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-   -   The sound of TDA7294 (http://www.diyaudio.com/forums/chip-amps/9536-sound-tda7294.html)

alvaius 6th January 2003 08:35 PM

The sound of TDA7294
 
First, yes I have searched and found previous posts on the TDA7294.....

Can anyone who has actually built something based on the TDA7294 or heard something built based on these parts give me some feedback. I am interested in high quality amps based on this chip, AKA Gain Clones with the National integrated chips.

I found a bunch of these in the junk bin and may build something up using them with a bunch of other items from the junk drawer.

Alvaius

arthur 7th January 2003 05:24 AM

jeff rowland model 8ti 9ti mc6 use 7294 with good results

sangram 7th January 2003 06:01 AM

I have used 7294s in the past, and am still using one.

I had built two of them a couple of years ago. One had blown under what I call mysterious circumstances, with no sign of distress, smoke, heat - it just switched off and has not been revived to date. The complete board is still lying around somewhere. The pair was then running at 35 volt rails (25 VAC 250VA) into 4 ohm loads, which is too far above spec to be serious.

Its mate has been resurrected into an instrument amplifier head. 70 watts is too much power to waste. It now runs off more sober 27 volts rails (20VAC, 120VA) and is mated to a set of preamps of dubious antecedents, which mix up three guitar inputs.

Before the preamp had been added, I ran a check to see what the amp sounded like. I only use 5% carbon resistors for my projects, and off-the-shelf polypropylene caps. Also mass produced, probably inadequate heatsinks. No specials (I could afford them, they're not available around here) !

Anyway I found that compared to my homebrewed STK 4191 bridge amp the sound was slightly thin on bass but presence and clarity were far superior. Treble was excellent, refined and non-plastic. I had one amplifier, so I could not test imaging etc. The only drawback was fan noise and transformer buzz (mechanical, not electrical) but since neither originated from the amp, I venture all was perfect with it.

When I had assembled the amps initially I remember being surprised by the punch and power. I got the same feeling in spite of strangling the amp with an underpowered transformer and low cap supply (I never like too many caps). Dead silent at idle, even through a pair of headphones feeding off the output terminals.

In its role as an instrument amplifier, the amp is unblievable. Acoustic guitar never sounded this good, even subsonics caused by heavy picking can be heard even through tiny 8" woofers, and string noise and harmonics are unbeleivably clear. I rustled up the amp 'cause I just happened to have it lying about, but I guess I know what's going into my next solid state guitar amp...

On a side note, Bose uses these in some of their Acoustimass series amps, to run the satellite speakers. Apart from quite a few high-end amps. With a nice large heatsink, probably with a fan added, good PCB layout and quality components, these have a lot of potential. I would love to know about the effects of capacitance. I have very little (5700 uF per rail only, 4700 uF on the supply and 1000 uF on the amp board) not as a design philosophy or due to budget, but simply because getting good caps in this country are like asking for the moon.

The downside is, This IC is simply not available in the country. Elektor had brought some in when they were selling kits based on their published article on the 7294, but since they stopped it's been a long walk looking for one. I dunno what I'm going to do if she blows, 3875 maybe but it's just not powerful enough...

vuki 7th January 2003 04:08 PM

Hi Alvaius,

I'm listening to TDA7294 based gainclone-style amp. In the last 2 years I also tried TDA1514, LM1875, LM3875 and LM3886 but I prefere TDA7294/93. Even in non-inverting configuration it outperforms (at least to my ears) LM3875 (inv or noninv.) which I consider to be the best of the rest (and TDA1514 being worst).
It's easy to build, so why don't you try it and listen for yourself?

Vuki

alvaius 7th January 2003 10:13 PM

Just the encouragement that I needed! Thank You.... will not take any more than scrounging the parts bin, though from Peter Daniels approach for gain close, I will be investing in some good signal coupling capacitors.

Alvaius

jkeny 9th January 2003 08:56 AM

TDA7294
 
Quote:

I'm listening to TDA7294 based gainclone-style amp. In the last 2 years I also tried TDA1514, LM1875, LM3875 and LM3886 but I prefere TDA7294/93. Even in non-inverting configuration it outperforms (at least to my ears) LM3875 (inv or noninv.)
Hi,
I just looked at the datasheet for TDA7294 - looks good - I may go this route myself and compare it to a LM3875 inverted gainclone (just being rebuilt)
I noticed that two sets of power supply pins are provided - one pair for signal amp and one pair for power amp - I wondered if these could be connected seperately - signal amp running off regulated PSu and power amp off unreg PSU?

Has anybody tried this?

Alvaius
Maybe this is something to try? Let us know how you progress

Vuki
What coniguration do you use? Any advantage to inverting config for TDa7294?

alvaius 9th January 2003 01:28 PM

If I am interpreting their "high efficiency" circuit example in the data sheet where they switch in different voltage supply rails, then yes, you should be able to run off different supplies for the two sections. You can bet I will try that. Give me a month or two to get this running. I have to finish some speaker stuff and I am debating another Class-A amp project.

Alvaius

Spherion 9th January 2003 02:14 PM

Hello,
I will try this amp next week, someone living close to me has
a twelve of them to sell for 25 pln (5 $) each...It's a beer money,
so I'll buy two and give them a try.
I also have some OPA627/BUF so will try to make such a small
integrated ampo and find out what how 'much' sound U can
have for so 'small' cash :)


Greetz

Spherion

sangram 10th January 2003 06:47 AM

Please check out the thread on 'Qs about a paralleled 7293....' on this forum before you attempt to run it off separate supplies. Some ICs have blown when the pins are connected with resistors etc.

Actually the supply source even in the high-efficiency circuits is differently connected: The preamp section runs off the higher voltage continuously (+40V?) and the power stage runs off a +/- 20v (?) supply which is bootstrapped to 40V on higher current loads. The source of the +40V is the same for the amp and preamp.

The 7294 is available in the local market at about $2.75 each. I'm gonna be buying a lot of these babies now...

I love the bridge config most of all, 170 W into 16 ohms sounds good for a dual drive sub - cheap!!

alvaius 10th January 2003 06:01 PM

My total cost at this point (taking out the good decoupling caps), will be close to 0, so I can see no reason not to at least try it. I owe my mom an amplifier to go with the DVD for her Christmas present, so at a minimum, this will do it. That way I can get my speaker test amp back...!

Alvaius


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