Silicon Chip ULD amp

[Greg Erskine]

Hi all,

I am after any information on Silicon Chip ULD 100 watt amp. I'd love to hear from anyone that has build one, or even if you have just heard one I'd be interested. I have all the Silicon Chip articles so I am really just after listening tests impressions.

I have done a search and only found one reference that was not very complimentary.

Here a link to the amp in question:

http://www.altronics.com.au/index.as...=item&id=K5155

If someone in Sydney has one, please drop me a PM.

Thanks

[David Lewis]

Yes, I built the shortform kit a few years ago when I got interested in DIY power amps. It's quite a reasonable performer. Sonically, you would say that it's a little sterile sounding and the treble is a little cool and metalic, but it gives a very detailed presentation, particularly through the mid band, and an excellent soundstage. I use mine to power my mid and bass in a bi-amped system and it's excellent for that job. The circuit is similar to other SC project amps and at a glance not dissimilar to the Doug Self blameless amp. The CFP output stage is very linear but not particularly well suited to class B operation, particularly into low impedances (ie. < 6 ohms). The cascoded VAS is employed to lessen the effects of non linear VAS miller capacitance loading the input stage. In his articles, Douglas Self did not advocate a cascoded VAS for class B operation due to the high collector impedance. However, it would probably work very well with the protection of a well designed class A buffer stage, although I never got around to such a mod.

[Greg Erskine]

Hi David,

Thanks for taking the time to post. I assume by the "shortform kit" you mean you bought the separate amp kits and possibly the power supply kit rather than the "complete" amplifier kit. Did you use the standard components?

I noticed the Douglas Self blameless amp resemblance, also it's a bit like a slightly more complicated ESP P3A with the cascoded VAS and split regulated/unregulated power rails.

Good to hear you are happy with it. Have you compared it to other amps and what are you using for the tweeters.

I was beginning to wonder if anybody here had actually built one and I still hope a few more people will respond.

Thanks again.

[David Lewis]

Greg,

Yes, I purchased the PCBs and parts, and I also sourced extra transistors in order to match vbe and beta in critical areas, and selected highest hfe. I built the power supply and amp modules in seperate cases and worked out a neat way of mounting (and insulating) high quality gold plated banana plugs to the underneath of the amp case and equivalent gold sockets on the top of the PSU case. The amp module can therefore be lifted on and off the PSU, and the PSU is of course magnetically shielded from the amp modules. For the unregulated supply rails I'm using 2 x 500VA (40-0-40) toroidals and 60,000 uF per voltage rail, per channel. I made up my own slow start or surge limiter which is powered from its own mini toroidal transformer. The regulated IS and VAS stages are also derived from a dedicated T T. And yes, I made up my own PSU PCB employing best practise layout.

So you see it's not exactly the same as the Altronics version. My bigger PSU probably gives the bass some extra authority but otherwise there's probably little audible difference to a well built Altronics kit.

My current tweeter amp is a low fb design with a push-pull Mosfet high bias Class AB output stage but I'm currently developing 2 new designs, one class A and the other 'AB'. They are still under development but if you like I can forward details when completed. I have a 24 bit AA so I can also let you see a distortion spectrogram and square wave performance too.

I'm going away for 4 days from early tomorrow so if you have further questions I'll be glad to answer them but it will be sometime mid next week.

Cheers,

[David Lewis]

Greg,

I forgot to mention, I have compared it to a Krell FPB 300 and an ME 1500 which Trevor Wilson carted over one evening. It wasn't as good as either but was in no way disgraced. Compared to the Krell it lacked hf resolution, and the transient attack and decay was a little less natural and life like. Compared with the ME 1500 it lacked some low end authority and dynamics. Of course both of those are far more expensive amplifiers and you would expect them to be better but the ULD was not disgraced and is a good 'all rounder'. It's probably comparable with something in the 3K - 4K price area.

[Greg Erskine]

David,

Thanks again for your detailed response. You obviously have a nice setup.

Funny thing is, and I don't know if you're aware of it, I originally startup this post to try and get some independant feedback on the SC ULD amp. Over at aus.hi-fi just about ALL the information on the SC ULD has come from Trevor Wilson over many years. Now you bring him into the equation here. Small world hey.

regards

[Geoff-AU]

2 x 500VA (40-0-40) toroidals and 60,000 uF per voltage rail, per channel.

Holy crap!!

Someone likes to have smooth DC rails

[wixy]

Sorry to resurrect an old thread, but I just bought the 100w ULD kit from altronics as my first foray into diy electronics.

Are there any basic mods worth doing to make the ULD amp better?

[pheonix358]

Originally Posted by wixy

Sorry to resurrect an old thread, but I just bought the 100w ULD kit from altronics as my first foray into diy electronics.

Are there any basic mods worth doing to make the ULD amp better?

New Amplifier - ULD Extreme

Terry

[wixy]

Originally Posted by pheonix358

New Amplifier - ULD Extreme

Terry

Thanks for the link, although I think that relates to the mk2 version of the ULD amp whereas the altronics kit is the mk1 version.