Ok, things are at least not on fire this time!
That's a good start.
28 V on the filament regulators is too much. I seem to recall the reservoir cap on the filament regulator being 470 uF, 25 V.
do you have the RD/YW and RD/WH (380/330 V) secondary wires swapped by any chance? 485 V is actually fine for the 21st Century Maida Regulator. It'll run a little cooler which is healthy for it.
-229 V is fine. You should be around 225 ±5 %. Maybe a tad less.
If you do indeed have the RD/YW and RD/WH wires swapped, I suggest swapping them and reconfiguring the board for 240 V operation. That'll lower that 28 V to something more reasonable.
What AC voltage do you measure on the two 15 VAC windings?
D2 sees 485 V over 200 kΩ -> 2.4 mA
D10 sees about 300 V over 220 kΩ -> 1.4 mA
D2 should be brighter than D10. They were never intended to be equally bright.
There I was having the silk screen saying one direction and the soldering pad saying "hello, plus here please" therefore the mistake. I could have turned the PCB around and verified the right correction but never did, stupid me.
Meh! Could be worse. Nobody died. Except the rectifier. May it rest in peace.
Tom
Happy testing!!
Ok, sat down now in the evening and had a thorough look at things. No cables to swap, nothing, start things up and.....
On the AC side I should have - did have
6.3 VAC - 5.59 VAC
15 VAC - 13.93 VAC
15 VAC - 13.93 VAC
60 VAC - 50.82 VAC
330 VAC - 322.1 VAC
380 VAC - 279.2 VAC
and on DC side should have - did have
20 VDC - 19.75 VDC
20 VDC - 19.75 VDC
-225 VDC - -229.9 VDC
525 VDC - 483.5 VDC
I think that it is close enough and why I did measured 28VDC feeding the fileament regulators yesterday I don't know, the only answer I have is that I made an error when reading 28-29 instead of maybe 18-19. I don't know but today it measure ok. Could it be that I have started the transformer some ten times now and that things have started to settle making that big of a difference??
With this confirmed I connected the Maida regulator, filament regulators and the driver board. Nothing burning, no smelling bad or anything.....??
It's working!!
Tonight I just confirmed some measurments on the tube sockets, output from the Maida regulator and the filament regulators and everything seem ok except for the fact that I couldn't get a correct reading on the 300B socket for the B+ pin.
The Maida leave 483 V to the driver board and since tomchr was happy with a little lower value here (running a little cooler) then I am happy with that.
The 5 V and 6.3 V filament regulators are leaving 4.987 V and 6.275 V which must also be concidered as really ok.
For the 300B sockets I had 4.987 V on the bigger pins and -228.7 V on one of the smaller pins but the second small pin...... I am not the one that can get a reading on this one. It should be around 400 V but I have my DMM saying like 150 mV working its way up and then strating all over again at around 120 mV. I suspect that I have bad contact somewhere so I will revise it tomorrow but if everything run this smoth in the weekend testing and verifying the boards then I will most likely have music playing sometime during next week.... Yes I have vacation so I will have time to make everything working!!!
Happy for tonight!
Ok, sat down now in the evening and had a thorough look at things. No cables to swap, nothing, start things up and.....
On the AC side I should have - did have
6.3 VAC - 5.59 VAC
15 VAC - 13.93 VAC
15 VAC - 13.93 VAC
60 VAC - 50.82 VAC
330 VAC - 322.1 VAC
380 VAC - 279.2 VAC
and on DC side should have - did have
20 VDC - 19.75 VDC
20 VDC - 19.75 VDC
-225 VDC - -229.9 VDC
525 VDC - 483.5 VDC
I think that it is close enough and why I did measured 28VDC feeding the fileament regulators yesterday I don't know, the only answer I have is that I made an error when reading 28-29 instead of maybe 18-19. I don't know but today it measure ok. Could it be that I have started the transformer some ten times now and that things have started to settle making that big of a difference??
With this confirmed I connected the Maida regulator, filament regulators and the driver board. Nothing burning, no smelling bad or anything.....??
It's working!!
Tonight I just confirmed some measurments on the tube sockets, output from the Maida regulator and the filament regulators and everything seem ok except for the fact that I couldn't get a correct reading on the 300B socket for the B+ pin.
