captainbeefheart

Judge bangs the gavel - "court is adjourned" The reason the amps still sound good is because most with Klipsch amps 15 watts is plenty but also the amp can produce the mid range to over 70 watts and the gross amounts of low frequency distortion are non-linear giving lower order even harmonics which sound harmonious being only an octave above the fundamental. It's like the old console amps or old tube budget amps with tiny output transformers, they still sounded good but show very high distortion at low frequencies. It's still a great sounding amp I am certain, it's just they marketed it maliciously as a true 75 watt hifi tube amp that puts out full power at 20Hz with low distortion <1% I still blame Frank, he markets these and is raking in the money from them. And they lied about the output transformer metallurgy when asked about the tiny output transformers. Unbelievable.

Well that's just it, many times these imperfections albeit are not suppose to be there and are not "faithful" to their inputs but sound good or are just benign. So you are correct in that even though technically it's an imperfection it's total effect on the overall acoustic output is either benign enough to not notice or the imperfection sounds good and adds something unique to the sound. Like harmonic distortion, not all distortion is dissonant, lower even orders are harmonious and somewhat benign, some even like the addition to 'warm' things up. It reminds me of people that give rave reviews of tube amps with tiny output transformers that tell us the bass is amazing. When in reality the core size isn't large enough to pass the low frequencies faithfully and the trailing edge falls apart giving rise to non-linear distortion. Well, non-linear distortion produces even harmonics and so at low frequencies this added harmonic distortion content fattens up the sound but is harmonious only being an octave above the fundamental. So something technically bad and is far from a faithful reproduction of it's input still sounds good. I have measured this many times on amps with small output transformers, distortion at 35Hz being 20% but still sounds good. Of course these amps shouldn't truly be called "hifi" many people like them. Not sure if you are following the Crimson 275 debacle but take that amp for example, people love the sound of it but the designer used over 600v for the plates and a load line to produce over 70 watts output but they use a 15 watt output transformer. The amp produces 75 watts with 2.8% THD at 1kHz, but at 35Hz and 32 watts output the distortion rises to 27%. People are just in disbelief of the specs but this was common with old console amps and such where output transformers would distort low frequencies but the amps still sounded great. There are some members here that have the Crimson 275 and love it but are a little miffed about the specs because the company are somewhat misleading with the specs, people are expecting less than 1% THD at 20Hz with 75 watts output. The stereo amp weighs 19 pounds, that should have a been a red flag right there.

There is a point where it doesn't sound like a delay and that's what they call a chorus effect because the time delay is so fast the two signals are almost in unison. In pro audio I believe anything over a 5mS delay is considered a 'delay' effect and that's where you can actually start to hear the second signal after the first. Anything under 5mS is considered a 'chorus' effect, like many people singing at the same time, the time delay is so fast it doesn't sound like a delay effect, it has a different sound to it that's hard to explain but sounds really good with instruments. It has a shimmering like rich tone to it that just sounds great. Here is a link explaining it but more importantly there is an audio clip on the page that has a guitar player playing a riff without it and then with it, you do not perceive it as a delay but it is still very audible. https://en.wikipedia.org/wiki/Chorus_(audio_effect)#Electronic_effect

I disagree. And millions of musicians will too. For example one of my analog 'Chorus' effects has adjustable time delays between 600uS and 10mS and you can hear the difference between them. 10mS is just too long and sounds more like a 'delay' effect than an actual chorus effect. I like it set to 1mS, with this setting I can clearly hear the difference between the effect on vs off.

Look at the frequency response on a Bode plot of all the outputs summed and you will see the stop band section of each filter crosses over one another at the "crossover" frequency. I believe this is where the name came from. The stop band section of the high pass filter network will crossover into the stop band section of the low pass filter network.

Phase is mostly relevant when two or more drivers are overlapped (at the crossover frequencies) and sum as the total acoustic output from each driver. This is most important during transients with fast rise times like a square wave, if each contributing driver is reaching it's peak at different times from phase lag in the networks then the wave forms will reach your ears at different times. My guess is these peaks reaching the ear at different times creates an apparent Doppler like frequency shift similar to vibrato effects. It may also have a similar delay effect, short delays are called chorus effects where it sounds full and pleasing similar to the vibrato. Probably explains why people have heard awful time aligned speakers and like the sounds of them. Sometimes technically perfect things aren't always best, or are they?

