I found this forum last week and have been lurking around. Let me give my thanks to the creators, moderators and participants for what is an excellent site.
As for me, I have been interested in audio engineering since about 1976. That year coincides with me being a junior in college studying Electrical Engineering, and the publication in Audio Magazine of Leach's Low TIM amplifier. It is interesting that I had never even heard of Audio before, but a friend brought a copy over to ask me my opinion of something that was in it, and I looked through the magazine and discovered the amplifier article (I still have that magazine buried away somewhere!). I was amazed with the amplifier (until then, I was drooling over Heathkit amplifiers) and set a goal right then that I would study the design, figure out how it worked and - after I graduated and when I had the money - I would build it.
It wasn't until about 1980 that I finally got around to working on it, with one of the first things I did before starting was to call up Dr. Leach himself to see if there were any updates. He told me the design had been replaced with the Low TIM 3 design, and he kindly mailed me the schematics and parts list, and I purchased the PCB's from him. The amplifier was built in a similar manner to that shown in the magazine (i.e. on a Bud box with everything exposed), but it worked great. I still use it to this day, with the only problems being that as it heats up, a hissing noise develops in one channel (I have been too lazy to get out the freeze spray and track it down) and I get some severe thumps when I power it down.
Anyway, I learned a lot about electrical design by studying the Leach Amp design. I had the fortune of meeting Josh Goldberg, who worked at a company that the company I was working for had a contract with, and he turned me on to Audio Amateur magazine. I subscribed to that for years, along with Audio, then to Speaker Builder for a while. I had lots of plans to design my own equipment - a new tri-amped speaker system of my own design; a preamp, true RMS power meters, etc. Nice plans, but as too often happens, the plans get interrupted when you get married. Something about spending too much time with a hot soldering iron than with her!
Well, with the advent of the Internet, a few years ago, on a whim, I typed in “Marshall Leach” and was happy to see that he had a web site and that his amplifier plans were posted. I emailed him just to say hello and thank him for the amplifier which spurred my entry into analog design engineering. He sent a nice reply and mentioned that he, to this day, still used that original Low TIM amplifier in his office. In 2000, I finally decided that I needed to rebuild my version 3 amplifier, so I ordered the latest PCBs from him - Version 4.4. I was surprised that they were smaller and only single sided. The version 3 had a ground plane. I asked him about that, and he said he realized that the ground plane really didn't help any. Being in aerospace/defense engineering, I like ground planes, but I recall unpleasant times with those plated thru holes of the version 3 board - you couldn't just pull a part out and stick in another - you had to either suck the solder out our heat the joint and cram the leads in.
After I got the boards, however, they sat in my office. Other things came up and I simply haven't had the time. However, my two children are reaching their teens and they like to listen to music (thankfully, so far, they like the same 70's era music that I do) and so I hope to embark on getting that amplifier rebuilt. Being in the business does help in getting samples, so I will be calling up a few sales reps to call in some favors!
But, after discovering this group, I may alter my path. I was looking at pictures of other people's amplifiers and I am challenged to do more than build my new amp on a Bud box and hide it behind the speakers. I now want an enclosure that looks as nice as the amplifier sounds. So, I will do some research into this.
Also, I am intrigued by some posters who say that electrical parts made of steel impact the sound. I am skeptical of this, but then I don't doubt that people at least _think_ that there is a difference. In reviewing the Leach Amp transistors, only the low power ones are plastic. Is there an all-plastic replacement for the TO-39 2N5415/2N5439? I suppose some SMD devices would work here. What about the TO-220 drivers (MJE15030/MJE15031)? I also suppose some SMD transistors might work - provided one can design the PCB with sufficient copper for heatsinking and/or an appropriate heat heat. I see some people use the TO-247 style for the output transistors, but isn't the metal backing make of steel, too? I guess there is less metal than with a TO-3, but as others have pointed out, the thermal dissipation will be worse. (I don't listen at high power levels, so this might not be a problem for me.) I would think that heated silicon would sound worse than cooler silicon, despite there being less metal. (Besides, the heat sink is made of metal. Yes, I am skeptical – but I try to keep an open mind.)