The Maida leave 483 V to the driver board and since tomchr was happy with a little lower value here (running a little cooler) then I am happy with that.
The 5 V and 6.3 V filament regulators are leaving 4.987 V and 6.275 V which must also be concidered as really ok.
For the 300B sockets I had 4.987 V on the bigger pins and -228.7 V on one of the smaller pins but the second small pin...... I am not the one that can get a reading on this one. It should be around 400 V but I have my DMM saying like 150 mV working its way up and then strating all over again at around 120 mV. I suspect that I have bad contact somewhere so I will revise it tomorrow but if everything run this smoth in the weekend testing and verifying the boards then I will most likely have music playing sometime during next week.... Yes I have vacation so I will have time to make everything working!!!
Happy for tonight!
Perfect.
Could it be that I have started the transformer some ten times now and that things have started to settle making that big of a difference??
Nah. Probably a simple mis-read of the meter. No worries.
Perfect.
Hmmm... Check the wiring to and of the output transformer. With the power off, measure the DCR of the primary. It should be relatively low. Maybe 100s of ohm maybe upwards of 1 kΩ. Certainly not an open circuit.
Tom
I like this!
Things do continue to develope and it seem to work out as it should.
According to the checklist I am going through (thank you tomchr cause it is very pedagogic and easy to follow for beginners like me) I would say that all values are within the marginal of errors.
I did plug in the driver tubes and tested them, diodes light up and light bulb in the bulb tester light up a little more but still nothing directly strange but then I had a minor question falling on my head.
The voltage over pin 6 on the driver tube should be about somewhere between 150-250 volts (tube dependant value) and come in on fairly ok 167 volts respectively 173 volts for the two channels so I am ok with that. Though on pin 3 on the 300B sockets I should have about -105 volts with the driver tubes plugged in but I only read -52 volts and that is strange, about half of what I should have. All other values are ok and stable so it is a little strange.
If I adjust bias pot the value fluctuate between -39 to -52 volt, is this because of the tubes and in that case is there an issue with the tubes or do I look for a resistor of wrong magnitude cause somthing is defenitely not correct here.
Since it is affecting the 300B bias I don't want to plug these in until I have resolved the problem so tomorrow I will measure some resistors to begin with.
Things do continue to develope and it seem to work out as it should.
According to the checklist I am going through (thank you tomchr cause it is very pedagogic and easy to follow for beginners like me) I would say that all values are within the marginal of errors.
I did plug in the driver tubes and tested them, diodes light up and light bulb in the bulb tester light up a little more but still nothing directly strange but then I had a minor question falling on my head.
The voltage over pin 6 on the driver tube should be about somewhere between 150-250 volts (tube dependant value) and come in on fairly ok 167 volts respectively 173 volts for the two channels so I am ok with that. Though on pin 3 on the 300B sockets I should have about -105 volts with the driver tubes plugged in but I only read -52 volts and that is strange, about half of what I should have. All other values are ok and stable so it is a little strange.
If I adjust bias pot the value fluctuate between -39 to -52 volt, is this because of the tubes and in that case is there an issue with the tubes or do I look for a resistor of wrong magnitude cause somthing is defenitely not correct here.
Since it is affecting the 300B bias I don't want to plug these in until I have resolved the problem so tomorrow I will measure some resistors to begin with.
I just responded to your email. If you want faster response times, email is better. Just make sure to pick one form of communication and stick with it.
Check that you still get -225 V (±5 %) on the bias supply with the driver tubes plugged in.
Good call on not plugging in the 300B yet. Get this issue addressed before plugging in the 300B.
Tom
Check that you still get -225 V (±5 %) on the bias supply with the driver tubes plugged in.
Good call on not plugging in the 300B yet. Get this issue addressed before plugging in the 300B.
Tom
Happy testing??
Well, the last two days have been a very steep learning curve and if it was not for a number of emails between me (full of questions) and tomchr (answering my newbie questions (that man have an enormous patience)) I would most likely still be sitting wondering about the future still but....
I had some issue with the amp not behaving as it should even though I was pretty shure that things were ok. I had earlier checked the PSU with a dim bulb tester and everything was working as it should.
