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Triode Project - The Good, The Bad and The Ugly
Well, after a week's heavy fettling (on and off) the triode amp is making
noises: http://www.apah69.dsl.pipex.com/keit...de_project.htm (I've written it up as 'tips for anyone considering it' as I get quite a bit of post from people on the subject of valve amps and getting into it.) The Good - Even in the very first few minutes of running this amp it's obvious that the sound quality is/is going to be quite simply *stunning*. The clarity gets you straight away, separation and imaging, tone etc. etc. are all quite remarkable. Swim said it sounded 'accomplished'.....?? The Bad - It's humming like a good 'un and I suspect it's going to be a bugger to sort.... The Ugly - Well, I think it's cute, but you'd never sell 'em looking like this...... http://www.apah69.dsl.pipex.com/keit.../ampkit136.jpg ......would you?? :-) |
Triode Project - The Good, The Bad and The Ugly
Keith G wrote:
Well, after a week's heavy fettling (on and off) the triode amp is making noises: http://www.apah69.dsl.pipex.com/keit...de_project.htm snip The Bad - It's humming like a good 'un and I suspect it's going to be a bugger to sort.... The Ugly - Well, I think it's cute, but you'd never sell 'em looking like this...... http://www.apah69.dsl.pipex.com/keit.../ampkit136.jpg .....would you?? :-) I like it, whats the damage to buy one???????????????????????????????? -- Dave xxxx http://www.davewhitter.pwp.blueyonder.co.uk/ Music is Art - Audio is Engineering Steam is Fun |
Triode Project - The Good, The Bad and The Ugly
"Dave xxxx" wrote in message ... Keith G wrote: Well, after a week's heavy fettling (on and off) the triode amp is making noises: http://www.apah69.dsl.pipex.com/keit...de_project.htm snip The Bad - It's humming like a good 'un and I suspect it's going to be a bugger to sort.... The Ugly - Well, I think it's cute, but you'd never sell 'em looking like this...... http://www.apah69.dsl.pipex.com/keit.../ampkit136.jpg .....would you?? :-) I like it, Ok, strangely enough so does Shiny Nigel (and me), so you are not alone........!! :-) whats the damage to buy one???????????????????????????????? Say £500 worth of parts (comfortably) and a week of my time, so that would be about £525 in total, but (as it is atm) it would hum loud enough to silence a washing machine...... ;-) Phil http://www.bluebellaudio.com/ says one of these ponced up with a fancy chassis would/will cost anyone about £3,000. How much he would charge for one made up in a similar 'lab style' (unpainted grey chassis, exposed trannies, screw heads, bloodstains everywhere....), I don't know - give him a call. I gotta say it, present hum notwithstanding, the sound really is *stunning* - and that's from a confirmed/committed valvie who's no stranger to the Wonderful Sound Of Valvey Things (and whose current valve amps are not ****e)......!!! (Phil's just about to put a couple of 300B triode amps on eBay apparently!) |
Triode Project - The Good, The Bad and The Ugly
On Sun, 4 Jul 2004 15:46:17 +0100, "Keith G"
wrote: "Dave xxxx" wrote in message ... Keith G wrote: Well, after a week's heavy fettling (on and off) the triode amp is making noises: http://www.apah69.dsl.pipex.com/keit...de_project.htm snip The Bad - It's humming like a good 'un and I suspect it's going to be a bugger to sort.... The Ugly - Well, I think it's cute, but you'd never sell 'em looking like this...... http://www.apah69.dsl.pipex.com/keit.../ampkit136.jpg .....would you?? :-) I like it, Ok, strangely enough so does Shiny Nigel (and me), so you are not alone........!! :-) whats the damage to buy one???????????????????????????????? Say £500 worth of parts (comfortably) and a week of my time, so that would be about £525 in total, but (as it is atm) it would hum loud enough to silence a washing machine...... ;-) Phil http://www.bluebellaudio.com/ says one of these ponced up with a fancy chassis would/will cost anyone about £3,000. How much he would charge for one made up in a similar 'lab style' (unpainted grey chassis, exposed trannies, screw heads, bloodstains everywhere....), I don't know - give him a call. I gotta say it, present hum notwithstanding, the sound really is *stunning* - and that's from a confirmed/committed valvie who's no stranger to the Wonderful Sound Of Valvey Things (and whose current valve amps are not ****e)......!!! (Phil's just about to put a couple of 300B triode amps on eBay apparently!) Keith - where's the MP3 of the hum? Maybe we can speed up the tracking-down process. d Pearce Consulting http://www.pearce.uk.com |
