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anthony
Posts 242
Joined on 08-18-2014

Post #: 181
Post ID: 25589
Reply to: 25588
More to do
 Romy the Cat wrote:
Anthony, 
 
First, your measurements again the “appropriate load resistor” has very little practical meaning. The drivers is a dynamic system that has impedance not resistance and the impedance varies with frequency. So, your measurement against 1R might be accurate for 30.5Hz but might not be accurate at 24.7Hz. So, the proper number at which the clipping might take place would be observable at the real load, or the real driver(s) you use.


I agree completely, of course.  I made these measurements with the purpose of checking the input voltage levels that I should aim for with the pre-amp project.  A secondary motive was to make sure the Bass OPT was doing something like the job it is supposed.  To be honest, driving sinewaves at circa 5V into the DSET is LOUD, so I have ordered and now received some appropriate load resistors for all channels so that I can be more thorough with re-testing without making my ears ring.

If I look at the impedance/frequency/phase plot of the Bass Cannons (below), 18Hz is pretty close to the most difficult load that amplifier channel will see.  Most of the passband is in resonance so *should* be easier to drive, however I do plan to re-do the measurements using the Cannons as the load.

DATS First Cannon (Left).jpg



 Romy the Cat wrote:

  
Then there is a definition of clipping. The clipping is situation when a channel has no power to drive the driver but power is current and voltage. You should not be concerned about juts clipping but you need to assure a SYMMETRIC clipping against you real driver across the whole range of the channel. You need to connect a scope to the channel output while driving your driver and drive a single frequency from a generator and increase the input voltage. Observe the shape of the sinusoid and as the input voltage rise you will see that the top or bottom of the sinusoid will bet distorted, or clipped, or flatted down. The top of the sinusoid is voltage insufficiency and the bottom of sinusoid is current insufficiency (or vise versa, I do not remember already). So, you objective should be to get the absolutely symmetric clipping point when the current and voltage clip at the same time. Then it means that you get out of you amp the max power again your given load. 
  


My procedure was pretty much as you described: put a sinewave into the DSET, watched that sine on the oscilloscope (software), change the voltage level to find when the top or bottom or both of the sine starts to flatten.  Not all channels showed symmetrical clipping and I cannot accurately remember how the Bass Channel clipped, but I think it was the bottom of the sine first having problems and will certainly take more notice when I re-do the measurements now that I have more load resistors to quieten the room.

 Romy the Cat wrote:

  
Second important aspect is that if you deal with an amplifiers then you need to understand when clipping comes from. If might come from many locations. The PS in driver stage, the coupling (in case transformers use), or the output stage PS, or the OPT and so on… The Milq was designed in a way that the any power restrictions are coming from output transformers, the way how SET should be designed and the DSET topology would take care of that limitation. So, the primary focus of your in the given topology should be the only the Channel A output stage. If looks like you beef up enough inductance in you OPT of the Channel A, which is good, not you need to make sure that you can pump power to the output tube. Here is there is another limitation. The 6C33C is indirectly heated tube and they type of tube as the enter to the operation what grid voltage approaches to bias voltage (class A2 or the mode of grid currents)  then this type of tubes do not do so well and they distort rather hard. The direct heated tubes if you feed them with enough current they can push through a little bit but the indirect heated cannot.  You it should be very important to you that in your case your Channel A as the input voltage goes up the Channel stags in Class A1 and the input voltage in the grid of 6C33C does not rise to the rise voltage. In fact, knowing how the Milq is designed this would be the ONLY measurement that I would care as it ejectively demonstrate the efficiency of you LF speakers projected to the acoustic size of you listening room.  I had  at my site a post where I described the measurements I took and posted my measurements in my room.  Here it is:

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PageIndex=1&postID=6057#6057


Thanks Romy.  This is the stuff of which I am uncertain.  I'll work through it...I think it is important for me to understand this aspect of the design, and also to evaluate the Bass OPT.
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