I can't believe I just read this whole thread.
The OP bought used amps and likes the way they sound with his speakers. He then goes to great lengths questioning if they were originally sold in contravention to FTC regulations? Weird.
I agree with Zennie. It's time to chill and enjoy the music.
1. They are used amps for chrissake, tested under unknown conditions.
2. In any event, truly needing any more than 500W into 8 ohms or 726W into 4 ohms is simply an indication of poor life choices when choosing squawkers.
The OP bought used amps and likes the way they sound with his speakers. He then goes to great lengths questioning if they were originally sold in contravention to FTC regulations? Weird.
I agree with Zennie. It's time to chill and enjoy the music.
1. They are used amps for chrissake, tested under unknown conditions.
2. In any event, truly needing any more than 500W into 8 ohms or 726W into 4 ohms is simply an indication of poor life choices when choosing squawkers.
It's a 240 Volts AC version and on behalf of the former owner the bias has been turned down to that value.
I'm still waiting for answers from the engineer how he conducted the the measurements, under which conditions and if he didn't find it strange why both amplifiers did not reach there specified values for power output at 8 and 4 Ohms.
In Germany the AC voltage in 2015 was already 230 Volts that's all I know. So there's a a possibility that he conducted the tests with a very bad 230 Volt AC line that would explain the 725 Watts, 1% THD rating at 4 Ohms for both amplifiers. He's in business for over 20 years and he serviced a pair of Krell KMA mk 2's which I had for a brief time that couldn't be repaired by a local highend repairservice and serviced a pair of Krell KRS-100's and both labreports of these amplifiers exceeded their specified ratings by a big margin. He seems to have serviced some more Pass Labs amps because he stated at the end of page 2:
"Die Bandbreidte ist aufällig wi bei vielen Pass Verstärker ehr bescheiden." meaning: "The bandwidth is something special because it's confined like with many Pass amplifiers." That suggests he has more experience with Pass Labs amplifiers.
Did I? Don't think that was my main point.
I covered that by the analogy of a bought muscle car specified to have 500 HP and when the owner had it on an Dyno the output was only 250 HP.
When confronted by the owner the seller says: "Well you can't drive any faster than 75 mph in the US so you won't need the 500 HP to reach that speed, so don't mock about that." Obviously the seller has a good point and probably the owner will realize he made a poor life choice and is indeed a squawker....
Suggestion:
Just ask that engineer of yours to re-wire the primary windings for 220V AC and properly set the quiescent current. Increasing the quiescent current may even change the sound character to your liking because at the moment... the H2 vs H3 ratio does not seem right (from one of your measured specsheet screen-shots you posted earlier).
As pointed out, several times already, but seems not enough: this amplifier is modified with decreased bias. How on earth can anybody expect factory declared performance?
Reducing bias in an A class amplifier, results in higher distortion and reaching 1% earlier than with higher bias. With low bias, H3 is considerably increased, especially after leaving A class envelope which is the case at max. power levels, making main contribution to measured 1% at lower output power levels.
That’s my understanding of this ‘mystery’. 😉
Reducing bias in an A class amplifier, results in higher distortion and reaching 1% earlier than with higher bias. With low bias, H3 is considerably increased, especially after leaving A class envelope which is the case at max. power levels, making main contribution to measured 1% at lower output power levels.
That’s my understanding of this ‘mystery’. 😉
Okay thanks for the suggestion.
I've seen the graphs of Nelson Pass supplied wit his Technical Article 'Leaving Class A'
So you probably right there but I'm truly satisfied with the performance I have now with the lower bias setting and the bonus of a lower AC intake ;-).
I've also never run out of power even with my inefficient and low impedance speakers so that's not a problem also for me.
Just for the record and not directed to you but to all:
I'm very very satisfied with these amps, they're the best I ever had and even if they're not performing as advertised I would still keep them.
Just wondered why the 500 Watts at 4 Ohm seem to have gone and as I found out in this thread it has probably something to do with the way the engineer conducted the powerrating tests so I asked him yesterday to shed some light on it.