Connected the driver tubes and started to get wierd readings on my way through the check list. Did go through all resistors and only came up with....??
At that point I realized that the only way to get things in order was to communicate with the constructor and so I did.
To make a long story (and some mails) short, here come a lesson for all newbies on the famous dim bulb tester:
Check your board with the dim bulb tester (for people who have not seen one, follow the link below), if everything is ok; UNPLUG YOUR DEVICE FROM THE DIM BULB TESTER, PUT THE DIM BULB TESTER AWAY AND PLUG YOUR DEVICE TO THE MAINS!!! DON'T MISS THIS CAUSE YOU MIGHT (as me) MOST LIKELY END UP WITH VERY STRANGE VALUES.
After tomchr had resolved this small mistake of mine I was good to plug in the 300B tubes, since in fact everything was ok, to get to the biasing.
Piece of cake! from 150 mV slowly worked its way up til about 600 mV and then I adjusted it to 850 mV, meaning 85 mA, to the OPT and then I let it run for another hour before powering down. During that hour I adjusted the bias two-three times and now it is running fairly stable at 845-852 mV after 10 min warming up.
Driver tubes run at 95 degrees Celsius and the 300B are running about 165 degrees Celsius so it is hot but not abnormally hot.
Since bias was set and done I could not hurry enough connecting some small trial and error speakers, my computer via DAC and on to the amp.
Holy Moses!!! (I hope no one is offended by the expression).
I do have fairly ok music equipment and I do concider my ears to be fairly ok (in fact I have paper on that) but I must say I AM BLOWN AWAY, PERIOD!!
I hear details that have never been heard, I don't have two speakers transmitting the soundwaves I have a concert hall in my basement. Tons of musicality.... and base, I have quick, responsive and accurate base while mids and highs are just mindboggingly sweet.
When I started buying things for the tube amp almost two years ago I had some hope that this Damn Good 300B amp should qualify higher or even very much higher than my Thule A60 (running as pre amp for the moment), even better than my Hiraga, Le Monstre (that need some renovation (an upcoming project for next year)) that is running in the living room today but that the difference should be this big, I couldn't even dream of.
Now I have listened for some hour and realize that I am not finished yet!
I still have some small issues and that I hope that someone (not necessarily tomchr cause he have defnitely done his big part already) can lead me in the right direction.
When I play music, not all music but some, then the base distort badly.
First I thought it is because of the bias, then the crappy speakers and lastly I have started considering the caps on the driver board. I use Janzen Red Audio caps and I have only positive to say about them but maybe they are not so well suited here in the DG300B. I have even started to suspect that with the details I hear it can be crappy recordings.
I do remember having read about fine tuning the DG300B in The Christiansen "DG" 300B Amplifier Build Thread so I will go through that thread again (I read it day and night a year ago but the memory... goes with age) cause I know that many things were handled in that thread but if someone here have an opinion I am glad to hear it cause now I want to see this project through without distortion in the bass.
Dim Bulb tester;
Compact Dim Bulb Tester Wiring | Audiokarma Home Audio Stereo Discussion Forums
Well, the last two days have been a very steep learning curve and if it was not for a number of emails between me (full of questions) and tomchr (answering my newbie questions (that man have an enormous patience)) I would most likely still be sitting wondering about the future still but....
I had some issue with the amp not behaving as it should even though I was pretty shure that things were ok. I had earlier checked the PSU with a dim bulb tester and everything was working as it should.
Connected the driver tubes and started to get wierd readings on my way through the check list. Did go through all resistors and only came up with....??
At that point I realized that the only way to get things in order was to communicate with the constructor and so I did.
To make a long story (and some mails) short, here come a lesson for all newbies on the famous dim bulb tester:
Check your board with the dim bulb tester (for people who have not seen one, follow the link below), if everything is ok; UNPLUG YOUR DEVICE FROM THE DIM BULB TESTER, PUT THE DIM BULB TESTER AWAY AND PLUG YOUR DEVICE TO THE MAINS!!! DON'T MISS THIS CAUSE YOU MIGHT (as me) MOST LIKELY END UP WITH VERY STRANGE VALUES.
