Gainclone Power Supply Design

[BobK]

I have recently completed the attached prototype of what I guess can be called a 3way monoblock Gainclone. It is a chassis that has a 3way active crossover with 3 of Brian's Gainclone boards.

The attached picture is before I completed the final grounding scheme. I am using this prototype with a open baffle speaker design I have been working on for some time. This design has a load impedence of less than 4 ohms in both the woofer and midrange passband. I find that the GC's run out of power on demanding rock concert DVD's but otherwise sound fantastic. I know that the GC is not the best choice on driving loads below 4 ohms but the sound of this configuration is so encouraging I would like to explore all posibilities.

I am in the process of installing a higher power Torroid but am curious if anyone has had any experience with using larger capacitors between the rectifier board assembly and Brian's gainclone boards?

I'm aware of the minimal design approach of the gainclone but am also aware of the fact that under dynamic demands the 1 to 1.5Kuf capacitors on these boards will definitely not be able to deliver the instantaneous requirements of some program material/speaker efficiency demands.

Are these requirements best met by the rectifier board assembely and its associated interconnect wiring and all of it's reactive impedence considerations, or could this dynamic requirement be met better by a capacitor bank between the rectifier assembly and the GC board?

BobK

[carlmart]

Originally posted by BobK

I'm aware of the minimal design approach of the gainclone but am also aware of the fact that under dynamic demands the 1 to 1.5Kuf capacitors on these boards will definitely not be able to deliver the instantaneous requirements of some program material/speaker efficiency demands.

That should be easily solved if you using a three-way active approach. Simply add more external capacitance on the module going to the bass unit. Up to 10000uF should be finely handled by the diodes and would provide a good punch control.

A 200 to 300VA toroid should be enough for dynamics and should not let the units run out of power.


Carlos

[Nuuk]

I understand that the 'best' way to add capacitance for a GC is to use a regulated supply. I am currently building one with 10,000 uF caps and LM338 regulators.

You can get more information on Pedja's web site .

[BobK]

I have 250VA transformers on order and was also considering 10kuf's on the bass amplifier. This would allow the reserve energy for the low end demands but keep the mid and highend performance everyone likes about the GC.

Pedja's postings about regulated supplies are interesting, I might give one a try. In the past I have not been impressed with the sound of amplifiers with regulated supplies but they have been evaluated running full range.

[tbla]

In the past I have not been impressed with the sound of amplifiers with regulated supplies

may i ask - what amps did you listen to....?

[BobK]

It's been a number of years ago that I listened to a regulated supply amp, and am embarrased to say I don't recall the commercial amplifier we auditioned. One unit was a heavily modified Dynaco 400 than one of my friends built. The unit tested very well but sonicly was somewhat disappointing.

[carlosfm]

Originally posted by Nuuk
I understand that the 'best' way to add capacitance for a GC is to use a regulated supply. I am currently building one with 10,000 uF caps and LM338 regulators.

I made a regulated PSU for my sub (two paralleled OPA549s) with LM338 and the result is fantastic.
Yes, with 10,000uf before the regulators.

A few days ago I was given a nice box.
I'm also scavenging an old amp, that has a (apparently) good trafo, but voltage is +/- 31v.
So, by coincidence, I'm just starting a regulated PSU with LM338 for another GC... NOW!

[BobK]

Carlos, good to hear you've had good success with your regulated supplies. Again, the experience I've had is dated, and was always evaluated full range. I could see advantages in a sub-amp application. In my design the three way unit I posted will be used with a sub, so the woofer amplifier will be used from 80 to 300Hz.

[carlmart]

Originally posted by Nuuk
I understand that the 'best' way to add capacitance for a GC is to use a regulated supply. I am currently building one with 10,000 uF caps and LM338 regulators.

That's not necessarily the best way, and I would probably not think of a regulator as a way to add capacitance. Perhaps a capacitance multiplier might be that.

The only thing in common between capacitors and regulators is that both lower the impedance, but the former does so in just one area.

A regulator should have other more important chores, like keeping a constant voltage no matter the voltage/current demands, lower and flatten the output impedance of the supply, lowering noise, etc.

The problem is that to do that they imprint their mark on the sound, because most use feedback to do so. It maybe a matter of taste also, so it's a debatable question whether a regulated amp sounds best than a properly designed one.

By properly designed I mean the transformer should be large enough and the capacitance attend the demands of the sound. On the tests I have done it became a taste option, if you liked good and controlled bass, whether to use up to 1500uF caps for better mid and highs, or more than that for better lower frequencies. In my opinion you should power the speakers separately.

There's an important tip though: a regulator should have better specs than the amp it's powering. Like higher bandwidth. In fact a regulator IS an amplifier.

Pedja's regulator, using an LM338, should be a very good place to start from.


Carlos

[Peter Daniel]

I would say the best way to add capacitance is to use batteries.

It seems like the batteries form a sort of buffer and even when charging circuit is connected the sound is not that bad. It is much worse when only charger is powering the amp (without batteries attached)