I'm not in any way implying that Pass Labs made false claims about the advertised power ratings although the way that they are represented without much context under which conditions they were made, leaves some margin for speculating as some members did.
Nelson Pass himself stated these where RMS values over the entire audio range made with a undistorted AC line and that gave some more context.
As soon as the engineer who made the measurements with my amps respond, I will let you know what he has to say about it.
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Probably a case of unreported maximum power, not a case of missing power. Due to previous user preference, bias setting was lowered. Tested at unspecified mains voltage (most probably < 240) shows 1% THD into 4Ω point was reached at much lower 792W. However, the amp would still have quite a bit more power in reserve before clipping albeit at THD > 1% which unfortunately was not reported.
Ok, let us know how it performs......
A DIY-project for such a device could be interesting.
In principle they are simple.
As far as I know the rectified mains is used for two powerful class A/B amps that are driven in differential mode to achieve the needed output voltage swing. Then a fairly clean digital sinus is used as input. Then one amp gets the sinus in phase and the other in reverse phase.
Flogging dead horses seems to be a thing on forums.
Even when the higher level ins and outs have been already discussed many times, literature has been shared conclusions have been made.
It's sometimes like people don't seem to notice?
Even more so when other important questions are being ignored.
I would personally care an awful lot more about compliance then an amplifier that seems to perform a little less. Especially from a device with this price tag.
From the engineer who made the measurements:
"All line measurements are made here with an AUDIO PRECISION SYS 2322: https://www.amb.org/ap/sys2322/
If the input is made via cinch, then of course pin 3 and 1 in the XLR socket are shorted.
As far as the results for the power measurement are concerned, I often have big differences with many devices compared to the specifications by the manufacturer.
Reasons for this:
"All line measurements are made here with an AUDIO PRECISION SYS 2322: https://www.amb.org/ap/sys2322/
If the input is made via cinch, then of course pin 3 and 1 in the XLR socket are shorted.
As far as the results for the power measurement are concerned, I often have big differences with many devices compared to the specifications by the manufacturer.
Reasons for this:
- Output stage runs on 240V (see type plate) We usually have around 225V here in the laboratory.
- Mosfets have a much higher internal resistance than bipolar transistors, therefore also higher losses lower impedances.
- The performance in the limit range (1%) can increase significantly if you only slightly exceed 1%. (I have already had amplifiers here that had more than 50% more power at 1.3%)
- The X600.5 are technically bridged stages and therefore there are 2 amplifiers in the signal path and internal resistance is even further increased.
- The manufacturers often polish up the output information. It just sounds great if the output stage doubles the poweroutput when the impedance is halved, but this is rarely the case in practice.
"All line measurements are made here with an AUDIO PRECISION SYS 2322 shoul be of course:
"All power measurements are made here with an AUDIO PRECISION SYS 2322
"All power measurements are made here with an AUDIO PRECISION SYS 2322
So PWK used qualifications as ******** for competitors that made outlandish claims in his eyes.Hope after after-lunch coffee I'll be able to determine on which side of verge of Trolling you're now
Ha ..... just trying to imagine reaction of Tim de P. or PWK, in case that this is discussion of their product
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Question should be how this felt for his audo colleagues when confronted by his ******** remarks...
I'm sure , neither he nor Tim de P. bothered further
in short - "I did my work, you go and learn your Drek"
in short - "I did my work, you go and learn your Drek"
I just finished my lunch and coffee is steaming on my desk. I have determined that RobertS61 is keeping his mind and eyes wide shut.
Explanation from the engineer is ‘run the mill’ blabbering, he has at ready to fend off time consuming customer questions.
Right question is was he aware that he’s takin measurement on an A class amplifier with reduced bias, at 10% less mains voltage than required? He should be perfectly aware what that means for taken measurements and mention that in his report, if he really is a professional. I’m not convinced he is.
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