DIY Digital amp? realy pheasable?

Just some ideas floating around in me noggin.

I see quite a few digital amplifier modules available.
Is it as simple as adding a good power supply and case?
The tripath eval boards seem fairly good, anyone tried these?

 

Yes, it's feasible, but getting the best from a digital amp is a little more tricky.

Class D (which does NOT stand for digital) can be split into two groups. Those with analogue inputs (which are just an audio signal and a triangle wave driven into a comparator, which drives the output FETs), such as the lcaudio, Zetex ZXCD, etc, and those with a digital input, which converts directly to PWM with no analogue stages in between, such as those from D2Audio, Apogee DDX, Texas Instruments and Zetex ZXCW.

Tripath is an odd one, because it takes an analogue input only, converts to digital and outputs PWM.

 

What the tricky bit?

Id be looking at one that takes an analogue input.

 

In terms of getting the best sound, you have to find the optimum way of driving the best output FETs, get the right balance between dead time and shoot-through. Circuit layout is a big deal, output inductor quality (often compromised because good inductors to take that sort of current are serious money), etc... Obviously with pre-built modules and eval boards these things are fixed (although by replacing components you may be able to play with some aspects).

Also, due to the transient current demands of a class D amp, generally switch mode power supplies are preferred.

 

It's not only feasible, I did it See here:

https://www.audio-forums.com/as-rediect/showthread.php?t=2770

The trickiest bit was making the holes in the case! The rest was pretty straightforward: big toroidal, PSU, 2 modules, some sockets, wire and a case and just hook it all up. Couldn't be simpler

Michael.

 

Isaac,
Could you explain about the transient current and SMPS, i dont see why a good TX and regulation couldnt be used. Or are you meaning comercial shortcuts?

Micheal,
Have you compared the LC unit to any pre-made digital amps?
Whats your impressions of it.

 

Better regulation is the big thing. Any audio band noise from the powersupply will be fed DIRECTLY to the speakers by a switching amp. Any out-of-band noise of a high enough frequency will be removed from the output by the output filter that removes the audio switching noise.

I'm surprised at the anti-switchmode feeling when people are talking about switching amplifiers. The technology used is the same. Compare the circuit diagram of a half-bridge SMPS to a half-bridge class D output stage...

In terms of the transient current demands, for a given price you can build a stronger switch mode power supply than linear (for anything of an appropriate size for a power amp). As the SMPS offers no disadvantage in the class D arena (as it could, not necessarily would), why would you spend the extra for the same from a linear, or not get a better psu for the money if you were going to spend extra?

 

I see you point Issac, but i thought SMPS put more noise on the mains. Not my area tho so not sure.

 

They can do, but they have to comply with limits in CISPR 13, EN 55013 and FCC part 15.

However, a digital input class D with an SMPS will not be drastically affected by such noise.

 

You can do lot better with psu's than smps its all compromises for mass market, for those That have to compromise. However they are no such restrictions for some

 

Was my line of thought Tone.
TBH, it looks like by the time you cost in all the parts your not far off the price of a s/h pre made unit.

 

You can build a class 't' 2 by 175w @8ohms for £600 including box and tranny and will get you 85-90% of a stock B/c.
A few guys have already done this quite successfuly
You can do a lot more, however this depends on how much you wish to spend

 

Tone
When you say 85-90%, is that twaekable?

Looking at them, im not sure if the eval board is OK or if it should be replicated with a view to higher quality components.

 

Penance, I haven't compared my LC Audio amp directly to any commercial PWM offerings but my impressions of it are that it's very good. It certainly blew my old Arcam FMJ A22 out of the water. I've heard a few BelCanto amps and the sound of mine is similar. Most impressive thing is bass control...but with 400W (into the 4ohms of my Dyns) you might expect that :MILD:

Michael.

 

That sounds good Micheal.
Have you played with different components in the PSU, or leave it as is?

 

I just left it all as is. Now that it's working and I'm very happy with the sound I can't be arsed to play around with trying various tweaks

Michael.

 

Fair comment.
If it aint broke...