I'm sure mine is always that thickness, I'll have to check it out
not very often are they as per the scheme,mostly alternatives, but these could be manufacture changes.
funny enough i dont get many that look like they have had alot of work, most have the original ELNA caps, are absolutly filthy l guess proberbly and generaly over driven.
The heatsink in these is very basic and im looking at ways to get a better one made to see what the difference is.I can get a copper one made, about the same gauge thickness for about £10, im thinking it could be a good modification to offer people who want to keep thier old units.
Im going to trial one and see what it is like.
some amps, not just the NAD ones, marantz and rotel were just as poor(cost i guess)
The existing ones tend to run at anything up to 55-60c at only half volume, i did have one higher than that.
still all good fun.
If you look at the output of your generator or look at the scopes 'Cal' output then it should be a single clear trace, no furriness. You should prove that is correct first,
Any thickening of the trace after that shows a problem either in the unit being worked on or in the measurement technique and set up. A pure sine from the generator should pass through the amp and look the same at the speaker output,
That's interesting. I wasn't aware that you can thrash a 3020 and get away with it for long!! Even now, the few I still come across are usually in the hands of ex-UK folk who tend to treat them gently and expect them to outlast everyone in earshot.
Wow....55-60C is rather hot for a 30W class AB amp. at half power - finger burning hot. Is there something wrong with the bias setting resistors or do they look like Mr Tinker has been at work? Perhaps there was something blocking the vents? (I was asked to check a 3020 variant which lived under a stack of newspapers once - the guy complained that it only worked for half an hour, went louder then shut off for a few minutes) Ahem!...one born every minute! Even in this climate, 3020s don't get all that hot in normal home use but we seldom have heaters running or play old gear very loud, so perhaps there's a seasonal effect.
That’s just a U-channel heat sink good for about 10 or 15 watts, right? Just bolting a finned radiator to it would go a long way.
Not having enough heat sink can cause thermal run away, emitter resistors or no emitter resistors.
Not having enough heat sink can cause thermal run away, emitter resistors or no emitter resistors.
Its probably good for a bit more, if the Japanese models in the 33W category of the 1970-80s were anything to go by. This short video gives us some perspective on the size and location of the U-channel. I imagine any decent size vertical fin extrusion tacked onto the long side would drop the temperature somewhat. No need for copper there, Al is quite good enough - it's the fin area and thick backplate you need. Where to get the extrusion though? Major distros in the UK seem to have little to offer.
If you want to see some thermal data for the 3020:
https://audiokarma.org/forums/index...stigation-with-pictures.978718/#post-15319547
https://audiokarma.org/forums/index...stigation-with-pictures.978718/#post-15319547
Yeah even with the bias set correctly they do get pretty hot. Most amps of that era had heat sinks that were a bit undersized, I've bolted on additional sections to existing ones and it makes quite a difference, also most are cheap soft mild steel, and poor conductors, that's why I had the idea of getting new heatsinks made of copper or aluminium, not just for the 3020's because as you rightly said people handle them more with kid gloves these days, but take a 3130,3240pe or one of the later 3020 mk's for example and I find they are purchased by reputation not only for thier sound quality, which is still good by today's standards, but for how Conservative they are rated power wise. I am a bit of a hifi buff, always have been and I prefer,the warmer sound of the older kit and I know alot of people who are swapping back frim newer digital kit for the same reason. It's like comparing CD to analog vinyl, IMO vinyl wins everytime providing they are well looked after, and played back through good quality kit. Wow sorry that was a ramble on wasn't it 😮👍
It's fine by me. I could listen to (ok, read) honest reasons why people like their audio systems, how they interpret the sound quality and musical story all day. It's like an extension of a dialogue I began with my late father who would both play and listen to classical music for hours most days. He was on a different wavelength but could recognize a decent amp. in a moment - uncanny.
It sound like we have a very simlar mind set.Your dad sounds like he was a very inteligent person.
Classical music isnt for everyone.I have a very diverse musical taste which does include some classical music.I listen to it while i am working at home most of the time,but it is always the first type of music i use when testing my amps,especialy piano as i find this to be the most challenging for the kit to deal with, all the transients etc ,anything that is 'struck' has the biggest impact on audible distortion, well thats how i was taught any when i used to visit the many listening rooms of audio specialists i frequented when purchasing Hi Fi gear years ago, so i use that method today when testing anything.