After tomchr had resolved this small
mistake of mine I was good to plug in the 300B tubes, since in fact everything was ok, to get to the biasing.Piece of cake! from 150 mV slowly worked its way up til about 600 mV and then I adjusted it to 850 mV, meaning 85 mA, to the OPT and then I let it run for another hour before powering down. During that hour I adjusted the bias two-three times and now it is running fairly stable at 845-852 mV after 10 min warming up.
Driver tubes run at 95 degrees Celsius and the 300B are running about 165 degrees Celsius so it is hot but not abnormally hot.
Since bias was set and done I could not hurry enough connecting some small trial and error speakers, my computer via DAC and on to the amp.
Holy Moses!!!
(I hope no one is offended by the expression).I do have fairly ok music equipment and I do concider my ears to be fairly ok (in fact I have paper on that) but I must say I AM BLOWN AWAY, PERIOD!!
I hear details that have never been heard, I don't have two speakers transmitting the soundwaves I have a concert hall in my basement. Tons of musicality.... and base, I have quick, responsive and accurate base while mids and highs are just mindboggingly sweet.
When I started buying things for the tube amp almost two years ago I had some hope that this Damn Good 300B amp should qualify higher or even very much higher than my Thule A60 (running as pre amp for the moment), even better than my Hiraga, Le Monstre (that need some renovation (an upcoming project for next year)) that is running in the living room today but that the difference should be this big, I couldn't even dream of.
Now I have listened for some hour and realize that I am not finished yet!
I still have some small issues and that I hope that someone (not necessarily tomchr cause he have defnitely done his big part already) can lead me in the right direction.
When I play music, not all music but some, then the base distort badly.
First I thought it is because of the bias, then the crappy speakers and lastly I have started considering the caps on the driver board. I use Janzen Red Audio caps and I have only positive to say about them but maybe they are not so well suited here in the DG300B. I have even started to suspect that with the details I hear it can be crappy recordings.
I do remember having read about fine tuning the DG300B in The Christiansen "DG" 300B Amplifier Build Thread so I will go through that thread again (I read it day and night a year ago but the memory... goes with age) cause I know that many things were handled in that thread but if someone here have an opinion I am glad to hear it cause now I want to see this project through without distortion in the bass.
Dim Bulb tester;
Compact Dim Bulb Tester Wiring | Audiokarma Home Audio Stereo Discussion Forums
I'm glad to hear that you got things working. Thank you for your comments about my help and patience. I do my best.
Without measurements, it's a bit hard to tell why you're experiencing distortion in the bass on some tracks. It is most likely due to the output transformer saturating. That's generally why tube amps have higher THD at lower frequency, in particular at higher output power.
Does the distortion go away if you lower the volume?
Tom
Without measurements, it's a bit hard to tell why you're experiencing distortion in the bass on some tracks. It is most likely due to the output transformer saturating. That's generally why tube amps have higher THD at lower frequency, in particular at higher output power.
Does the distortion go away if you lower the volume?
Tom
Two hours later.....
As usual tomchr, you are most likely spot on again!
I suspect that it is the OPT that become saturated cause lowering the volume affect the distortion. When I bought the OPT from Lundahl they have different specifications on one and the same transformer. I have the ones called LL1623/90mA and I have not confirmed with Lundahl but I think that those 90mA are close to the limit of what the transformer will take so when I bias the amplifier at 85mA then I am close to the limit of saturation. I did lower the bias to about 80mA and that helped also.
It is also so that the current set up is directly from computer via DAC to the power amp. When I take it up in the living room I will run my Thule A-60 as pre amp and I think that one have a gain of abour 6-12 dB so that will help a little and I am about to finish a Aleph P1.7 also and that one have a max gain of 22dB so if I can not push the power amp more then I might do it in the pre amp.
Ok, done is done. If I have a little money over at some point then I can consider buying the ones specified at 120mA instead, those would have left me with a little more head room. I know that you surgested the 120mA version long ago tomchr but when I spoke to Peter Lundahl he said that the 90mA version was well suited for the 300B, maybe he missed that I should bias at 85mA.
Is there anything I can do to improve the situation?
I am anyway going to play with some caps to see if Janzen is the best choice.... I know that Sceleratus at Head HiFi did use Jupiter Beewax so there is a lot of caps to choose from if you concider the price range from Janzen to Jupiter.
