Silicon Chip ULD amp

[Circlotron]

Matter of fact I just powered it up about 2 hours ago. Bought as a kit and it has a 5-star difficulty rating and they weren't kidding. I really didn't enjoy making this amp. It is to replace my old 50+50 watt 53 kilogram mosfet class A lump. In the 7 or so years since made that thing I have lost a lot of interest in hifi and also my ears have a bit of tinnitus. Turned on the new amp, played a single track to see that it worked and then went off to do something else. If I had realised how much work it would take to put this new amp together I think I would have paid someone else to do it.

[Ian Finch]

A few comments fly in the face of the ULD Mk1 design brief in this thread. The ULD amp is an "8 ohm only" design, and yes, you would expect it to have problems supplying high current into 4 or even 6 ohm loads. That's an unfortunate choice and even the 300VA toroid, is only just enough for that.

The unusual design choices, I expect, were as much to avoid plagiarism as try other variants from Self's list of options. The design first appeared in 1999 as an electronic hobbyist's project, mounted in a mid-tower PC case for cost reasons. The concept was not what we now commonly seek in amps. As Greg referred to the later Altronics makeover kit, you can see how tight things are in Circlotron's kit build. At the special price, I think you still have a great amp and there's little stopping a retrofit of the newer ULD II EF thermaltrak modules and removing the regulated input stage PS, if the CF topology offends you.

There has been a huge amount of discussion and development since DIYAudio went online and popularised High-end design at budget prices. Commercial kits like this one are virtually as costly as a retail product so the price will reflect a lot of economies we may not, in our enthusiasm, wish to make. To supply a 100 W kit to current standards with the features of the ULD kit would cost more like $1,000 AU now.

I reckon you did well for the money there Circlotron, I hope it runs like a dream. I'm very happy with my "A" class choice for all the hassle the kit saved me. Now, we just need a few worthwhile simple mods to tweak it. If Sandyk is about, I'm sure he'd be willing to share.... .

[Circlotron]

Originally Posted by Ian Finch

The design first appeared in 1999 as an electronic hobbyist's project, mounted in a mid-tower PC case for cost reasons.

Looks very similar to the front-cover amp of April 1996 even.

[Ian Finch]

Cool! Old-school SC! I bet you wished the ULD was as easy to build as that one!

[Agisthos]

I remember reading about this kit in Silicon Chip mag in 2001. The build looked too complex and time consuming for someone of my capability.

I just bought one fully assembled for $175. Bargain?

[Ian Finch]

That's interesting and cetainly a real bargain, Agisthos. I guess you have the Altronics kit which was based on the first, rather complex, design. 'Nice kit though and many say it sounds better than version II with the simplified Thermaltrack output stage or even the newest, MKIII version.

I think there may have been some hasty conclusions drawn there since you can't simply swap the amplifier boards for fair comparison. There are separate. regulated supplies to the input and cascoded VAS stages for starters.

So - has anyone actually checked out the sound quality of this newest, Nicholas Vinen's, version yet?

[Agisthos]

ahhh... another ebay purchase that has a problem ...... wonderful.

The right channel volume is soft / or cuts in and out, until hitting about 10am on the knob. After that is fine... but any normal/low level listening is not possible.

Would this be a volume pot issue or a problem with one of the amplification modules?

[Ian Finch]

Assuming this is the Altronics Mk1 kit, there are no electronic switches in the signal path so the fault will be mechanical, unless accompanied by distortion in the right channel which should be obvious. Before getting serious, disconnect the left channel speaker and verify the sound quality of the right channel as you rotate the volume control. If it is faulty, the mechanical sound as you rotate it about the 10 0'clock position should demonstrate that cause more obviously.

If the switching in or out is more abrupt and sounding like an on/off switch, there is something mysterious to discover, indeed. All the same. wiggle the control about to make sure that weak soldering of the connections is not the culprit either.

Considering the probable age. use and budget quality of the pot. a replacement is the likely solution and I'll wager it's had a few knocks in it's exposed position too.

So, what do you find?

[djk]

"Would this be a volume pot issue or a problem with one of the amplification modules? "

Could be, does it have a speaker relay?

[Agisthos]

It is as you described Ian. Distortion while moving the pot, and distortion while wiggling it. Must have been damaged in transit. whew!