Anyway, if I change transistors as indicated, I will need a new layout. I am skilled at designing PCBs (but not fabricating them), so this may be a fun thing to do. I do believe that keeping the leads short between the drivers and the output transistors is good, and a different PCB/heatsink combination may be helpful here.
Also, I have read of the sonic characteristics of different parts. I remember some of early publications in Audio Amateur (I think – by Marsh, or maybe it was in Audio) about the sonics of capacitors. My first Leach Amp made use of polycarbonate capacitors as a result. Today, I am reading about resistors, and it is quite confusing. Some love carbon comp's, other hate them. (Those carbon comps will drift all over the place. We had a project where we used them and we had to literally bake them for a day to drive out the moisture to get a stable resistance, then quickly solder them in and conformally coat them, or they would fail testing.) I had been planning to use metal film (both military RNC/RLR types, as I can scrounge them from my company, and the generic Panasonic's from Digi-Key). The discussion of the very expensive Vishay's, etc. is interesting. I don't buy the argument that a tight tolerance resistors impacts the sound, but the fact that a tight tolerance part is better constructed and that, in turn, impacts the sound, does have some merit for serious discussion. I will probably stick with metal film, but I might use some expensive ones in the feedback look – if I can get a sales rep to sample them to me!
Well, this is turning into a much longer intro than I had hoped. I think it will be fun to participate in the group, and while I am an experienced analog designer, I do not claim to be an expert in audio design by any means. I am here to learn and I hope that later on I may be able to give something back.
Thanks for reading, and happy building to all!
Jeff R.
As for me, I have been interested in audio engineering since about 1976. That year coincides with me being a junior in college studying Electrical Engineering, and the publication in Audio Magazine of Leach's Low TIM amplifier. It is interesting that I had never even heard of Audio before, but a friend brought a copy over to ask me my opinion of something that was in it, and I looked through the magazine and discovered the amplifier article (I still have that magazine buried away somewhere!). I was amazed with the amplifier (until then, I was drooling over Heathkit amplifiers) and set a goal right then that I would study the design, figure out how it worked and - after I graduated and when I had the money - I would build it.
It wasn't until about 1980 that I finally got around to working on it, with one of the first things I did before starting was to call up Dr. Leach himself to see if there were any updates. He told me the design had been replaced with the Low TIM 3 design, and he kindly mailed me the schematics and parts list, and I purchased the PCB's from him. The amplifier was built in a similar manner to that shown in the magazine (i.e. on a Bud box with everything exposed), but it worked great. I still use it to this day, with the only problems being that as it heats up, a hissing noise develops in one channel (I have been too lazy to get out the freeze spray and track it down) and I get some severe thumps when I power it down.
Anyway, I learned a lot about electrical design by studying the Leach Amp design. I had the fortune of meeting Josh Goldberg, who worked at a company that the company I was working for had a contract with, and he turned me on to Audio Amateur magazine. I subscribed to that for years, along with Audio, then to Speaker Builder for a while. I had lots of plans to design my own equipment - a new tri-amped speaker system of my own design; a preamp, true RMS power meters, etc. Nice plans, but as too often happens, the plans get interrupted when you get married. Something about spending too much time with a hot soldering iron than with her!
Well, with the advent of the Internet, a few years ago, on a whim, I typed in “Marshall Leach” and was happy to see that he had a web site and that his amplifier plans were posted. I emailed him just to say hello and thank him for the amplifier which spurred my entry into analog design engineering. He sent a nice reply and mentioned that he, to this day, still used that original Low TIM amplifier in his office. In 2000, I finally decided that I needed to rebuild my version 3 amplifier, so I ordered the latest PCBs from him - Version 4.4. I was surprised that they were smaller and only single sided. The version 3 had a ground plane. I asked him about that, and he said he realized that the ground plane really didn't help any. Being in aerospace/defense engineering, I like ground planes, but I recall unpleasant times with those plated thru holes of the version 3 board - you couldn't just pull a part out and stick in another - you had to either suck the solder out our heat the joint and cram the leads in.