Well anyway, lowering the volume and listening to Nils Landgren playing the trombone and you can hear the lips moving towards the mouthpiece.... goosebumps!!!!
I do enjoy every piece of music coming through that amp already and it have only been playing for maybe 5 hours in total and still there can be more done. This will be really good when everything have had its time to settle.
I am about to test that now so if you wait til tomorrow I will be able to answer that
As usual tomchr, you are most likely spot on again!
I suspect that it is the OPT that become saturated cause lowering the volume affect the distortion. When I bought the OPT from Lundahl they have different specifications on one and the same transformer. I have the ones called LL1623/90mA and I have not confirmed with Lundahl but I think that those 90mA are close to the limit of what the transformer will take so when I bias the amplifier at 85mA then I am close to the limit of saturation. I did lower the bias to about 80mA and that helped also.
It is also so that the current set up is directly from computer via DAC to the power amp. When I take it up in the living room I will run my Thule A-60 as pre amp and I think that one have a gain of abour 6-12 dB so that will help a little and I am about to finish a Aleph P1.7 also and that one have a max gain of 22dB so if I can not push the power amp more then I might do it in the pre amp.
Ok, done is done. If I have a little money over at some point then I can consider buying the ones specified at 120mA instead, those would have left me with a little more head room. I know that you surgested the 120mA version long ago tomchr but when I spoke to Peter Lundahl he said that the 90mA version was well suited for the 300B, maybe he missed that I should bias at 85mA.
Is there anything I can do to improve the situation?
I am anyway going to play with some caps to see if Janzen is the best choice.... I know that Sceleratus at Head HiFi did use Jupiter Beewax so there is a lot of caps to choose from if you concider the price range from Janzen to Jupiter.
Well anyway, lowering the volume and listening to Nils Landgren playing the trombone and you can hear the lips moving towards the mouthpiece.... goosebumps!!!!
I do enjoy every piece of music coming through that amp already and it have only been playing for maybe 5 hours in total and still there can be more done. This will be really good when everything have had its time to settle.
Awesome. I love feedback like that. Thanks.
You're probably dealing with OPT saturation as you mention. Many run the 300B at 360 V, 60 mA and get a few watt of output power. I find it sounds better at 400 V, 85 mA and it produces 2-3x the power, so that's what I recommend. Lundahl may have assumed that you wanted 360 V, 60 mA.
I'd either lower the volume or lower the 300B idle current. Play with the B+ voltage as well. Turn the Maida all the way down (probably 380 V or so) and aim for 65 mA or there about on the 300B. I ran that with some mesh plate 300B and they sounded heavenly. The mesh plate tubes also look really nice in the dark!
I wouldn't mess with the caps. I measured Sceleratus' Mundorf silver/oil $20 caps, my Solen $2 caps, and the $0.50 Panasonic polypropylene cap I recommend on the BOM. The Panasonic actually outperformed the other two. The Solen cap had slightly worse ESR but was very close to the Panasonic. The Mundorf was the worst. In listening tests, I couldn't tell any difference. I'll use the Panasonic or Solen from now on.
Tom
I love feedback like that. Thanks.You're probably dealing with OPT saturation as you mention. Many run the 300B at 360 V, 60 mA and get a few watt of output power. I find it sounds better at 400 V, 85 mA and it produces 2-3x the power, so that's what I recommend. Lundahl may have assumed that you wanted 360 V, 60 mA.
I'd either lower the volume or lower the 300B idle current. Play with the B+ voltage as well. Turn the Maida all the way down (probably 380 V or so) and aim for 65 mA or there about on the 300B. I ran that with some mesh plate 300B and they sounded heavenly. The mesh plate tubes also look really nice in the dark!
I wouldn't mess with the caps. I measured Sceleratus' Mundorf silver/oil $20 caps, my Solen $2 caps, and the $0.50 Panasonic polypropylene cap I recommend on the BOM. The Panasonic actually outperformed the other two. The Solen cap had slightly worse ESR but was very close to the Panasonic. The Mundorf was the worst. In listening tests, I couldn't tell any difference. I'll use the Panasonic or Solen from now on.
