captainbeefheart

Going back to the dielectric differences, you can see the difference in linearity on a scope. Not all dielectrics have the same constant which lends certain types to have more distortion than others. Kinda like looking at B-H curves for magnetics. Let's not forget about hysteresis either leading to distortion from non-linearity. Paper in Oil is actually more linear or 'cleaner' compared to polyester which is probably why it just sounds the smoothest overall and people seem to prefer them.

If you do choose to get PIO capacitors make sure they are hermetically sealed types, especially if they are NOS like the surplus Military types I suggested from Ebay. For capacitors it's best to divide them up into dielectric types because that is where the difference in specs/performance is. As some suggested today's polyester film types have higher ESR compared to polypropylene which although are on paper is a much better dielectric in terms of the lowest dissipation factor (tan) which when multiplied by reactance gives you the ESR. Since reactance changes with frequency so does ESR, that's why it's best to look at a constant like dissipation factor or quality factor. In this case polypropylene are too perfect giving lower ESR which people have described as 'too bright'. I personally do not think I would be able to hear the difference in a double blind test but I have to agree, the PIO caps do sound 'correct' whether it's psychological or not I prefer them in my La Scala's and pretty much any heritage speaker I have heard with AA crossovers. We played a cruel trick on one of my good friends that gets caught up in lots of the audiophile snake oil stuff and he wanted these extremely expensive capacitors installed in his Cornwalls with AA networks. I had installed all Electrolytic capacitors in the network 'back to back' to make them bipolar. He was blown away by the sound, honestly myself and another friend that was in on it were also completely baffled how good the speakers sounded. It sounded so good the friend other guy there had me do his Heresy I's all over with all electrolytics and again they sounded very good. They guy with the Cornwalls wasn't thrilled electrolytics were in his speakers and had me swap them out with the ones he wanted originally which sounded good too but I swear the lytic's sounded better for whatever reason. I wish I took some measurements of the boards with lytics to compare technically but I think we were all impressed with the sound and that's all that matters right.

If you have to choose use 2.2uF. IF you want to retain the same type of sonics as the original type capacitors then get some PIO capacitors. These are very good if you ask me and they are not very expensive either. https://www.ebay.com/itm/353676391302?hash=item5258c17386:g:6psAAOSwajVURk76

You do not need to load the output stage with a choke, a gyrator load will outperform a choke and at a fraction of the cost.

Capacitors are not expensive, you can re-cap them for less than $50 if you know how to solder.

I see no advantage to bi-wire unless you have a very long speaker cable run. Then, in this case you can run an very large gauge wire for the woofer for good damping, this wire will now have enough inductance to possibly effect the high frequency response so you run a smaller gauge high strand count wire for the mids and tweeter that doesn't require the amount of damping the woofer does. Other than that I see zero advantage to bi-wire.

I seriously was cringing while reading what he wrote. I mean if that's their 'senior tech' which I always took that title as the head honcho that knows their stuff then that is pretty scary. That is extremely embarrassing for the whole company for that to now be posted and quoted on these forums forever. Not a good look.

Nothing in that statement makes any sense. No tube on earth can magically change the laws of physics of output transformers. The amp has a very simple global feedback circuit just like almost all tube amps have, there is nothing 'special' about it. I believe he is confused about the 'DC restorer' circuit which has nothing to do with the feedback, it is just another name for sliding bias where he uses some 1N4148 diodes at the control grids to slide the bias more negative at higher output power keeping the tubes running cooler. When testing amplifiers on a bench almost all techs use 1kHz, some I have seen use 400Hz but the industry standard is 1kHz, yes the amp can produce 75 watts at 1kHz at 2.8% THD, the problem is they obviously never tested the amplifier output at bass frequencies which is where the problem lies with this amplifier. Of course these people have to try and cover this up, they are in business with these amps and need to make profits. Regardless of that whoever wrote that has no idea what they are talking about proven by the ridiculous things said in that statement. "neat feedback circuit" and "kt120's are pretty strong so the amp can be light" These statements should make any engineer or anyone that knows enough tube amps to just cringe. It's actually quite sad this company lets this person make a public statement like that as it's completely ridiculous.

The power supply needs no modifications to switch output transformers, the only issue is when the output stage tubes are swinging past a certain voltage swing (15 watts) the output transformer doesn't have enough flux density to keep up at low frequencies. The signal just falls apart and you get a grossly distorted waveform. When installing a properly rated output transformer if you decide to get one with multiple taps it really has nothing to do with the amps power supply, the extra taps are on the secondary and provide the proper reflected impedance to the primary.

