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Old 15th August 2008, 11:38 PM   #11
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I forgot to ask:

The new power switch I bought has a blue LED which is supposed to iluminate in the on position. The LED dosent come on?

On the rear of the switch are 3 connections, +, A, and Earth. Ive no idea what the correct wiring is for this switch so I wired the positive pin and 'A' pin to the PCB where the original switch was, left the earth alone. It works fine but the LED dosent come on, any ideas what ive done wrong?

(The switch is after the smoothing cap and rectifier so its only switching the 12v supply to the chip).

Heres a pic of the switch showing the pins:

Click the image to open in full size.
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Old 15th August 2008, 11:40 PM   #12
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Default Update.

I had a play with the switch. Wired the ground to a ground point on the pcb (where the original LED was) and wired the A (must mean annode) to the annode connection on the PCB. I decided to read up on LED's before I did this so Im sure it should have worked, but it didnt. I think ive blown the LED so I'll get another switch and try it again.

The next thing I want to do is try a star gound. (Im new to this so this project serves for learning, and is simple enough that it allows an easy gradient to the process) Ive done some studying on the theory and I think I know what Im going to do.

Its pretty simple:

The input ground on the phono sockets will be the star point. I'll connect the main PCB ground, minus speaker terminals, chassis, and mains earth to this point. I experimented with connecting the speaker 'minus' to the input ground and this did sound better. Another option might be using the negative point on the main smoothing cap as a star point?

A more elaborate idea is to seperate every ground point on the pcb and wire each one to a common star, but this would be difficult and time consuming so I'll leave the idea to one side for now. It would be interesting to see if it made a difference though.

Probably the biggest bug I have at the moment is that when I touch the Volume control I get a hum. Can anyone tell me why this is happening? Also there is contact noise from the pot, it crackles when I turn it?

I soldered copper legs on to the main smoothing cap and mounted it sideways on the PCB facing the TX. This seems to have improved the sound slightly in the treble.

For the wiring I think I'll use solid copper for the ground and silver plated copper - teflon insulated wire for the signal and output. I'll probably use 1mm for the signal and 1.5-2.00mm for the output.

Still researching caps for the input (0.22-1.00uF) and output decoupling (470uF).
For the output Im thinking about 470uF Oscons with Polypropylene box caps under the pcb as bypass. Does anyone know if this will be a good idea?
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Old 16th August 2008, 11:06 AM   #13
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Default Re: Update.

Quote:
Originally posted by mikesnowdon
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?
If you want to skip them, you will need a different amplifier with split power supply. Bypassing them with a smaller MKP cap is a good idea. Using those high-priced components may however be a waste of money.

Quote:
Originally posted by mikesnowdon
On the rear of the switch are 3 connections, +, A, and Earth. Ive no idea what the correct wiring is for this switch so I wired the positive pin and 'A' pin to the PCB where the original switch was, left the earth alone. It works fine but the LED dosent come on, any ideas what ive done wrong?
Here is the datasheet of a similar switch with schematic. You will need a resistor between the Earth pin of the switch and your 0V. The size depends on the voltage. 0,68 to 1k should work for 12V. The smaller value gives you the highest brightness, the bigger one increases the lifetime. Not that the latter would be a big issue with LEDs.

Quote:
Originally posted by mikesnowdon
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?
For safety reasons you should absolutely earth your chassis.

Star grounding is a technique you use to avoid possible hum loops. If you have no hum, leave your grounding as is (Never change a running system ). On the other hand you might get hum once you connect earth to the chassis, as this indicates
Quote:
Originally posted by mikesnowdon
when I touch the Volume control I get a hum
When you touch the volume control your body forms a connection to earth through your feet and the floor. You may be forced to do star grounding still after earthing your chassis decently. And connect the volume pots metal parts to the ground as well.

The pot seems to be worn. The crackling appears, when the wiper loses and makes contact to the resistor. You can try contact spray to deal with that for the moment, but sooner or later you will need a new pot.
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Old 16th August 2008, 02:47 PM   #14
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Quote:
Here is the datasheet of a similar switch with schematic. You will need a resistor between the Earth pin of the switch and your 0V. The size depends on the voltage. 0,68 to 1k should work for 12V. The smaller value gives you the highest brightness, the bigger one increases the lifetime. Not that the latter would be a big issue with LEDs.
Thanks for that, I was looking for a diagram but couldnt find anything.

Quote:
For safety reasons you should absolutely earth your chassis.

Star grounding is a technique you use to avoid possible hum loops. If you have no hum, leave your grounding as is (Never change a running system ). On the other hand you might get hum once you connect earth to the chassis, as this indicates
I think I'll run the input ground to the PCB input and run the earth, chassis, and negative speaker terminals to the input ground on the rear of the RCA's. Would this be a good idea? What about the connection of the chassis to the ground? Should I just use an crimp 'eye' and bolt it to the bottom of the case? (this is all my CA Amp has).