Tom
i hope the opt are not wrongly labelled..
you actually should bias exactly to that value for best resultscan you measure mA AC flowing through primary? use variac ~100V
30H= 9.425k Ohms @50Hz 10,6mA AC
Good and bad!
Ok, things are sounding and it is not bad but I am disappointed in a way.
When you buy "The Worlds Best Transformer" and pay appr. $650 for only the output transformers then it should not saturate at the levels we use in this amp I think, so I made a telephone call to Per Lundahl friday afternoon and he explained that those OPT specified at 90 mA, that is the transformer operating point so he either couldn't understand the massive distortion in lower frequencies. He asked me to arrange with a couple of pictures during the weekend because he suspected that the connections where wrong.
As I am keen on getting things ready to listen to then I started reading everything about output transformers that I could find cause I felt that I couldn't wait til monday to get an answer and then I found this site;
How to choose a Lundahl output transfomer, by tube type
Since all 300B tubes were showing that I should connect 8 ohm speakers with a schematic C I and tomchr were both sure about schematic B I started searching for WHY (I can assure you that understanding the description from Lundahl was not an easy task and I am used to read technical papers and descriptions and I suppose that tomchr also do that a couple of times per week but....)? I found another site that was showing how many windings that are needed for the different impedance connections shown in the schematics for the LL1623 and tralalalala......
tubetalk
Now I understand a lot more about the OPT so I went down and reconnected the OPT since I, from the beginning have had them connected for 4 ohm speakers using only two windings but for 8 ohms I need three windings, and that have most likely been the root to the bad distortion.....Ahaaa!
After the reconnection of the OPT:s the distortion is gone........ lovely.... almost....
I now notice that I have moved the distortion higher up in frequency but the really bad distortion is gone and that I am glad for....
Sitting listening and evaluating the result I get the idea to disconnect one of the channels to see if the distortion is only present in one channel or it is in both and......
What the .........???
When I disconnect right channel I have still music in the right speaker so here is something still very fishy. Tonight, eventually later this afternoon I will have to start checking all signal lines and of cause the connections to the OPT again.....
I do believe that this, could you call it "crosstalk", is the mother of this distortion in the higher frequency range now. It is not that bad, you can still enjoy music but if I have come this far I will defenitely not accept some distortion at all.
Otherwise the amp is dead quiet, just when it start up I can hear the main transformer but as soon as the tubes start emitting it is dead quiet.
The only thing I have noticed, but I have head that all tube amps are the same, is that if you start the amplifier first then it has a little concert by itself until a source is connected so now I have learnt that the source is first started and then the amplifier and then it is quiet.
Ok, if you sit with the ear to the transformer you can vaguely hear it but on the other hand... if you do that, you burn your other ear on the tubes so no one will ever do it.
Ok, things are sounding and it is not bad but I am disappointed in a way.
When you buy "The Worlds Best Transformer" and pay appr. $650 for only the output transformers then it should not saturate at the levels we use in this amp I think, so I made a telephone call to Per Lundahl friday afternoon and he explained that those OPT specified at 90 mA, that is the transformer operating point so he either couldn't understand the massive distortion in lower frequencies. He asked me to arrange with a couple of pictures during the weekend because he suspected that the connections where wrong.
As I am keen on getting things ready to listen to then I started reading everything about output transformers that I could find cause I felt that I couldn't wait til monday to get an answer and then I found this site;
How to choose a Lundahl output transfomer, by tube type
Since all 300B tubes were showing that I should connect 8 ohm speakers with a schematic C I and tomchr were both sure about schematic B I started searching for WHY (I can assure you that understanding the description from Lundahl was not an easy task and I am used to read technical papers and descriptions and I suppose that tomchr also do that a couple of times per week but....)? I found another site that was showing how many windings that are needed for the different impedance connections shown in the schematics for the LL1623 and tralalalala......
tubetalk
Now I understand a lot more about the OPT so I went down and reconnected the OPT since I, from the beginning have had them connected for 4 ohm speakers using only two windings but for 8 ohms I need three windings, and that have most likely been the root to the bad distortion.....Ahaaa!
After the reconnection of the OPT:s the distortion is gone........ lovely.... almost....
