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Correction on Minimum Ripple

71.50.25.51
Posted on June 9, 2015 at 16:51:08
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Hello,

Earlier this month, I suggested, from many years of PSUD2 modeling, that 850 mVAC was the maximum ripple that was acceptable on a 2A3 SE amp.

Now, I THINK I can see that I was wrong.

I was not actually measuring 2A3 amps, but simply PSUD 2 simulating supplies, since 2006.

I just fired-up ( for the first time today ) a Type 45 SE amp, which I had carefully simulated and PSUD 2 predicted it at about 550 mVAC ripple P-P, feeding the Finals stages.

I was "astounded" when my Fluke DMM read 155-180 mVAC as the ripple feeding the Finals stages !!! Heck, actual measured ripple was 1/3 of PSUD 2 predicted ripple. Does anyone know whats going on, and can they explain it to me ?? Peak to Peak, RMS or ??. All other operating voltages, and currents, appear to be spot-on as to how I had computed it .

Its a Fluke 8020B / AG multimeter, never calibrated. I can also check this supply tomorrow with a Fluke 8060A "big dog" meter.

What gives, better techies,...... any ideas ??

Jeff Medwin

 

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RE: Correction on Minimum Ripple, posted on June 9, 2015 at 18:35:17
Paul Joppa
Industry Professional

Posts: 7295
Location: Seattle, WA
Joined: April 23, 2001
 Most meters read rms. 155-180mVrms is 438-509mVp-p, so PSUD was pretty close. PSUD shows an rms value at the far right of the data section. If you did not include the primary DCR adjusted by turns ratio squared when simulating the power transformer, that might cover the rest of the difference.

155-180mV at the finals, assuming a 20:1 turns ratio in the OPT and allowing for the tube's rp, still leaves 5-7mV hum in the output, which I (and a noticeable portion of Bottlehead's customers) find excessive if the speakers are more than around 98dB/w/m efficiency. But many with lower-efficiency speakers are not bothered by it at all. Hum is fortunately not correlated with signal envelope fluctuations so, like vinyl surface noise, it is easier to ignore than some seemingly more subtle issues.

 

RE: Correction on Minimum Ripple, posted on June 9, 2015 at 20:12:27
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Paul,

Thanks, just what I was looking for .

Yes, I actually do take the turns ratio and DCR of primary and secondary into account. I thought it was something simple - like Peak to Peak vs RMS, but you, and one other helpful person, nicely confirmed it for me.

Like so :


" The 550 is peak to peak. 550/2 = 275 peak. RMS (what you meter reads) is peak times .707

275 X .707 = 194mv ac rms so the PSUD was not that far off.

You see, all this stuff is really just a matter of math and science. :-)"

Well, I am breaking-in this 45 DC amp on Willie Nelson and Johnnie Cash tonight. Need to tube - test all my RCA and Telefunken smooth plate 12AX7s, and get the best in there. Am pleased with the presentation so far, the 45 is pristine in a good DC amp. Only three hours on it, heck - the solder joints aren't even settled-in !!

Jeff Medwin

 

RE: Correction on Minimum Ripple, posted on June 10, 2015 at 02:00:49
Frihed89
Audiophile

Posts: 15703
Location: Copenhagen
Joined: March 21, 2005
 You are looking at ripple reduction from a measurement standpoint and then correlating it with the noise people hear through high efficiency speakers. Could some of that noise we hear be coming from someplace else, like low frequency noise from the power line and DC offset that makes transformers hum? I'm not sure if powerline conditioners take care of this and i am not sure you can detect this additional noise at the output without being able to experimentally isolate with some kind of external filter. So maybe this is just a non-sequitor.

 

RE: Correction on Minimum Ripple, posted on June 10, 2015 at 05:27:32
deathtube 667
 Look at the small H chokes and amount of uF's in the filtering.

That is most likely the issue causing some mVAC at the OPT secondaries.

If you sit far enough back from the speakers, it is probably not a big deal once the music is playing loud enough.

If you need a really quiet SE 45 amp, try active parafeed finals with C4S plate loads.



 

Yes indeed ..., posted on June 10, 2015 at 13:19:15
Paul Joppa
Industry Professional

Posts: 7295
Location: Seattle, WA
Joined: April 23, 2001
 ... hum (and buzz) have very many possible causes, even if this particular discussion focuses on just one of them. Sorting them out is always going to be a challenge :^)

 

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