A DIY audio amplifier design

[tinears02]

Ahh yes, ILP modules... that sure brings back memories of the days when I
had more hair and reading Everyday Electronics magazine. It is now "EPE", I understand. I would have bought a few in the whole line if funds permitted then, but student pocket money was never going to be adequate.

The first diy amplifier I made used a plastic molded part instead of the potted one, with the venerable LM380. It made a nice racket with the crystal set and transistor radio, with an open-baffled, paper-cone Sanyo speaker :)

tinears

Alan wrote :
"I was rooting around in the garage this morning and I found what is surely the last word in 'integration'.

ILP, a British company, took an audio amplifier idea not dissimilar to the kit (previous posts) and potted it into a cavity in an enlarged die-cast heat sink. That means, after they tested the assembled circuit board, they poured a thermo-setting epoxy over it to completely seal it from the atmosphere. So what we have here is an even more highly 'integrated' power amplifier. I'm not sure if it's still available, but I believe that they sold tens of thousands of these over the years. We considered using some in active speakers but the heat sink protruded too far from the back panel of the speaker and would have been damaged in transit or use."

[jr_41]

This is my DIY chip amp based on the National LM3876 using only 12 components per channel, including the power supply. It's built onto an old cutting board for now, using a piece of aluminum stock for the chassis and heat sink. I've ordered some proper heat sinks for it and am building a nice aluminum chassis for it using scraps from a local metal supplier. Sounds very nice with the Harbeth P3ESR and took just a few hours to assemble.

Very nice jplaurel! A perfect example for this thread I'd say.

[A.S.]

That's a really lovely amp assembly. Perhaps I've been to hard on myself dismissing my little kit and not considering taking it to the next stage and mounting in in an attractive case/stand. Very well done to you.

It's making me think .... should I assemble my kit or not?!

[jplaurel]

Thanks Alan. Yes, you should certainly build your amp and share your impressions here. I plan to build a case for mine, but I do enjoy peoples' reactions to it as it is. No one can believe the P3ESRs sounding so beautiful driven by an amp built onto an old wooden cutting board!

Decades ago, it was common for hi fi enthusiasts to build amps and speakers. Now that's what I call a hobby - creating, experimenting, learning. The hi-fi "hobby" today seems like just endless... buying. Speakers are tough. There's practically no way a DIY hobbyist could build a loudspeaker as good as the Harbeth without access to all the research, materials and tooling and even then, you'd have to be incredibly brilliant or incredibly lucky to get even remotely close. But it is possible to build your own amplifier and end up with something that sounds world class.

This thread must give you some pause because I'm sure you don't want to start seeing RADIAL drivers coming back to the factory with burned out voice coils because of improperly designed DIY amps that sent too much DC down the speaker wire.

That's a really lovely amp assembly. Perhaps I've been to hard on myself dismissing my little kit and not considering taking it to the next stage and mounting in in an attractive case/stand. Very well done to you.

It's making me think .... should I assemble my kit or not?!

[jplaurel]

Here are a pair of DIY Class D amplifiers that I just finished assembling. These are a good option for those of you who'd like to dabble a little in amp construction, but don't want to go to the extent of building an amp out of discrete components. All you have to do is install the module into a chassis and wire it up. Each amp took me about 4 hours to assemble.

These little amplifiers use the Bang & Olufsen ICEpower 125ASX2 module. These modules are used by a number of well-regarded manufacturers, such as Bel Canto Design, Wyred4Sound and Jeff Rowland. Each amp supports two channel operation and produces 120 watts per channel into 4 ohms (115v). The two channels in the 125ASX2 can be bridged, a mode that ICEpower calls "BTL" mode. In that mode, each amp module supports a single channel and produces 450 watts per channel into 4 ohms with 115v. I don't know how they accomplish this and I barely understand the operating concept of Class D, but those numbers are from the spec sheet.

