2. amps-preamps
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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
lou_setriodes's avatar
lou_setriodes
688 posts
 
I realize I'm only on pg 7 of this wonderful blog, but I must chime in.

Dear Mr. Modjeski,

Thank you so much for taking all of this time to provide such great information for all of us.  Your honesty and humility is so refreshing and the graceful way you handled the adversity of some of these comments has been truly amazing.  I have owned a couple of your products in the past and I can only mirror the other comments mentioned here.   

From michaelgreenaudio on 11-29   

"Sigh, in the best way possible. The RM-5, one of my favorite components of all time regardless of price.

Speaking of Harry, I was tuning up two of his systems, one with the CAT and one with the Classe. I had my RM-5 with me and me and Harry listened to it for about two hours.

Man did I ever love that preamp! You could mate the RM-5 with anything and it would transform that amp and speaker combo. When Kenny started dampening his Pre-amp it was all over for me, I kept the RM-5 close by. It tuned better than all of them. I think I toured with the RM-5 for about 3 years.

mg


I too owned the RM-5 (serial #0023) for about 5 years (89-94) and yes - Man, did I ever love that preamp too!  It sounded absolutely amazing with everything I threw at it, all except for one amplifier.   First off, aestethically, in silver with the older graphics, I thought it was beautiful to look at, with a great fit n finish.  It sounded absolutely wonderful with a B&K ST140, McIntosh MC225, B&K EX442 Sonata, Paoli M70 monoblocks and Music Reference RM-9; unfortunately, it didn't seem to mate up at all well with the cj MV50?  I don't know why because I really wanted to like the MV50.  At one point, there was a little problem with the mute circuit, so I sent it back to you in VA and you updated it the current RM-5 MkII.


Here's the part that gets interesting and has become the basis for my theory on our aural memory.  When the RM5 was with you getting repaired and updated, the dealer loaned me a Dyna PAS2 preamp to go along with my B&K ST140 and ProAc Studio 1 speakers.  After a short time, I really started enjoying the PAS2 preamp and it sounded wonderful and lush.  After a couple of months the RM5 mkII was returned.  You had mentioned the changes weren't very drastic but when I got it back, my ear had become so accustomed to the PAS2, that I really hated to see it leave and actually thought it sounded better in my set up than the RM5.  I understand its all about system synergy so perhaps the PAS2 added that extra lushness to the ST140; whereas with the MC225, the RM5 balanced out its lushness.  And if I had the opportunity to try the PAS2 with the MC225, it would have probably been like putting too much sugar on top of your already sweet grapefruit.  


Unfortunately, while I do not possess the electrical knowledge to be able to repair or build gear, I have learned an awful lot from reading literally 100's of issues of TAS, Stereophile, HiFi Heretic, HFH & RR, Listener and others over the years.  And what I've realized over the 35+ years of being an audiophile and changing gear sometimes seasonally, sometimes less often (whenever I have solid state gear, I'm wanting to change gear a lot more often, and when I own tube gear I make a lot less changes) is that I believe there is an aural memory that we all have that you get accustomed to.  Whenever I make a change in gear, even if its an upgrade, my mind needs time to get used to that new change in sound.  Sometimes, it takes a week or two, sometimes longer for my ear to adapt to the new change in my system to where I can really enjoy the new piece in my system.


I'm grappling with this very issue now as I've recently sold some classic gear for a friend and in a short term have switched from a McIntosh MC225/MX110/Rauna Tyr II combo to a B&K ST140/Technics SU9070 preamp/Rauna combo to a moded GemTune EL34 SE int/Rauna combo and the differences have been pretty profound, but I'm loving the journey.  These little concrete speakers from Sweden were the first speakers I ever heard when I went into my first real high end store in the mid 80's and my jaw dropped & now I own a rare pair.


I apologize for my very long-winded response here, but if you have a chance, perhaps you can shed some light and your thoughts on this non-technical subject. 


Sincerely,

Louis  



      

   

   
fleschler
2,021 posts
 
Well ramtubes, we have 100% opposite opinions concerning the necessity for well designed power cords.  I am a beta tester for a boutique manufacturer.  I've sampled at least 50 designs and tested them against all types of high end cables.  When substituted at audio shows, they were the equal of or blew away the comparable high end and expensive cables.  The worst power cables were from High Fidelity with their patented magnet design.  (I've have 8 friends and two high end homeowners who did testing on their equipment as well and the latter two dumped their HF cables).  Two posters have thought HF cables are supreme.  We (10 of us), have found them to be hard, bright, forward sounding and harmonically thin on a wide range of tube Class A, A/B SE and SS amps, pre-amps and phono pre-amps.  

I don't have any electrical engineering degree or knowledge concerning transformer design or household current.  Basically, after auditioning so many PCs on so many high end systems, it appears that you could conclude that all the auditioned equipment was faulty do to poor transformer or power supply designs or implementation.    I disagree.  My own various custom made Class A/B tube equipment are greatly altered based on the power cables and I do not believe they are poorly designed.  They sound magnificent.  The chassis and transformers remain cool to the touch (maybe 80 degrees) after hours of use at sound levels averaging 90 db with challenging impedance speakers (Legacy Focus) with 6 - 12" woofers in a 5,000 cuft room.  The EAR 890 amps Class A chassis and transformers are burning up trying to drive those speakers (no problem with the Signature IIIs at 1 ohm higher impedance and 6-10" woofers).  
jafox
1,460 posts
 
Hello Roger,

Years and years ago I re-tubed my ARC SP-10 with your RAM tubes and the phono stage quieted down mighty well.  And then a year or so later I heard your RM200 amp at a dealer in Phoenix and that was a very nice sound as well.  Thirty years later, I have a question that I imagine you or some of the other techie gurus might be able to answer.

I swap between amps with some that only have single-ended inputs and others with only balanced inputs and others with both.  My preamp has outputs for both.  I recently acquired a very nice 4m balanced IC.  For the cases when I want to use the single-ended input only amp, the CAT JL-3 monos, I will need to use an XLR to RCA adapter into the amp.  The adapter I bought has the neg line tied to ground.  But this results in the preamp's neg output line being shorted to ground which does not seem to be a good thing.  Would it make more sense to put a 10k, 50k, 100k, etc., resistor inside the adapter from the the neg pin to ground to more accurately simulate what the cable would otherwise see as the amp's input impedance?

Any thoughts here would be greatly appreciated.

John


atmasphere's avatar
atmasphere
11,861 posts
 
I swap between amps with some that only have single-ended inputs and others with only balanced inputs and others with both.  My preamp has outputs for both.  I recently acquired a very nice 4m balanced IC.  For the cases when I want to use the single-ended input only amp, the CAT JL-3 monos, I will need to use an XLR to RCA adapter into the amp.  The adapter I bought has the neg line tied to ground.  But this results in the preamp's neg output line being shorted to ground which does not seem to be a good thing.
Its probably not- check with the manufacturer of the preamp. If the output is transformer coupled, then this is required. So it really depends on the preamp!

But if I were you, I would simply use the RCA output if using an amplifier with a single-ended input. There is no advantage of using the really nice balanced cable if you are going single-ended- the single-ended requirement actually results in the **entire** connection being single-ended so the cable is not operating as designed and intended.

gdnrbob
4,452 posts
 
Ralph, couldn't he use a Jensen transformer to make he XLR to RCA change? Would it still offer the proper grounding?
Bob
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