Hi all,
I discovered that I had cross coupled the anode caps on one channel. That produced an interesting audible singing from the transformer and was messing up the voltages (-100V on the 807 grids). Bad oscillation !
With a fresh head this morning I substituted a resistor for the CCS's and fired her up. With the other problem solved I don't seem to be getting the huge voltage peaking I was yesterday - just up to about +30V. I think I will try rebuilding the LM317 CCS. If that fails I will go looking for something a bit more rugged such as the FQP2N90.
Shoog
I discovered that I had cross coupled the anode caps on one channel. That produced an interesting audible singing from the transformer and was messing up the voltages (-100V on the 807 grids). Bad oscillation !
With a fresh head this morning I substituted a resistor for the CCS's and fired her up. With the other problem solved I don't seem to be getting the huge voltage peaking I was yesterday - just up to about +30V. I think I will try rebuilding the LM317 CCS. If that fails I will go looking for something a bit more rugged such as the FQP2N90.
Shoog
Rigged up some new LM317 CCS for one side. Powered up. One survived one power up the other died straight away. Second power up the other went as well. Obviously the instantanous power up was to much.
I will rebuild using the "Baby Huey" bias blocks when I can sort out some suitable transistors.
Shoog
I will rebuild using the "Baby Huey" bias blocks when I can sort out some suitable transistors.
Shoog
Your all on the edge of your seats by now (all two of you).
Well I built some of the Baby Huey bias blocks and installed them. They have survived about 5 power up by now and have clocked about an hour. They run a little hotter than I would like.
I got the scope on it. There is 0.2Vpp on the output, but this is common mode and doesn't come through on my test speaker which is dead quiet. Haven't grounded any of the heaters so far so this may be the source of that signal. No obvious nasty oscillations that I can see so far. I haven't sent a test signal though yet as I need to find some hook up wire to go onto the input transformers.
Will hopefully have a bit more to report later today.
Shoog
Well I built some of the Baby Huey bias blocks and installed them. They have survived about 5 power up by now and have clocked about an hour. They run a little hotter than I would like.
I got the scope on it. There is 0.2Vpp on the output, but this is common mode and doesn't come through on my test speaker which is dead quiet. Haven't grounded any of the heaters so far so this may be the source of that signal. No obvious nasty oscillations that I can see so far. I haven't sent a test signal though yet as I need to find some hook up wire to go onto the input transformers.
Will hopefully have a bit more to report later today.
Shoog
Couldn't resist hooking it up to my computer and the test speaker. Had a bit of worry for a moment because it was distorting badly, but it turned out to be my media player overloading the soundcard. Sorted that out and have been listening to Beth Orton for the last half hour. Sounds really nice without anything wrong jumping out at me. The scoped up waveform looks good and clean.
I will run my signal generator through it later and then box it up for test in the main system.
Shoog
I will run my signal generator through it later and then box it up for test in the main system.
Shoog
Hi Shoog
I am also following your work with attention! Not only the Tabor clone (+ own creativity), but also the pre based on the vacuumstate preamp, the 6AS7 amp, the ECL82 headphone amp and the different posts on your experiences with the toroidals as audio transformers!
Therefore my congratulations on the accomplishments, and I hope you enjoy the new amp pretty much!
Erik
I am also following your work with attention! Not only the Tabor clone (+ own creativity), but also the pre based on the vacuumstate preamp, the 6AS7 amp, the ECL82 headphone amp and the different posts on your experiences with the toroidals as audio transformers!
Therefore my congratulations on the accomplishments, and I hope you enjoy the new amp pretty much!
Erik
Thanks Erik.
I hooked up the other channel yesterday. Unfortunately all is not well with this channel as it would appear that one of the CCS is passing no current at all. Can't quite work out whats going on yet so will need a bit of thinking time. The surprising thing is that the channel still produces good sounds if the signal is small without any significant bass. Certainly the fears about saturation of toroidal outputs might be a fraction overstated.
I'm also getting some flashover in the 807's on power up. I will have to rig up a time delay circuit for the +B.
Shoog
I hooked up the other channel yesterday. Unfortunately all is not well with this channel as it would appear that one of the CCS is passing no current at all. Can't quite work out whats going on yet so will need a bit of thinking time. The surprising thing is that the channel still produces good sounds if the signal is small without any significant bass. Certainly the fears about saturation of toroidal outputs might be a fraction overstated.
I'm also getting some flashover in the 807's on power up. I will have to rig up a time delay circuit for the +B.
Shoog
I rebuilt the dodgy channels CCS (using transisters salvaged from a CFL 
). Powered her up and everything is great. I am listening to her now on my test speakers. Lovely detailed sound but still very relaxed in presentation. I have been hearing lyrics in certain songs which have always just been mumbles before.
I will build the switch on delay and then throw her at the main system tomorrow.
Great !!!
Shoog
). Powered her up and everything is great. I am listening to her now on my test speakers. Lovely detailed sound but still very relaxed in presentation. I have been hearing lyrics in certain songs which have always just been mumbles before.I will build the switch on delay and then throw her at the main system tomorrow.
