Author Topic: Class A amps DIY anyone? (Read 9870 times)

JojoD818 · « **on:** Nov 12, 2003 at 10:10 PM »

Hi,

A much debated topology in power amps is the Class A. I hope that this thread serves like a collection of some of the do-it-yourself Class A amps around. It maybe tube or SS but still Class A.

Personally, I haven't tried it myself but will soon commence because there are lots of Class A amps that are very simple to build.

Best Regards,
JojoD

joan2 · « **Reply #1 on:** Nov 13, 2003 at 08:35 PM »

jojo,
some peoply find tip trasistors as yukky!!! let's find out, i suggest you use the following parts, TIP35C/36C as output, TIP29C/30C as drivers, and bc556/546 as small signal for the Hiraga 20w....they are cheap and reaily available....

JojoD818 · « **Reply #2 on:** Nov 14, 2003 at 02:16 AM »

hey joan2,

I think I have some of those tip29c/30c and some used bc546/556 somewhere. Well, at least, if I find them, the outputs are just the only ones I need to buy.

By the way, in Class-A, is it really necessary to design a fairly huge heatsink? I really want to build one for experience or shall I say "so that I can experience the sound of a class a".

JojoD

joan2 · « **Reply #3 on:** Nov 14, 2003 at 08:40 AM »

jojo,
yes, for classA you need a fairly large heatsink...you may also want to make your transformer bigger than ussual to keep the temps down.....

jerix · « **Reply #4 on:** Nov 14, 2003 at 08:57 AM »

hi guys,

i dont know where to ask this pero pwede ba d2 nalang?

i want to hav a separate amp for my surround back kasi the speaker m using is alil bit hard to drive and sometimes i wanted to have a louder sound comin from my back. my receiver can support the option becuase it has a terminal out prepared for a separate amp for all channels. my problem is the type of amp to use. where can i buy a mono type of amp? Me gumagawa ba dito? thnk you--

joan2 · « **Reply #5 on:** Nov 14, 2003 at 09:10 AM »

sorry i am not into selling amps right now, maybe jojo can help you, i am here to inform maybe educate those who would like to understand ss amps better as to how and why the amps behave the way they do....

JojoD818 · « **Reply #6 on:** Nov 14, 2003 at 11:36 AM »

jerix,

Why only mono? Dba 2 yun rear speakers mo? I can build an amp for you or I can help you build your own amp.

JojoD

jerix · « **Reply #7 on:** Nov 19, 2003 at 01:54 PM »

Quote from: JojoD818 on Nov 14, 2003 at 11:36 AM

jerix,

Why only mono? Dba 2 yun rear speakers mo? I can build an amp for you or I can help you build your own amp.

JojoD

I really dont know if i should use mono or stereo for my surround back center. my receiver has only one audio out for the center and back surround, while the front and surround left and right have two each. i wanted to pump more power to my surround back center thats why m lookin for an appropriate amp for this.

bro jojo, magkano kaya kung ppgawa ako sa u?

JojoD818 · « **Reply #8 on:** Nov 19, 2003 at 06:32 PM »

jerix,

Center surround pala ang application mo, akala ko yun surround which is left and right, my mistake. Anyway, mono amp ang kailangan mo. How much power do you need?

JojoD

jerix · « **Reply #9 on:** Nov 20, 2003 at 08:02 AM »

hi jo,

siguro mga 120 w but i really dont know. kasi receiver ko is 120 x 6, but the 6th channel which is my surround back has two speaker output terminal. however, medyo humihina ng konti ang output nya kung dalawang speaker ang nakakabit sa surround back, so what i usually do is to decrease the DB level of my fronts and side surrounds into almost half of the signal going to the surround back, to balance it.

thats the reason why m thinkin of hooking a separate amp for my back, so that i will have a separate control for the back. m using big bookshelves for my surrounds because i want to have some punch from my surrounds. a good amp can help me on this setup i supposed.

some say that i'd better use a stereo amp but i have to use a Y connector from the single audio output of my receiver's surround back out, to the dual left and right input of the aMP. what can u say bro? thnks

JojoD818 · « **Reply #10 on:** Nov 20, 2003 at 01:29 PM »

jerix,

A better solution would be to power your bookshelf speakers with a stereo amp but in mono due to the single rca output of your receiver.

