Leach Superamp, round 2

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Yes, the Hafler circuit can be run on much lower voltage. Notice the connections to the rails are power resistors followed by zeners forming a shunt regulator. Yes, economy of parts. The same circuit was probably used throughout the product line with a change in series resistor value.

You could run the circuit off of a 12-0-12 v transformer and further reduce the waste powering the relays. It's easier to use a ready made unit than make another pcb.

And it's good that you find it so revealing. I recently had an ear opening experience with the "Close to the Edge" SACD. Good recordings matter. Even the cd layer of that edition is much better than most.
 
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Funny. I ended up playing it through some Boston speakers. Sort of dumbed it it down a little so I could listen to singers without hearing all the affects/filtering they had used on their voices. However, I love the way a sax or string bass sounds, I can hear the breath on the reed and finger coming off the string. Beautiful! I need to get some symphony music to listen to.
 
Leach Amp clone by Jens Rasmussen

Does anyone know of a source for Professor Leach's Low TIM and SUPERAMP
PCB's? Let me know. I would like to build both of these as a tribute to Professor Leach. I hope his school keeps his WEB site active and expands on it as a
place for power amplifier designs.:)

Actually I was myself looking for some left overs of that 10 output transistor version made by Jens Rasmussen.
I was hoping he was still active and around (Jens that is), but he seems to have dropped below radar and the delta audio web site is full of dead links and has obviously been left to rot for years now.
I'm sure there were many GBs for the PCBs and there must be left overs somewhere.
The gerber files are still posted and downloadable, but I also was hoping to find the eagle source files for it, if anyone has them...
What I would like to do is make a 12 transistor version making use of the NJL4281/4302 and with the 12 diodes from those transistors, pairing them 2 by 2 in parallel, then 3 x in series, would make the bias temperature sensor.
I would probably run this at 90 or 95V rails...
Any comments?
Cheers,
 
Last we heard from Jensen he had just become a father. That likely explains his disappearance.

Jens was very reluctant to give out his eagle files because they include his license information. It could potentially lead to pirated copies of the full version. After paying full price for the program to support diy audio I can't say I blame him.

Thermal trak parts are end of life. Why mess with them?
 
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Last we heard from Jensen he had just become a father. That likely explains his disappearance.

Jens was very reluctant to give out his eagle files because they include his license information. It could potentially lead to pirated copies of the full version. After paying full price for the program to support diy audio I can't say I blame him.

Thermal trak parts are end of life. Why mess with them?

There are still 1000s of those thermal trak parts in stock, even as end of life, those are really a nice step up, I don't understand their motivation to discontinue them, as they were really going in the right direction for audio amps.

Nothing comes close to what those thermal trak parts can do. The "sticking" of diodes or burrying of a transistor in a hole in the heatsinks are a bad idea, full of extra wires. Jens had a good idea in putting the diodes on a small pcb, but then the thermal contact can never be good enough and they're always too far away from the power transistors' junctions.

I too have become a father, and the kid is so soliciting all the time, but I still want to spend time doing audio stuff.

I was tickled in the early 80s when Matti Otala's TIM breakthrough started getting serious attention and I've been into power amps ever since. It's too bad Dr. Leach has left us, as he's been a whole lot more active in his days than Otala when it comes to DIY amps.

I was just wondering when looking closely at Jens' PCB designs, since I don't have any board in hand, I can't see it better than the photos, he seems to have littered the PCB with a whole lot of via holes. I suspect it's only in the ground planes and they join together the top and bottom planes, perhaps making shields around certain areas...

One thing I would've done differently is to split the big filter caps into many smaller ones. At some time we could've used the black gate caps, but they're gone, although now we have the silmic II...

We all look for that perfect DIY amp to make and sometimes some good ideas come out.
 
The "big caps" can/should be fairly low value used as local bypass as are the film caps near the outputs. Then have a string of smaller caps in your PSU.

On the other hand you can fit 22,000 uf there and with 5 uf film bypass per rail you may not need any other caps. IIRC Prof. Leach only specified 12,000 uf per rail in the original stereo PSU. I have a 4 cannel Leach that sounds great with only one big 39,000 uf per rail and 100 uf local bypass. Once the cases get here we'll see if going overboard with 4 x 10,000 uf per rail makes a difference.
 
I really can't hear much difference between the Superamp and the Low TIM. They are almost identical in sonic texture and output. The Symasym has a lot more gain and seems to be more detailed but it may just be emphasizing different frequencies. The KSA 50 has a little more laid back sound to my ears. I don't listen to it as much right now because it is summer. I've actually been enjoying my P101 lately. My room, and the JBLs tend to accentuate the highs a little too much and the P101 is a little more subtle than the others and seems to sound better on music that has a lot of vocals.
 
I took some time today and listened more closely to some of the amps. I started with the KSA 50. It sounds pretty nice. Decent bass, smooth mids and clear highs. I played a few jazz albums through it. Very nice. Then I put on a Blues CD and the vocals were a little grating. I had to turn it down. So I switched over to the Superamp. I must say I was pleasantly surprised that I was able to turn it up louder than I had the Krell and it was very nice. It's becoming my favorite amp.
 
I will have to listen to it tomorrow and get back to you. It is tricky compare with my other amps because it has a lot higher gain, so I always have to adjust the preamp volume. I'll try to give my best opinion. I have always really liked the Symasym for its detail. Let me give the bass a closer listen.
 
I found that the symasym has a boomy bass.

Gajanan Phadte

Hmm, I never really noticed it before but it is slightly more boomy than the Leach but still very musical to my ear.

I wonder if the vocals were getting clipped with the lower output Krell?

I don't think so. I am not driving them that hard. I'm in a fairly small room with hard painted drywall walls and VCT flooring. The room becomes overwhelmed if you get it too loud. I keep promising myself I will do some wall treatments some day.

I listened some more today with different music. Some jazz vocals as well and didn't hear it. To be honest, I think it is just the different sonic emphasis each amp places on the music. I believe the Krell just highlighted something that is present on that particular recording that wasn't so noticeable on the other amps. The problem is that these are all such wonderful amps that unless you are comparing them sided by side, you never notice any of these things. Also, I am doing most of my listening through some older JBL speakers and those titanium drivers are not always so kind to some recordings.

Blessings, Terry
 
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