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10-20-2015 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 61
Post ID: 22137
Reply to: 22136
Be carefully however.
fiogf49gjkf0d
Anthony, I truly do not know. I presume any rise of a temperature around a wood would make wood prone to crack. From different perspective it is possible to come up with some thermal multilayered shields. I am sure if to make it as objective then with today materials it possible to do anything you want and to protect wood. Find somebody who knows and I am sure they would assist you. The only think that I would recommend is to re-asses your objective and make sure that you really want to integrate acoustic system with amps. I admit it sounds very lucrative BUT it also bind the amp with speakers. Generally those binding solutions might be blessing or a souse of major pain in ass in future. So, be very positive that it will be your last amp, last room and last speaker. I was very positive about it at least 5 times....


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
12-21-2015 Post does not mapped to Knowledge Tree
anthony
Posts 187
Joined on 08-18-2014

Post #: 62
Post ID: 22331
Reply to: 22137
All about bass
fiogf49gjkf0d
Hi Romy,

So it is time to think about the bass output transformer in my DSET.  My bass channel will be 8 x 25W/8565-00 each side set in a sealed box and will cover the frequency range below say 100Hz.  These drivers can be wired anywhere between 1R and 64R which gives quite a bit of flexibility for adjusting the amplifier/speaker system damping factor.  Reading your threads about your Scanspeak arrays it is evident that the system damping factor is important for the bass channel and is influenced by the OPT decisions, how the 6C33C is loaded and most likely by how the speaker is wired.  

I propose to wire the drivers in parallel so that they present a nominal load of 1R to the amplifier which in effect will maximise the system damping of the drivers, which from what I take from your writings could be a good thing.  Then I will have a bass OPT wound with a secondary of 1R or 1.1R that will pass 450mA and cover say 5Hz - 800Hz before rolling off.

Romy, given your experience with the amplifier and the drivers, are you able to offer any advice regarding the OPT or wiring of the drivers before I give the transformer winder my final specs?

Regards,

Anthony
12-22-2015 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 63
Post ID: 22334
Reply to: 22331
Approaching the LF DSET
fiogf49gjkf0d
 anthony wrote:
Hi Romy,

So it is time to think about the bass output transformer in my DSET.  My bass channel will be 8 x 25W/8565-00 each side set in a sealed box and will cover the frequency range below say 100Hz.  These drivers can be wired anywhere between 1R and 64R which gives quite a bit of flexibility for adjusting the amplifier/speaker system damping factor.  Reading your threads about your Scanspeak arrays it is evident that the system damping factor is important for the bass channel and is influenced by the OPT decisions, how the 6C33C is loaded and most likely by how the speaker is wired.  

I propose to wire the drivers in parallel so that they present a nominal load of 1R to the amplifier which in effect will maximise the system damping of the drivers, which from what I take from your writings could be a good thing.  Then I will have a bass OPT wound with a secondary of 1R or 1.1R that will pass 450mA and cover say 5Hz - 800Hz before rolling off.

Romy, given your experience with the amplifier and the drivers, are you able to offer any advice regarding the OPT or wiring of the drivers before I give the transformer winder my final specs?
   
Anthony, this is a very good and a very complicated question.  The question is boil down to the following: to connect in parallel and drive low impedance or to connect to series and to drive high impedance. There is no right answer to it in my view as not one did a methodologically clear experiment and got the empirical answers. I would outline for you my thoughts on the subject and what I would do, under no circumstances take it as “right way” to do it as there is no right way. Examine my reasons yourself and with your other advisers and make a decision for yourself.
There are 5 main points that shall be taking under consideration when you think about the subject: output tube, transformer, cables, drivers, usability. Let me to describe each of them.
 
The Output Tube. I personally do not think that there is any difference for the tube to drive low or high impedance behind a proper transformer.  Let pretend your tube wants to “see” 1.500R.  If you have on secondary 0.5R or 64R it would not be any difference for tube with appropriate transformer that converts 0.5R or 64R to 1.500R. It would be a different transformer ratio (and to a degree a deferent transformer design) but I doubt that tube will see some kind of “reactance” on secondary. Consult on the subject with some smart tube amp designers (good luck to find them) but my vote goes to the statement “tube does not care”. 
 