However, a stereo amp would mean higher cost than a mono but a tereo amp is more flexible, you can use it for other applications...

JojoD

tolits · « **Reply #11 on:** Nov 22, 2003 at 07:31 PM »

mga bro pwede ba makisali,how about subwoofer circuits which is better low pass filter or active crossover with an amp. pahingi naman ng design.

joan2 · « **Reply #12 on:** Nov 22, 2003 at 10:16 PM »

tolits,
send me an email and i will send you subwoofer speaker design with active cross-over network....you can email me at: [email protected].....

JojoD818 · « **Reply #13 on:** Nov 23, 2003 at 06:44 AM »

tolits,

you can also go here: http://www.geocities.com/jojod818/index.html

I onced designed a commercial version of a subwoofer plateamp. I'll try to find it for you..

JojoD

p@rekuy · « **Reply #14 on:** Nov 24, 2003 at 10:23 PM »

Sir Jojo,

I've seen the Subwoofer that you've built on your website, looks pretty cool!!!

May i ask how much have you spent on building your DIY Subs?

JojoD818 · « **Reply #15 on:** Nov 25, 2003 at 01:27 AM »

@udiophillia,

The sub I used is a Targa 12" Dual Voice Coil Sub. It costs around 1,400.00 and I just used pre-cut wood that I can find since it's just a test sub. I used screws and spray painted it flat black. Not much to look at but it really shakes the house.

Currently, it is powered by my 150W ss amp and the active crossover that can also be found in my site.

All in all, this sub project cost me about 6,500.00 including the amp, crossover, wood (particle board) etc. The cost may seem the same as commercially availabe subs but with more power.

Hope this helps,
JojoD

FASTBACK · « **Reply #16 on:** Nov 25, 2003 at 04:57 PM »

JojoD818

What op amp did you use in your project that is posted in your web site?

Is it the LM 12 op amp? I am planning to build this since I have alot of LM 12 but not sure about the quality of these type of configuration. Is it good to power a sub?

p@rekuy · « **Reply #17 on:** Nov 25, 2003 at 05:00 PM »

Quote from: JojoD818 on Nov 25, 2003 at 01:27 AM

@udiophillia,

The sub I used is a Targa 12" Dual Voice Coil Sub. It costs around 1,400.00 and I just used pre-cut wood that I can find since it's just a test sub. I used screws and spray painted it flat black. Not much to look at but it really shakes the house.

Currently, it is powered by my 150W ss amp and the active crossover that can also be found in my site.

All in all, this sub project cost me about 6,500.00 including the amp, crossover, wood (particle board) etc. The cost may seem the same as commercially availabe subs but with more power.

Hope this helps,
JojoD

Thanks for the info JojoD818!

JojoD818 · « **Reply #18 on:** Nov 25, 2003 at 07:01 PM »

@udiophillia,

Your welcome!

JojoD

JojoD818 · « **Reply #19 on:** Nov 25, 2003 at 07:05 PM »

Fastback,

Welcome to the thread!

No, I didn't use the LM12 power opamp. The LM12 is a high power opamp! But it is also expensive.

It is a good thing that you have lot's of them . Yes, you can use it to power a sub. Maybe a parallel/bridge configuration and a huge power supply and it will be unbeatable! As for the power supply, ask tony (joan2), he has lot's of experience in psu design.

Cheers,
JojoD

FASTBACK · « **Reply #20 on:** Nov 25, 2003 at 08:45 PM »

JojoD818

Thanks for the info.

I was skeptical on building this one because of its simplicity on design, before I was wondering if this can really provide the power for the subs. Hearing from you I think I'll push thru with the project.

Yes the supply needed for this is very demanding though. I'll do ask joan2 regarding power supply design.

Nice work on the Leach Low TIM power amplifier.