Triode Project - The Good, The Bad and The Ugly
In message , Keith G
writes "Dave xxxx" wrote in message ... Keith G wrote: Well, after a week's heavy fettling (on and off) the triode amp is making noises: http://www.apah69.dsl.pipex.com/keit...de_project.htm snip The Bad - It's humming like a good 'un and I suspect it's going to be a bugger to sort.... The Ugly - Well, I think it's cute, but you'd never sell 'em looking like this...... http://www.apah69.dsl.pipex.com/keit.../ampkit136.jpg .....would you?? :-) I like it, Ok, strangely enough so does Shiny Nigel (and me), so you are not alone........!! :-) whats the damage to buy one???????????????????????????????? Say £500 worth of parts (comfortably) and a week of my time, so that would be about £525 in total, but (as it is atm) it would hum loud enough to silence a washing machine...... ;-) Phil http://www.bluebellaudio.com/ says one of these ponced up with a fancy chassis would/will cost anyone about £3,000. How much he would charge for one made up in a similar 'lab style' (unpainted grey chassis, exposed trannies, screw heads, bloodstains everywhere....), I don't know - give him a call. I gotta say it, present hum notwithstanding, the sound really is *stunning* - and that's from a confirmed/committed valvie who's no stranger to the Wonderful Sound Of Valvey Things (and whose current valve amps are not ****e)......!!! (Phil's just about to put a couple of 300B triode amps on eBay apparently!) Do you think the hum is coming from the directly-heated filaments of the 300Bs, or from the HT line? (Heater hum is likely to be 50Hz, HT hum is more likely to be 100Hz) If it's the filament, then you could try using a resistive centre-tap on the winding and earthing the CT, (or taking it to the bias circuitry or whatever). You may have a CT filament winding already of course.... -- Chris Morriss |
Triode Project - The Good, The Bad and The Ugly
I don't know if you ever work when you're tired, but if you do you can make odd
mistakes. I shouldn't do it but I did this weekend - put a 220k cathode resistor in place of a 220 ohm. Wondered why it measured funny for a while! (eventually sorted - got some 7951s going in place of 6L6s, bags more detail) Sometimes you have to just go over the dumb ordinary bits until you notice something you overlooked. === Andy Evans === Visit our Website:- http://www.artsandmedia.com Audio, music and health pages and interesting links. |
Triode Project - The Good, The Bad and The Ugly
"Don Pearce" wrote Keith - where's the MP3 of the hum? Maybe we can speed up the tracking-down process. OK, here's a clip from the record I've got on atm - Branford Marsalis 'Scenes In The City': http://www.apah69.dsl.pipex.com/keith_g/show/hum002.mp3 2.5 Mb/1:49 The hum is before, during and after this 'end of track/beginning of next track' snatch of music - which is to give you a sound level reference. Recorded with an open mic, so it's a bit 'boggy' - no 'Line Out' luxuries here, I'm afraid!! :-) (Recording's another thing I've got no clue about! - Also not me best speakers....!! ;-) |
Triode Project - The Good, The Bad and The Ugly
On Sun, 4 Jul 2004 16:58:57 +0100, "Keith G"
wrote: "Don Pearce" wrote Keith - where's the MP3 of the hum? Maybe we can speed up the tracking-down process. OK, here's a clip from the record I've got on atm - Branford Marsalis 'Scenes In The City': http://www.apah69.dsl.pipex.com/keith_g/show/hum002.mp3 2.5 Mb/1:49 The hum is before, during and after this 'end of track/beginning of next track' snatch of music - which is to give you a sound level reference. Recorded with an open mic, so it's a bit 'boggy' - no 'Line Out' luxuries here, I'm afraid!! :-) (Recording's another thing I've got no clue about! - Also not me best speakers....!! ;-) Mmmmm... that hum is 100Hz, not 50, so it pretty certainly comes from the power supply rails, not stuff like ground loops. Do you have a spare fat electrolytic you could hang across power supply in parallel with the one already there? See if that kills, or at least reduces, the level. d Pearce Consulting http://www.pearce.uk.com |
Triode Project - The Good, The Bad and The Ugly