Output transformer. Here is what the thing become complicated. Of you drive ultra-low impedance with step down transformer then your secondary turns will decrease. They primary will have whatever they have for all case but secondary will go lover and lower as load impedance drop and might even become foil-made. That is for sure will make the transformer faster and better for transients BUT your need LF DSET transformer it means you need inductance. As you will be losing your turn on secondary you will be losing inductance and the only way to get it back would be to increase the core size.  You need to put your transformer maker on the task and see if you will be able to obtain a transformer core for half amper gap, no secondary turns and 5Hz at full power. That will be a small refrigerator size piece of iron and it might be very expensive. 
 
Cables. Driving 1R you will be driving current. Driving 64R you will be driving voltage. Some of the cables/connectors behave differently under voltage vs current conditions. Also if you drive 1R with low voltage then you might pick some on like interferences. 
 
Drivers. If you go with 8 x 25W/8565-00 then make sure that your make the right boxes and over dump them. I would use 4 individual boxes by 2 drivers each. I do not think that drivers would care how they are connected. The difference would be in case of driver mismatch. In real world all drivers will be slightly different. You are not a large speaker builder and you won’t be able to pick among 100s driver the best matching drivers. So, if one driver has Fs 20Hz and another 24Hz then the question is: would it be betters for them to be connected in parallel or not. I do not know the answer and I am not informed enough to make a guess. You need to consult with somebody else, BTW, if you do them post a received answer. 
 
Usability. That is bitch. First thing first: how do you know how much your tube need to be loaded? Pretend that it is 6C33C and pretend that you need to load it with 600R to get a balance MF sound. Idle tube more you dive you less harmonics, faster sound, in a way over-burned transients. Loading the tube more five you “slower”, more euphonic sound and more power. That would be true for MF but at LF you will have much less negative impact of tube idling and you might find VERY beneficial to load your 6C33C with 1 kR or 1.2kR. That are not exact number but I just give you an idea. Also, the differences at 1R load are huge. Each change of 0.1R loading will give you a large difference in sound. You will need to hit very prissily and you as you start will not know where to aim. I can only presume that you will be in the realm of 1200-1500R, or perhaps higher but with “odd” transformer and a few other variable it is very hard to predict anything. Do not also forget that with limited wiring on the secondary you will have very limited opportunity to have multiple taps on your transformer as the filling of the barbing will be suffering. 
 
Usability continue. There are more ugly things: as you ideal more your bass tube and get better sound (to a degree) you will be losing power. Even with 8 drivers and let say a single 6C33C you will need a sealed room of let say no more than ~300sq feet or you will be driving your 6C33C into A2, which is a clipping for this tube.  If you have a normal listing room of 600+ with open floor plan then you are way out of your DSET capacity with 6C33C unless you super load the tube and then you have shity sound. Even if you did resolve your problem with power somehow then the ugly truth that it will take time for you to understand what type of bass you need. My estimation that it would be good to stay with properly doe bass for 2-3 months in order to “get” where/how to move next with bass.
 
So, from all that I said above if I were in your position I would not go final DSET solution with bass now but rather did it incrementally.  Make your bass sections, connected them conventionally, let say 16R each and drive them with some kind of SS amp. Then take the SET that you would like to use as DSET and drive it into the bass channel. Play with loading, find the best configuration and make a judgment about sufficiency of power. Then go for a DSET that would be against a conventional load. 4x16R in parallel = 4R. That would be a conventional load and you can use many different amps to try, including your SET, If you test everything with your SET, find a proper loading and get conformation about power then you can converts the found transformer ratio to any another load. 
 
That is basically what I did over the time and this is what I would do if I do it again. Do not forget that your situation might be very different from what mine was in my old city home. Your bass channel will be running under 100Hz and your room dissipation at 100Hz might be very different then at 40hz, so you might need much more power than you might think. It is nice to learn about it experimenting with SET then to pay a lot of money for DSET OPT and then learns that you have not enough DC gap to add another tube in parallel or that you need to lose another 10% turns on secondary and the cost of shipping of the transformers will cost more than a pair of new one.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
12-22-2015 Post does not mapped to Knowledge Tree
anthony
Posts 187
Joined on 08-18-2014

Post #: 64
Post ID: 22335
Reply to: 22334
Many thanks
fiogf49gjkf0d
 Romy the Cat wrote:

Output transformer. Here is what the thing become complicated. Of you drive ultra-low impedance with step down transformer then your secondary turns will decrease. They primary will have whatever they have for all case but secondary will go lover and lower as load impedance drop and might even become foil-made. That is for sure will make the transformer faster and better for transients BUT your need LF DSET transformer it means you need inductance. As you will be losing your turn on secondary you will be losing inductance and the only way to get it back would be to increase the core size.  You need to put your transformer maker on the task and see if you will be able to obtain a transformer core for half amper gap, no secondary turns and 5Hz at full power. That will be a small refrigerator size piece of iron and it might be very expensive. 

