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PostPosted: 04 Nov 2009, 12:56 
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Just use any diodes that can handle the voltage and current. Going overboard is good with diodes though and they are always available cheap at high voltage and decent current. Try for something that will handle 6 or more amps and 100 or more volts. MUR840, MUR860, MUR1510, MUR1560 all are great options. Snub each diode with a .1uf cap of equal or greater voltage capability. Film or ceramic.
Uriah

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PostPosted: 04 Nov 2009, 14:00 
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Thanks again, you've been very helpful!

One last question; I do have a lot of BYT03-400, do you think those would work? And why is the capacitor placed across the diod?


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PostPosted: 04 Nov 2009, 15:33 
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Hi Guys!

Uriah wrote:
Just use any diodes that can handle the voltage and current. Going overboard is good with diodes though and they are always available cheap at high voltage and decent current. Try for something that will handle 6 or more amps and 100 or more volts. MUR840, MUR860, MUR1510, MUR1560 all are great options. Snub each diode with a .1uf cap of equal or greater voltage capability. Film or ceramic.
Yep - that's an option. Snubbing the diodes or the rectifier bridge also is optional.
Olof wrote:
One last question; I do have a lot of BYT03-400, do you think those would work?
IMO - not so good. Their values are slightly above the limit (rated at 3 amperes) if you want to use the suggested 120VA transformer.
Olof wrote:
Will the GBPC2510W diode bridge work for the PSU?
This is way better than using the BYT diodes! I would go for this option and engage two of them (one for each transformer winding). The GBPC rectifier bridges will stay cool and i think they are able to handle very high current spikes and possible high "backflow currents". They are a bit "softer" than the MURs. MUR diodes are not neccessary and more expensive than 2 simple 25A / 35A bridges. I would use MURs on "high current" power supplies.
Olof wrote:
And would you prefer a 25k or 50k potentiometer?
Hmm - good question... I use the 50k log. "Blue Velvet" from Alps, since i made some bad experiences with "cheaper" types. 50k is my rule of thumb and it always worked fine. 25k should be a better match for the input impedance and it also provides a good volume control, but it's hard to get one from Alps here. If you have a good(!) 25k log. in your box - use it.

I hope that was a little help ;-)

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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: 06 Nov 2009, 17:16 
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Hi all!

Some words about transformers, rectifiers and an important "NULL"...

What transformer do i need to build the amp and what is "centre tapped" or "dual secondary"?? What is the "ground" and how do i build it?? At least - what the heck is "NULL" (or simply 0)?? OK - here it is.

At first:
To build the amp like on the project page, you will need a "dual secondary" transformer with 2 x 18 Volt AC. A dual secondary transformer has 2 seperated windings with 18Volt AC (alternating current) per each. Usually, such a transformer is labled with something like: 2 x 18VAC - 120VA or 18VAC//18VAC - 160VA.
It is recommended to use this dual secondary transformer. As said: 2 x 18VAC - 160VA. This transformer is a very usual type and you can get it nearly everywhere. If you already call other transformers your own, you also could use them. It is not(!) especially needed to use the 18VAC. One 15VAC / 12VAC, found in your "scrapbox", will also do the job. But, the output power will be less with every volt that goes below 18VAC. I suggest to choose a transformer with at least 120VA. This VA rate can deliver 3,3 Amperes per rail @ 18VAC. VA? VA! VA: is the apparent power. Just divide the AC output voltage with the VA factor and the result is the current capability per rail / winding. = 18VAC / 120VA = 3,3 Amperes per rail (6,6 in total).
Please don't go above the 18VAC suggestion with the transformer. The max. IC input is 25VDC. That is reached by using the 18VAC transformer. Every Volt above 18VAC will result in senseless voltage regulators and efforts, that are not worth the time and more grey hairs.

Centre tapped?!:
A "centre tapped" transformer has one (1) single winding that is tapped at the centre of this winding. This types are always labeled like "18 - 0 - 18 VAC" or "18VCT". Please read the transformers manual, or ask your dealer, if you are not sure with the transformer descriptions, or if you don't know if the offered type is a dual or CT.
Transformers are always rated with AC (Alternating current) and never in DC (Direct current)!.

