Pity, Shoog
I cant help with the trafo but what value cap do you need?
Edit: I know you don't like the idea of using 6AR8 tubes as phase splitters/vol control but I have some & could send them down if you are interested - don't know how this would fit in with the schematic or if it's feasible but just a suggestion!
I cant help with the trafo but what value cap do you need?
Edit: I know you don't like the idea of using 6AR8 tubes as phase splitters/vol control but I have some & could send them down if you are interested - don't know how this would fit in with the schematic or if it's feasible but just a suggestion!
Hi all,
My latest status report. I have finally got all the CCS working properly and as a result all the voltages have settled to exactly those predicted in the design stage. Unfortunately the CCS heatsink is up at about 60 centigrade which is a little higher than I am comfortable with - a little bit of a rethink might be in order on that one. I introduced a 5uf input cap to produce a resonant hump at about 200hz, a tempory sticking plaster solution. I have it playing in the main system and it sounds nice, unfortunately the sonic signiture of the whole amp is dominated by the input transformer which still has bad overshoot and a rising response. I would say that the amp itself is doing a perfect job of amplifing exactly what is given to it by the input transformer. I feel that this transformer might find a good home in a Zeus clone (hey John). I have looked at the waveform from my computer sound card and can see the descrete voltage change steps - with the slight leading edge overshoot introduced by the input transformer.
I have about 2x the gain that I need even after a a 2:1 step down. This leads me to think that I might get good result from a toroidal transformer with 110V:24V ratio. The step down should overcome the intrinsic interwinding capacitance of the toroidal transformer. I also will order the following transformers from Farnell;
http://ie.farnell.com/jsp/search/browse.jsp?N=500008+1001641&Ntk=gensearch_001&Ntt=bbh+windings&Ntx=
The description says that they have seperate bobbins for the twin primaries and secondaries for reduced interwinding capacitance. They are also wound onto a circular silicone grain orientated core (sounds like a toroidal to me) for reduced leakage inductance. At about €7.00 it certainly worth a shot.
Shoog
My latest status report. I have finally got all the CCS working properly and as a result all the voltages have settled to exactly those predicted in the design stage. Unfortunately the CCS heatsink is up at about 60 centigrade which is a little higher than I am comfortable with - a little bit of a rethink might be in order on that one. I introduced a 5uf input cap to produce a resonant hump at about 200hz, a tempory sticking plaster solution. I have it playing in the main system and it sounds nice, unfortunately the sonic signiture of the whole amp is dominated by the input transformer which still has bad overshoot and a rising response. I would say that the amp itself is doing a perfect job of amplifing exactly what is given to it by the input transformer. I feel that this transformer might find a good home in a Zeus clone (hey John). I have looked at the waveform from my computer sound card and can see the descrete voltage change steps - with the slight leading edge overshoot introduced by the input transformer.
I have about 2x the gain that I need even after a a 2:1 step down. This leads me to think that I might get good result from a toroidal transformer with 110V:24V ratio. The step down should overcome the intrinsic interwinding capacitance of the toroidal transformer. I also will order the following transformers from Farnell;
http://ie.farnell.com/jsp/search/browse.jsp?N=500008+1001641&Ntk=gensearch_001&Ntt=bbh+windings&Ntx=
The description says that they have seperate bobbins for the twin primaries and secondaries for reduced interwinding capacitance. They are also wound onto a circular silicone grain orientated core (sounds like a toroidal to me) for reduced leakage inductance. At about €7.00 it certainly worth a shot.
Shoog
Hey Shoog,
Good to hear some progress!
Are these the LL1517 trafos I emalied you about?
Funny you should mention the Zeus, today I got an input audio & output toroidal trafo to test from Radionics. I would be interested in testing your trafo
Can you order from Farnell without a €35 minimum charge?
BTW, I can't see reference to twin bobbins in the datasheet of the BBH trafo you referenced?
Good to hear some progress!
Are these the LL1517 trafos I emalied you about?
Funny you should mention the Zeus, today I got an input audio & output toroidal trafo to test from Radionics. I would be interested in testing your trafo
Can you order from Farnell without a €35 minimum charge?
BTW, I can't see reference to twin bobbins in the datasheet of the BBH trafo you referenced?
Yes they are the LL1715.
The mention of the twin bobbin is in the catalogue.
There is a minimum order with Farnell but I have to order a big PA driver soon.
I was researching the Zeus last night. I was thinking something more along the lines of using the mosfets in place of Pentodes in a typical valve circuit. This would take the strain off of the transformers which will be the weak link in the design. I was thinking of something like the Baby Huey/Tabor with Mosfets.
Shoog
The mention of the twin bobbin is in the catalogue.
There is a minimum order with Farnell but I have to order a big PA driver soon.
I was researching the Zeus last night. I was thinking something more along the lines of using the mosfets in place of Pentodes in a typical valve circuit. This would take the strain off of the transformers which will be the weak link in the design. I was thinking of something like the Baby Huey/Tabor with Mosfets.