I can't see the transformer being small under any circumstances.  My transformer winder is very smart and level headed so I think that I have a good chance of getting a good result with the OPT if I can tell him what to build.

 Romy the Cat wrote:
   Cables. Driving 1R you will be driving current. Driving 64R you will be driving voltage. Some of the cables/connectors behave differently under voltage vs current conditions. Also if you drive 1R with low voltage then you might pick some on like interferences. 

I had not even though about cables, but of course you are right.

 Romy the Cat wrote:
 
Drivers. If you go with 8 x 25W/8565-00 then make sure that your make the right boxes and over dump them. I would use 4 individual boxes by 2 drivers each. I do not think that drivers would care how they are connected. The difference would be in case of driver mismatch. In real world all drivers will be slightly different. You are not a large speaker builder and you won’t be able to pick among 100s driver the best matching drivers. So, if one driver has Fs 20Hz and another 24Hz then the question is: would it be betters for them to be connected in parallel or not. I do not know the answer and I am not informed enough to make a guess. You need to consult with somebody else, BTW, if you do them post a received answer. 

I am a little worried about driver mismatch.  The first thing for me to do in this regard is to run them in on signal for a while and then measure their parameters, matching them driver by driver into groups.  I know just the person to talk to about driver matching so I will give him a call after Christmas to pick his brain.
 
 Romy the Cat wrote:
Usability. That is bitch. First thing first: how do you know how much your tube need to be loaded? Pretend that it is 6C33C and pretend that you need to load it with 600R to get a balance MF sound. Idle tube more you dive you less harmonics, faster sound, in a way over-burned transients. Loading the tube more five you “slower”, more euphonic sound and more power. That would be true for MF but at LF you will have much less negative impact of tube idling and you might find VERY beneficial to load your 6C33C with 1 kR or 1.2kR. That are not exact number but I just give you an idea. Also, the differences at 1R load are huge. Each change of 0.1R loading will give you a large difference in sound. You will need to hit very prissily and you as you start will not know where to aim. I can only presume that you will be in the realm of 1200-1500R, or perhaps higher but with “odd” transformer and a few other variable it is very hard to predict anything. Do not also forget that with limited wiring on the secondary you will have very limited opportunity to have multiple taps on your transformer as the filling of the barbing will be suffering. 

Yes, the tube loading is something that I need to play with in order to more fully understand its effects.  To be honest this is the part that worries me most.

 Romy the Cat wrote:
 
Usability continue. There are more ugly things: as you ideal more your bass tube and get better sound (to a degree) you will be losing power. Even with 8 drivers and let say a single 6C33C you will need a sealed room of let say no more than ~300sq feet or you will be driving your 6C33C into A2, which is a clipping for this tube.  If you have a normal listing room of 600+ with open floor plan then you are way out of your DSET capacity with 6C33C unless you super load the tube and then you have shity sound. Even if you did resolve your problem with power somehow then the ugly truth that it will take time for you to understand what type of bass you need. My estimation that it would be good to stay with properly doe bass for 2-3 months in order to “get” where/how to move next with bass. 

The room is 280sq feet and sealed.  It has a raked ceiling but to offset that there is also a degree of soundproofing which reflects energy back into the room.  I had considered to use a SS amplifier for the bass as a benchmarking tool...I think that I would be foolish not to.
 Romy the Cat wrote:
 
So, from all that I said above if I were in your position I would not go final DSET solution with bass now but rather did it incrementally.  Make your bass sections, connected them conventionally, let say 16R each and drive them with some kind of SS amp. Then take the SET that you would like to use as DSET and drive it into the bass channel. Play with loading, find the best configuration and make a judgment about sufficiency of power. Then go for a DSET that would be against a conventional load. 4x16R in parallel = 4R. That would be a conventional load and you can use many different amps to try, including your SET, If you test everything with your SET, find a proper loading and get conformation about power then you can converts the found transformer ratio to any another load.
That is basically what I did over the time and this is what I would do if I do it again. Do not forget that your situation might be very different from what mine was in my old city home. Your bass channel will be running under 100Hz and your room dissipation at 100Hz might be very different then at 40hz, so you might need much more power than you might think. It is nice to learn about it experimenting with SET then to pay a lot of money for DSET OPT and then learns that you have not enough DC gap to add another tube in parallel or that you need to lose another 10% turns on secondary and the cost of shipping of the transformers will cost more than a pair of new one.