Thanks again

joan2 · « **Reply #21 on:** Nov 25, 2003 at 09:10 PM »

Hi,
class A ss amps are not really meant meant to be used as sub-woofer amps, but they will do wonders in the mid and highs.....giving tube amps a good run!!!

there was an article that came out in 'Radio Electronics Magazine' a few years back, it included a pcb lay-out as well, i do not have the files with me now, it's in the province, i will retrieve it later....as far as power supplies go, the chip used a +/-35 volts rail, same as with its lm338/3875 plastic cousins....you may want to use 4 of them in a bridged configuration, so a rule of thumb says you will need at a minimum a 350va transformer, with 220 volts primary, and 24-0-24 volts center tapped secondary....

FASTBACK · « **Reply #22 on:** Nov 25, 2003 at 11:55 PM »

Class A amps are not really meant to be used as a Sub woofer amp, it is meant for mid and highs because:

Class A amps:
"An amplifier, with or without negative feedback, having the greatest fidelity in faithfully reproducing the input with the least distortion. It is however the least efficient, in as much the power delivered to the load is only a small percentage of the d.c. power used up in the amplification process"

The ideal setup for a sub woofer amp would be a Class D amp. A class-d amplifier has an efficiency degree of normally more than 90%. That means that more than 90% of the power which is delivered into the amp from the power supply is transferred to the load, and less than 10% is transformed into heat.

I opted to use an LM12 IC since I have around 20 pcs of it and since this is a power op amp, I thought of using this to power sub woofer. I'm sorry if I am of the topic of Class A amps DIY.

JojoD818

If you want to try building an amp using this LM12, I would be happy to lend you this IC.

joan2

Thanks for the power supply help.

JojoD818 · « **Reply #23 on:** Nov 26, 2003 at 12:05 AM »

Fastback,

I have an article which used that power opamp in TO-3 package. It also has a recomended input buffer/preamp since the LM12 chip requires a large input voltage to reach it's optimum power output. I'll post details as soon as I can.

Hey, thanks for the offer. I might try that for experiment and evaluation so that our friends here can have a taste too.

BTW, that chip cost about 700+ almost 2 years ago! Price is what makes that chip a rare DIY candidate.

JojoD

JojoD818 · « **Reply #24 on:** Nov 26, 2003 at 12:31 AM »

Fastback,

I just realized that this thread is for class a amps...

I hijacked my own thread!

Maybe we should continue our discussion regarding this chip at this thread... "gainclone diy anyone?" also here at pinoydvd.com

Cheers,
JojoD

joan2 · « **Reply #25 on:** Nov 26, 2003 at 09:27 AM »

class d amps is the 'wave of the future' it is not a new technology, maybe about 20 years old, but more and more products are coming out using this technology, high power pa systems use this a lot, talk about QSC, Rane, Amcron, and many others....you will find them in concerts and live performances.....

JojoD818 · « **Reply #26 on:** Nov 27, 2003 at 11:13 AM »

joan2,

I have heard a QSC amp and it really is a beauty. Very powerful but at the same time, it's so slim! So small is the heatsink, must be due to the inherent efficiency.

JojoD

JojoD818 · « **Reply #27 on:** Dec 13, 2003 at 07:55 AM »

Hi Fastback,

How is your LM12 gainclone?

JojoD

venzboard · « **Reply #28 on:** Mar 14, 2004 at 02:22 PM »

hi, i'm looking for somebody who could help me build my own subwoofer. i own a boston acoustics rally series 10" sub designed actually for car audio & i'm planning to use it for my home theater set-up. I had a sealed box made for it & all i need now is an amp to power it. I need at least 100watts RMS of power, can you help?

JojoD818 · « **Reply #29 on:** Mar 14, 2004 at 07:17 PM »

Quote from: vesuvius on Mar 14, 2004 at 02:22 PM

hi, i'm looking for somebody who could help me build my own subwoofer. i own a boston acoustics rally series 10" sub designed actually for car audio & i'm planning to use it for my home theater set-up. I had a sealed box made for it & all i need now is an amp to power it. I need at least 100watts RMS of power, can you help?

All you need is a crossover with line and speaker inputs (from your AVR) and an amp. I have been using a 150W solid state amp for several sub projects for home theater fans like you. If you want, I can build it for you. However, I am still engaged with other orders.