.1 via your soundcard. The sub should provide an active crossover which filters out the frequencies above ~200MHz (depending on the specs)
thus you can also use the rear channel plug (2nd stereo - Y adaptor) on your soundcard to drive the sub. Usually the sub / center out only works with 5.1 programmed material.
Maybe your software driver provides an option to detour the stereo signals to the sub / center out plug.
If not, use the rear channel plug and set the driver to "quadraphony" or 4.1.

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 17 Oct 2011, 11:38 
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Oh my - sorry!

crossover at 200Hz not 200MHz...

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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 22 Oct 2011, 11:14 
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On the new PS parts list can you clarify the value for the bleeder resisitor? The value in the table for Rb it shows 4k7 and below that it shows (2200 ohm). Thanks.


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PostPosted: 22 Oct 2011, 19:55 
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Hi marv,

yes - my bad. Not so very good.. (there is also a "Cout" from another table...)
2K2 for the bleeders is OK and verified. I've added a new list. BTW - 4K7 will also work fine - only just a bit slower..
Attachment:
PSU partlist_corrected.pdf

Thank you marv - for pointing this out. I owe you one!

@ Gio - if you are also in here - please delete the "old" psu partlist from the project page and add the new one. Thanks a ton!


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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 23 Oct 2011, 12:56 
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Joined: 07 Oct 2011, 15:06
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Location: WI, USA
I am about to order parts and am having difficulty finding suitable pot for the amp. I have located a dual 20k audio taper (Bourns) that I think should work (only $1.00 US). It is quite a bit less than the 25-50k you mention. Do you see this as a problem? The input to the amp will only come from my PC for front speakers.

marv


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