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
 
@rsf07

 I wish I could tell you more on the specs of the speaker but there's little info. Roger Sanders does use a dbx Venue360 DSP unit he modifies (there are no crossovers or transformers in the speakers that I'm aware of). When you say "direct drive" amps since I'm non-technical what are you referring too? Can you send links to your own direct drive amps?Much appreciated.

I will soon publish something about my amp, but as you can see without your information my specs will do you no good.

I can build up to about 5,000 volts. Beyond that its like building a radio transmitter. 

My speakers work at that peak and 2,500 V polarizing. I contend running the polarizing high for sensitivity causes air gap saturation. Ive heard it!

Once again try to get some info on your speakers. Look at the DIY and ESL forums. Call the manufacturer. 

Here is the essence of direct drive. 

A direct drive amplifier is a bridge where each electrode goes to one side of the bridge. One side goes up while the other goes down. 

The problem with step-up transformers has been covered widely. What is not ever discussed is how much capacitance they have compared to what they are driving. There are very few people designing or making step ups these days and my objection to the Plitron has been covered here in depth. 

The problem is that designing such transformers is close to a lost art. Without some numbers I cannot say if the King transformers are good or not.

I found this link. The minimum is 1.8 ohms at 25 Khz, sensitivity 83 db  http://kingsaudio.com.hk/D001.jpg.

Not horrible, but choose your amp wisely. Its strange that none of their amplifiers will drive this speaker at all. I havent looked at the rest which are rather Martin Logan style. 
noromance's avatar
noromance
9,611 posts
 
@cakyo Use electrolytic capacitors with a 105°C rating over the 85°C versions.
unreceivedogma's avatar
unreceivedogma
928 posts
 
Hi ramtubes,

thank you for that and here’s a followup.

If triodes are low impedance and OTLs like high impedance, what was Jon doing then when he switched the OTLs to triode?

i can tell you that the amps sound better after the conversion, and they are more stable too. The bias and the balance don’t drift anymore.

Jon Specter made the conversion with some guidance from George Kaye of Moscode. Both formerly worked at NY Audiolabs.
russellstone
2 posts
 
Hi. I was turned off tubes when a Mac 2275 couldn’t properly drive my ML Summit X’s (yep, ‘soft’ bass’). After some searching I found an Accuphase E-600 matched beautifully. My question is: how can Accuphase make a class A amp that runs cooler than many A/B amps, and substantially cooler than other class A amps that can give you serious burns when touched?
devilscucumber's avatar
devilscucumber
13 posts
 
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.

Thanks for your reply.

The original panels had lost their top end, sounded rolled off, tried washing them as per instructions, the ML SL III clearspan replacement panels were just too bright with the Plinius 9100, (which for a 120W intergrated is pretty robust, but may have been stretched driving the unpowered subs as well as the electrostatic panels), plus I notice you say torroidal transformers are not ideal for electrostatics, which this amp has, (there was no futzing of the cross-overs), it really did make sense to bi-amp. The old Mos-fet Perreaux looks like a PA amp, XLR inputs and limiters (volume controls) on the front, which assisted the bi-amping.
Is there a particular Direct Drive Amp you can recommend to drive the panels? (Again I’m in a 240V 50Hz country).

I don’t generally drive my stereo too loud, and have been using the pre-amp in the Plinius to feed the Perreaux it all sounds pretty sweet just hankering for that tube sound.

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