Does anyone care to ask an amplifier designer a technical question? My door is open.

@cakyol I am therefore using 1800 VA toroidal and a 270 amp rectifier. Caps are 4 x 47,000 uF but s I mentioned, at 85 degrees C the caps are rated at 2000 hours. Therefore they are the weakest links in the amp. I saw some Nichicons with 105 degrees C at 10000 hours but they were about $250 EACH (phew). The rectifier, altho likely to be used for welding applications, has soft switch characteristics AND it is quit fast, so would be suitable for audio.

Electrolytic cap life is much longer than the ratings. Im not sure why they are being so conservative. Perhaps thats all they want to guarantee. They all do it. I was surprised by it too when I first saw the short lifetime. My experience was that the life was much longer.  

I have nice nichcon caps in my RM-9s that ate 35 years old and just fine. They probably run at 150 F.. The thing that kills lytics is the loss of moisture over time. If the moisture stays in the caps go on forever.

So you dont need to spend $250 each. Those older caps on eBay will suit you fine, expecially if they are NOS. If one fails, no biggie since you know what to do. Please fuse accordingly with the lowest current slow blow that will get you past the inrush or come up with an inrush limiting device.

Roger nice job handling Teo. IMO he embodies everything that is wrong in high end audio these days. 

@bdp24 

@ramtubes, I finally got around to reading the review by Herb Reichert of the Cary SLI-100 in the December Stereophile. Damn, what a piece of junk! Cary specs the amp at 100w/ch from a pair of KT150 power tubes per channel; John Atkinson, using 1% THD and noise as the definition of clipping, measured the amp’s output from the 8 ohm tap into an 8 ohm load as a mere 3.2 watts! Out of a pair of KT150’s! You have to work REALLY hard to make an amplifier that bad. Whomever designed this boat anchor should find a new line of work; amplifier design is obviously beyond his abilities. 3.2 watts/ch for $5995? Not a "very good value" ;-) .

And what does this tell us about Herb Reichert, who very much likes the sound the amp produces? That Herb apparently likes distortion, I would say. You are now justified in completely disregarding anything and everything Reichert has to say about hi-fi. If one "likes" a power amp this bad, what doesn’t one like?

RM: "He (Harry Pearson) was an idiot." At an instore talk in the 1980’s at a S. California hi-fi shop to introduce a new product, Bill Johnson told this story about Pearson: Bill had sent Harry a new pre-amp for evaluation and review, and soon received a call from HP, saying the pre was defective. Bill had Pearson return the pre to ARC, where it was tested and found to be operating perfectly. A phone call and questions revealed the source of the problem; Harry had installed shorting plugs, not into the pre’s unused input jacks, as they are intended to be used, but into it’s output jacks. Well duh! Should anyone that ignorant really be considered a "reviewer", and empowered as such?

Its good to have  voice of reason here. I do know Herb and he listens at low levels. Remember he was in the Single Ended camp for many years so he doesn't need much power. 

As I have said before, at very low power, less than a watt, that amp and many others will sound just fine. Its in its class A range as far as distortion is concerned. However if someone has Maggies and listens loud it will not be pleasant. If they truly need a 100 watt amp this is not the one to get.

Now HP is another matter. While he created a lot of the language we now use, some good some bad, he was essentially ignorant of electronics, amplifiers, anything technical. I am amused at the story about the shorting plugs. 

While I would enjoy having Jon Atkinson's job I would not enjoy being a reviewer. They have to come up with all sorts of drivel on everything they test. I only read the subjective review if the measurements are way off. 

We did some testing the other day with the QUAD 57. Both myself and my friend listen around 80-90 db. At those levels the 57 required only 10 volts peak. Sometimes 20 V on loud passages. Almost any amplifier can provide that. 

I plan to write up our listening session sometime soon. It is a laborioius project to make a strict, level matched A/B, not blind test. The listener knows which amp he is listening to. Its not a test of the listener, its a test of the amp. 

@tomic601    ......so these A/B
can describe some of the switch gear involved as a DIY project

In essence one takes one or more relays and switches a single speaker (or pair) from one amplifier to the other. That is simple. However the output levels, using pink noise, must be closely matched within 1/4 dB or better. It is well known that if one amp plays louder than the other the louder one will be preferred. Its a well known trick on how to sell the inferior product, just play it a little louder, but not enough to make the volume difference audible. 

To match levels you need a pot that switches also, or the pot need not switch if the amps are ok playing unloaded, which most are. 

What is hard to deal with is all the wires and little things like the long wire to the button, matching levels, checking and double checking everythings.

However this is how I evaluate my amp, my mods and other amps. I am starting to mod some popular amps that I feel I can improve. This is a new area of interest for me and I want to make sure I am not going backward. Therefore I leave one channel (or one mono) stock and compare it to my mod. 

One has to know what one is looking for and what kind of music at what level will expose the differences. I try as wide a range of music as any listener might himself. Only 1 of 10 CDs I find to be useful. Some are horribly compressed, some already muddy, some dont have the right kind of instruments. For instance a harpsichord is not going to reveal distortion, Its already full of harmonics. 

Perhaps here is a good place to modify my statement about the difficulty in designing amps vs preamps. Its not about the difficulty and I wonder who started that. Probably some self serving designer who doesnt know how to design a power amp. There are companies like that where their power amps do not exist or are just horrible.  I simply find power amps more interesting to design so my work has focused there. 

I think the RM-5 is one of the best full function 3 tube preamps out there. If I did it today, 37 years later, I would do it the same way. The RM-1 is lower distortion, wider bandwidth but a lot more complicated. I did not want to make 1,000 of something so complex, support it and deal with the people who buy the really expensive stuff. I wanted to make something that sounds good, works forever, is affordable and brings joy to the user. 

I have had the opportunity to work on many higher end preamps and they are difficult, they go through tubes at an alarming rate, cause the owners much frustration and cost in keeping them going. Sadly they often don't sound that great either. If the phono EQ is fudged thats a no no. 

@atmasphere

Hi Ralph. Im curious if you use an inverse RIAA network to check your EQ. If so where did you get the values? I built mine from the advice of Peter Moncrieff, Mitch Cotter and Dick Sequerra who were the first to discover that many RIAA EQ curves were off. Of course I used precision parts.

Since then I have used my "box" to test dozens of preamps from as many manufacturers and found all of us to be in agreement within 1/2 dB except for the one we had at the SFAS phono pre shootout and yours.