Request for input and feedback on a circuit idea
#31 Re: Request for input and feedback on a circuit idea
OK things have moved on and I've built a prototype (single channel) based on the circuit below. For now I'm using AC heaters with each pair in parallel - I'll replace with the DC heater boards when I get them.
It's all hastily cobbled together at the moment, with many of the low current wires just using clip leads for speed. I've been testing the heater voltages as I went through, but I put the last PSU and signal leads in place last night and was ASTONISHED that all the voltages measure within a couple of volts from target. Quite honestly you could have knocked me down with the avian flying tool of your choice ...
What's more I connected a very old sony bookshelf speaker in place of the dummy load, hacked a quick input together just feeding in music from the headphone jack on my phone and ... MUSIC ! Not very loud (my phone playing Jack Johnson at full volume scoped at around 30mV) but audible, no buzz or noise I could hear, the voice sounded like a voice and the tom-tom sounded like a tom-tom.
I haven't built a PP amp before, so I'm shamelessly taking that as a success and bragging about it. Nothing short of several beers will stop me.
It's all hastily cobbled together at the moment, with many of the low current wires just using clip leads for speed. I've been testing the heater voltages as I went through, but I put the last PSU and signal leads in place last night and was ASTONISHED that all the voltages measure within a couple of volts from target. Quite honestly you could have knocked me down with the avian flying tool of your choice ...
What's more I connected a very old sony bookshelf speaker in place of the dummy load, hacked a quick input together just feeding in music from the headphone jack on my phone and ... MUSIC ! Not very loud (my phone playing Jack Johnson at full volume scoped at around 30mV) but audible, no buzz or noise I could hear, the voice sounded like a voice and the tom-tom sounded like a tom-tom.
I haven't built a PP amp before, so I'm shamelessly taking that as a success and bragging about it. Nothing short of several beers will stop me.
#32 Re: Request for input and feedback on a circuit idea
Nice one, nothing wrong with using clipleads
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
#33 Re: Request for input and feedback on a circuit idea
Thanks - certainly helped speed things up. They are rated at 0.5A so I didn't use them for heaters. Also it becomes a bit spaghetti like, so I clip-leaded each stage, measured it, then replaced with soldered leads before doing the next.
No voltage rating on them but I figured ok for a prototype.
#34 Re: Request for input and feedback on a circuit idea
Bit of history
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
- Mike H
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#35 Re: Request for input and feedback on a circuit idea
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
- Mike H
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#38 Re: Request for input and feedback on a circuit idea
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#39 Re: Request for input and feedback on a circuit idea
Shoddy!
PS. that means good on here
PS. that means good on here
Analogue, the lost world that lies between 0 and 1.
- andrew Ivimey
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#41 Re: Request for input and feedback on a circuit idea
Crikey! Must be good then...
I intend (One day) to fix a 26 heater power supply. I use lead batteries which work very well indeed but are cumbersome. Did you really get away with 2 volts at 1 amp a.c.??!!!
I intend (One day) to fix a 26 heater power supply. I use lead batteries which work very well indeed but are cumbersome. Did you really get away with 2 volts at 1 amp a.c.??!!!
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
#42 Re: Request for input and feedback on a circuit idea
Yeah. When we put it on a lowther today it sounded great but there is hum. Couldn't hear it on the Sony.
#43 Re: Request for input and feedback on a circuit idea
The 26 is actually 1.5v (AC or DC) @ 1.05A. I used a 2.5vAC transformer (because I had several to hand) rated at 3A and connected across both valves in parallel for 2.1A, with dropper resistors to take it down to 1.5v. Like I say it sounds good, but I have high hopes that the DC heater boards from Andrew will improve it and help get rid of the hum - which isn't as bad as I expected but still, hum is the devil's work and is to be chased back into the very hell from whence it cometh !!!!andrew Ivimey wrote: ↑Sat Mar 17, 2018 7:53 pm Crikey! Must be good then...
I intend (One day) to fix a 26 heater power supply. I use lead batteries which work very well indeed but are cumbersome. Did you really get away with 2 volts at 1 amp a.c.??!!!
Next step is to strip out the frames I built my first SE prototypes in (all my builds are in wooden frames to date) and build the second channel into it so it's safe to move around and use. I'm wondering if I can get 2 built in time for Owston, which I think is June ?
Really looking forward to meeting everyone at Owston.
- IslandPink
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#44 Re: Request for input and feedback on a circuit idea
Some noble materials in there. Haven't used my 71A'a in anger yet. Wish I could get to Owston
"Once you find out ... the Circumstances ; then you can go out"
#45 Re: Request for input and feedback on a circuit idea
Question: When I switch the prototype off, there's a brief but high-pitched squeak. Definitely something I would need to eliminate.
I've never noticed anything like that on any of my SE amps. Anyone know what that could be ? It's done it every time I've switched it off (ok maybe half a dozen times). The caps are obviously still providing energy to the valves in that split second after the power is switched off, but that's BAU. I'd be guessing at something in ...
- AC parallel heaters, power instantaneously withdrawn from both valves, some sort of short-lived oscillation ?
- PP oscillation on power off in either the OPT or one of the PP ITs
As you can see I'm guessing. Any pointers gratefully received.
I've never noticed anything like that on any of my SE amps. Anyone know what that could be ? It's done it every time I've switched it off (ok maybe half a dozen times). The caps are obviously still providing energy to the valves in that split second after the power is switched off, but that's BAU. I'd be guessing at something in ...
- AC parallel heaters, power instantaneously withdrawn from both valves, some sort of short-lived oscillation ?
- PP oscillation on power off in either the OPT or one of the PP ITs
As you can see I'm guessing. Any pointers gratefully received.