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Old 26th July 2008, 12:20 AM   #1
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Default TEA2025 alternatives

I have a little 'learning' project on the go and need some help finding possible upgrades for the TEA2025 chip.

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Details:

I will be using a amp module which ive salvaged from a pair of old PC speakers. This will be rehoused in a good chassis and powered from a better supply. (15VA Tx and 4700 Pana fc smotthing cap) I'll also be playing with caps to try and improve the sound. Details here:

Ive been searching for compatible chips as a possible upgrade but im a novice so Im having trouble finding one.

Can anyone help?
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Old 26th July 2008, 02:51 AM   #2
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I'm not aware of any pin-compatable chips.
I've played with some PC-speaker amps before,for use as headphone amps. I would suggest using better caps,and perhaps upgrading the PSU a bit. Regulation might be good,it seemed to help a bit on my experiments.

It's never going to be "hi-fi" but you can tweak them to get a little better performance.
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Old 26th July 2008, 11:33 AM   #3
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Cheers, I thought as much.

Ive ordered a chassis and 15VA 9v Toroid, and some caps to play with: Tant beads, Nichion Muse, Rubycon ZA's, and a pair of 1uf MKP's to try on the chip input. Hopefully Theres no DC on the output then I can remove the decoupling caps. I'll be bypassing the tone control and removing the swith on the left which is '3D Surround' so the signal path is a bit clearer.

Im hoping that the Adding the Tx and a 4700uf Pana FC will improve things considerably as the amp is currently driving 88db 8ohm speakers so the added headroom should be good.

Ive read the datasheet and found out that the chip's output power is dependant on the supply voltage. Obvoiusly with peak current demand from heavy bass etc the voltage will drop so Im considering adding a reg to the supply but Im not sure how to do this, or if it will solve the problem. Isnt the purpose of a reg to maintain a constant voltage? Any ideas for a beginner?
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Old 26th July 2008, 12:04 PM   #4
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Just been looking at regs and It seems easy to do. Ill be looking at fitting one of the Generic 7805 types for simplicity as this is my first amp project. Of the chip style regs which is the best in terms of low noise?

Also I cant tell how much Amps I need to feed this TEA2025 chip. The datasheet says 'Quiesent current' is 40 - 50mA. Does this mean anything?
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Old 27th July 2008, 02:21 AM   #5
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I used a 7809 (+9V) regulator on mine,and it worked well.Driving headphones the regulator didn't even get warm.It will probably run warm since you're driving speakers,a small heat sink should suffice.(or just screw it down to the chassis)

The output caps are needed to block the DC on the output.The output pins of this chip 'float' at 1/2Vcc.

Quiescent current is what the amp draws at idle.(no signal input.)
During music peaks,it will go up.
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Old 27th July 2008, 11:29 AM   #6
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I just found this article: Here

So I need a 12 Tx if im to use a 12 v reg. Im still a litle confused as the guy I ordered to Tx from said I only need a 9v one (unregulated) to get 12v on the chip? Help!
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Old 27th July 2008, 06:31 PM   #7
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9Vac transformer gives about 12-13Vdc(or even more) after rectification.Not enough for regulation with 7812 type of regulators.12Vac transformer would be suitable.

As TEA2025 has supply voltage of 3-12 Volts (absolute max. 15V),you could use a 9v regulator with your transformer.You don't get the maximum power but maybe the sound is even better than with 12V,who knows.
Other possibility is to use the transformer "unregulated" if the voltage stays under 15V.The chip may get too hot with this voltage,so do it in your own risk.
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Old 27th July 2008, 10:27 PM   #8
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Quote:
Originally posted by pikkujöpö
9Vac transformer gives about 12-13Vdc(or even more) after rectification.Not enough for regulation with 7812 type of regulators.12Vac transformer would be suitable.

As TEA2025 has supply voltage of 3-12 Volts (absolute max. 15V),you could use a 9v regulator with your transformer.You don't get the maximum power but maybe the sound is even better than with 12V,who knows.
Other possibility is to use the transformer "unregulated" if the voltage stays under 15V.The chip may get too hot with this voltage,so do it in your own risk.

Thanks. I allready ordered a 9v Toriodial on the advice of a freind. I believe this should be ok to run unregulated. I'll do it ths way to begin with and try a regged supply later and see what difference it makes.

