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.


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ramtubes's avatar
ramtubes OP
460 posts
 
@twoleftears 

But a popular US-based, US-manufactured, relatively inexpensive, tube integrated did hum, not a lot, from *both* the transformers and through the speakers, enough that when combined the hum could be heard from listening chair when music fell silent
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Does the maker publish a hum level in his specs?  With input shorted any more than 0.5 mV hum is not good. Needs to be even lower with sensitive speakers, close listening, quiet room. 

I know one US maker whose limit was 2.0 Mv. That is 12 dB more hum than my limit. 

I think it wouldnt matter where you put that amp, it just has inherent hum. Many people make the mistake of thinking that all products that reach the market are good products. This is not the case. Would you care to tell us what amplifier this was?
ramtubes's avatar
ramtubes OP
460 posts
 
@desktopguy
Wish I could hear your more recent designs, because based on the RM-9s, they must be very very good. 

I like my new stuff, especially the RM-10. For those who have difficult loads, play loud and need power the RM-200 is designed precisely to do that. 

The 9 is a fine amp, excellent potted transformers, UL, Triode for you . Lots of work to make. They are starting to bring more money on the used market so dont let them go for under 3,000 each. With the triode switches even more. We only made a few like that.

I hope to get a few more amps out this coming year now that I am getting more help around the shop.
ramtubes's avatar
ramtubes OP
460 posts
 
@chubaka   What are rails and what to they do?


Good question. In a Solid state amp there are generally equal positive and negative supplies centered around ground. A 100 watt/8 ohm amp will typically have 50 Volts plus and minus supplies. We call those the rails. It is where we draw the current to send, via the output transistors. to the speaker. The rail voltage will determine the power of the amplifier. 75 volt rails will give you 200 watts and 100 volt rails 400 watts.

Rails were not much talked about until the advent of the SS power amps that were direct coupled to the speaker. In action the positive rail pushes the speaker cone out while the negative rail pulls it in. Again the output transistors determine how much which determines what the speaker reproduces. 

In a tube amp we have several power supplies of different voltages and currents. We call the main high voltage B+, a term that goes back to early 1900s radio. A tube amp may also have a negative bias supply, filament supply, driver supply, lots of supplies in tube amps. 
ieales's avatar
ieales
1,201 posts
 
The whole idea of tuning a system with cables seems rather weak to me.
The missus once said "Those wires are the only ones where the clarinet sounds like a clarinet." [She had perfect pitch and played the clarinet.] We had decent amp and speakers, so the "wires" were the final tweak.

Unless one subscribes to the idea that cables do not alter the sound, surely it makes more sense to replace bad cables than a good amplifier to correct system deficiencies.
ramtubes's avatar
ramtubes OP
460 posts
 
@devilscucumber

 Hi Roger,I have some old Martin Logan Sequel II's which when repanelled no longer sounded pleasant with my Plinius Integrated 9100 (100w), they became overly bright and shouty. I ended up bi-amping with a Perreaux 6000B (300w mos-fet) running the panels, while the Plinius now drives the subs, my question is can you recommend a cost effective tube amp to drive these speakers, (which dip down to 2 ohms?) I live in NZ (240V/50Hz). I must admit most of the discussion on this thread is well over my head, but your experience in these matters is invaluable to help novices such as myself


First I wonder what happened to the speakers? Were they repanelled at the factory? Did some fool with the crossover? 

Thats a hard speaker to drive and a 100 watt integrated mignt not be up to the task. The Perreaux is much larger and probably more tollerant of the low impedance. 

An RM-200 will drive your speakers from the 2 ohm tap to some reasonable level. How loud do you listen, at what distance and what is the sensitivity of the speaker?

The best amp for you would be a Direct Drive to the ESL. Thats what I use.

I have a keen interest in ESL speakers and have measured many. What I have found is that the hard part of driving them is often the transformer, not the panel. Going direct to the panel makes a big difference. My DD amplifiers produce about 1200 VA into a capacitive load. 
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