This is a much more balanced approach than I was considering.  Yes, I should build the bass arrays first and test them in my room with SS to be sure that a SET can power them in that situation.  That has to be step number one.  Then, if warranted, experiment to sort out the DSET OPT specs.  Luckily, my transformer guy in Australia has finally agreed to build this OPT, so freight will be inconsequential compared to the international transit that I was facing a while ago.

Thanks Romy for your thoughtful and and considered input here.  It is very much appreciated.

Regards,

Anthony

12-22-2015 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 65
Post ID: 22336
Reply to: 22335
SS amps do generally very bad bass.
fiogf49gjkf0d
Interesting. with sealed 280 sq feet and 8 drivers per side along a long wall you very much migh be able to use a singe 6C33C. With proper loading, good trasformer, DSET and these drivers you should be able to get bass that I doubt you will be able to get from any SS amp.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
12-24-2015 Post does not mapped to Knowledge Tree
anthony
Posts 187
Joined on 08-18-2014

Post #: 66
Post ID: 22352
Reply to: 22336
The long wall?
fiogf49gjkf0d
Romy, I have seen you mention setting speakers up across the long wall before but never got to the base of your reasoning?  Could you please elaborate?  Is it to do with the delay of first reflections?

12-24-2015 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 67
Post ID: 22354
Reply to: 22352
Multiple reasonings…
fiogf49gjkf0d
 anthony wrote:
Romy, I have seen you mention setting speakers up across the long wall before but never got to the base of your reasoning?  Could you please elaborate?  Is it to do with the delay of first reflections?

The line-arrays that I used do load rooms with MUCH less problems across the long wall, it pretty much any acoustic system topology has more linear lower octave behavior across long walls. The positioning of bass section outside of the horns makes the system spread wide long wall positioning give you a lot of room of maneuver. With wall positioning you have wider room to play and you can find that precise location when system drops center image and breaks the imaging curve. If you use a short wall then this location might be just a few inches from you on the left and right but you never get there because there will be a walls on your way.  I always love how any acoustic systems image extended toward to mid of the rooms and across long walls. I do not feel that good thinks can’s not be done across short walls but if I have a chose then I would always go wide.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
12-25-2015 Post does not mapped to Knowledge Tree
noviygera


Chicago, IL
Posts 137
Joined on 06-12-2009

Post #: 68
Post ID: 22356
Reply to: 22336
This is interesting!
fiogf49gjkf0d
 Romy the Cat wrote:
Interesting. with sealed 280 sq feet and 8 drivers per side along a long wall you very much migh be able to use a singe 6C33C. With proper loading, good trasformer, DSET and these drivers you should be able to get bass that I doubt you will be able to get from any SS amp.

Romy,why do you feel the SS amps will not provide as good bass as tube amp? Since there is such a big selection of SS amps, also hybrid one, is it a general rule, regardless of amp power and type? Is it the type of distortion that's inherent to tube amps that makes them specially enjoyable in the bass region? 
12-26-2015 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 69
Post ID: 22357
Reply to: 22356
Why do you feel what I feel? I do not.
fiogf49gjkf0d
 noviygera wrote:
Romy,why do you feel the SS amps will not provide as good bass as tube amp? Since there is such a big selection of SS amps, also hybrid one, is it a general rule, regardless of amp power and type? Is it the type of distortion that's inherent to tube amps that makes them specially enjoyable in the bass region? 
Well, can answer a question why do I “think” and bring many existing theories why SS do not do bass well. I do not know what theory would be “right” but I do not particularly care “why”. So, what I do it use purely imperial evidence without caring too my “why”. If I look at the best SS amps that I even hear and compare the bass they produce with best SET that I heard then it is very clear to me that no SS amp can even close to state to a good SET in bass performance. If you do to bass DSET world and do proper uploading of Triode and manage to maintain bass still in Class A then in my view (feeling) you get the best bass audio is capable to produce. Why? Well, I have too much on my plate now to care. I would prefer to listen the Poulenc’s Organ Concerto then to wax poetry about reasons that will not able to proof anyhow.
 