I do of course use other music to test after, but always classical first.
Im a bit like your dad, i can tell almost instantly, differences in most amplifier quality just by listening,providing the rest of the hardware is of good quality,and i like think my own personal set up at home would at least go some way to qualify for that.👍
Classical music isnt for everyone.I have a very diverse musical taste which does include some classical music.I listen to it while i am working at home most of the time,but it is always the first type of music i use when testing my amps,especialy piano as i find this to be the most challenging for the kit to deal with, all the transients etc ,anything that is 'struck' has the biggest impact on audible distortion, well thats how i was taught any when i used to visit the many listening rooms of audio specialists i frequented when purchasing Hi Fi gear years ago, so i use that method today when testing anything.
I do of course use other music to test after, but always classical first.
Im a bit like your dad, i can tell almost instantly, differences in most amplifier quality just by listening,providing the rest of the hardware is of good quality,and i like think my own personal set up at home would at least go some way to qualify for that.👍
so all up and running now with this and the lost channel i had was a broken link to the 25v rail.
we still have the following issues though that i have to now look at with the scope
Lower/duller volume on the left channel
distortion on both(more on left) when turned right up.
both channels still get a bit distorted when turned right up, and it isn't the speakers
Not sure if you would call this harmonic distortion or not, but classical music really 'heightens it' especially choral at mid/high frequency
my money is on the 'still' slightly wandering of the bias for the distortion, as it still goes a little haywire as the volume is increased, its fine at lower levels, nothing like it was though to start with.
I have tried to ensure transistors are matched as near as possible on both channels.
And it appears to run out of steam some what when elevated-power supply maybe?/filter caps?
we still have the following issues though that i have to now look at with the scope
Lower/duller volume on the left channel
distortion on both(more on left) when turned right up.
both channels still get a bit distorted when turned right up, and it isn't the speakers
Not sure if you would call this harmonic distortion or not, but classical music really 'heightens it' especially choral at mid/high frequency
my money is on the 'still' slightly wandering of the bias for the distortion, as it still goes a little haywire as the volume is increased, its fine at lower levels, nothing like it was though to start with.
I have tried to ensure transistors are matched as near as possible on both channels.
And it appears to run out of steam some what when elevated-power supply maybe?/filter caps?
For testing most stability problems, you should be using dummy loads to check the actual working performance of the amplifiers, using a steady, pure tone input signal source of maybe 100Hz, 1kHz and 10kHz. Monitor the loaded output of the amplifiers with the 'scope, by checking the output for stable level and the waveform symmetry. A dual channel 'scope can also be used to scale and superimpose the input on output signals to see if anything subtly different is happening by comparing input and output waveforms directly. Differential mode testing may be ideal for this but it's both expensive on equipment and demanding to do properly so 'not a good idea unless your pockets are overflowing with cash and you have a well paying electronics career to justify it.
The tiny NAD power supply is the practical limit to how hard you can drive the channels continuously for a proper test. The load resistors should be big, as in 20W+ rated and as close as possible to 4 or 8 ohm and mounted on a heatsink, cooled in a large container of cold water or a similar arrangement that can dissipate either amplifier's full rated power output.
In caution, beware that things will get hot and you need to quit testing promptly when something changes, overheats or hums unexpectedly. Take care and read up what you need to know about load testing small to medium amplifiers so that you understand what you're trying to achieve and also prevent unnecessary damage.
The tiny NAD power supply is the practical limit to how hard you can drive the channels continuously for a proper test. The load resistors should be big, as in 20W+ rated and as close as possible to 4 or 8 ohm and mounted on a heatsink, cooled in a large container of cold water or a similar arrangement that can dissipate either amplifier's full rated power output.
In caution, beware that things will get hot and you need to quit testing promptly when something changes, overheats or hums unexpectedly. Take care and read up what you need to know about load testing small to medium amplifiers so that you understand what you're trying to achieve and also prevent unnecessary damage.
The scope is the right tool for the job here. Use your generator and check the channel matching and also the overall frequency response to see if one channel has any HF roll off.