2. amps-preamps
  3. 140029-80294

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

I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.

I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer.
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Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.

I like to tell true stories of my experience with others in this industry.

I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.

On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.

I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.

Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.


128x128ramtubes
ramtubes's avatar
ramtubes OP
460 posts
 
@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. 


ramtubes's avatar
ramtubes OP
460 posts
 
@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. 



ramtubes's avatar
ramtubes OP
460 posts
 
@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.
ramtubes's avatar
ramtubes OP
460 posts
 
@krelldreams
What differentiates a passive “preamp” from a “tube buffer” with level and switching control? I really like the idea of a simple level control with switching capability, but as I stated earlier, my first try at using a passive, albeit a very inexpensive example, was less than stellar. Specifically, I’m looking at a Schiit Saga to try as a replacement for my tubed preamplifier. I’m weighing options for use with a tube amplifier, but I’d also like to understand what a tube buffer does differently than a tube preamp. Also, would the gain of a preamp “help” a lower powered amp sound more muscular, or is that more “made up” information?

A passive preamp has not active stage. A buffer is an active stage (tube or transistor) with unity gain. It has a high input impedance andlow output impedance which helps drive a long cable. However is the cabe is short and of low capacitance a buffer is not needed.

I dont know why this is blue, its just another problem with this sometime frustrating app.

Im sorry you had a disappointing adventure with the passive. Perhaps its specs would reveal why. Do you have some specs?

I looked at the Saga, Web page is hard to navigate and its all black.. Mike Moffatt has a good reputation, the product is likely ok , but the lack of any technica info is annoying. They are putting out a lot of product in a short time. That concerns me.

I did find the specs, you do know its a hybrid, thats odd for a buffer which is usually a cathode follower. The input impedance is rather low at 10K but most modern sources an handle it. If you are driving something easy then there is no need for the buffer. Im sure many will disagree.

If you have a good preamp, why change?

As to the muscle, No, that is made up, who is saying so?
bdp24's avatar
bdp24
9,868 posts
 

When the ARC SP--3 was considered THE pre-amp to own, Frank Van Alstine took a look at it. He found the RIAA eq to be a little too off to be acceptable, the basic circuit to have a little too much non-linearity, and the power supply to be somewhat weak. He came up with solutions to all those faults (correcting the RIAA eq, reducing the distortion, and increasing the power supply's "stiffness"/lowering it's impedances), and offered a modestly-priced mod to correct the faults in the SP-3. Yet Bill Johnson continued to be considered a designer above all others by the High End community, and his ARC products therefore came attached with a certain cache' that others lacked. Some things never change ;-) .

For anyone looking for a modestly-powered tube amp, rather than pay $5995 for a poorly-designed amp that produces only 3.2 watts into 8 ohms and 1.2w into 4 (and at a very high output impedance, which will change the frequency response of almost all loudspeakers), take a look at, say ;-), the Music Reference RM-10 Mk.2. 25 watts pure Class A (a 35w Class A/B is also available, I believe), low output impedance, very long tube life, great sound, all for $5000. @twoch, if that strikes you as "B. kicking", so be it!

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