Quote:
When you touch the volume control your body forms a connection to earth through your feet and the floor. You may be forced to do star grounding still after earthing your chassis decently. And connect the volume pots metal parts to the ground as well.

The pot seems to be worn. The crackling appears, when the wiper loses and makes contact to the resistor. You can try contact spray to deal with that for the moment, but sooner or later you will need a new pot.
What would be a good quality pot to use then? Obviously a ALPS blue would be a waste on this amp, but are there any good quality (in sound terms) pots which would be ok?

For the input I have some 10uF Oscons and tiny wima's which I'll use under the pcb as bypass.

Im wondering if doubling up the 4700uF smoother is worth it. Obviously with only 2.5wpc I'll never get earth shaking bass but adding the 4700uf Pana made a hugge difference so adding one more might be a good idea. If I did this Id probably get one of these PCB's and new diodes. Then If I want to I can add a 7809 reg and cap later.
Click the image to open in full size.
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Old 16th August 2008, 07:11 PM   #15
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I see three things:

There's great variety amongst capacitors, so you might try various capacitors in your collection for the speaker output capacitor. The range seems to be 470uF to 1500uF, depending on speaker load. Just try a few and go with whatever sounds best--such an easy way to make an improvement.

If you have an input coupling capacitor, the Nichicon MUSE ES series is worth a try. Something like the 10uF 50v plus a 100nf monoceramic (a "powerful" and clear prosound presentation). OR, a nice plastic cap, about 1uF to 2uF.
And. . .
If the input filter (dc block) cap is located between the pot and the amplifier, then its possible that a far smaller value will roll off bass that won't come out of the speakers, thereby resulting in more usable power from that 2.5 watts. A probable working trick is paralleling a pair (or 3) of 22nF polyester caps--that'll either work great or terribly, but it'll be obvious either way.

The power supply. . . the faster that is the more low bass you get, and the slower that is, the more "old fashioned" rounded sound you get. Whether you see this or not is highly reliant on what it takes to drive your speakers--naturally well-damped speakers have less need of electronic dampening from strong motor control. One thing I see is that there's just one cap in the power supply. Its getting hit hard by the rectifier. Using two may do nothing or may help.

EDIT: With these three things, and some of the above mentioned touch-ups, you can aim for the most detailed and musical presentation, probably resulting in hi-fi. Have fun!
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Old 16th August 2008, 08:04 PM   #16
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Quote:
Originally posted by mikesnowdon
I think I'll run the input ground to the PCB input and run the earth, chassis, and negative speaker terminals to the input ground on the rear of the RCA's. Would this be a good idea? What about the connection of the chassis to the ground?
Both questions have already produced heated debates on this forum.
Here are several links about correct grounding and earthing. The gist of it is
a) For safety reasons the earth must always go directly to the chassis.
b) Wherever the best point for the star ground is, you will probably not notice the difference in your amp as long as you have no hum loops.
c) Connect the audio ground to earth, if you can. That makes it more stable against disturbances. If a connection form earth to ground already exists anywhere else in the audio chain, you are likely to get hum. Then you will have to make your personal assessment, how to deal with it. Either leave the ground floating in the amp as long as the earthed component is connected, and connect the amp ground to earth when it is not connected. That is what "ground lift switches" are for. Or you make a fixed connection and go to lengths to find a way to break the resulting hum loops by other means.

Quote:
Originally posted by mikesnowdon
are there any good quality (in sound terms) pots which would be ok?
This might help you choose.
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Old 16th August 2008, 09:06 PM   #17
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Default Re: TEA2025 alternatives

Quote:
Originally posted by mikesnowdon

I have a little 'learning' project on the go and need some help
finding possible upgrades for the TEA2025 chip.
---------------------
Ive been searching for compatible chips as a possible upgrade
but im a novice so Im having trouble finding one.
Can anyone help?

There are plenty of small Stereo Power chips
that are made for Single Supply. Often in range 6 to 12 Volt DC.

I know you may have decided for using TEA2025, because you want to reuse the PCB you have.
TEA2025 is a very old and not very hi-fi chip.
According to datasheet quick look,
it will not put out more than like 0.2-0.5 Watt / for THD max 0.2 %
And never more than like 2 Watt.
-----------------


I would, if possible for you, go for something better and slightly more powerful.
So for next project you may try some better chip.

Japanese Sanyo are know for their good audio transistors and good electronics.
I know there are 100-reds of even more modern chips, that may be as good and better
..... but
LA4270 from Sanyo is one stereo IC
that can put out like 2 x 6 Watt max at higher Power Supply
and like 2 Watt THD 0.1 % into 8 Ohm speakers
and like 1 Watt THD 0.2 % into 4 Ohm speakers


You can find one LA4270 for 2.88 incl VAT here (Sheffield)
http://www.irwinelectronics.co.uk/semiconductors.html

If you want to look & read about this chip
and see the basic PCB layout for it
download this LA4270 datasheet from Sanyo:
http://www.semiconductor-sanyo.com/ds_e/ENN1724D.pdf



Regards Lineup
Lineup Audio Lab
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Old 16th August 2008, 09:50 PM   #18
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Quote:
Originally posted by danielwritesbac
I see three things:

There's great variety amongst capacitors, so you might try various capacitors in your collection for the speaker output capacitor. The range seems to be 470uF to 1500uF, depending on speaker load. Just try a few and go with whatever sounds best--such an easy way to make an improvement.