Great !!!
Shoog
CCS went down again today. It was after about an hour of listening.
I think its a combination of startup stress and thermal stress.
Found a time delay valve which I will use for the time delay. Will make a new set of CCS with new components and mount them on a much bigger heat sink.
Hopefully that will put it to bed.
Shoog
I think its a combination of startup stress and thermal stress.
Found a time delay valve which I will use for the time delay. Will make a new set of CCS with new components and mount them on a much bigger heat sink.
Hopefully that will put it to bed.
Shoog
Excellent to see your progress on this - as you said it's been a long time in the gestation process & is having a few minor birthing issues but I've no doubt will be your favoured child once it has reached independent existence!
Looking forward to hearing it as I was stunned by your ECL82 headphone amp & I believe that was your proof of some concepts going into this amp!
Looking forward to hearing it as I was stunned by your ECL82 headphone amp & I believe that was your proof of some concepts going into this amp!
Finally got it into my main system today. Sorted out the CCS problem - which was a solder splash. Realised I have referenced the 6AU6's heaters to earth rather than the neg rail - will sort that tomorrow. The gain is much more than I need so I will reconfigure the input transformer to give me a 2:1 step down. Have a very annoying buzz which I can only guess it origin. The inputs are floating, as are the outputs, I am reluctant to tie either to earth - but this might possibly be contributing to the buzz.
The sound is hugely detailed, yet effortless. It sounds as if there is plenty under the hood so that anything that is asked it could deliver with plenty in reserve.
John - I think you are right about this been the big daddy of the ECL82 headphone amp. It seems to share all of the qualities that were in that, but writ large. I just hope I can iron out the last few niggles and I will be a very happy bunny. Can you believe that I think it betters the DC7 by a very large margin.
Shoog
The sound is hugely detailed, yet effortless. It sounds as if there is plenty under the hood so that anything that is asked it could deliver with plenty in reserve.
John - I think you are right about this been the big daddy of the ECL82 headphone amp. It seems to share all of the qualities that were in that, but writ large. I just hope I can iron out the last few niggles and I will be a very happy bunny. Can you believe that I think it betters the DC7 by a very large margin.
Shoog
Wow,
This sounds so good I'm nearly getting in the car & traveling down to you to hear but that would be madness, wouldn't it, 3 hour drive at 12:40 pm? Still, maybe..............
I can hear your excitement! It sure is something to say that it outperforms the DC7 by a VERY LARGE margin. It's that VERY LARGE that is incredible. I didn't think there was much more left to be gained sonically after the DC7.
Problem is of course, that those who hear it will be unhappy with their own systems!. What have you unleashed?
Edit: Marry this up with an LDR vol control & good preamp & well, it doesn't bear thinking about
This sounds so good I'm nearly getting in the car & traveling down to you to hear but that would be madness, wouldn't it, 3 hour drive at 12:40 pm? Still, maybe..............
I can hear your excitement! It sure is something to say that it outperforms the DC7 by a VERY LARGE margin. It's that VERY LARGE that is incredible. I didn't think there was much more left to be gained sonically after the DC7.
Problem is of course, that those who hear it will be unhappy with their own systems!. What have you unleashed?
Edit: Marry this up with an LDR vol control & good preamp & well, it doesn't bear thinking about
Good news folks. I shifted the heater reference to the neg rail and that seems to have resolved the buzz - if only all hums were that easy. I also reconfigured the input transformer to a step down and now its got about the same input sensitivity as the DC7.
I will have a day of extended listening and will report back later.
Shoog
I will have a day of extended listening and will report back later.
Shoog
The problem with the CCS has returned - I must be missing something. Might be a short between the transistor tab and heatsink that only manifests as it heats up - who knows.
Also another major issue has arisen. I was listening this morning to some bass heavy rave music, and it seemed a bit bright - but not in the ultra high frequency ringing department. So I took her down and put my signal generator onto her. Seems that she is peaking in a broad sweep centered around 7KHz. No wonder she sounds involving and exciting. I think I have traced this peak right back to the input transformer (LL1715). So now I've got to try to work out how to flatten the response.
Shoog
Also another major issue has arisen. I was listening this morning to some bass heavy rave music, and it seemed a bit bright - but not in the ultra high frequency ringing department. So I took her down and put my signal generator onto her. Seems that she is peaking in a broad sweep centered around 7KHz. No wonder she sounds involving and exciting. I think I have traced this peak right back to the input transformer (LL1715). So now I've got to try to work out how to flatten the response.
Shoog
Spent the day messing about with the input transformer. No loading that I tried seemed to have any effect. Seems that its the wrong transformer for the job,
I also think the CCS problem is actually a leaky electro cap, I'm running out of suitable cap so it might be a struggle to resolve that one.
Problems, problems.
Shoog
I also think the CCS problem is actually a leaky electro cap, I'm running out of suitable cap so it might be a struggle to resolve that one.
Problems, problems.
Shoog
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