Technics-goy
Super Member
Hi everyone,
well I am new here on the forum and thought I post a little about my recent winter project. As I have become very much a fan of Technics amplifiers and since these beauties with these wonderful VU meters seem to become really rare these days I thought why not revive the 80's technology a bit and make it a cool DIY project.
And so I decided to replicate the trusty SE-A5 New Class A circuit and give it a new spin and add a few minor features to it. My goal was to have 5 identical channels housed in one case so I had to scale down the output power a bit to fit it all in. I settled for 100W sine CW into 8 Ohm. The reduced power (and operating voltage) offers a really relaxing operating environment for the semiconductors which I expect to outlast me at this point. I added a staggered gentleman's soft-start to minimize inrush currents and I replaced the output relays with two 200A power mosfets. I added an option for balanced input as well. The amp modules are monitored and controlled by a Cypress FPGA chip.
Eventually to most part I was able to source original semiconductors altho I had to substitute a few for some newer vintage I also selected where needed more powerful transistors as I did not like to see them run so hot as in the original A5. Where it made sense I matched all semiconductors as far as possible which I doubt was actually done in the original amps. I had posted on the DIYAudio forum but interest, with exception of one , seemed to be NIL. I guess the cool and wonderful Class D is where it is at these days. Very very little do people actually know what they are missing when opting for a Class D.
I have a restored and modernized SE-A5 and was able to do direct comparison of my amp modules to the original A5. Using a set of DSS-7 and streaming FLAC I can not tell the difference to the good old trusty A5.
I measured flat frequency response up to 65kHz and step response with a 1us rise/fall time pulse. Group delay is about 0.5us as seen below. Currently I can not measure spectrum and had to resort to the cheesy channel math with the scope. But the measurement is encouraging anyway as the difference between the input signal to the output signal is effectively nil. Whatever little difference may be registered seems due to group delay more so than distortion, I'd say.
All boards are gold plated to improve somewhat the prettiness factor and the main circuit boards have 2oz. copper clad.
I wanted find out for myself if I can pull it off and preserve the 80's sounds as I was quite dissatisfied with newer vintage off the shelf amps like Denon, Bryston and AudioNet which surprisingly disappoint considering they are advertised with very reasonable spec's and sell anywhere between 6000 and 9500 suggesting they are serious competitors, which they are not (at least in my books), but at fortunately they look pretty on a stack.
Here are some snaps
well I am new here on the forum and thought I post a little about my recent winter project. As I have become very much a fan of Technics amplifiers and since these beauties with these wonderful VU meters seem to become really rare these days I thought why not revive the 80's technology a bit and make it a cool DIY project.
And so I decided to replicate the trusty SE-A5 New Class A circuit and give it a new spin and add a few minor features to it. My goal was to have 5 identical channels housed in one case so I had to scale down the output power a bit to fit it all in. I settled for 100W sine CW into 8 Ohm. The reduced power (and operating voltage) offers a really relaxing operating environment for the semiconductors which I expect to outlast me at this point. I added a staggered gentleman's soft-start to minimize inrush currents and I replaced the output relays with two 200A power mosfets. I added an option for balanced input as well. The amp modules are monitored and controlled by a Cypress FPGA chip.
Eventually to most part I was able to source original semiconductors altho I had to substitute a few for some newer vintage I also selected where needed more powerful transistors as I did not like to see them run so hot as in the original A5. Where it made sense I matched all semiconductors as far as possible which I doubt was actually done in the original amps. I had posted on the DIYAudio forum but interest, with exception of one , seemed to be NIL. I guess the cool and wonderful Class D is where it is at these days. Very very little do people actually know what they are missing when opting for a Class D.
I have a restored and modernized SE-A5 and was able to do direct comparison of my amp modules to the original A5. Using a set of DSS-7 and streaming FLAC I can not tell the difference to the good old trusty A5.
I measured flat frequency response up to 65kHz and step response with a 1us rise/fall time pulse. Group delay is about 0.5us as seen below. Currently I can not measure spectrum and had to resort to the cheesy channel math with the scope. But the measurement is encouraging anyway as the difference between the input signal to the output signal is effectively nil. Whatever little difference may be registered seems due to group delay more so than distortion, I'd say.
All boards are gold plated to improve somewhat the prettiness factor and the main circuit boards have 2oz. copper clad.
I wanted find out for myself if I can pull it off and preserve the 80's sounds as I was quite dissatisfied with newer vintage off the shelf amps like Denon, Bryston and AudioNet which surprisingly disappoint considering they are advertised with very reasonable spec's and sell anywhere between 6000 and 9500 suggesting they are serious competitors, which they are not (at least in my books), but at fortunately they look pretty on a stack.
Here are some snaps