I've just finished this hifi amp. I tried to keep it simple with the best sound possible (mostly by listening). I've put all the voltages there to show it all.
Is there anything too unusual my design? Thanks for any feedback, good or bad. I've re-uploaded the schematic hopefully without the errors.
Is there anything too unusual my design? Thanks for any feedback, good or bad. I've re-uploaded the schematic hopefully without the errors.
An externally hosted image should be here but it was not working when we last tested it.
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You have NFB from the secondary via a 15k that looks like it is shunted to ground via the 22uf cap.
The 470k resistor between the 1st and 2nd cap in the power supply would make a very large voltage drop.
Does it make any sound? If yes, then your schematic is wrong. See the OPT connection, it's connected between the plate and screen grid and yes, also the feedback is shunted to ground.
Yes, for several reasons that can't be the actual circuit of a working amplifier.
Also, why draw the PSU upside down? There are circuit drawing conventions because, like written and spoken language, such conventions aid communication and mutual understanding.
Also, why draw the PSU upside down? There are circuit drawing conventions because, like written and spoken language, such conventions aid communication and mutual understanding.
several drawing errors - see attachment
remove 22uF cap from NFB to ground - otherwise FB will not work
increase bypass cap on cathode of 6v6 - otherwise sound will be thin
add grid stoppers - to prevent parasitic oscillations, solder as close as possible to socket pins
remove 22uF cap from NFB to ground - otherwise FB will not work
increase bypass cap on cathode of 6v6 - otherwise sound will be thin
add grid stoppers - to prevent parasitic oscillations, solder as close as possible to socket pins
Attachments
The 470k is meant to be 470 ohm. Sorry I've corrected it, the schema was just a quickie one to put up.
The OT is connected between the plate and screen grid, that's correct. I've copied that from the amp the OTs were removed from years ego. Not sure why is it so but it works fine.
The NFB... oh yes, somehow I forgot about the cap. I was building without NFB at first. Maybe that's why the amp sound somewhat dull. Glad you've mentioned that.
It's been quiet few years since I build anything and seem to have forgotten a bit. Also have noticed that there were a tons of good schemas of all kinds on the Net still about 10 years ego, but now seem to be much less and mostly guitar amps so I'm having hard time to find suitable references.
The OT is connected between the plate and screen grid, that's correct. I've copied that from the amp the OTs were removed from years ego. Not sure why is it so but it works fine.
The NFB... oh yes, somehow I forgot about the cap. I was building without NFB at first. Maybe that's why the amp sound somewhat dull. Glad you've mentioned that.
It's been quiet few years since I build anything and seem to have forgotten a bit. Also have noticed that there were a tons of good schemas of all kinds on the Net still about 10 years ego, but now seem to be much less and mostly guitar amps so I'm having hard time to find suitable references.
There is nothing wrong with the OT between plate and screen, it's the positive that has to be at the screen not the plate 🙂The OT is connected between the plate and screen grid, that's correct. I've copied that from the amp the OTs were removed from years ego. Not sure why is it so but it works fine.
Why is there a hole in the centre of your schematic ?
Mona
I had to put a hole in it so I can nail it to the screen 🙂, nah, just ignore it's leftovers.
The NFB goes to positive, how can that be wrong?
The NFB goes to positive, how can that be wrong?
If connected in the wrong direction the NFB become PFB.No worry, you will hear the difference. :lol:
Mona
Mona
The amp all works fine, I just need to remove the cap on the cathode as one of the members mentioned here and maybe add some grid resistors to stop parasitics thou I can't hear any.
The amp all works fine, I just need to remove the cap on the cathode as one of the members mentioned here and maybe add some grid resistors to stop parasitics thou I can't hear any.
You won't. They are typically well up the frequency range. Your dog might!
The NFB goes to positive, how can that be wrong?
The polarity of the output transformer secondary is drawn incorrectly.
The amp all works fine,......
Is that because it makes some sound? Look at the diagram of any amp and you'll see the B+ goes into the OPT on one end first and to the G2 before it goes to the plate FROM the OPT other end. You are filtering the output from the plate as it is now drawn. The signal on the G2 is driving the output.
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The B+ is correct. It can be done that way, I've copied this design from a physical amp some years ego. An old technician back than explained to me why is that an advantage, wish I could remember tho.
The main error I had in this design was forgetting the bypass cap in while adding NFB. With the cap removed it's just fine now.But I'm still tweaking it a bit, than I'll draw the chema properly.
The main error I had in this design was forgetting the bypass cap in while adding NFB. With the cap removed it's just fine now.But I'm still tweaking it a bit, than I'll draw the chema properly.
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I don't know which diagram we are now working from, but certainly the original diagram had the OPT between g2 and anode, and supply rail to the anode. Someone pointed out that the supply rail should go to g2 - then we have a pentode output with g2 at supply rail voltage.
Leaving it as it was you get a much smaller output from g2 alone, with the anode current wasted. This is not an advantage, unless perhaps you want a low power practice amp?
Leaving it as it was you get a much smaller output from g2 alone, with the anode current wasted. This is not an advantage, unless perhaps you want a low power practice amp?
You mean the supply rail should go to g2? I must admit I don't fully understand why is it connected this way but it is exactly what I've copied from an old amp. It has plenty of power I'd say more than my other 6V6 SE amps I've build but that could be also due to the OTs which I must mention were NOT grounded either at primary or secondary. (Ignore the + and - I got on the OT, those are just red and blue wires on the OT primary)
It confuses me too the way it is, it is the only amp I've build like this. Others are build the common way - anode to primary on OT, the other OT side to ground.
Maybe I should to take a pic?
It confuses me too the way it is, it is the only amp I've build like this. Others are build the common way - anode to primary on OT, the other OT side to ground.
Maybe I should to take a pic?
A good diagram of what you actually built would help. You don't ground the primary of an OPT. Taking output from g2 would give audio but much less than from the anode; given efficient speakers or a small room you might not notice the difference. I don't take a huge amount of notice of what someone hundreds/thousands of miles away assures me he has done; experience tells me that what people have done and what they think they have done is not always the same thing, however confident they are.
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