If you have an input coupling capacitor, the Nichicon MUSE ES series is worth a try. Something like the 10uF 50v plus a 100nf monoceramic (a "powerful" and clear prosound presentation). OR, a nice plastic cap, about 1uF to 2uF.
And. . .
If the input filter (dc block) cap is located between the pot and the amplifier, then its possible that a far smaller value will roll off bass that won't come out of the speakers, thereby resulting in more usable power from that 2.5 watts. A probable working trick is paralleling a pair (or 3) of 22nF polyester caps--that'll either work great or terribly, but it'll be obvious either way.

The power supply. . . the faster that is the more low bass you get, and the slower that is, the more "old fashioned" rounded sound you get. Whether you see this or not is highly reliant on what it takes to drive your speakers--naturally well-damped speakers have less need of electronic dampening from strong motor control. One thing I see is that there's just one cap in the power supply. Its getting hit hard by the rectifier. Using two may do nothing or may help.

EDIT: With these three things, and some of the above mentioned touch-ups, you can aim for the most detailed and musical presentation, probably resulting in hi-fi. Have fun!
Thank you, thats probably the most positive feedback I've had on this project.

It all started on pinkfishmedia.com with a thread I posted called 'Just for a laugh.....HERE:

And followed up with a new thread. HERE:

Im still confused about the grounding. Of course I could leave it as-is and connect the Earth to the case. However, while having a poke around the other night I tried connecting the speaker ground to the input ground and it did sound slightly better. A safe option might be star grounding the 'signal ground' and connecting the earth to the chassis. One article I read said it was best to have all grounds/earth and chassis conected at the signal input RCA?
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Old 16th August 2008, 11:34 PM   #19
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Quote:
Originally posted by mikesnowdon
. . . However, while having a poke around the other night I tried connecting the speaker ground to the input ground and it did sound slightly better. A safe option might be star grounding the 'signal ground' and connecting the earth to the chassis. One article I read said it was best to have all grounds/earth and chassis conected at the signal input RCA?
The case of a very small op amp on a single supply. . . If it sounded better, you did something right.

Also, check that pot and make sure its 20k or 15k or 10k (something approximating line level).
In comparison, a 100k or 50k pot would sound like that noise when connecting a live guitar amp (BUZZ) when your hand goes near.
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Old 17th August 2008, 02:45 AM   #20
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Default Update.

I had a snooze this afternoon which lasted 4 hours so I've been up late working on the amp.

Heres a list of the changes:

Connected the IEC earth terminal to chassis, and shortened the wires from IEC to Transformer.

Made a mini star ground at the input ground, this connects to the negative speaker terminals and connects to the PCB ground @ the input solder pad, all wired with solid core copper I stripped from some T.V. coax.

Removed the negative return wires from the binding posts to the PCB. Only positive wires run from PCB to positive terminal using 1.5mm stranded copper milspec wire.

Re-wired the positive input connections with a twisted pair each of .5mm milspec stranded copper wire (got that from work fro nowt!).

Changed the input caps to 10uF Oscons and bypassed under PCB with .22 wima foils.

Changed feedback caps to 100uF Tants.

Theres caps that link from pins 14, into the output, (not sure why?) I changed them to 100uF Rubycon ZLH.

I taped the shaft of the volume pot in a crude attempt to isolate it from the knob.

Chassis earth:

Click the image to open in full size.

Star ground:

Click the image to open in full size.

Main PCB:

Click the image to open in full size.

New wiring:

Click the image to open in full size.

The above has made a difference to the sound in a positive way.

The midrange and treble has more detail, the overall sound is cleaner, and theres no hum when I touch the vol knob! The only thing is now there seems to be slightly less bass, its still there and its not bad, just a little quieter than before. Maybe adding another 4700uF cap will help as well as upping the value slightly (and quality) of the output caps. Its late night so I cant turn the wick up. I hope after a couple of days the bass will come back and the sound will get warmer as things settle in. Initial listening is positive and im quite happy with the improvement.

However, there is a strange thing thats happened which I can see the cause of. The speakers were out of phase. This was easy to solve by swapping the plugs on one speaker. Maybe I wired my speakers wrong when I changed the internal wire. who knows, its wierd. I'll check them later. Nevertheless, Im happy with what I've done and will let you all know how things sound once settled in.

I'd still like some advice on a reasonably good pot to use please.

Thanks all,
Mike.
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