Speaking of Bob Carver, when he talked to Stu Hegeman about tube amp designs Stu said he wished he never got caught up in the UL fad and making Ultra-linear amps, he made one and said it was the biggest blunder of his career and he would never make another ultralinear amp ever again, and he didn't. The tube plate pulls the transformer end winding down so low the screen tap gets pushed down so far it renders the tube unable to drive difficult loads. That and UL amps usually eat power tubes because of the idle screen dissipation is often very high. UL amps test great on a static resistive load but when asked to drive real loads especially some reactance they kinda fall flat on their face. I'm with Stu and obviously Bob Carver found the same thing as he never makes UL amps either, they are all pure pentode mode.

That is not entirely true, I do know exactly what you are saying but you don't know what I am saying. I will try and think of a different way to show you with some actual examples.

If you don't understand that I have no idea how to continue the conversation. I feel it's fairly clearly stated. The delay issue is between two drivers correct? So the phase difference is between the two outputs connected to those two drivers, not the difference between the output and filter network input.

Peak flux is proportional to the applied voltage and inversely proportional to the frequency and number of turns in the primary. The higher your flux is the more steel you need in the core in order to maintain flux density. The lower the frequency the bigger the transformer gets. Look at sinusoidal signals, say on a scope, I am sure you noticed that for lower frequencies you see more time between vertical divisions. So it takes longer in time for it to complete the full 360°waveform. So you need more energy in the transformer to maintain the waveform for a longer period of time. Tube selection is determined by the impedance ratio or primary impedance from a reflected load. For pentodes there is a sweet spot of load impedance for power vs distortion. For Triodes the higher the impedance the less distortion but lower the output power. And of course depending on your tube selection will tell you how much power out into a load you will have, this dictates the size of the transformer you need to select. The higher the power you have from the circuit the larger the output transformer you will need to accurately produce a 20Hz sine wave. Using an undersized transformer you can clearly see the flux density just falls apart on the trailing edge of the sine wave as it runs out of energy to accurately follow the transfer function of the sine wave. Basically it doesn't matter what topology, power is power and if your circuit can provide 100 watts of power and you decide you want to have low distortion down to 20Hz you need to select a transformer designed for the correct impedance ratio to load the tubes correctly and also one that is rated down to 20Hz for specified power. So say a push pull EL84 circuit is producing 17 watts of power into a 8k plate to plate load then you look for an 8k:8 output transformer for an 8 ohm speaker that can produce at 17 watts cleanly down to 20Hz. Usually you have a choice of output power and won't find exactly a 17 watt output transformer you select a 25 watt output transformer and you know you will never run out of energy in the output transformer to faithfully produce a 20Hz sine wave at 17 watts power. BTW for 8k:8 that's an impedance ratio of 1000:1 and a turn ratio of 31.6:1. For 17 watts into 8000 ohms we need an applied primary voltage of 373 volts. The secondary into 8 ohms is 11.66v. There is just no way a 15 watt output transformer can do what they claim, it's just impossible as size limits number of turns you can have and the size core you can have. I truly believe they are using peak power or some odd 'technique' of measuring power. There are books on how to calculate all this to design a properly sized transformer. It's not an easy subject.

In that response he states 'depending on the measuring technique' which is what I would be worried about. They never specifically state RMS power, just power, which could be peak power. The bottom line is he never once denies using the 15 watt edcor transformers which jives with the 19 pound weight of the amplifier, and unless the laws of physics have changed this amp cannot produce that amount of power even at 80Hz like he mentions. My guess is we need to ask them how exactly they test for output power and get them in writing to claim the rated output power in RMS. Also someone really needs to ask how they rate the output power and distortion for the different speaker loads given they don't have separate taps for them.

You are making the same exact point I am. That the input of filter to output filter phase doesn't really matter it's the summed output to output that is important. I don't know how much clearer I could have stated that but we are saying the same damn thing.

Pretty much exactly how I explained it, phase and delay are one in the same because if two drivers producing the same frequency are out of phase they reach their peaks at different times giving a time delay. Paul feels you can get away with 4mS delay but I think his prior mention of 2 feet or 2mS is closer to accurate because when we were discussing delay and chorus effects for pro audio the majority go down to 500uS or 1mS which is still audible. I certainly agree anything under 1mS delay is purely academic as it shouldn't be noticed or heard. 1mS is about 1 foot at 1kHz

I never said phase was a simple concept/subject, in fact earlier I said it's quite complex. You are talking about input of filter network to output of filter network phase. My simplification was only saying ideally you want each driver's peaks to be time aligned when they are reproducing the same frequencies. Is that not a valid statement?