How do they sound? Well, they sound pretty much like Class D amps, which nowadays are very good indeed! The Bel Canto integrated amplifier in my previous post also uses the same 125ASX2 module, so of course the sound is very similar. I've noticed that Harbeths seem to work very well with the new Class D amps. And another benefit of Class D is that they are very efficient (over 80%). Each of these monoblocks only consumes around 15w of power - about as much as a hallway night light.

http://gallery.me.com/jplaurel/10015...13348007740001

And here they are in my test system with the Harbeth P3ESRs. The Squeezebox Touch is feeding a Wyred4Sound DAC2, which is connected to the two ICEpower monoblocks via balanced XLR.

http://gallery.me.com/jplaurel/10015...13348007520001

The modules are normally only sold to audio equipment manufacturers, but I was able to source this pair from a very nice gentleman in Shanghai, who offers them in kit form, complete with the chassis and all the hardware you'll need. And all for a very reasonable price under USD $300 shipped. PM me privately if you would like his contact information.

{Moderator's comment: Harbeth cannot warrant this very interesting experiment. You should also investigate after-care and remember that DIY is never a substitute for a long term relationship with an experienced audio dealer in your area.}

[jplaurel]

While the risk of something going with these particular modules is low, since they are supplied completely built from ICEpower, you can do serious damage to your speakers or even associated equipment if you get the wiring wrong. As the Moderator implies, you are on your own in the DIY world, with no support from anyone. I would like to restate that when you are building your own amps, be sure to carry out the proper measurements before connecting any valuable speakers. I have an old pair of speakers that I use for testing purposes. Many DIYers use salvaged car speakers and things like that.

Also be aware that there is a risk of personal injury. On an amp like the Class D project above, the risk is limited to potential exposure to the mains leads. But if, like me, you enjoy building tube amplifiers, always be aware that the extremely high voltages in those things are instantly lethal. And they can continue to be lethal even hours after the amp has been powered down. So please get some training and follow the proper precautions before you start fooling around with this stuff.

The upside is that you will get immense satisfaction from building your own audio gear and learning new things.

[Spindrift]

While the risk of something going with these particular modules is low, since they are supplied completely built from ICEpower, you can do serious damage to your speakers or even associated equipment if you get the wiring wrong. As the Moderator implies, you are on your own in the DIY world, with no support from anyone. I would like to restate that when you are building your own amps, be sure to carry out the proper measurements before connecting any valuable speakers. I have an old pair of speakers that I use for testing purposes. Many DIYers use salvaged car speakers and things like that.

Also be aware that there is a risk of personal injury. On an amp like the Class D project above, the risk is limited to potential exposure to the mains leads. But if, like me, you enjoy building tube amplifiers, always be aware that the extremely high voltages in those things are instantly lethal. And they can continue to be lethal even hours after the amp has been powered down. So please get some training and follow the proper precautions before you start fooling around with this stuff.

The upside is that you will get immense satisfaction from building your own audio gear and learning new things.

Hi jplaurel,

could you elaborate on the three RCA- and double XLR inputs per chassis? Perhaps a photo of the rear?

Am I correct in assuming that this supplier makes an input board for balanced sources with psu for the lit on/off switch?

Bel Canto also uses an input board, with XLR option and a groundswitch (to short pin 1 to 3 in single-ended mode). I'm not too convinced of XLR inputs on domestic amplifiers but some swear by them.

[jplaurel]

Hi jplaurel,

could you elaborate on the three RCA- and double XLR inputs per chassis? Perhaps a photo of the rear?

Am I correct in assuming that this supplier makes an input board for balanced sources with psu for the lit on/off switch?

Bel Canto also uses an input board, with XLR option and a groundswitch (to short pin 1 to 3 in single-ended mode). I'm not too convinced of XLR inputs on domestic amplifiers but some swear by them.