"Don Pearce" wrote Mmmmm... that hum is 100Hz, not 50, so it pretty certainly comes from the power supply rails, not stuff like ground loops. Do you have a spare fat electrolytic you could hang across power supply in parallel with the one already there? See if that kills, or at least reduces, the level. OK, that's interesting and would be good if I *don't* have any ground loops. No I ain't got any spare electrolytics, but I can damn soon rectify*** that! (I actually managed to use up all the components - I've come a long way from me motorcycle-fettling days when I always ended up with a jamjar full of 'leftovers' for each bike..... :-) Interesting thing is that, now that I've got it on the computer, I 'scoped it**: http://www.apah69.dsl.pipex.com/keith_g/show/humpic.jpg The different traces swap places exactly when I switch the leads over, so summat's up. (Buggered if I know what tho' - I'm not much cop at scopes either!) Which reminds me I haven't had an answer yet to an earlier question - that top trace will slowly slide down the screen over a period of time. Anybody got any idea what causes that? **You sods are turning me into a bloody techie!! ***techie pun? :-) |
Triode Project - The Good, The Bad and The Ugly
"Chris Morriss" wrote Do you think the hum is coming from the directly-heated filaments of the 300Bs, or from the HT line? (Heater hum is likely to be 50Hz, HT hum is more likely to be 100Hz) It's looking like the hum is 100Hz, but my scope telling me that it's left-channel weighted. (If the scope can be trusted.....???) If it's the filament, then you could try using a resistive centre-tap on the winding and earthing the CT, (or taking it to the bias circuitry or whatever). You may have a CT filament winding already of course.... The filaments have their own transformers where the CT (if it is one - grey and blue secondaries twisted togetther??) is taken up to a 200V rail which it shares with the cathode resistors and bypass capacitor as in: http://www.apah69.dsl.pipex.com/keit.../ampkit124.jpg The red and yellow secondaries supply 2.5V @ 3A directly to the filament (measured about 2.69V, IIRC) |
Triode Project - The Good, The Bad and The Ugly
On Sun, 4 Jul 2004 18:13:43 +0100, "Keith G"
wrote: "Don Pearce" wrote Mmmmm... that hum is 100Hz, not 50, so it pretty certainly comes from the power supply rails, not stuff like ground loops. Do you have a spare fat electrolytic you could hang across power supply in parallel with the one already there? See if that kills, or at least reduces, the level. OK, that's interesting and would be good if I *don't* have any ground loops. No I ain't got any spare electrolytics, but I can damn soon rectify*** that! (I actually managed to use up all the components - I've come a long way from me motorcycle-fettling days when I always ended up with a jamjar full of 'leftovers' for each bike..... :-) Interesting thing is that, now that I've got it on the computer, I 'scoped it**: http://www.apah69.dsl.pipex.com/keith_g/show/humpic.jpg The different traces swap places exactly when I switch the leads over, so summat's up. (Buggered if I know what tho' - I'm not much cop at scopes either!) Which reminds me I haven't had an answer yet to an earlier question - that top trace will slowly slide down the screen over a period of time. Anybody got any idea what causes that? **You sods are turning me into a bloody techie!! ***techie pun? :-) OK, if you have no major bits left over, you *definitely* built it wrong - that's the law. Good scope traces, though - but what are they of? I have the circuit diagram of the amp (sadly not the power supply) in front of me. d Pearce Consulting http://www.pearce.uk.com |
Triode Project - The Good, The Bad and The Ugly
On Sun, 04 Jul 2004 17:22:21 +0100, Don Pearce
wrote: On Sun, 4 Jul 2004 16:58:57 +0100, "Keith G" wrote: "Don Pearce" wrote Keith - where's the MP3 of the hum? Maybe we can speed up the tracking-down process. OK, here's a clip from the record I've got on atm - Branford Marsalis 'Scenes In The City': http://www.apah69.dsl.pipex.com/keith_g/show/hum002.mp3 2.5 Mb/1:49 The hum is before, during and after this 'end of track/beginning of next track' snatch of music - which is to give you a sound level reference. Recorded with an open mic, so it's a bit 'boggy' - no 'Line Out' luxuries here, I'm afraid!! :-) (Recording's another thing I've got no clue about! - Also not me best speakers....!! ;-) Mmmmm... that hum is 100Hz, not 50, so it pretty certainly comes from the power supply rails, not stuff like ground loops. Do you have a spare fat electrolytic you could hang across power supply in parallel with the one already there? See if that kills, or at least reduces, the level. Actually, one of the nice things - the *only* nice thing? :-) - about valve amps is that the HT current drain is low enough that you can use a classic CLC 'pi' filter to virtually eliminate 100Hz problems on the supply rail. I'd give it a go - if you find some spare space on the chassis for more iron bits! -- Stewart Pinkerton | Music is Art - Audio is Engineering |
