18-05-2011, 12:29 PM
Sorry for the delay in replying to recent comments but I was nearly all morning drawing that diagram and have had, and indeed have, other things to do as well.
The idea of a valve amp has been floating 'round my pumpkin for a while, Rob. It's a bit early in my career to start designing my own circuits but one day... You did prompt me to look up what "Single-ended" meant so that's a bit more knowledge filed away.
I don't have a lot of 'junk' to experiment with (yet!) and it's the cost of an output transformer that somewhat puts me off. That said, I think I read somewhere that you can use a 12v mains one backwards. As for power supply I'd do it AC/DC style with a dropper or may emulate Pilot's example and just use a transformer for the LT.
As I said though, that's for the future - "walk before you try to run" and all that.
The 'plywood' is as you describe, David. It's that sort with a very thing outer layer, a thick one, another thin one, thick then a thin one at the other side. It would be better described as double-deck miniature blockboard. The main problem was the outer layer coming unstuck. I don't mean just after setting about it with power-tools but even 200 grade glass-paper. It's been stored in a shed but plenty of 'proper' stuff has as well and I've never had trouble with that. Pusser multi-ply has nice looking edges, like some of your laminated turnings, so would have been well worth polishing.
Nick Clegg shouldn't complain about your 're-cycling' efforts in his neighbourhood. Odd how he's my MP and his predecessor was Richard Allan, though he didn't do anything as useful as make good quality loud-speakers.
Thanks for the suggestion, Mark. This was very much a trial and error design. I thought the same about Rs but with the speaker connected direct it just made a horrible noise. With a 3.3Ω one in place it was OK at low volumes and with two of them completely fine. The odd thing is that it likes those two specific resistors as it was playing up if I tried others of similar value. They're the green cylinders on the photo.
As for de-coupling I've never tended to bother but this has usually been as much about lack of parts and or space. This doesn't apply in this case so I'll certainly try it and see what happens.
I did try the chip with NOTHING except power, input and output plus speaker, and it even worked like that, though how long the speaker would have latest is a moot point - it wasn't the decent one!
I still regard it as a beta-version and I could be said to have failed in my intention of making a rough-and-ready workshop tool as it sounds far too good. I've had my radio playing through it all morning in preference to my workshop hi-fi. I've got a bread-board on order so when that arrives I will do more fiddling.
All the best
- Joe
The idea of a valve amp has been floating 'round my pumpkin for a while, Rob. It's a bit early in my career to start designing my own circuits but one day... You did prompt me to look up what "Single-ended" meant so that's a bit more knowledge filed away.
I don't have a lot of 'junk' to experiment with (yet!) and it's the cost of an output transformer that somewhat puts me off. That said, I think I read somewhere that you can use a 12v mains one backwards. As for power supply I'd do it AC/DC style with a dropper or may emulate Pilot's example and just use a transformer for the LT.
As I said though, that's for the future - "walk before you try to run" and all that.
The 'plywood' is as you describe, David. It's that sort with a very thing outer layer, a thick one, another thin one, thick then a thin one at the other side. It would be better described as double-deck miniature blockboard. The main problem was the outer layer coming unstuck. I don't mean just after setting about it with power-tools but even 200 grade glass-paper. It's been stored in a shed but plenty of 'proper' stuff has as well and I've never had trouble with that. Pusser multi-ply has nice looking edges, like some of your laminated turnings, so would have been well worth polishing.
Nick Clegg shouldn't complain about your 're-cycling' efforts in his neighbourhood. Odd how he's my MP and his predecessor was Richard Allan, though he didn't do anything as useful as make good quality loud-speakers.
Thanks for the suggestion, Mark. This was very much a trial and error design. I thought the same about Rs but with the speaker connected direct it just made a horrible noise. With a 3.3Ω one in place it was OK at low volumes and with two of them completely fine. The odd thing is that it likes those two specific resistors as it was playing up if I tried others of similar value. They're the green cylinders on the photo.
As for de-coupling I've never tended to bother but this has usually been as much about lack of parts and or space. This doesn't apply in this case so I'll certainly try it and see what happens.
I did try the chip with NOTHING except power, input and output plus speaker, and it even worked like that, though how long the speaker would have latest is a moot point - it wasn't the decent one!
I still regard it as a beta-version and I could be said to have failed in my intention of making a rough-and-ready workshop tool as it sounds far too good. I've had my radio playing through it all morning in preference to my workshop hi-fi. I've got a bread-board on order so when that arrives I will do more fiddling.
All the best
- Joe