I now notice that I have moved the distortion higher up in frequency but the really bad distortion is gone and that I am glad for....
Sitting listening and evaluating the result I get the idea to disconnect one of the channels to see if the distortion is only present in one channel or it is in both and......
What the .........???
When I disconnect right channel I have still music in the right speaker so here is something still very fishy. Tonight, eventually later this afternoon I will have to start checking all signal lines and of cause the connections to the OPT again.....
I do believe that this, could you call it "crosstalk", is the mother of this distortion in the higher frequency range now. It is not that bad, you can still enjoy music but if I have come this far I will defenitely not accept some distortion at all.
Otherwise the amp is dead quiet, just when it start up I can hear the main transformer but as soon as the tubes start emitting it is dead quiet.
The only thing I have noticed, but I have head that all tube amps are the same, is that if you start the amplifier first then it has a little concert by itself until a source is connected so now I have learnt that the source is first started and then the amplifier and then it is quiet.
Ok, if you sit with the ear to the transformer you can vaguely hear it but on the other hand... if you do that, you burn your other ear on the tubes so no one will ever do it.
Fishy or not, help!
I must have missed something very fundamental.
To me, if I unplug the source on one channel, it should be dead quiet in the speaker where I have unplugged the signal. Here it is not!
When I check with my DMM for continuation in the circuit then I find that both right hand and left hand channel signal in are transferred via the driver tubes to both 300B tubes which mean that if I unplug incoming signal from one of the channels it doesn't leave me with a quiet speaker...???
Is it me who have missed something fundamental and is it ment to work this way?
Here I do need some help understanding cause I thought that I did understand the way the signals are handled in the circuit but now I get very doubful since I have tear down the driver board to search for faults but I don't find anything. Everything is well soldered and I don't see any broken traces and so on.... but I can not grasp that I have right hand respectively left hand signal on both 300B tubes.
I must have missed something very fundamental.
To me, if I unplug the source on one channel, it should be dead quiet in the speaker where I have unplugged the signal. Here it is not!
When I check with my DMM for continuation in the circuit then I find that both right hand and left hand channel signal in are transferred via the driver tubes to both 300B tubes which mean that if I unplug incoming signal from one of the channels it doesn't leave me with a quiet speaker...???
Is it me who have missed something fundamental and is it ment to work this way?
Here I do need some help understanding cause I thought that I did understand the way the signals are handled in the circuit but now I get very doubful since I have tear down the driver board to search for faults but I don't find anything. Everything is well soldered and I don't see any broken traces and so on.... but I can not grasp that I have right hand respectively left hand signal on both 300B tubes.
I made the mistake of going straight to a pcb for my valve mixer.
The results were terrible, loads of hum and noise.
No amount of hacking would fix it.
I did learn a lot from the exercise.
1/ Keep transformers away from valves.
2/ Keep high volts ac away from audio and valves.
3/ Keep input circuit as short as possible and as close to valve as possible.
4/ Use grid stoppers right up against the grid pins.
5/ Use copper pours for zero volts and make sure the copper plane goes right under the valve.
6/ Keep heaters AC away from audio.
I found using these tips I didn't need DC heater supply.
You shouldn't have much coupling between channels. There will always be some, but if you unplug the source to one channel and ground the input, you should have music in one speaker and the other should be quiet. Is that not the case for you?
Good to hear that you got the OPT figured out.
Tom
Good to hear that you got the OPT figured out.
Tom
According to above I see that tomchr have done his homework cause the PCB follow the mentioned points.
Tomchr, I have no experience what so ever with tube amps so this is my way of raising the curtain to an new playground and as I have already said, this is not the last tube amp. That said I don't know how much crosstalk is acceptable and what is not. First time in my life that I run into it but I see, when going through the schematics for the drive board that there must, or at least can be some crosstalk because of all shared voltages.
When disconnecting the input signal I can still hear music in the speaker, yes! Not as loud as before but there is defenitely music playing. I did dismantel the driver board and revised it late in the night, cleaning it with isopropanol (learnt a new lesson, comment further down) when I had it out and checked the circuit for continuation.