Triode Project - The Good, The Bad and The Ugly
Keith G wrote:
It's looking like the hum is 100Hz, but my scope telling me that it's left-channel weighted. (If the scope can be trusted.....???) Do you still get this if you swap the probe leads around? If the disparity of amplitude shown on the scope doesn't swap around, your scope set up is wrong. -- Wally www.artbywally.com www.wally.myby.co.uk |
Triode Project - The Good, The Bad and The Ugly
In message , Keith G
writes "Chris Morriss" wrote Do you think the hum is coming from the directly-heated filaments of the 300Bs, or from the HT line? (Heater hum is likely to be 50Hz, HT hum is more likely to be 100Hz) It's looking like the hum is 100Hz, but my scope telling me that it's left-channel weighted. (If the scope can be trusted.....???) If it's the filament, then you could try using a resistive centre-tap on the winding and earthing the CT, (or taking it to the bias circuitry or whatever). You may have a CT filament winding already of course.... The filaments have their own transformers where the CT (if it is one - grey and blue secondaries twisted togetther??) is taken up to a 200V rail which it shares with the cathode resistors and bypass capacitor as in: http://www.apah69.dsl.pipex.com/keit.../ampkit124.jpg The red and yellow secondaries supply 2.5V @ 3A directly to the filament (measured about 2.69V, IIRC) Here's an idea. I guess your input stage valves are capacitor-coupled to the grid of the 300B. You could therefore run the amp with only the output 300B valves in and see if the hum is still present. If it is you know that the +ve feed to the anode of one of the 300Bs is wrong in some way. If the hum goes away, but comes back with the input valves in, then you might have faulty decoupling on these in some way. I see the URL you gave shows the PSU schematic poking out from under the chassis. The 40u + choke +100u should give adequate smoothing for the output triodes. -- Chris Morriss |
Triode Project - The Good, The Bad and The Ugly
On Sun, 4 Jul 2004 17:50:52 +0000 (UTC), Stewart Pinkerton
wrote: Mmmmm... that hum is 100Hz, not 50, so it pretty certainly comes from the power supply rails, not stuff like ground loops. Do you have a spare fat electrolytic you could hang across power supply in parallel with the one already there? See if that kills, or at least reduces, the level. Actually, one of the nice things - the *only* nice thing? :-) - about valve amps is that the HT current drain is low enough that you can use a classic CLC 'pi' filter to virtually eliminate 100Hz problems on the supply rail. I'd give it a go - if you find some spare space on the chassis for more iron bits! -- Stewart Pinkerton | Music is Art - Audio is Engineering True, but what bothers me is that this is a kit, which presumably should work OK without going to those lengths. I'm wondering if the HT for the first stage has perhaps been taken from the wrong spot on the RC chain. Have a look at http://www.worldaudiodesign.com/pdf/sup5688upg.pdf It is interesting that they are using KT88s, but haven't bothered with ultralinear tapping of the output transformer. d Pearce Consulting http://www.pearce.uk.com |
Triode Project - The Good, The Bad and The Ugly
On Sun, 4 Jul 2004 18:27:01 +0100, "Keith G"
wrote: "Chris Morriss" wrote Do you think the hum is coming from the directly-heated filaments of the 300Bs, or from the HT line? (Heater hum is likely to be 50Hz, HT hum is more likely to be 100Hz) It's looking like the hum is 100Hz, but my scope telling me that it's left-channel weighted. (If the scope can be trusted.....???) If it's the filament, then you could try using a resistive centre-tap on the winding and earthing the CT, (or taking it to the bias circuitry or whatever). You may have a CT filament winding already of course.... The filaments have their own transformers where the CT (if it is one - grey and blue secondaries twisted togetther??) is taken up to a 200V rail which it shares with the cathode resistors and bypass capacitor as in: http://www.apah69.dsl.pipex.com/keit.../ampkit124.jpg The red and yellow secondaries supply 2.5V @ 3A directly to the filament (measured about 2.69V, IIRC) The MP3 has virtually identical hum on both channels - it certainly doesn't have anything like the disparity that the scope picture shows. http://www.donepearce.plus.com/odds/keith_screen.jpg d Pearce Consulting http://www.pearce.uk.com |
