Well, for those of you not so bored that you have wandered off, this is taking shape. The boards are finished and attached to an ally bracket, the heat sinking arrangement is sorted. That was a nice bit of engineering. I am now sorting the PSU, it came in a case which I have had to modify. The thing that's surprising me is the amount of time necessary for these one-off engineering jobs. As an example, there should be 10,000uF caps on the boards to smooth the power input. They are too tall to go in the case. No problem, I'll just mount them on their sides and devise a means of connecting them to the BR and the boards by flying leads. Pom pom pom, tumtitum, OK, I'll do it this way...need to be able to test the boards without unsoldering everything or doing oceans of disassembly...tumtitum...oh there goes 2 hours. It was the same with the heat sinks, I reckon I must have spent an afternoon sawing the heat sink to fit, and that was after the angle grinder had decided to let the magic smoke out. I now have a newfound respect for people who build one-offs or short run items for a living, the cost in time is significant.
John Linsley Hood Class A or similar
- Thread starter stevec67
- Start date
James
Lord of the Erg\o/s
I contemplate thrice, measure twice and cut once. Even when I recently built a pair of Troels Gravesen loudspeakers for a mate, it took me three times as much time as I anticipated. But that's where the fun is. I wouldn't build one-offs for a living, unless paid on a time and materials basis.
Evening gents, I'm having another look at this now the weather is conducive to staying in. I have a trafo with 35Vac, the off-load DC voltage across the rectifier is 48V. 35 x 1.4 =48. Laws of physics unchanged here in Leeds tonight, good to know. My question to the panel is - is this excessive? If so I can put the centre tap onto the rectifier, this will give 17V5 ac and 24V5 dc, which means I will be down on power (10W needs 35V) but it won't catch fire. Advice?
Barrymagrec
pfm Member
Sounds O.K to me - if you are worried you could try using a dummy load resistor in place of the amp to see how much it pulls down.
Thanks Barry, I just wanted to avoid seeing it go pop. I could always start off running it at 24V to be fair, it would be a simple wiring change and it might double the time taken from switching on to magic smoke release. Actually as power goes up according to voltage squared I might get 4 times as long to wonder why it won't work before it starts glowing.
Arkless Electronics
Trade: Amp design and repairs.
48V is excessive. You need it to be reasonably close to 35V to get everything biased correctly. I've no idea of the details of your supply but it will drop under load, how much depends on mainly the transformer regulation which is dependent on the size of the transformer. It's unlikely to drop from 48 to 35 unless it's far too small a transformer anyway! A 24V transformer of about 200VA should be about right with UK 240V and TX usually rated at 230V. Schottky rectifiers will get you a Volt or so extra and run a bit cooler.
Thanks Arkless, I shall modify it to 24V dc with the 17V5 centre tap. Lower voltages are recommended for lower impedance loads in any case, IIRC. If I like the thing and need Moar Powaaaah I can always find a second trafo with a 24V secondary or do a buck/boost on the original. I have a 12V trafo so 12V off the 35Vac would work well as a buck.
I have used an old BR out of the bits box. I've had it since I was a kid, it must date from the early Jurassic so I don't think that it will be Schottky. I'm surprised it's not thermionic if I'm honest. Works though.
I have used an old BR out of the bits box. I've had it since I was a kid, it must date from the early Jurassic so I don't think that it will be Schottky. I'm surprised it's not thermionic if I'm honest. Works though.
jtgofish
pfm Member
I have one of these on loan.A Chinese made one like in the pictures
My advice would be to build a version with much less negative feedback.Having owned amplifiers with variable negative feedback I can really hear this one has too much.It sounds pretty decent but has flat imaging and sounds dry and a bit dirty through the midrange.Treble is very nice though and it sounds quite musical.
My advice would be to build a version with much less negative feedback.Having owned amplifiers with variable negative feedback I can really hear this one has too much.It sounds pretty decent but has flat imaging and sounds dry and a bit dirty through the midrange.Treble is very nice though and it sounds quite musical.
chiily
PFM Special Builder
Over on DIYA I stumbled across a link to JLH version aimed at ESL57 owners, though I assume as a higher power version it could have plenty of applications.
https://sound-au.com/tcaas/jlhesl.htm
There are a Gerber files for the amp boards but not the regulators.
I'll see if the Gerber files work and I'd be happy to order a few sets if people were interested.
Original DIYA post. https://www.diyaudio.com/forums/solid-state/3075-jlh-10-watt-class-amplifier-197.html
Post #5901
https://sound-au.com/tcaas/jlhesl.htm
There are a Gerber files for the amp boards but not the regulators.
I'll see if the Gerber files work and I'd be happy to order a few sets if people were interested.
Original DIYA post. https://www.diyaudio.com/forums/solid-state/3075-jlh-10-watt-class-amplifier-197.html
Post #5901
Barrymagrec
pfm Member
In my experience the original JLH drives ESL57s extremely well but some may feel the need for more power.
russel
./_dazed_and_confused
My advice would be to leave it, it sounds fine as it is. It much more important to get the wiring correct so there are no earth loops, fortunately this is easy to do on the JLH as it’s so simple.
Arkless Electronics
Trade: Amp design and repairs.
That looks familiar... Could well be the version I built years ago but with all different transistors and only one set of output devices plus lower rails.
Arkless Electronics
Trade: Amp design and repairs.
Yes but don't ever attempt to change the feedback on anything without lots of test gear and the requisite knowledge. Unless you are trying to make a power oscillator of course!
jtgofish
pfm Member
My point was that it does not sound fine because it sounds very 2D.If a stereo amp can't produce a convincing stereo image you have to question what is wrong with it.
russel
./_dazed_and_confused
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jtgofish
pfm Member
Yes it could just be the version I have.
Which version do you recommend?
I have since tried it with different speakers and it does sound better on some of them.Indeed the imaging on one pair is pretty decent.Not quite the depth and layering I would like but getting there.As I said everything else is very good and it has especially good articulation and timing so is very musically engaging.