Now in the morning I was down checking the resistance on those signal paths and if I measure from right signal IN to the 300B tube I have only 0.1 ohm difference on the both 300B tubes. That mean that the signal from right channel have almost the same resistance to either of the triodes, then the signal should not differ very much to the speaker either, or could it still?
I can not see any errors in the boards, faulty soldering or anything that would catch my attention so to my knowledge everything is as it should but to be shure about the soldering I will go over these since it was done more than a year ago. I have learnt a lot during the passed time and gained much more experince when it come to soldering since then so it will at least not be of harm.
I'll come back with a report in the evening (swedish time)
Lesson learned today; don't wash boutiqe caps with isopropanol!! Many of those have stamped markings instead of plastic sleave. Plastic sleave resist isopropanol, paint don't!!
My Janzen caps doesn't look that nice any longer but the function is still there!
"From right signal in to the 300B tubes" do you mean you have a connection from the input RCA/XLR to the 300B? That should not be there.
I've done tons of testing in mono using my stereo DG300B amp. I used to measure my speaker/amp combo that way. I have always gotten dead quiet in one channel if I ran the amp with a signal to one channel only.
I do remember measuring the channel separation. I don't recall the number, but it certainly didn't raise any eyebrows or I would have fixed whatever issue was there. If you hear signal in both speakers when you unplug one of the inputs, you have a wiring error. I guarantee it.
All shared voltages are not in the signal path and are well bypassed. You will not get any meaningful coupling through those paths. I did in fact do the math on those...
Tom
I've done tons of testing in mono using my stereo DG300B amp. I used to measure my speaker/amp combo that way. I have always gotten dead quiet in one channel if I ran the amp with a signal to one channel only.
I do remember measuring the channel separation. I don't recall the number, but it certainly didn't raise any eyebrows or I would have fixed whatever issue was there. If you hear signal in both speakers when you unplug one of the inputs, you have a wiring error. I guarantee it.
All shared voltages are not in the signal path and are well bypassed. You will not get any meaningful coupling through those paths. I did in fact do the math on those...
Tom
Right again tomchr!
I have a wiring error that is for shure but I am not entirely shure it is in my /your amp now.
"The more you learn, the more you know, how little you know!" I am there now!
Yes, I did check for continuation between different points on the board yesterday evening without tubes plugged in, and yes from RCA/XLR positive, I do get a continuation signal on the DMM to each 300B tube. Reheated all connection points to assure that I don't have cold soldering somewhere.
Connected the board again, checking all the connections like five times and, by the way I also did push the Maida board a little to squeeze out the intended 400 V to the 300B tubes (new lesson learned, comments down) and ran the amp. Setting bias and everything was just as before.....
Still have the slight distortion and I am there sitting listening to music when I get the ingenious idea to unplug right channel again and hold it against the RCA ground connection instead...
Distortion is gone totally and I did get an entirely new experience about the amplifiers possibilities when it come to tree dimensional sound stage. Unplug everything and switch the cables and reconnect the lot again, run the amp and back to the "as before boring" soundstage....??? Hmmmm Ground....
Retract right channel RCA until the shield let go and voila, I got my fantastic soundstage back and no distortion!
When I now disconnect one of the channels it is dead quiet also.
It appear that I have a phase shift in either the computer soundcard or the DAC that I was not aware of, most likely to cause the general distortion (have never experienced it before and most likely because it is vary vague but when you now hear it, it gets annoying).
I have to redo my cables leaving the ground shield disconnected towards the amp, single ended you know....
Have not had such issues before with my other amps and maybe that is why I should consider running balanced in the future.
Yes, the lesson... when you do push things, things want to resist and those things then run hotter.... heatsink to be changed cause 78 degrees Celsius is not optimal, you burn your fingers and the tubes run hotter, 6N6P at 105-109 dergrees and 300B at 172-174 degrees Celsius. I am not worrying so much about the tubes but the heatsink for the STW12NK95Z need to be little bigger even if the power Mosfet manage 150 degrees I don't want to risk burned fingers. Since the heatsink sit on the aluminium plate back it will be a little better when mounted correctly but since I have all connectors on the same aluminium plate I don't want to hight temperatures cause it will affect plastic washers and such, me no like!
Slowly I get there.... and a lot of lessons learned on the road, can't be better.