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
07-28-2016 Post does not mapped to Knowledge Tree
anthony
Posts 187
Joined on 08-18-2014

Post #: 70
Post ID: 22690
Reply to: 22334
First bass OPT prototype...
fiogf49gjkf0d
 Romy the Cat wrote:

 
Output transformer. Here is what the thing become complicated. Of you drive ultra-low impedance with step down transformer then your secondary turns will decrease. They primary will have whatever they have for all case but secondary will go lover and lower as load impedance drop and might even become foil-made. That is for sure will make the transformer faster and better for transients BUT your need LF DSET transformer it means you need inductance. As you will be losing your turn on secondary you will be losing inductance and the only way to get it back would be to increase the core size.  You need to put your transformer maker on the task and see if you will be able to obtain a transformer core for half amper gap, no secondary turns and 5Hz at full power. That will be a small refrigerator size piece of iron and it might be very expensive. 


My transformer winder has completed the first prototype DSET bass OPT.  He was quite excited when he called me and used the word "phenonomenal" to describe its performance into a reflective 1R load.  At 4Hz it is down 0.5dB and at 10kHz and 20KHz it is down 1dB and 3dB respectively.  We were certainly not chasing the high frequencies but they seem to be there nonetheless...it is quite a full range OPT.  The tube load is 2kOhm, which is higher than intended, but it still puts out 9w at 5% distortion into 4Hz at 1R, virtually all 2nd harmonic.  The filter caps in the test circuit are only 680uF and they are visibly pulsing when seen on the oscilloscope so are struggling at that output but the 15kuF caps for the amplifier should improve the performance some more.  Lucas says the square wave at 1w is "almost perfect".

So, I have to make a decision regarding the direction for a second prototype, if indeed I should bother with a second at this stage. I think that 9w output into 1R will be fine athough if the plate is loaded more lightly then I may pickup another watt or more.  It is the 2kOhm plate load that concerns me...is it too high? Is it just right?  Who knows?  Shortening the primary or secondary is going to affect inductance but this may be overcome by going up not one, but two core sizes and using larger wire.  Then of course I could wire the speakers up so they load at 2R which would give more secondary wire, more inductance and the primary could be shortened to reduce the tube load to something more moderate.  

Could any of these things improve the sound?  Does the first prototype sound ok?  All questions with no real answers.  I am tempted to stay with the 2kOhm plate load as we have in the first prototype and see how well I can make it sound.

Anthony


07-28-2016 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 71
Post ID: 22691
Reply to: 22690
I do not know.
fiogf49gjkf0d
 anthony wrote:
My transformer winder has completed the first prototype DSET bass OPT.  He was quite excited when he called me and used the word "phenonomenal" to describe its performance into a reflective 1R load.  At 4Hz it is down 0.5dB and at 10kHz and 20KHz it is down 1dB and 3dB respectively.  

 
That all make sense ONLY if we are taking about max power. You will not get from your transformer 0.5dB at 4Hz and 3db at 20KHz at max power and the fact that your guy gives you the numbers at a fraction of power does not make me too happy about him….


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
07-29-2016 Post does not mapped to Knowledge Tree
anthony
Posts 187
Joined on 08-18-2014

Post #: 72
Post ID: 22692
Reply to: 22691
Yes, that is right...
fiogf49gjkf0d
 Romy the Cat wrote:
 anthony wrote:
My transformer winder has completed the first prototype DSET bass OPT.  He was quite excited when he called me and used the word "phenonomenal" to describe its performance into a reflective 1R load.  At 4Hz it is down 0.5dB and at 10kHz and 20KHz it is down 1dB and 3dB respectively.  

 
That all make sense ONLY if we are taking about max power. You will not get from your transformer 0.5dB at 4Hz and 3db at 20KHz at max power and the fact that your guy gives you the numbers at a fraction of power does not make me too happy about him….