After I got the boards, however, they sat in my office. Other things came up and I simply haven't had the time. However, my two children are reaching their teens and they like to listen to music (thankfully, so far, they like the same 70's era music that I do) and so I hope to embark on getting that amplifier rebuilt. Being in the business does help in getting samples, so I will be calling up a few sales reps to call in some favors!
But, after discovering this group, I may alter my path. I was looking at pictures of other people's amplifiers and I am challenged to do more than build my new amp on a Bud box and hide it behind the speakers. I now want an enclosure that looks as nice as the amplifier sounds. So, I will do some research into this.
Also, I am intrigued by some posters who say that electrical parts made of steel impact the sound. I am skeptical of this, but then I don't doubt that people at least _think_ that there is a difference. In reviewing the Leach Amp transistors, only the low power ones are plastic. Is there an all-plastic replacement for the TO-39 2N5415/2N5439? I suppose some SMD devices would work here. What about the TO-220 drivers (MJE15030/MJE15031)? I also suppose some SMD transistors might work - provided one can design the PCB with sufficient copper for heatsinking and/or an appropriate heat heat. I see some people use the TO-247 style for the output transistors, but isn't the metal backing make of steel, too? I guess there is less metal than with a TO-3, but as others have pointed out, the thermal dissipation will be worse. (I don't listen at high power levels, so this might not be a problem for me.) I would think that heated silicon would sound worse than cooler silicon, despite there being less metal. (Besides, the heat sink is made of metal. Yes, I am skeptical – but I try to keep an open mind.)
Anyway, if I change transistors as indicated, I will need a new layout. I am skilled at designing PCBs (but not fabricating them), so this may be a fun thing to do. I do believe that keeping the leads short between the drivers and the output transistors is good, and a different PCB/heatsink combination may be helpful here.
Also, I have read of the sonic characteristics of different parts. I remember some of early publications in Audio Amateur (I think – by Marsh, or maybe it was in Audio) about the sonics of capacitors. My first Leach Amp made use of polycarbonate capacitors as a result. Today, I am reading about resistors, and it is quite confusing. Some love carbon comp's, other hate them. (Those carbon comps will drift all over the place. We had a project where we used them and we had to literally bake them for a day to drive out the moisture to get a stable resistance, then quickly solder them in and conformally coat them, or they would fail testing.) I had been planning to use metal film (both military RNC/RLR types, as I can scrounge them from my company, and the generic Panasonic's from Digi-Key). The discussion of the very expensive Vishay's, etc. is interesting. I don't buy the argument that a tight tolerance resistors impacts the sound, but the fact that a tight tolerance part is better constructed and that, in turn, impacts the sound, does have some merit for serious discussion. I will probably stick with metal film, but I might use some expensive ones in the feedback look – if I can get a sales rep to sample them to me!
Well, this is turning into a much longer intro than I had hoped. I think it will be fun to participate in the group, and while I am an experienced analog designer, I do not claim to be an expert in audio design by any means. I am here to learn and I hope that later on I may be able to give something back.
Thanks for reading, and happy building to all!
Jeff R.
Welcome, Jeff
Looks like you'll enjoy being around and we'll enjoy having you around.
funny thing, that parts/wires type stuff - we generally have two types here - those who swear by such things and those who swear at such things -
I am basically cynical/skeptic or skeptical/cynic depending on which week it is.
However, I do believe that some physical differences in parts can mean a subtle and audible difference in certain situations.
The problem is that these subtle differences are not easily explained or measured.
That's where part of the fun is too
glad to have you here
Ken
Looks like you'll enjoy being around and we'll enjoy having you around.
funny thing, that parts/wires type stuff - we generally have two types here - those who swear by such things and those who swear at such things -
I am basically cynical/skeptic or skeptical/cynic depending on which week it is.
However, I do believe that some physical differences in parts can mean a subtle and audible difference in certain situations.
The problem is that these subtle differences are not easily explained or measured.
That's where part of the fun is too
glad to have you here
Ken
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