I bought a 2 x 18VDC transformer. What's to do now?
Simple! Just refer to the project page and build the power supply that is shown on the "supply section".
The 2 x 18VAC guy is hooked up by using that way:
Attachment:
dual.GIF
Again - you will surely see the positive rail (+), the negative rail (-) and the ground rail. The ground rail is the rail, that is connected in the middle between the 2 capacitors. This rail is also called "NULL" or "0". This "null" rail provides a point where both potentials (+/-) are equalized. That's important for the electron flow and to define the rail potentials as positive and negative. Without the null, you wouldn't have a negative potential. Please take care of the rectifier bridge setup. The upper bridge is "null to negative" and the lower is "positive to null".

I bought a 18-0-18 VAC or a 18VCT (Volt AC - centre tapped) transformer. Is that wrong? What can i do now??
Now - that's not a mess and you surely can use it. How?
Attachment:
centre_tapped.GIF
Just change the supply input a little bit for use with one (1) single rectifier bridge, because you don't need to build a "centered" PSU like the one above. The PSU is centered by the transformer because the transformer is (now guess what) - centre tapped ;-).
Whoops - why don't we use it as standard? Because the performance is slightly lower and centre tapped transformers (VCT) are not usual sold types. I want to say, that it's way easier to get a dual secondary type.

Which rectifiers do i need? Just use a pair 25A to 35A silicone bridge rectifier. This rectifiers are standard and available everywhere. There is no need to use "ultra fast forward / recovery diodes". The bridges are cooler anyway and "softer".

--
Please regard, that the 2 pictures above, only show the basic layout and how to connect the transformers to the rectifiers. The complete and accurate scheme for the PSU (with ALL components) is still on the project page.
--
Please regard that my English still isn't the best... If you find some errors - feel free to do the corrections!
--
I hope, that the PSU section is complete now. Have fun!


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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: 06 Nov 2009, 17:50 
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Hi again!

Something about the input caps... Several builders have played around with the input caps / input configuration. I have received some feedback about this, and now i want to share an overview from the informations.

The input caps that were used are WIMA MKP10, WIMA MKP4, Orange drops, Electrolytic Panasonics, Audyn caps, Mundorf caps, Bipolar Electrolytic caps and Roederstein / ERO caps (blue MKP types).

The TDA sometimes sounds a bit sharp, depending on which type of music you prefer to listen. Here are some caps that seem to be very good for the TDA input section:

WIMA caps (or the Vishay MKP) MKP10 or MKP4 make the amp sounding a bit softer at higher frequency levels. All of the sound appears clear and detailed, but the heights are a bit smoother. The sharpness decreases a little bit by using this types.

Orange Drops (the 715 type) are a good descision if you like a "all over" smoother sound, without compromises on the sound quality. They will add some kind of "sweetness" to the amp. The Bass is kicking and the mids should be clear and rich detailed. The heights are much softer but still very clear.

Electrolytic caps or bipolar electrolytic caps are very different to each other - depending on the type you might wish to use. They are cheaper and easier to get and that's the way how they can(!) sound. Some have found, that the details and the sound quality can(!) be good within using e-caps. But more people don't like them in the input sections. Many people say, that electrolytic caps don't pass the details to the IC. "They steal parts of the sound". But high capacity caps can take away the heights - or let's say - they can act as high frequency filter. IMO - i also use them in coupling / decoupling sections, but not straight at the input or bypassed with smaller MKPs.

Audyn and Mundorf caps are the cuties that i prefer. I can say that they provide a superior quality at the input. They sound very detailed, rich and they (nearly) don't touch the frequency range.
The other side is that they can make the amp sound sharp, because of their quality. They pass everything to the amp, and the amp isn't too shy to amplify the higher frequencies to a snakes "sss"... OK - not so good, Al. (No - they are very good! Me, i like crystal heights). That's subjectiv and every one has other impressions.

