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In Reply to: RE: OK now I am totally confused... posted by Lew on June 05, 2012 at 07:01:19
The reason you can reduce the capacitor value is that the resistor and cap set the crossover frequency, without the resistor the impedance of the circuit at the crossover frequency is considerably higher. In fact so much higher that I suspect that 10-15uf is closer to the mark.
The transformer can be saturated by low frequencies but saturation is very different from actual damage. I think you will find it pretty hard to damage the transformer! Saturation, OTHO will manifest as temporary distortion on transients. If you were able to keep the transformer in saturation, eventually you could overheat it but it would sound bad and most reasonable audiophiles would turn the volume down at that point so there would be no time from the transformer to heat up enough for actual damage. Just my opinion mind you, but damaging the transformer seems remote, and if you have the cap (above) installed its just not going to happen.
This will result in a bumpy impedance curve. In stock form the speaker has a fairly flat curve through the midrange, caused by that resistor, and that curve is hard to drive because the resistor is where most of the power is going- that is why its rated with such a large wattage. However it appears that even transistor amps benefit from getting rid of the resistor, despite the resulting impedance curve! That is because the energy made by the amp is radiated into the room rather than being converted to heat.
Follow Ups:
the reason for the 24 uF is that i had a few on hand from the old crossover, but it is obviously way too big grrr. So the resistor is back in the circuit and the PIO as well. Is there a reasonable way to determine what cap i need in series of the torroid to make this work? If i could get it sound good with the torroid, i would not bother with the AU90 transformer. Because of the whole setup i is too hard on the MA-1s, I have not put the MA-1 back i am using the big-ass Llano CAS-300s in a vertical biamp mode.dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
Edits: 06/06/12
What is a "Llano CAS300"? If it is a solid state amp and you like it, just put everything back to stock and enjoy it. If your speaker sounded lousy just from removing the parallel resistance and changing the capacitance from 36 to 24, then something else is wrong, probably having to do with hook-up. I cannot make a diagnosis at this distance, unless you tell us more. Most of all, the mod should not have made the sound worse with the MA1; the sound should be better.
it is a bit of a pain to get them back behind the speakers....
I thought the solid state thing would work just fine too without the resistor. I could try the experiment again with the grond lifted off the resistor :) Makes a pretty good soldering post. I was somewhat surprised. I do not like the Llano that much, i bought the MA-1s because i want to use them with the A1s...but they just run out of juice with the current crossover in the backpanel.
let you know what i find.
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
i think i need to get some drawings done and post it...really weird
dee
;-D
.
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
How were you able to tell the cap was too big? What did it sound like?
:)
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
And taking the cap out sorted that out??
But putting back the 8 ohm resistor in parallel with the torrid and the 36 uF in series.Dee
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
Edits: 06/07/12
So - reinstalling the original parts is what worked?
which makes me confused again...it seems like i am getting confused left and right by this thing....after all there is no DC going into the torroid from the apm, there is a series cap in there, unless there was something wrong with the cap i was using....but it measures 23.64 uF does not show a short or any issues...I am using the Llano in a vertical bi-amp. I have two stereo units. but if they work with the normal 36 uF (really big ass oil cap) 8 ohm high pass filter in form of the torroid, it should work without it, unless there is something very strange is going on. I will keep looking at and try just lifting the resistor off the ground so only the 36 uF cap is in series. but not tonight. Now i only did one of the backplates...maybe i will try the other one and see if there is a difference.
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
It might be that the higher impedance of the speaker is limiting the power of the amps. Solid state amps can double power as the impedance is cut in half which is another way of saying that if you double the impedance the power is cut in half. That is why tube amps are usually preferred on Sound Labs- they don't loose so much power into the higher impedances (so you have power to play the bass).
It might be that you are simply clipping the amps?
Interesting. the beast can put 300W/channel into 8 ohms and double when going down to 2 ohms to 1200Ws has more FETs in it than a doughnut shop has cops...but let's say it could only put out 35 w into 64 ohms? due to maxing out to the rail voltage? but even 35W would be really loud, would it not be? And i was not changing the volume. between resistor in and out..It would almost seem that this mod would make the speakers SS amp unfriendly, right? What puzzles me is why does the distortion go away when i put back the BAR (Big Ass Resistor)
Should i just say screw it take out the resistor, put the MA-1s in place and never look back?