That was all data given to me over the phone in real-time as he measured the setup late at night.  He did some more testing today and it turns out that there is a bit more there than 9.5watts at 5% distortion...it was not the opt running out of puff but the the amplifier he was using for the signal generator...the tube and opt were still quite accurately passing the signal as it came to it from the generator.  With that rectified and some full power testing for bandwidth it became clear that the tube is too stiff when loaded at 2kOhm and that the grid clips before the opt does, but at 5.1w into 1R (which is where the grid was clipping) the output was down 0.6dB at 4 Hz, so at full power it still should be well under 10Hz

So, after all that and studying the tube curves the decision made is that the tube definitely needs to be loaded closer to 1500R as was originally intended and to do that we need to go up two core sizes (no inductance gain if we go up only one core size) and use larger diameter secondary wire.
08-07-2016 Post does not mapped to Knowledge Tree
anthony
Posts 187
Joined on 08-18-2014

Post #: 73
Post ID: 22702
Reply to: 22692
DSET Grounding
fiogf49gjkf0d
Hi Romy,

I am designing the power supply chassis for the DSET at the moment and hope that you can remember some things about how you managed the grounding.

All power supply components up to but not including the filter caps for each power supply will be held in the PS Chassis with the remainder held in the Amp Chassis.  I assume that this is how you managed things.  My question is basically whether you amalgamated the DC ground inside the PS or whether you waited until the Amp Chassis to join to common ground?  If the grounds for the various power supplies are joined in the PS Chassis then we would get away with fewer ground wires in the power cables between the boxes but this is not an issue for me, there are plenty of wires in my cables and connectors.  

I suppose this question then extends to the Bias PS, the centre tap for the filament transformers and the electrostatic screens for the various transformers...do you ground those in the PS or Amp Chassis?  According to the schematic, the Bias PS will be attached to common ground in the Amp Chassis.

Thanks for your help,

Anthony 
08-08-2016 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 74
Post ID: 22703
Reply to: 22702
As far as I remeber.
fiogf49gjkf0d
Anthony, I do not remember details now but the basic was following. I selected on PS and Control chassis single locations that I considered the main grounding points. Within PS chassis if was a negative terminal of the last filtering cap and within Control chassis it was negative side of the input RCA jack.  Those locations I called main negative thermal and they were connected direct via thick cable between PS and Control units. The main negative thermals I made think. I think it was 4-6 8ga wires and flooded with solder. I connected everything to them as star join with a difference that I made main negative thermals long like snake and positioned them in the chassis strategically in order to optimize and shorten the length of the negative wires to the ground. Do not forget the in Milq the negative thermals are cathode supplies and it is kind of important.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
10-19-2016 Post does not mapped to Knowledge Tree
anthony
Posts 187
Joined on 08-18-2014

Post #: 75
Post ID: 22821
Reply to: 22703
DSET Bass OPT is wound
fiogf49gjkf0d
The Bass OPT's for my DSET have been wound.  We have come back to a 1000R plate loading and into 1R the 6C33C grid clips at 9.36W and 5.8% distortion.  The -0.5dB points at full power are 5.9Hz and 5kHz.

A nice result really, and about where I thought the power would end up, although obviously it would be nice to have a little more.  9W before grid clipping should be enough in my room, and even if things are pushed harder the 6C33C/OPT will still push 15W at 10% distortion into 1R.

I also had Lucas test the output into 5R, and we got 17W at grid clipping and about 2.7% distortion.

When using such a low speaker impedance as 1R, the quality and type of connections between the OPT and the transducers really makes a difference...so it looks like I am going to have to hard-wire this channel.  Think about the effect of a 0.5R binding post in addition to a 1R speaker load...that is a large percentage of the nominal.
10-19-2016 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,495
Joined on 05-28-2004

Post #: 76
Post ID: 22822
Reply to: 22821
1R vs 16R
fiogf49gjkf0d
With near 1R impedance I presume you will have multiple bass drivers paralleled. That is perfectly legitimate way to operate but there are a few things you might consider.   

The mistakes at 1R are more effective then at high impedance. If you have 16R then you get some difference of sound if you change from 16R to 12R. You will have the same sonic difference if you change from 1R to 0.9R. The operation point at low impedance point is a bit too sensitive. Driving 1R you will have more sonic difference when you change from 250mA to 300mA on 6C33C’s plate then it would be driving 16R. The symmetrical clipping become a bit more aggressive with low plate loading. I do not know why but I did observed it. At 16R the voltage and current clippings were more gently introduced then with 2R loading. The speaker cable behave a bit differently then what I was accustomed. The cable are running in “current mode”, so the “best” cable for 16R load would not be not the best for 1R. 
 
Still, if everything is done properly then there is no difference what loading impedance would be 1R or 16R. The 1R has some advantages as the DCR of the transformer is lower and the bass drivers matching become a bit less critical…


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
12-07-2016 Post does not mapped to Knowledge Tree
anthony
Posts 187
Joined on 08-18-2014

Post #: 77
Post ID: 22873
Reply to: 22822
I've started building the power supplies...
I designed up a steel chassis for both the Fullrange and DSET Melquiades.  Here they are screwed together for the first time.  