What frequency and amplitude is the ripple at the output? That may help us track the source down. There is a voltage divider coming off the 225v node, 390k and 39k 39000 / (39000+ 3900000) = .09 .09 * 225 = 20v So the heater center tap is elevated to 20vdc

Thank you! I try and bring some sanity to some of the more subjective topics in audio like capacitors and cables, which honestly are fairly objective when getting down to the details. Always good to know a lawyer

Multiplexer ? Basically taking information and splitting the output ports by frequency

Don't forget the cathode voltage across the cathode resistor is derived from the sum of plate current and screen current, So if you aim for 12 watts dissipation your really at around 11 watts. So even if you are getting something like 12v on the cathode with the 150 ohm cathode resistor and you calculate out 13 watts, don't panic because your really not quite there because of the screen current. You can of course measure the screen current and deduct it from the combined cathode current you calculate and get a more precise dissipation but as long as you understand this concept I don't bother, I just make sure I am 13 watts or under on the calculations and I can sleep sound at night knowing the tubes are within their maximum ratings. I have had tubes running like this for years, it's when things go unchecked and your at 120% max dissipation or more the tubes just burn out quick.

The reason why I said these amps run the tubes near max dissipation is because you pretty much have to with cathode bias or else when they go into Class B you will get some nasty crossover distortion. Ideally you want to bias these amps for around 11-12 watts plate dissipation, the tubes will last longer and you don't get the crossover distortion. It's when these amps push the tubes well past 12 watts is when the tubes crap out once a year, it's just too much for them. Also tubes back then lasted longer and took more abuse for the most part. I see people chasing their tails upping the cathode resistor because with less current the B+ increases and you kinda end up back to where you were in regard to dissipation. Except now you have pushed the operating point over to where you will get crossover distortion so it's a lose lose situation, you don't really reduce dissipation but you lower the current changing the operating point making it sound awful from the crossover distortion. The only way to fix these amplifiers is to reduce the B+ to the output transformer. I still like to use 150 ohms, with 11 volts at cathode your at 37mA per tube which puts your target plate voltage around 335v for 12 watts dissipation. 335 - 11 = 324 11/150 = .073 .073 / 2 = .037 or 37mA 12 watts / .037 = 324 volts So when I reduced the B+ I had a goal of getting ~335v on the plates.

This is why we do what we do. Some may think it's to poke holes in peoples gear but that just is not the case, we are only trying to keep the manufacturers from taking advantage of consumers. The worst part is some of these larger corporations have the money to threaten slander and have these types of informative threads taken down. If a company is being deceptive in their marketing it's only fair to get the word out so people can make an educated decision on whether to purchase the product or not. If you decide to keep the amp after the smoke clears I would just save some money and have a tech install some real output transformers that can handle the power that circuit can provide. Then you will truly have one killer amplifier for only a few hundred bucks more. https://edcorusa.com/collections/tube-amplifier-push-pull-output-transformer/products/cxpp70-3-5k-70w-3-5k-ohms-push-pull-tube-output-transformer I wouldn't even put them under the cover. I would have Edcor send black end bells and go to Napa and have them match up the red color the 275 uses and paint the end bells the same color. Black would look nice too but just a little extra effort I think in matching the chassis red color on the end bells would look really nice.

I take it half the screws (nuts) are under the PCB board? Ya that's a pain in the butt and don't blame you for just waiting. Looks kinda like the board can be flipped over somewhat easily but ya still a pain in the butt.

One more thing to throw into this mess is the fact that in the specs list power at different output load impedances yet the output transformer does not have separate secondary taps for different loads. If you use a single impedance tap for two different loads, say 4 and 8 ohm loads you certainly will not have the same power or distortion figures respectively. For this amplifier to claim such a thing it would need separate secondary taps for different loads in order to reflect the same primary load to the tubes. With one tap you are reflecting different loads to the power tubes (halve or double) which will give very different load lines and subsequent different performance specs. This thing just gets weirder and weirder. Oh I went back and read about what people were saying about the peak power in the owners manual, they extrapolated the data from the fuse section where they discuss power in peak terms for music. I don't think this is a valid enough connection to conclude the output power specs are in peak. The math doesn't even work out for what is measured to claiming the 75 watts is peak power, I truly believe because they get 75 watts RMS out at 1kHz with 2.5% THD that is how they are rating the amplifier which is still bogus because we want the power rating to be where distortion and bandwidth all coincide with each other which would make this a true 15 watt amplifier.

I am still hoping the owner removes the output transformer cover so we can see the output transformers, it's just 4 screws and probably take all of 10 minutes.

I don't know when you purchased the amplifier but do still have the owners manual? Some have stated that the newer owners manuals states that the 75 watts of power is 'PEAK' power which would explain the 15 watt continuous power actual rating. I am very interested if you can find where it says this in the owners manual, it would explain a lot and in fact settle this whole debacle.