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
I put this idea on SLOG a few hours ago. It is possible that your SS amplifier is unstable when asked to drive the capacitative load of the SL speaker without the resistor in the circuit. This has nothing or very little to do with its power capability. Some SS amplifiers decompensate when asked to drive such a load. The presence of the resistor in the circuit ameliorates the capacitative nature of the SL speaker, over all. (I believe that Dr. West even gives this as one reason not to remove the resistor.) When you remove the resistor, the speaker becomes, essentially, one huge capacitor. SS amps don't like to drive capacitors. One notable example is Krell, maybe not the current models, but in the old days they were notorious for shutting down when driving ESLs.
On SLOG, I suggested you might try to borrow a Parasound or Pass amplifier. Both of those are probably OK with the capacitance of the SL speaker load. Later I thought maybe you might try horizontal bi-amping, instead of vertical. Just for the heck of it.
blow the dust off the MA1 and put it in service. I like the sound of the tubes better anyway
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
I am not buying the Amp SS or tube not working....
From the work i have done on All ESLs.....in these setup of the high frc tranfourmer..With the res. Caps.in front an then caps in the mixer....this sets up a push-back to the amps Tube are SS... Not with this new mod..pulling the res. an cap OUT....this is OVERCOME...now i have a pr of 50watt amps driving my set today....thay have NEVER sounded so good as with this mod..before the mod...i could not get the speakers play with 500watt amp... like thay sound with 50watts ...gofig
But however all a esl is Bias...heres a way to test an get the right bias on Any ESL...
put a 2ohm 20 watt res. in the neg input leg of the base tranfourmer... then setup you speaker like you play them get you bias set like Dr. west tell all to do then play cds an the after 10 min...tuch the res.. if the bias is low the 2ohm res well be hot...if all is well the res. well just be worm...
this has work for me for years....the res. was put in to the Acoustat to help with the base tranfourmer overlode..the res get hot not the tranfourmer...Play my setup loude... 2ohms get just worm.....goodluck
Edits: 06/09/12
Maybe :)
I think those that are on the SLOG forum can say better, but as I understand it this mod is helpful for solid state amps too, as the resistor is absorbs substantial amplifier power.
But I am finding out that not everyone who is excited by this idea has a thorough understanding of what they are doing when fiddling with the crossover and the transformers, and I do not wish to be responsible for the possible negative consequences of that. However, I agree it would sound very bad long before the transformer would actually burn up.
Contrary to one small element in your post, I found that the impedance curve of my speaker is more flat now through the midrange than it was "before". If you look at the measurements made by Kevin Covi about 10 years ago, the parallel resistor created an impedance dip around 500 to 1kHz. This caused a midrange "suck-out" when driving the SLs with your OTLs that was always audible despite all my prior efforts to fix it, including the use of the Zero Autoformers. (That suck-out was probably not evident if one drives the old crossover with a solid state amplifier, as does Sound Lab at their factory.) The midrange dip in the speaker response is completely gone once I converted fully to the Australian transformer (and even just by removing the resistor from the input of the SL toroid), and if you will review the measurements I made, this audible result is concomitant with the fairly stable impedance from around 400 Hz up to 2kHz (using the AU transformer).
This is what Dr. West sent me late last year, which is probably a lot more recent.
The one with the peak is with no resistor if I have his notes right. Sorry for the bad resolution but this is how I got it. So I have base a lot of my conjecture on this chart, but it is quite clear that it probably does not represent all speakers- probably just the newer ones. That peak though being up to 40 ohms says to me that the cap can be about 1/4-1/3 of its original value in those models after the resistor is removed.
Since I can see none of the numbers on the X or Y axes, and since the curves are not labeled, the graph means little to me, except to say that my measurements are nothing like that, assuming the bottom two curves are of impedance. There is no such huge peak at whatever frequency that is, with no resistor, using either their toroid or the AU transformer. My speakers were built in late spring of 2011. Anyway, if that peak is up to 40 ohms, then the impedance at lower and higher frequencies would appear to be too low to be ideal for our amplifiers. Looks like 5 to 10 ohms mostly. OK for an MA2 but nothing lesser.Edit: After sleeping on this post overnight, I decided that I over-stated the problem. In fact, an MA1 should also be able to drive the load(s) represented in that graph. (I think the lower two curves show impedance vs frequency, and the upper two curves show amplitude in db vs frequency.) But things get a lot better than suggested by those data, when one removes the parallel resistance in the hi-pass filter, which was my main point.