I think people are talking about two different phase relationships here and that is what is getting confusing. Sometimes we are referring to the input of the filter network to the outputs of the filter network phase shifts, and then myself especially talks about the phase shifts between two outputs. The latter is the only one that will make any difference. If the time difference between two outputs is different for the same given frequency that will create the misaligned peaks during transients, one lags behind the other. You can view the phase shift from input of filter network to each output and figure out the differences between the outputs for any given frequency, it gives you the same answer as viewing the direct difference in phase from output to output.

Let's simplify the mechanisms. Phase shift is the time difference between two signals. Between the input to the filter networks to each output you will have phase shift, the largest at crossover frequencies. That means the output of the filter network is no longer on the same time domain. The speaker voice coil moves in response to the output from the filter network. At the crossover frequencies is where you will find two drivers contributing to the total acoustic output of the same frequencies, the phase shift between the two drivers means they will not reach their peak at the same time. That is all you really want in regard to phase, you want the leading edge of a transient wave form (square wave) to reach it's peak at the same time with both drivers. Both drivers will reach their peak excursion at the same time, that's the goal. The more phase shift between two drivers the longer the delay one reaches it's peak compared to the other. So constant delay, constant phase, all this terminology just gets confusing, all you need to do is remember you want each driver to reach it's peak for the same shared frequencies at the same time.

I agree. Really when you think about it the transformers are the majority of the production cost and for what they charge for this amplifier there really shouldn't need to be an increase in retail price to use the the correctly rated output transformers. Either that or just market the amplifier as a 15 watt amplifier and reduce the retail price. Especially since as you mentioned you will get a wholesale price on them. Two proper transformers at wholesale cost would be in the ballpark of $200. The rest of the amplifier parts are peanuts compared to them. Well, power transformer might be $50 wholesale. These sell for $2500!!!

Proper output transformer for that amplifier is $180, two are needed for a stereo amp; $360 total The 15 watt Edcor is $35 and total for two is $70 360 - 70 = $290 Multiply that by say 5,000 units $1,450,000 I'd say it adds up to extra profit

Someone over on Audiogon that purchased theirs through Music Direct got tired of waiting and removed the circuit board and took the transformer covers off and sure enough, 15 watt Edcor output transformers. The guy is upset of course and looking into what the company is going to do about it.

What a wonderful hobby!! I sold my vintage guitars since getting a Collins Soco Deluxe, it's the only guitar I play anymore. And you are spot on, tell your friends they would have to most likely find the exact magnets used for those guitars, then hand wind the bobbin and pot in wax. Make about 100 of them and then test and play them all, they may find a few 'magical' sounding pups of the lot that fit the magic parameters of sounding 'good'. Honestly I think the ones that got the most turns on the bobbin ended up being the best ones as they will have more inductance and a hotter output. Now couple that extra output with some alnico magnets with the right BH curves where they slightly saturate giving off slight non-linearity and you got your mojo back baby!!

Another crazy thing to think about is this only has an 8 ohm tap, yet it's rated for 4 ohm speakers. Now 2k6 plate to plate when halved when using a true 4 ohm speaker it's going to be a tough load on the power tubes so I would imagine distortion would increase fairly substantially. With only one secondary tap going either up or down from 8 ohms will result in changes of distortion and output power yet the spec sheet says nothing of this. I have never seen a transformer coupled tube amplifier claim the use of different speaker impedances without providing separate taps for them. I wonder how Frank is going to handle this. How are the vendors that sell these amps going to handle this. Refunds? Clearly there is some serious false advertising that shouldn't be too hard to prove but I worry the they were vague enough in the specifications to get away with it.

I found it I think: here is the guys response "The Crimson 275 I bought (from Music Direct) uses 15w Edcor OPTs. UGH!!!! Frank Malitz, can you please explain this? While I love the sound of this amp, this hurts my ability to pair it with less efficient speakers, hurts resale substantially, and isn't cool---UNLESS, Frank, you can get Bob Carver to issue a statement explaining how this amp can make specified output. Finally, if you're reading this please note: Before folks throw Bob under the bus, remember the following. Bob designed this amp with another esteemed audio sage. He reportedly sold the amp and the rights to sell it to Frank Malitz and/or Carver Corporation--and Bob is not an owner of the company. Frank told me he's a designer only. When Frank says Bob was angry/sad/emotional about the issues being debated on the forums concerning this amp, that may be true. And Bob may have never intended to post faulty specs, etc. Frank Malitz/Carver Corporation, can you have your partners at Wyred4Sound test the output and reconcile it with your specifications for the product? I'm more sad than angry about this. It's still a hopping little amp, but now I know it won't work in my big room (16 x 23 x 10 tall) with inefficient speakers. Currently I use 102dB efficient in this space, so as I said before I had not way of knowing if this thing could power such speakers. This is a very sad day for me. Great amp. More than likely false advertising. Should I ask Music Direct for a refund?"