Shoog
Hmm, Interesting, Stephen
The two big issue with the Zeus are:
- the quality of the transformers (although Susan Parker has used toroidal mains transformers for both input & output giving about 70% of the final sound)
- the biggest one - the difficulty in choosing a preamp to drive the 600ohm impedance of the input trafo.
Do you reckon these issues would be addressed & the simplicity of the Zeus retained in this Tabor/Baby Huey circuit?
The two big issue with the Zeus are:
- the quality of the transformers (although Susan Parker has used toroidal mains transformers for both input & output giving about 70% of the final sound)
- the biggest one - the difficulty in choosing a preamp to drive the 600ohm impedance of the input trafo.
Do you reckon these issues would be addressed & the simplicity of the Zeus retained in this Tabor/Baby Huey circuit?
The official Sowter trafos cost 76*2 + 145*2 (nearly 600 euro)
BTW, I have some bobbins & E cores for trafos & I was just wondering how suited they might be to audio use: http://ie.farnell.com/1190595/electrical-circuit-protection/product.us0?sku=EPCOS-B66325GX127
BTW, I have some bobbins & E cores for trafos & I was just wondering how suited they might be to audio use: http://ie.farnell.com/1190595/electrical-circuit-protection/product.us0?sku=EPCOS-B66325GX127
Your entering the big league if your going to go trying to wind your own transformers.
I was thinking of having a Mosfet/opamp preamp stage built into the amp and driving the LL1716 transformer. Unfortunaterly this would require a coupling cap between the preamp stage and the transformer - S**t that wont work because the coupling cap will need to be huge due to the very low output impedence.
You could put a LTP preamp infront of the transformer so that you could maintain balanced drive and keep DC out of the transformer. Its starting to look a bit more complex than my little though experiment suggested. Still the LTP could be a pair of low powered matched on one chip transistors for perfect balance. It needn't be overly complex - but you are definately moving away from the elegant simplicity of the original Zeus.
Shoog
I was thinking of having a Mosfet/opamp preamp stage built into the amp and driving the LL1716 transformer. Unfortunaterly this would require a coupling cap between the preamp stage and the transformer - S**t that wont work because the coupling cap will need to be huge due to the very low output impedence.
You could put a LTP preamp infront of the transformer so that you could maintain balanced drive and keep DC out of the transformer. Its starting to look a bit more complex than my little though experiment suggested. Still the LTP could be a pair of low powered matched on one chip transistors for perfect balance. It needn't be overly complex - but you are definately moving away from the elegant simplicity of the original Zeus.
Shoog
Thinking about what you proposed, I imagine the beauty of the Zeus configuration would be lost i.e the Mosfets are just used as assists to the output transformer to generate current and so are less influential in the final sound!
Edit: Cross post, Shoog - is trafo winding so difficult? Again the Zeus site seems to indicate that bifilar winding is not that difficult - just wondering if these cores were adaptable to audio use - I think they are designed as inductors?
Edit: Cross post, Shoog - is trafo winding so difficult? Again the Zeus site seems to indicate that bifilar winding is not that difficult - just wondering if these cores were adaptable to audio use - I think they are designed as inductors?
So I got all the main issues ironed out. I decided to run a signal sweep through the amp again just to check my earlier findings. Well what a surprise, all the ringing and overshoot seems to have disappeared. I am getting a small bit of overshoot on the square wave - but not enough to worry about. Frequency response extends out to past 50khz (though the square wave is triangular by then). With a 150ohm drive frequency is about 1db down at 100hz, with 600ohm drive it down a bit more.
I have put her back in the system and she sounds sweet. Haven't had a chance to do any serious listening because of the family. I have two remaining issues. There is way to much gain. Also there is a buzzing hum which is unusual because it disappears if I touch the input jack sleeves but doesn't respond to grounding the sleeves.
I ordered those transformers, but it looks like I might not need them after all. If not i will try building a really small MOSFET amp with them - something like 3watts.
Stephen
I have put her back in the system and she sounds sweet. Haven't had a chance to do any serious listening because of the family. I have two remaining issues. There is way to much gain. Also there is a buzzing hum which is unusual because it disappears if I touch the input jack sleeves but doesn't respond to grounding the sleeves.
I ordered those transformers, but it looks like I might not need them after all. If not i will try building a really small MOSFET amp with them - something like 3watts.
Stephen
Just solved the hum - hadn't got a good enough connection to earth. All is sweet
I think what was happening was that the problem with the CCS was overloading the power supply and causing saturation and ringing which was bleeding through to the outputs.
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It should be a simple matter of a days work to lash up a Mosfet Tabor to test the concept. i should be able to do it with the transformers I have just ordered and selvaged parts. Unfortunately i will be very busy with other things for the rest of the month so I don't think I will have anything to report for a while.
Shoog
I think what was happening was that the problem with the CCS was overloading the power supply and causing saturation and ringing which was bleeding through to the outputs.
--------
It should be a simple matter of a days work to lash up a Mosfet Tabor to test the concept. i should be able to do it with the transformers I have just ordered and selvaged parts. Unfortunately i will be very busy with other things for the rest of the month so I don't think I will have anything to report for a while.
Shoog
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