Triode Project - The Good, The Bad and The Ugly
"Don Pearce" OK, if you have no major bits left over, you *definitely* built it wrong - that's the law. Yes, that *is* a bit worrying! :-) Good scope traces, though - but what are they of? OK, they are the 'hum' from the Branford Marsalis clip played from the computer to a little Technics amp which is connected to the scope - one pair of speaker outlets (A) drive a pair of speakers, the other speaker outlets (B) are connected to the scope. Enables me to hear tones at the same time as I can see them**. (Crosstalk between the speaker outlets notwithstanding) The thing is that a) the better of the two traces (left channel) showed the 'fuzziness' of hum and appeared to confirm your 100 Hz (I didn't do the sums - I just saw 2cm waves @ 5 ms/cm) and b) the traces swapped over exactly when I reversed the leads from the speaker outlets..... I have the circuit diagram of the amp (sadly not the power supply) in front of me. OK, I've posted the ps circuit.... http://www.apah69.dsl.pipex.com/keit.../pscircuit.jpg .......but I daren't post the whole thing as I don't know what the form is with publishing people's circuits??? **not so dusty for a thick git, eh? ;-) |
Triode Project - The Good, The Bad and The Ugly
In article , Keith G
writes "Don Pearce" OK, if you have no major bits left over, you *definitely* built it wrong - that's the law. Yes, that *is* a bit worrying! :-) Good scope traces, though - but what are they of? OK, they are the 'hum' from the Branford Marsalis clip played from the computer to a little Technics amp which is connected to the scope - one pair of speaker outlets (A) drive a pair of speakers, the other speaker outlets (B) are connected to the scope. Enables me to hear tones at the same time as I can see them**. (Crosstalk between the speaker outlets notwithstanding) The thing is that a) the better of the two traces (left channel) showed the 'fuzziness' of hum and appeared to confirm your 100 Hz (I didn't do the sums - I just saw 2cm waves @ 5 ms/cm) and b) the traces swapped over exactly when I reversed the leads from the speaker outlets..... I have the circuit diagram of the amp (sadly not the power supply) in front of me. OK, I've posted the ps circuit.... http://www.apah69.dsl.pipex.com/keit.../pscircuit.jpg ......but I daren't post the whole thing as I don't know what the form is with publishing people's circuits??? **not so dusty for a thick git, eh? ;-) They reversing the 5 volt heater windings?, hasn't the GZ34 got a cathode???? -- Tony Sayer |
Triode Project - The Good, The Bad and The Ugly
On Sun, 4 Jul 2004 19:08:29 +0100, "Keith G"
wrote: "Don Pearce" OK, if you have no major bits left over, you *definitely* built it wrong - that's the law. Yes, that *is* a bit worrying! :-) Good scope traces, though - but what are they of? OK, they are the 'hum' from the Branford Marsalis clip played from the computer to a little Technics amp which is connected to the scope - one pair of speaker outlets (A) drive a pair of speakers, the other speaker outlets (B) are connected to the scope. Enables me to hear tones at the same time as I can see them**. (Crosstalk between the speaker outlets notwithstanding) The thing is that a) the better of the two traces (left channel) showed the 'fuzziness' of hum and appeared to confirm your 100 Hz (I didn't do the sums - I just saw 2cm waves @ 5 ms/cm) and b) the traces swapped over exactly when I reversed the leads from the speaker outlets..... I have the circuit diagram of the amp (sadly not the power supply) in front of me. OK, I've posted the ps circuit.... http://www.apah69.dsl.pipex.com/keit.../pscircuit.jpg ......but I daren't post the whole thing as I don't know what the form is with publishing people's circuits??? **not so dusty for a thick git, eh? ;-) You'll be an engineer by the time you're done! Well, see another post where I look at that file, and the hum on the two channels is essentially identical. The PSU circuit doesn't seem to quite stack up with the power amp one I have. There are connection points A-D, presumably along a chain of resistors and capacitors, for the various valves. Does the input valve anode resistor connect to point B on the PSU? d Pearce Consulting http://www.pearce.uk.com |