The ole Roederstein / ERO caps are a real deal on nearly all amps (if you can get them somewhere). They are rich detailed and heavenly great over all the bandwith. I use a pair on my LM3886 GainClone and i can say that they are yummy ;-) Yes, they are - but are they worth the effort to get them? No, they are discontinued and only a few dealers should have some on stock - for heavenly high prices. Forget it, if you don't have them in your box! It's not worth the effort.


The best descision is to use WIMA MKP10 or Orange Drops 715, if you think, that you want a smoother and softer sound. You can also go to set up a little input signal conditioner. That may sound complicated, but it isn't. Just add one small 180Ohm - 240Ohm resistor, after the input cap (in series to the IC) and then, after this resistor, a small 68pF - 10nF capacitance (also WIMA / Vishay / Orange drop or Mica) to ground. This should slightly cut the HF capability to lower levels and this also should decrease the sharpness to a bit lower levels.

Have fun,
Tom.

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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: 08 Nov 2009, 14:05 
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Hm..another question popped up in my head earlier today. Is it possible to add a equalizer circuit to the amp?

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PostPosted: 08 Nov 2009, 14:21 
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Could this be a option? http://www.zen22142.zen.co.uk/Circuits/Audio/3band.htm

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PostPosted: 08 Nov 2009, 16:36 
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Yep - that's an option. Or see:

http://sound.westhost.com/project97.htm.

http://sound.westhost.com/project02.htm.

http://sound.westhost.com/dwopa2.htm.

http://www.circuit-projects.com/audio/baxendall-tone-control-circuit-bass-and-treble-control.html.

This one is used in my Baxandall pre amp version (still not ready to release):http://www.zen22142.zen.co.uk/Circuits/Audio/t-ctrl.htm.

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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: 08 Nov 2009, 20:19 
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Hi all just joined.

Think someone mentioned a 'boxy sound' a while ago.... hope you remembered to phase the speakers!

That is ensuring the + speaker terminal is connected to the speaker out on the amplifier and the -ve speaker terminal is connected to the ground on the amplifier so that the cones move in the same direction.... if one is in anti phase one cone will be moving back whilst the other is moving forward.

This will give it a 'boxy sound' and also the stereo image will be poor..... a couple of ways here to check this.... well, three if you do a visual inspection.

Use a 1.5 volt cell battery and tap them on the speaker lead and not which way the cone moves... I did say tap not hold them on!! The both want to move the same way.... and easier way is to feed a mono signal through both amplifiers, if correctly wired the sound should come exactly half way bewteen the speakers - if they are out of phase it will be very difficult to tell!

Thought I'd just mention this.... let you carry on. Cheers

Davy


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PostPosted: 09 Nov 2009, 04:38 
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Back on topic... re Tone control.

Builders would be using varying transformer meaning slightly varying supply voltage to the tone control, would it not be better to use a stabilized supply say from a 12V zener diode or a LM7812 regulator... that way you'll know all circuits built will be performing almost identical.

The DC supply lines on the PCB ought to be a little thicker because of the high peak current when used at hefty volume levels, the speaker track out also to be a little wider... just my feelings.

Would it not be wise to incorporate some fusing system say 3.15 Amps on the AC secondary or secondaries of the transformer or at least a 2 amp on the primary side.... otherwise that thin track on the PCB is gonna just melt under fault conditions.. especially if built on on Vero board which I hate - OK for lash ups n' testing....

... there are many transformer and rectifier combination's here possibilities here but better to stick to one standard design to reduce complications.... I do think 25A is a overkill here, stick my neck out and say a 5 or 6 amp device for each amplifier or say a 10 amp for both amplifiers - don't forget we are not running the amplifier under DC conditions we're using speech and music... I don't think the heat sinking has been mentioned yet, these are only a TO220 package and gonna need shift heat at full output!

Also the earthing is very important...use a common single point earthing for the speakers and other amplifiers which should be at the 0v junction of the smoothing capacitors... this is the point that is usually grounded or earthed to the metal case or chassis.... otherwise hum and instability may result.

Davy


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