Hi Spindrift-
Here is a shot of the back panel. The B&O ICEpower 125ASX2 supports single ended inputs via RCA jacks in stereo mode, but if you bridge the two channels ("BTL" mode), it supports a single balanced XLR input. To enter BTL mode, you short two terminals on the board. You can see the switch on my amp that accomplishes this. Note that when you bridge the two channels of a 125ASX2 in BTL mode, you must connect the speaker like this:

positive right channel amp output -> negative speaker input
positive left channel amp output -> positive speaker input

You can imagine that there is a lot of room for user error here. Further reinforcing the Moderator's point above, idiot-proofing is a big part of the added value that manufacturers like Bel Canto and Wyred4Sound offer when they integrate these modules into their products.

Full into on the 125ASX2 with specs and detail on its various operating modes here:
http://www.icepower.bang-olufsen.com...ns/125asx2.pdf

On the far left of the panel, you can see an XLR output and another RCA input. The purpose of these is to facilitate single ended input when the amp is in BTL mode. In BTL mode, the 125ASX2 is a monoblock, but the only natively supported input in this mode is balanced via the XLR. So if you want to use the amp in BTL mode as a monoblock but with RCA input, you need a transformer, which the kit supplier provides. To use it, you simply connect your input to the RCA jack, then run a short XLR patch cable between the transformer board's XLR output to the 125ASX2's XLR input. Now you have a monoblock that accepts single ended input.

The transformer adds a tiny bit of background noise that can be heard a few inches from the speaker drivers. In native stereo or BTL mono mode, the 125ASX2 is completely silent at idle.

The RCA-XLR transformer board uses the 125ASX2's 24V auxiliary power supply. The LEDs get their power from the transformer board, but if you omit the transformer, you could just connect them to the 125ASX2's aux power supply.

Balanced connections generally have less noise than single ended, even more so if the back of your equipment rack is a tangle of wires. Whether they will make a big difference in your system will depend on where you live, the wiring in your house, other active devices nearby, etc. I use balanced whenever possible and in my case, it does make a difference on certain systems. But it's hard to know whether that has to do with the balanced connection rejecting common mode interference or the implementation of the inputs. For example, when I connect my McIntosh C22 preamp to the MC275 amp via single ended outputs/inputs, you can put your ear to the speaker and hear just a little hiss starting from around 6 inches away. With balanced connections, it is dead silent, but on the MC275 the single ended inputs pass through an additional 12AX7 tube which could account for the additional noise. On the other hand, the single ended and balanced connections on my C50 and MC452 are indistinguishable from one another. Then again, it's in a different part of the house... As you can see, a lot of variables are involved.

http://gallery.me.com/jplaurel/10015...13348007370001

[renanj]

Alan, can you please post information about the small DIY Amplifier that you showed in the picture? Where can I locate this so I can build one? Thanks.

[DSRANCE]

I think it's a Gainclone type of amp and there is loads of info on DIYaudio about these. For you in the US, this company might make a good start -

http://www.audiosector.com/lm3875.shtml

and also -

http://www.decdun.me.uk/gaincloneindex.html

These amps look to be dirt cheap on the surface, but it's the transformers and casework that cost the real money, as in real-world amplifiers. "Don't skimp on the transformer" is my advice...

Listening.

By now I have come to expect something quite special from these little chip amplifiers and once again I was not disappointed. This time I have used just one 120VA transformer and a single rectifier bridge but the amount of bass produced by this amplifier is astounding! Clarity is one area definitely improved from the old Arcam circuit and the impression overall is that a new lease of life has been breathed into this 22 year old amplifier. A successful project, and given the small outlay, I am very satisfied with the result.

[A.S.]

The only amp you would ever need from a top-flight audio designer?

Worth a pair of M40s if you could tell it apart from a $$$$$$$$ amp?

[BAS-H]

Crumbs! What an offer. I'd love to take part in such a challenge but the logistics are difficult. Not for the chance of winning the leviathan M40s (which my little flat couldn't handle) but to get my 'most amps sound different' opinion quashed. I've read so much to the contrary that I'm beginning to doubt my own mind. Out of interest, does any other amp qualify? Even my £800 8W valve job?

Ben

(<oderator's comment: this subject was thrashed to death in other forums last year with over 50,000 hits.... nobody stepped forward.}