One of the main reasons for this project is to learn some basics before diving into my main amp with a hot iron. It will be interesting to hear the difference between regluated and non-regulated. I suspect the amp will handle low bass and dynamic swings easier with a regged supply, also the higher VA rating of the new TX and larger smoothing cap should help.

As the amp is standard exept for a 220uf Blackgate cap on the main smoother (1000uF) which I had spare. Theres quite a lot of noise when no input is selected. Hiss and a light buzzing sound on the speakers. The biggest obvious drawback with it as-is, is the noisy transformer. Theres loads of mechanical vibration and the plastic enclosure resonates. Im expecting the Tx and Pana FC smoothing cap will help reduce this (and the new enclosue ive ordered). Of course, the chip might not be the best quality so some of the noise may be the chip itself. Another possibility could be the pots causing noise maybe?

What are the miain offenders with regard to noise?
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Old 27th July 2008, 10:35 PM   #9
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Quote:
"you could use a 9v regulator with your transformer.You don't get the maximum power but maybe the sound is even better than with 12V,who knows."
I guess it would be easy to find out. I'd just need one 7812 and one 7809 and see which sounds best. Assuming I re-order a 12v Tx instead of 9v. As I beleive study of a new subject is better done on an easy gradient I'll stick to 9v unregulated for now and try the option above later.

PS: I have added a IEC chassis filter to the amp and will continue use one when I re-house it in the new chassis. I know some say these are not good for audio but the amp is for the PC so its getting dirty mains and the filter is probably necessary here.
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Old 15th August 2008, 11:37 PM   #10
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Ive finnished the preliminary assembly.

The tone pot was removed and its associated componentry, and the '3D-Surround' switch and components removed as they were not required and I wanted to keep the signal path as simple as possible. The datasheet for the chip (TEA2025) stated a massive 470uf cap was needed for the output decoupling, so swapping for polyprops was out of the question due to size and cost. Instead I used a few of the holes (made available from the pot and switch removal) to mount a pair of 0.15 Mundorf MKP bypass caps to the 470uF lytics (linked underneath).

I had initaily played with 1uF Mundorf MKP's on the chip input, in place of the 100uF lytics which were there before. This had very good results but ufortunately I played around with the Mundorfs too much (adjusting their position) and broke one of the leads! I've put in a couple of 100uF tants for now.

I also had a Blackgate STD 220uf cap spare - so I added this in place of the 100uF decoupling cap on the chip. Also added a small heatsink to the chip as it gets rather hot driving the Missions!

I have some Tants, Rubycon, and Nichion Muse caps to play with in the feedback area (feel free to advise any better options here), and I also plan to get some more 1uF or 2.2uF Polyprops for the chip input. Rather than Mundorfs I want to try those small square ones (rookie alert!) as they will fit in the limited space better. Incidentaly, the chip datasheet suggests a value of 0.22uF on the chip input but the amp originally had 100uF lytics?

TEA2025 datasheet: http://www.datasheetcatalog.com/data.../TEA2025.shtml

There are only 2 manufacturers of this chip so as I allready have the UTC one I decided to buy a 'ST' one too. I'll try the other chip and see if theres a difference and I have a spare incase I cook one.

Well, the amps only been up and running for a few hours so I wont say much about sound quality. I can say that the beefed up power supply has made a diffrence. For a start the new Tx runs really quiet and the hiss/hum issues I had previously are solved. The sound has more guts now, sounding warmer and fuller.

Click the image to open in full size.

Internals:

Click the image to open in full size.

Click the image to open in full size.

Theres a couple of things to resolve before im happy the project is complete:

Im not unsatisfied with the hookup wire. I used some cheap Cambridge audio coax for the signal inpput and 1.5mm stranded copper wire for the output to the speaker binding posts. What would be a better wire to use? (silver would be ott for this project), some kind of OFC stuff perhaps?

I havent connected the earth pin on the IEC to the chassis yet. Im wondering about a star earth (connecting all the grounds on the terminals together) but I dont know enough about that yet. Any advice?

Lastly, is there a better soloution for the output decoupling caps? The main consideration here is that according to the datasheet anything less than 470uF will reduce bass output. Any better ideas than what I've allready done?

Please feel free to advise any other possible mods Ive not noticed.

As a closing remark, I'll say that this is my first amp and Ive really learnt alot from it so far and its been fun. Thanks to all who helped on the original thread, in particular PD.

Cheers,
Mike
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