Triode Project - The Good, The Bad and The Ugly
"Don Pearce" wrote You'll be an engineer by the time you're done! Oi! You watch yer language!! Well, see another post where I look at that file, and the hum on the two channels is essentially identical. The PSU circuit doesn't seem to quite stack up with the power amp one I have. There are connection points A-D, presumably along a chain of resistors and capacitors, for the various valves. Does the input valve anode resistor connect to point B on the PSU? Don, I think we are at cross-purposes - see other reply..... |
Triode Project - The Good, The Bad and The Ugly
"Don Pearce" wrote True, but what bothers me is that this is a kit, which presumably should work OK without going to those lengths. I'm wondering if the HT for the first stage has perhaps been taken from the wrong spot on the RC chain. It ain't a kit, other than a 'kit of parts' - see: http://www.apah69.dsl.pipex.com/keit...de_project.htm |
Triode Project - The Good, The Bad and The Ugly
Keith G wrote:
OK, they are the 'hum' from the Branford Marsalis clip played from the computer to a little Technics amp which is connected to the scope - one pair of speaker outlets (A) drive a pair of speakers, the other speaker outlets (B) are connected to the scope. Enables me to hear tones at the same time as I can see them**. (Crosstalk between the speaker outlets notwithstanding) The scope's probes will be very high impedance - you can just bung it on a bit of circuit, and you'll still be able to hear what's going on. I'd suggest chucking out everything other than the iffy amp (with a load) and the scope, and trace the circuit through - compare the trace at the same point on left and right channels. OK, I've posted the ps circuit.... If the hum is definitely in one channel, then I think the PSU will be okay. -- Wally www.artbywally.com www.wally.myby.co.uk |
Triode Project - The Good, The Bad and The Ugly
On Sun, 4 Jul 2004 19:45:55 +0100, "Keith G"
wrote: "Don Pearce" wrote True, but what bothers me is that this is a kit, which presumably should work OK without going to those lengths. I'm wondering if the HT for the first stage has perhaps been taken from the wrong spot on the RC chain. It ain't a kit, other than a 'kit of parts' - see: http://www.apah69.dsl.pipex.com/keit...de_project.htm Ah! I think Chris had a good idea, though - pull out the input pentodes and see if the hum goes away. If it does, then pretty certainly you need to improve the smoothing on that stage. The Blumlein pair of triodes following should have a bit of power supply immunity, so they shouldn't be anything like as much a source of bother. d Pearce Consulting http://www.pearce.uk.com |
Triode Project - The Good, The Bad and The Ugly
Hi,
In message , Keith G writes OK, that's interesting and would be good if I *don't* have any ground loops. No I ain't got any spare electrolytics, but I can damn soon rectify*** that! (I actually managed to use up all the components You *can't* be a proper techie. If you haven't got any spare bits left over at the end of a kit build, either you haven't build it properly, or you got it from IKEA and only half of it arrived in the first place :-) - I've come a long way from me motorcycle-fettling days when I always ended up with a jamjar full of 'leftovers' for each bike..... :-) Now that's more like it. My local garage do that, then offer to sell them back to you as spares. The records are great, btw. Lionel is doing his thing at the moment. Ta very much! -- Regards, Glenn Booth |
Triode Project - The Good, The Bad and The Ugly
"Chris Morriss" wrote Here's an idea. I guess your input stage valves are capacitor-coupled to the grid of the 300B. Nope, the whole point of the amp is that the input valves are *direct* coupled to the 2A3 triodes. You could therefore run the amp with only the output 300B valves in and see if the hum is still present. I don't think that we a very good idea... If it is you know that the +ve feed to the anode of one of the 300Bs is wrong in some way. If the hum goes away, but comes back with the input valves in, then you might have faulty decoupling on these in some way. I see the URL you gave shows the PSU schematic poking out from under the chassis. The 40u + choke +100u should give adequate smoothing for the output triodes. The money's still on an earthing problem atm, but the 100Hz frequency is a bit mysterious.... |