Edits: 06/06/12
Right!
We have enough people using MA-1s with the Sound Lab to know that they do work :) Doing the mod really helps them out
The big increments on the graph are 5 ohms. You can see on the left that the scale goes from double digits down to one single, and Roger mentioned something to me about a 40 ohm peak, which does correspond to the graph. That puts the minimum impedance of the bass transformer at about 7 ohms. The far right side of the chart appears to be 20KHz. I suspect that with all the other mods (not just the resistor) that 1.5-2 ohm value comes up a little.
I posted my own numbers for impedance vs frequency on SLOG, I think. You can see that my new 845PXs with the AU transformer and no resistor/no capacitor never get anywhere near to being as low as 5 or 7 ohms, except above 2kHz. Having measured two different speakers, my own plus my neighbor's U2PXs, I have come to believe that there are differences among the speakers probably in relation to the many versions of the stators, the diaphragm coating, the mylar, etc, that SL has experimented with over years. (The U2PXs had been upgraded to full PX about 4-5 years ago.) Also, although I did not do any direct measurements to prove it, I believe the impedance will vary according to the setting of the bias voltage. If so, no two speakers will ever be exactly alike.But the important point is that there is NO huge impedance peak in the curve for my speakers OR those U2PXs. (40 ohms is 5X to 8X the baseline of 5 to 10 ohms that is shown in the graph you posted.) The bass transformer, which is the same whether or not one uses the new mod, never gets anywhere near 7 ohms in my speakers (at all frequencies, the impedances I measured were higher), perhaps because I measured without the parallel resistor (which would tend to bring down the impedance as the natural impedance of the spkr is also falling with rising frequency). I did not measure with the parallel resistor in place. In fact, since a resistor would be expected to have a linear effect with frequency upon impedance, I don't see how removing a resistor could give you such a huge peak where there was none WITH the resistor, except to guess that it causes some aberrant resonance in the toroidal treble transformer, which is maybe why RW wants us to use the resistor with the toroid. This reveals an issue with the toroid, not an issue with the speaker itself.
Edits: 06/07/12
I don't see how removing a resistor could give you such a huge peak where there was none WITH the resistor, except to guess that it causes some aberrant resonance in the toroidal treble transformer
The resistor does 'linearize' the impedance curve, without it the transformer expresses its natural inclination to have a high impedance at the lower end of its range. It does this at a different range of frequencies than the bass transformer because its wound differently.
I'm thinking that there are variances in the transformers used as well as variances in panel spacing, materials and the like.
You wrote, "without it the transformer expresses its natural inclination to have a high impedance at the lower end of its range. It does this at a different range of frequencies than the bass transformer because its wound differently."
This is all true, but if you measure overall speaker impedance with both transformers hooked up and the parallel resistor and the series capacitor in front of the treble transformer and the series inductor in front of the bass transformer, the removal of the resistor (only) should not cause that peak, unless there is something else going on peculiar to the toroidal treble transformer. This is my point. How do you "wind" a transformer so it gives you a resonant peak at upper midrange frequencies? This is not something you do on purpose, I would think.
I think it has mostly to do with the turns ratio and the capacitance of the speaker. I'm pretty sure if you removed that transformer from the speaker you would find no such peak :) I'm pretty sure the bass transformer plays a role too.
"The bass transformer, which is the same whether or not one uses the new mod, never gets anywhere near 7 ohms in my speakers (at all frequencies, the impedances I measured were higher),"
I have info from one SLOG member who told me that the bass transformer DCR has changed over the years. I suppose it is hard to ensure uniformity through the years.
DCR would have little to do with large differences in speaker impedance except maybe it's an indication that they also played with the turns ratio over the years. The turns ratio is by far the primary determinant of the impedance seen by the amplifier, but a change in turns ratio would probably be reflected in a small change in DCR.
Right. IOW this has to do with how the driver interacts with the transformer. I'm not sure I'm on board with the idea that the peak represents a resonance. If that were the case then bass would really be a problem with our amps since the impedance is so high in the bass, but its not.
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