Yes those poor tubes were screaming away at 15-16 watts plate dissipation. The plate voltage being too high was the main problem, higher than the schematic says which should be 345-ish. Even still the cathode resistor they chose is a little on the low side, I find 150 tends to work better for most EL84's which is slightly higher than 130 ohms most datasheets call for. So between lowering the B+ and using 150R on the cathodes they biased up much better. You're still near max plate dissipation but that's what this amp wants. I didn't increase that big 10 watt 100 ohm resistor like some people I read do because it sagged the amp down too much during testing so I went with a zener string on the high voltage secondary center tap. I was on the fence of adding bucking transformers but never did it. I know you gutted it and re-wired. I have found on many of these amps you sometimes get noise issues that can drive you nuts, it ends up being a poor ground connection from the tag boards because they use a rivet to mount them to the chassis and that grounded lug is what's used to ground the circuit. I drilled the rivets out, cleaned the oxidation and used hardware with lock washers and little loctite on threads.

They weigh 19lbs Absolutely no way a 75 watts per channel all tube stereo amplifier that gets full power down to 20Hz with less than 1% THD only weighs 19 pounds. Two output transformers for that much power down to 20Hz would weigh around 25 pounds.

That's all it boils down to is if you really like the amplifier who cares about the specs. It obviously isn't cool the way they advertise the specs but this isn't anything new in the amplifier business. The reason McIntosh held their clinics was for this very purpose. For many of us 18 watts is more than enough, and as noted the 275 can put out more power, just at a reduced quality. With 104db speakers you never probably got the amp into the poor performance region. It's kinda slightly better than having a straight up 18 watt amplifier because with say a transient the 18 watt amp would go into clipping with anything past 18 watts where the 275 will at least push more power but the distortion of course is high. Basically I don't think anyone here is questioning the actual sound quality of the amplifier, it's just designed and marketed poorly. Well, marketed poorly for the consumer but great for sales and profits.

This would be very helpful to many people that have either purchased the amplifier or are thinking of buying one. It's also very generous to not only test the amp but also pay shipping one way. Honestly it's only 4 screws holding the transformer cover on, a couple pictures of the output transformer will instantly tell us what it is capable of. Obviously that wouldn't be as definitive as actual test measurements but darn close enough for what we need to know.

Here is how it is advertised. As you notice each spec is separated, they never say it puts out 75 watts from 24Hz to 28kHz at less than 1% THD.

They are not stupid people, they kinda covered their behinds, I'll explain. Because of the load impedance and high plate voltage it can put out 75 watts, BUT really only in the midrange and with a ridiculously high amount of distortion because the transformer is saturated and does not have enough energy to faithfully maintain reproduce the signal cleanly. Notice how they list the specs for the amplifier, they do not say "less than 1% THD at full rated output power and bandwidth". They just list everything separately like; Power - 75 watts Distortion - <1% Bandwidth - etc............ That way there they can say "well it does put out 75 watts" or "it can reproduce signals from this frequency to this frequency" etc.... Sneaky Sneaky

I am always trying improve anything I do so I really appreciate the feedback. I will read my posts a few times before posting them to make better. Those comments about explaining the concepts better for people was not intended to say "I know about this subject and you people don't". It was meant to try and reach people not having technical understanding of things, in this case phase which comes up a lot with many people I talk with which have a tough time with the concept. And rightfully so, it is not an easy subject for anyone. Your quote misses the emoticon in the last sentence about the contributing members even learning something, that was just a joke and not meant to be taken seriously which is why I added the winky face. Another example of things just not coming across through texting/messaging properly because it's just impossible to perceive tone and body language to know someone is just busting your chops as a joke. I just want to move forward, I really like many of you I met on here and would hate to be looked at as a jerk. I am actually quite easy going and always joking in person. I use lots of sarcasm and busting chops is an sign endearment to myself and many of my friends, it's a regional thing (Boston) me thinks.

A good friend of mine has always been a Coca Cola fanatic and always looking for collectibles to add to his collection. I remember him complaining about how the corporate penny pinchers like to claim they have not changed the recipe and when confronted with facts about exact changes like using high fructose corn syrup they claim it has zero effect of flavor and mouth feel. Your average consumer can even notice a difference let alone a coca cola fanatic that has been around for the major changes done. Besides the high fructose corn syrup the recipe once used real caramel which is what gave it the color, now they just use a caramel coloring additive which isn't caramel, it's just a dye which I believe was at one point in the 80's or 90's labeled as carcinogenic in California. I remember the old timers talking about when they would get it at soda fountains in pharmacies before it was bottled up and distributed across the country. You could mix in as much syrup into the carbonated water as you wanted, many claim this was the best coca cola ever tasted.

Mid fifties ahh the good old days!! The gas did actually smell good, like actual gasoline not like the crap at the pump now that gives you a headache. I roughly remember paying around a quarter $.25 a gallon. Coke tasted different too, maybe real cane sugar or the actual flavoring formula has changed? This was around the time when cans started to replace the nice glass bottle. I remember talking to friends about how the Coke in the can tasted different compared to the bottles. Mcdonald's was becoming it's fast food empire. Nothing like a bunch of friends jumping into a Chevy Bel Air and going and getting Hamburgers for $.20