[Jonathan DA]

Hey all, anyone out there want to breathe some solder fumes? Last night at Colin's another HTF member mentioned to me that he's thinking of building a Welborne Ultrapath bp preamp and asked if I could assist. It looks like an interesting project, and the assembly would mesh well with my own plans to build a World Audio Design Kel84 integrated amp. I thought perhaps if anyone else had an electronics projects in mind we might get together for an afternoon and build some toys.

Ultrapath bp:


Kel84:

[Nils Luehrmann]

Count me in on offering an extra pair of hands. I'm not interested in building either for myself, but would be happy to help out any way I can.

[Dave Elliott]

Jonathan,

Ok, I'll bite. I sorted through some of the information on the site. What did you pay for the Kel84 kit to the states? They look affordable given the conversion rate.

When I used to work at a high-end audio place years ago (in Ohio) one of my favorite amps was a Luxman tube amp. Despite its VERY low rating (12.5wpc IIRC) it would absolutely render music brilliantly. Much better sounding than some of the high-power transistor amps we sold at the time (Denon, Carver). Even on some less-than efficient speakers. I really loved the warmth of those tubes.

One reason I just bought the Denon 3803 receiver is that it has a ton of features and highly-regarded processing for the $$$. I figured that the 3803, for $850, would make a good pre/pro down the road if I were to get a good 2ch amp for music. I'd use the 2 channel amp for my tower mains, and use 5 of the receivers 7 channels for the remaining HT speakers. Then, the 2 channels left on the receiver can be configured for multi-room multi-source output, which is great as I need two channels for my poolside outdoor speakers. 7.1 Movies in the house, CD's jamming on the patio!

Anyways, I'm curious if you think these DIY amp kits would be effective for HT mains given their low power?

-Dave

[Jonathan DA]

It all depends on the sensitivity of your speakers as to whether or not little tube amps are usuable for HT. Assuming that the speakers would be set to "small" and the LFE would be handled by a solid state amp then I'd say it would work given speakers of 89dB sensitivity or better.

For example, here's the volume level attainable at various power levels for a 90dB sensitve speaker, not taking into account room gain:
Watts,2 spkrs at 1 meter,2 spkrs at 2 meters
1,93,87
2,96,90
4,99,93
8,102,96
16,105,99
32,108,102

Moral of the story, if you have sensitive speakers you don't need a lot of power. 99dB is REALLY FREAKING LOUD.

[Jonathan DA]

As for the cost of shipping, unfortunately I think it will cost almost $100 to have it shipped from the UK. I'm having a tough time finding reasonably priced amp kits in the U.S. Most of what I've found is either in Europe or east Asia.

[Dave Elliott]

Jonathan,

My front speakers are very efficient -- 92db @ 1m. While more power is generally better, my personal experience is that power (wattage) and current (amperage) are equally important, the latter sometimes being overlooked. I've seen some high current low wattage amps that are just devastatingly clear AND loud. Citation & Proceed particularly (something about Harman and their amp circuits).

When I was into car audio, the most impressive amp I ever heard was a Soundstream Class A-50. Only 25wpc, class A discrete power supplies. It was .5 ohm stable, where it could conceivably put out ~200wpc. I ran 13 speakers (all in parallel) on mine and it never shut down. It had a sonic quality that added a spatial feeling to music that nothing else (at the time) could do. I still have that amp, I just need to get off my butt and install it in my car with the rest of the stuff I have laying around.

Well, when you get your Kel84 I'll definitely be interested in hearing it. I have serviceable soldering skills, but I'm a bit rusty.

-Dave

[Mark Hayenga]

It may not be tubes, but what about the Pass Zen amp? Single-ended solid state class A, PCB's and Q-packs are available pretty cheap from passdiy.com.

And yeah, I'll help out if you guys are willing to put up with my antics


Mark

[Jonathan DA]

I haven't heard a Zen amp, but Nelson Pass is one smart dude, if anyone is looking for a sweet sounding amp I'd wager the Zen fits the bill. I did listen to an Aleph at DIY2002 as well as Pass' new Rushmore active 4-way speaker at CES. Both were very nice. It's hard to comment on sound differences between solid state amps, most of them sound so similar that I only notice their differences after a long period of time. No, I'm not a "subjectivist" but I do think that some amps sound different than others. But I digress, Pass amps are way cool.

Okay I'm gonna get crap about this from Mark (I can hear the Curmy jokes already)...

Speaking of different sounding amps, Scott H. and I listened to the Jolida 502B ($1125) and VTL IT-85 ($2750) today. After listening to these two integrated tube amps we both decided that if we're going to spend over $500 for a kit of unknown sound quality we'd rather spend a bit more and approach the sound quality of the VTL (which was fabulous). How? Ditch the kits, we're rollin our own! Nothing definite yet, but we'll probably do something using EL34s in tetrode mode. That should put out around 50 watts per channel if done right. Stay tuned (but don't hold your breath, this could take a while).

[Scott Oliver]

Jonathan,
Have you looked at the Edison 60 by Audion. It is an English company but they are distributed in the US by OSS Audio (www.ossaudio.com).

On Audion's website they are listed as costing around 400 pounds.

Just a thought.

[Jonathan DA]

When the kits start to approach $1000 I think we can design a better one for the same price. The law of diminishing returns favors the DIYer. It is a nice looking kit, but for that amount of money I trust our engineering skills over someone elses whose stuff I can't listen to before buying. What? No I'm not arrogant, why do you ask?

[Edit] Ah, I see the Edison 60 manual is online, we'll give a look thru.

[Hank Frankenberg]

I'm a solder-slinger from way back. My first big project was building an H.H Scott LK-48B 24 watt per channel integrated tube amp kit that I bought in '63 or '64. Luckily, I still have it and have discovered that many people say it's one of the best P-P amps ever designed, holding its own with current designs. I plan to refurbish it, replacing the electrolytic caps and the coupling and bypass caps, a few resistors and replacing the selenium rectifier with a silicon job. Supposedly the phono section is one of the best ever. I can't wait to hear how it will sound. I also have a Hafler DH220 SS power amp that I will replace the output boards on and have already built a replacement bridge rectifier from individual hyper-fast Harris diodes.

Gentlemen, heat your irons!

Say, if my Scott integrated amp actually does sound really good, we could clone it. If suitable power and output transformers are available, it could be done as all other components are available and the tubes are not hideously expensive.

Yes, the challenge of working with Mark is his "Curmy" jokes.