Triode Project - The Good, The Bad and The Ugly
"Don Pearce" wrote The MP3 has virtually identical hum on both channels - it certainly doesn't have anything like the disparity that the scope picture shows. http://www.donepearce.plus.com/odds/keith_screen.jpg Yes and the waveforms are the same height in SoundForge, so I'm suspecting the scope and/or leads atm. (No big deal, the scopes only a learning tool atm.) |
Triode Project - The Good, The Bad and The Ugly
Hi,
In message , Keith G writes It's looking like the hum is 100Hz, but my scope telling me that it's left-channel weighted. (If the scope can be trusted.....???) A spectrum analysis in Cooledit reckons that the channel difference is tiny - within 0.5dB. I'd say it's happening to both channels. -- Regards, Glenn Booth |
Triode Project - The Good, The Bad and The Ugly
Keith G wrote:
You could therefore run the amp with only the output 300B valves in and see if the hum is still present. I don't think that we a very good idea... Should be okay, I'd have thought. The money's still on an earthing problem atm, but the 100Hz frequency is a bit mysterious.... 100Hz is post-rectification - I'd have a look at the ripple on the supply. -- Wally www.artbywally.com www.wally.myby.co.uk |
Triode Project - The Good, The Bad and The Ugly
In message , Keith G
writes "Chris Morriss" wrote Here's an idea. I guess your input stage valves are capacitor-coupled to the grid of the 300B. Nope, the whole point of the amp is that the input valves are *direct* coupled to the 2A3 triodes. You could therefore run the amp with only the output 300B valves in and see if the hum is still present. I don't think that we a very good idea... If it is you know that the +ve feed to the anode of one of the 300Bs is wrong in some way. If the hum goes away, but comes back with the input valves in, then you might have faulty decoupling on these in some way. I see the URL you gave shows the PSU schematic poking out from under the chassis. The 40u + choke +100u should give adequate smoothing for the output triodes. The money's still on an earthing problem atm, but the 100Hz frequency is a bit mysterious.... Oh!, Didn't realise they were 2A3s. Sorry. -- Chris Morriss |
Triode Project - The Good, The Bad and The Ugly
In message , Keith G
writes "Don Pearce" wrote True, but what bothers me is that this is a kit, which presumably should work OK without going to those lengths. I'm wondering if the HT for the first stage has perhaps been taken from the wrong spot on the RC chain. It ain't a kit, other than a 'kit of parts' - see: http://www.apah69.dsl.pipex.com/keit...de_project.htm I've just had a look at one of the links to the original schematic from your site. I see that the original used a 460R resistor from the input ground to the B-. Does your design do the same? I'm a bit concerned about having a common B- for both L and R amps, and also a common input 'cold' return line. -- Chris Morriss |
Triode Project - The Good, The Bad and The Ugly
In article , Keith G
writes "Don Pearce" wrote The MP3 has virtually identical hum on both channels - it certainly doesn't have anything like the disparity that the scope picture shows. http://www.donepearce.plus.com/odds/keith_screen.jpg Yes and the waveforms are the same height in SoundForge, so I'm suspecting the scope and/or leads atm. (No big deal, the scopes only a learning tool atm.) If U get really stuck run it over to Cambridge Keith ve haf ways of de-'umming valve amps:-)) -- Tony Sayer |
Triode Project - The Good, The Bad and The Ugly
Keith G wrote:
The Bad - It's humming like a good 'un and I suspect it's going to be a bugger to sort.... Well, I'd expect it to hum. A single-ended design doesn't have the inherent 'hum rejection' of the push-pull output stage configuration. Also, triodes have fairly mediocre anode impedances which make them more prone to supply ripple effects than tetrodes / pentodes. I'd suggest an extra stage of LC smoothing on the HT. Graham |
Triode Project - The Good, The Bad and The Ugly
Keith G wrote: The money's still on an earthing problem atm, but the 100Hz frequency is a bit mysterious.... Not at all. It's supply ripple. For reference, 50 Hz would indicate a 'hum loop' type problem, 150 Hz would indicate pickup from the power transformer @ 3rd harmonic. Graham |
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