Chaip amp

Petervg · 26th October 2002, 09:59 PM

I've seen quite a few posts where the national LM388x chips are discussed. Does anybody know of similar chips that can have a higher supply voltage? I already have a 2x30Vac transformer here, and I'm afraid that kind of voltage will destroy the LM388x..

planet10 · 26th October 2002, 10:22 PM

Quote:

Originally posted by Petervg
I've seen quite a few posts where the national LM388x chips are discussed. Does anybody know of similar chips that can have a higher supply voltage? I already have a 2x30Vac transformer here, and I'm afraid that kind of voltage will destroy the LM388x..

The 3875/3886 has a max of 84V and the 1875 is less so the usual suspects are out unless you used the two secondaries in parallel (or separate windings for a stereo amp) and created a virtual ground or used a single ended supply (the 3875 ap note illustrates the SE supply). You'd only end up with about a 20 W amp thou -- not too bad thou, these are optimum at about 25 W max.

dave

pinkmouse · 27th October 2002, 08:15 AM

Hi Petervg

I am using a 30-0-30 300va supply for my experimental inverted gainclone,(using LM3875), and it works fine, I have had it running for a day or so driving 50w 85dB speakers to reasonable room levels, with no problems, (so far!!!

)

joensd · 27th October 2002, 09:51 AM

Hi,
one important thing with those overture series amplifier chips is the protection circuitry which will depend on the load impedance you will connect to your amplifier.
If you use 4Ohm speakers for example I wouldn´t use your transformer cause the output power will be limited.
You get full 68W at 4Ohm load with +-28V which is the voltage I use for my LM3886 amp.
Connecting an 8Ohm load to +-28V you won´t get full power then
(for full power +-35V) so you should think about what you´ll use and carefully read the datasheet.
Another concern is power dissipation which will be of course higher with higher voltage and is one of the few big limits to those chips.
Owning this transformer already I would choose to use the TDA7294,7293 (Can´t remember which was the improved version).

Petervg · 27th October 2002, 12:26 PM

Hmm, the TDA7293 looks like a solution to me, but is it possible to put two or more of them in parallel to be able to drive a 4 ohm load when the supply is +/-40Vdc? I've seen people doing this with the overtures using either very accurate resistors in the gain circuit or by using a servo... If It's really that simple, I'll put 2 or 3 of them in parallel to be sure they can handle the dissipation well.
Anybody have any experience with this?

P.

joensd · 27th October 2002, 06:18 PM

Hi Petervg,
you can parallel or bridge the TDA7293.
Just have a look in the datasheet.
It´s all well described.

Petervg · 27th October 2002, 07:09 PM

Ah yes.. that slipped past me. On page 8/13 they mention the parrallel operation of these chips. Looks simple enough for me. Anybody tried this before? Or am I gonna be a pioneer :-) ?
you recon they can be used to drive a 4Ohm subwoofer at +/-40Vdc suply?

P.

lohk · 27th October 2002, 11:08 PM

Linn does it - with quite a commercial success. I suppose.

26th October 2002, 09:59 PM	#1
Petervg diyAudio Member Join Date: Aug 2002 Location: Belgium	Chaip amp I've seen quite a few posts where the national LM388x chips are discussed. Does anybody know of similar chips that can have a higher supply voltage? I already have a 2x30Vac transformer here, and I'm afraid that kind of voltage will destroy the LM388x..

27th October 2002, 08:15 AM	#3
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Hi Petervg I am using a 30-0-30 300va supply for my experimental inverted gainclone,(using LM3875), and it works fine, I have had it running for a day or so driving 50w 85dB speakers to reasonable room levels, with no problems, (so far!!! ) __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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27th October 2002, 09:51 AM	#4
joensd diyAudio Member Join Date: Dec 2001 Location: Germany	Hi, one important thing with those overture series amplifier chips is the protection circuitry which will depend on the load impedance you will connect to your amplifier. If you use 4Ohm speakers for example I wouldn´t use your transformer cause the output power will be limited. You get full 68W at 4Ohm load with +-28V which is the voltage I use for my LM3886 amp. Connecting an 8Ohm load to +-28V you won´t get full power then (for full power +-35V) so you should think about what you´ll use and carefully read the datasheet. Another concern is power dissipation which will be of course higher with higher voltage and is one of the few big limits to those chips. Owning this transformer already I would choose to use the TDA7294,7293 (Can´t remember which was the improved version).

27th October 2002, 12:26 PM	#5
Petervg diyAudio Member Join Date: Aug 2002 Location: Belgium	Hmm, the TDA7293 looks like a solution to me, but is it possible to put two or more of them in parallel to be able to drive a 4 ohm load when the supply is +/-40Vdc? I've seen people doing this with the overtures using either very accurate resistors in the gain circuit or by using a servo... If It's really that simple, I'll put 2 or 3 of them in parallel to be sure they can handle the dissipation well. Anybody have any experience with this? P.

27th October 2002, 06:18 PM	#6
joensd diyAudio Member Join Date: Dec 2001 Location: Germany	Hi Petervg, you can parallel or bridge the TDA7293. Just have a look in the datasheet. It´s all well described.

27th October 2002, 07:09 PM	#7
Petervg diyAudio Member Join Date: Aug 2002 Location: Belgium	Ah yes.. that slipped past me. On page 8/13 they mention the parrallel operation of these chips. Looks simple enough for me. Anybody tried this before? Or am I gonna be a pioneer :-) ? you recon they can be used to drive a 4Ohm subwoofer at +/-40Vdc suply? P.

27th October 2002, 11:08 PM	#8
lohk diyAudio Member Join Date: Apr 2001 Location: Northern Noricum, near the Limes	Linn does it - with quite a commercial success. I suppose.