Four Ned Kellys.jpg


Then I have made sure all the cutting and drilling has been in the correct places by quickly putting the parts in their places.  The Fullrange Melquiades will has a separate power supply just in case I take things further and make it three channel.  There is plenty of room to add more iron in there.  First the bottom shelf...

Mockup Fullrange Front.jpg

Mockup Fullrange Top.jpg



The DSET power supply is much more hefty with no spare room.  The bottom shelf...

Mockup DSET Bottom 1.jpg


...and the middle shelf...

Mockup DSET Mid 1.jpg



Power supplies are down the bottom, diodes in the middle and chokes are on the top shelf.

The cases are made from steel but the aluminium platforms are used to keep the magnetics at least 20mm from any ferrous material.  I have used sorbothane bushings to isolate the individual platforms from the steel chassis in an effort to minimise vibrations.  All iron (apart from the toroid for the services supply) are custom wound by a very smart fellow in Melbourne (Lucas Cant from Black Art Audio) and are built on large cores for tight regulation (generally 1% or 2% regulation), low heat gain (no more than 20 degrees) and low impedance.

Everything has been painted or powder-coated since these photos were taken and I am currently building all four supplies in my evenings and whatever spare moments I can grab.

12-08-2016 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 450
Joined on 01-07-2006

Post #: 78
Post ID: 22874
Reply to: 22873
Steel singing
Anthony, have you tried powering this all up (with dummy loads) to see if the outer steel skin will not sing? 20mm is nothing for LF magnetic induction.

Best luck,
N-set



Cheers,
Jarek
12-08-2016 Post does not mapped to Knowledge Tree
anthony
Posts 187
Joined on 08-18-2014

Post #: 79
Post ID: 22877
Reply to: 22874
Not yet
Hi N-Set, I am three quarters of the way through assembling the first power supply to power-up stage so I have not tested the "singing" as yet.  It is something that I have thought a lot about.  First and foremost I wanted a steel skin around the power supply for EMF/RFI suppression as well as trying to mitigate the flow of stray flux into the room from the power supply itself...there is a lot of iron in those boxes.  So I went with relatively thick 4mm steel panels partially for mass (to appropriately load the industrial footers I have ordered), partially for ease of working (I prefer to work with something that is difficult to bend or dent) but mostly to have adequate steel thickness to shield the room from the magnetics.

The 20mm gap was something that I talked to my transformer winder about and that number was decided as a reasonable distance where there would still be some magnetic coupling but its strength would be somewhat reduced.  I could use larger distances for lower coupling but then the power supply case gets enormous and they are big enough already.  Internally, I have a minimum separation between individual pieces of iron of 50mm, usually a little more.  So with the knowledge that I will have coupling I introduced a couple of measures to mitigate it:  the aluminium platforms sitting on sorbothane bushings; a constrained layer damping for the steel panels.

From my calculations, the properly loaded sorbothane bushings should be capable of decent isolation for mains frequency vibrations and harmonics.  I have not tested it yet of course, but if the iron couples strongly enough to the steel panels the sorbothane should be effective at allowing the iron to move a little whilst isolating that movement from the chassis itself.  Whether this works in part or in full is yet to be seen, but that is my hope.

Secondly, on the inside of the 4mm steel panels I plan to apply a vicoelastic polymer and 1mm thick aluminium sheet to act as constrained layer damping so that any ringing is snuffled before it becomes a problem.  This material is specially designed to damp ringing steel panels in industrial applications and has some decent measurements to back it up so hopefully I can apply it effectively.

Cheers,

Anthony

PS:  My hope is that the power supplies feel "soft" to move around...a product of the anti-vibration measures I have used.
12-09-2016 Post does not mapped to Knowledge Tree
N-set
Gdansk, Poland
Posts 450
Joined on 01-07-2006

Post #: 80
Post ID: 22878
Reply to: 22877
Copper?
Ok, quite impressive measures, I also once had an idea of sandwitched cabinet construction. Hope it will work. 4mm steel is quite rigid but weights a lot.  If $$$ permits you may consider copper for the inner layer instead of alu to create a good electrostatic shield as well.

Best,
N-set



Cheers,
Jarek
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