Is DIY amplifier worthwhile

[captrajesh]

I found TDA7293 relatively easy and less expensive.

For now I am trying to guess the total cost.

TDA7293 chip may be relatively less expensive but I suggest you work out the total cost before pulling the trigger. I do not know about the sonics of TDA7293 but MyRef SQ is very good and having built one, I vouch for it.

 

[GeorgeO]

I agree with the last post. It is important that you make a cost estimate prior to the build-planning and educating yourself is as important as the actual build, more so when you are newbie.

 

[Kannan_madhu]

A question about capacitors , is there some specific kind of non polrised capacitors used for amplifiers or the commonly available ceramic capacitors will do ? i have seen the amp build pics where mostly some box kind of capacitors used .

 

[Audiodoc]

Capacitors are of various types:

Polarized ones like electrolytics and tantalums or non polarized ones like polypropylenes, polyesters, ceramic etc. Each have their advantages and disadvantages and thereby each variety is a better at one place or the other in a typical circuit.

Check

Capacitor - Wikipedia, the free encyclopedia

 

[Kannan_madhu]

I was planing to build my first gain clone using the LM1865 based on the reference circuit by national but they have not mentioned what kind of capacitors to use . What Type of capacitor to use for C1 C3 and C4.

 

[Audiodoc]

The 2.2 mFD capacitor should preferably be a polypropylene, the polarized ones should be electrolytics while rest can be either polypropylene of cheaper polyester. Snubber caps should be ceramic.

Check this kit will give you some ideas of the design. You may order a PCB and buy high end components if you want.

http://www.ebay.in/itm/LM1875-Power-Amplifier-DIY-kit-Components-LM1875T-20W-/260425122111

 

[sunilj]

Hi Kannan,

Not to discourage by any means but may I ask why the 1875 project, when the 3886 is almost the same. A beefier tranny and more power in the end.

I've personally found the 3886 to be the smoothest of the National lot, among the 1875 /3875 /3886 & 4780.

 

[Kannan_madhu]

Thank you doc , i think they are using "0.1u WIMA", are these commonly available ? or the normal ceramic can be used in its place ? Its hard to find a diy project using freely available componets in india :sad:

 

[Kannan_madhu]

Sunil, since its my first project i thought of doing some thing less expensive and easy to do , i got the 1875 for Rs 50 , also i am thinking about going for a 5.1 based on five of this and may be a 3886 for sub

 

[Audiodoc]

I dont think they are freely available if you want some linuxguru uses wima polypropylenes in his kit, you can also order from kitsnspares/element14 or else buy the yellow colored polypropylenes from CTR they are available in India.

 

[sudhir_rr]

On SP road, there is some shop on first floor opposite to Vishal Electronics named Universal Transformers etc. Just ask at Vishal or Chetan Ele folks for Custom made transformer maker.

Any idea about prices?
Thanks.

 

[omishra]

Any idea about prices?
Thanks.

Prices there were okay for standard voltage transformers but more for custom made single piece.

One more place where price was reasonable and quality was best in EI class. On SP road if you enter from OM Ele side then take right toward that Speaker (king?). Opposite to Pooja Ele one shop had Denon made EI transformers, pricy by 10% but those never got hot in 24x7 usage but always slightly warmer. Now I am forgetting names.

 

[sudhir_rr]

The current mentioned by a shop is RMS AC current. So VA rating can be obtained by multiplying it by Secondary RMS AC voltage. So For 30-0-30V secondary, 1A current, VA rating will be 60VA. Generally 60VA suffices for a sustained load of 55W or so, although that's not a rule per say.

If you want an idea of how much secondary voltage drops on a load check this graph. It shows load versus secondary voltage for a 200VA transformer. As you can see there is a clear drop below rated secondary voltage when you cross 200W load.

In general post rectification load capacity will be approximately same as unrectified load.
This graph shows secondary voltage drop as as post rectification current grows. There is more information on this website for those interested in ripple voltage as well.

pardon me posting here , one doubt about transformers ,most of the Diy projects in net shows transformer specification as 60VA , 80VA but here in local shops they are available in Amp specification only like one amp 5 amp etc . How we can convert VA to Amp ?

 

[rajeshm]

Thanks for this information. I am interested in limiting power supply ripple to 0.5Vrms since that's what is mentioned in TDA7293 datasheet. I'll prefer building power supply from locally purchased components since it'll be cheaper. Any idea what is the value of Electrolytic capacitors used in their unregulated power supply? Will 10,000uF suffice for 100W per channel of speaker power?

The current mentioned by a shop is RMS AC current. So VA rating can be obtained by multiplying it by Secondary RMS AC voltage. So For 30-0-30V secondary, 1A current, VA rating will be 60VA. Generally 60VA suffices for a sustained load of 55W or so, although that's not a rule per say.

If you want an idea of how much secondary voltage drops on a load check this graph. It shows load versus secondary voltage for a 200VA transformer. As you can see there is a clear drop below rated secondary voltage when you cross 200W load.

In general post rectification load capacity will be approximately same as unrectified load.
This graph shows secondary voltage drop as as post rectification current grows. There is more information on this website for those interested in ripple voltage as well.

 

[Kannan_madhu]

it seems getting 2A 18 0 18 is difficult , is a 15-0-15 2A sufficient to drive lm1875 x2 ?

 

[kaushik]

go for 5 amps if EI ..hardly it costs much, instead of beating head with formulae...

El-cheapo tripath build here http://www.hifivision.com/diy/22080-tripath.html

 

[Kannan_madhu]

Any suggestion for power supply

will this be sufficient( with out optional section ). if i am using a 5A transformer these components can handle it ?

 

[Audiodoc]

Its always better to use a regulated supply for the preamplifier. Something like the following which can operate from the same transformer.

http://www.ebay.com.my/itm/320770162304?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

or if you want something cheaper something using 7815/7915 regulators (Care should be taken that these don't operate at high voltages).

Why don't you buy a toroid from torotrans. That will be cheap and they can make according to your order. Just post them a mail at [email protected].

 

[omishra]

Any suggestion for power supply

will this be sufficient( with out optional section ). if i am using a 5A transformer these components can handle it ?

For preamp power supply need to be looked like this .
Ignore the upper aux part.

 

[Audiodoc]

The posted ebay supply has the same standard positive and negative rail design as given by the schematic in the previous post. Just change the elna filter capacitors to about 50V ones if you are using higher voltage otherwise they can explode!