Some of you are not familiar with the outstandingly musical products the we produce here at Musical Concepts and Musical Design. What better way to get some familiarity with our products than to read the response of audiophiles like yourself to gain a better understanding of our mission and how we are fulfilling that mission.

The great majority of the comments below are taken from our e-mail responses. Without any further ado here is the opinion of others.

Read a few Warranty / Customer Comment postcards:

For Musical Concepts/Hafler Amp mods - Card A

For Musical Concepts/ Adcom amp mods - Card A, Card B, Card C, Card D,

For Musical Concepts Amp Options - Card A, Card B

For Musical Concepts Interconnects - Card A

For Musical Concepts CD player mods - Card A


Musical Concepts Customer Testimonials

Musical Concepts PA-6 mods for his DH-220 and more……….

Hi John. This is Charles M. You recently worked on my DH220 amp and I wanted to send some feedback. The difference is absolutely amazing. Beyond any expectations. Much more air,  detail and a vivid soundstage along with amazing bass response. I'm satisfied to say the least. Couple of questions if I may. You modified my DH101 about a year ago with your LXII Elite upgrade. Would like to know your thoughts on doing the PasPro1 upgrade as well as adding the outboard power supply. Also any thoughts on the Hafler PH50 would be appreciated. Thanks again.    

Charles M.


DH-500 to sophisticated listener(in the biz)(03-03-17) - PA-6 Elite driver boards, PS-500 power supply board, excellent connectors.

Hi John,

I just wanted to let you know the Hafler w/ PA-6(Elite-ed.) mods made it to me safely.  

I'm already impressed by what I'm hearing.  Liquidity is improving by the day and the amp is very transparent and superb dynamics and authority.

The noise the fans makes isn't too bad.  I'd prefer silence, but I'm glad it didn't deter me from this great unit...  In fact, I'm tempted to sell my Musical Design D-75B and put another of your Haflers in my living room.

How long do you think the burn in should be on this unit?(we answered 3.5 to 6 weeks-ed.)


Fred A.


Nicely modified original version Adcom GFA-535(03-03-17) - amp had PS-200J power supply, latest upgrade to previous Signature modification, excellent connector package.

Look's good inside, it will at least need 50 hrs of break-in time. I'm sure you have an opinion but to be honest John I'll put this up against other high end amps costing 2 or 3 times it's price, good job sir. - Mark R.


Modified Quicksilver Preamp(04-24-16)

John, I got the matched Mullard 12AX7's from you and now have tried your fully modded Quicksilver Linestage Preamplifier with Mullard versus the JJ-ECC83S/12AX7's you included.  And now with 33.5 hours of run-time on the preamp, it just continues to sound better and better.  Yes, the Mullard's have a much different sound than the JJ's, but both are really quiet and the sound stage is actually as good as compared with the Adcom 750 Elite Mod you performed last year.  I know you get a lot of credits for great designs and mod work, and I am certainly your fan, believer and follower.  You do great work and I appreciate all your indulgence and help in making my music experience a quality moment in life.  Don


Hafler DH-200 with PA-4SE mod and PS-100(premium caps 15K)(03-27-16)

Hi John!  

You Can Kindly print This On Your Site With My Permission:  Hearing So Many Good Reports Of Amplifier Modifications And Having So Many Power Amplifiers , I Decided To Purchase One Of Musical Concepts Modified Amplifiers, A Hafler DH-200 (well a Hafler chassis really)   After hearing This Jewel Of An Amplifier And Comparing This To Every Other Amp I've Ever Had (and I had like a dozen amps)  This Comparatively Small Sized Amp Delivers Sound That Blew Away All My Old Ones To Shame!   You Do Not Hear Just Mids, Highs, And Bass That Is All Just One Loud Sound Together.  You Hear Silky Smooth Mids, Deep Controlled Bass, And Cymbal Highs Like Your At A Live Concert!!!!!   These Guys Take Audio To A Whole Other Level,  A Very High Degree Of Art!!!!!  You Cannot Purchase A New Amplifier Out Of A Box That Can Match The Sheer Magnitude Of What These Guys Do With High Fidelity Sound!!!!!   I Am So Happy I Purchased One Of Their Fine Modified Amplifiers, It Is Truly Worth Every Penny!!!!!!   So, If You Are Serious About The SOUND OF FINE AUDIO MICRO DETAILS, THEN GIVE JOHN A CALL AT MUSICAL CONCEPTS !!!   YOU WILL BE SO HAPPY YOU DID!!!   



Hafler DH-101 with Elite LX mod

You knocked it out of the park again!!! Peter C ,   Alamosa, CO


Adcom 750 preamp - Elite mod

John, it sounds OUTSTANDING! So much that I can't believe the difference between it an my Quicksilver Line Stage preamp which uses 2-12AX7 tubes.!!!

It is absolutely quiet, even in combo with my tube amps!

Question, can you do this same magic on my Quicksilver Linestage preamp? Make it quiet and with the same improved dynamics? If so, I would like to discuss an upgrade. Please call me......


Don’s further comments

John, I know you probably don't need further praise on the Adcom 750 GFP mods you did but I just have to tell you that it just keeps getting better! I now have 36.7 hours of play time since putting in my system and it now has a depth and overall soundstage that is unparalleled by any preamp I have ever owned. I have had Precision Fidelity, Cary, McIntosh, Sonic Frontiers and Quicksilver. This puts all of them to shame! It is absolutely quiet, and I mean quiet....I have AvanteGarde Duo speakers @ 107+db efficiency and you hear absolutely nothing with gain set to zero, even with 300B and AudioPaks mono tube amplifiers, and even with FirstWatt F6 solidstate amplifier!   But, most important, the imaging on no less than my Marantz 150 Tuner is so realistic that it can only be enjoyed with a little champagne. You did an incredible job and I now look forward to every moment I can rest and listen to your achievement. Thank you again. You are a real professional.



Happy PasPro 1 owner - PasPro 1 link  Installed in Hafler DH-101 chassis with custom outboard power supply


I want to thank you again for the superb pre-amp you built. If it could sound better it would probably take younger ears than mine to notice.

My system sounds as good or better than those that are 5 to 10 times the cost.

I also appreciate the interconnects you sent along with the package. Very nice!

Best Wishes!

Adios! Jack


PA-4, worth thrice the price


I wanted to drop you a note and tell you how pleased I am with my rebuilt Hafler dh-220. The sound is head and shoulders above the stock unit. This is the best money I've spent on my system in years.

…........Most people just don't know how good this amp can sound, you would probably have to spend several thousands of dollars to equal this level of performance.

thank you

Bob C., N Quincy, MA


PA-4 / PS-200 / Hafler DH-500 Fun


I can't say thank you enough for the parts and the help with my amplifier.  My Hafler DH-500 in awesome!!  I put the PS-200 and the PA-4 Elite boards in.  It is so impressive and clean sounding.

Thank you for taking the time to walk me through getting them installed correctly (I'm not an electrician).

I hope many others can enjoy your products and service.

Pastor Cory F.


CHAMELEON PREAMP - in prototype. David is a beta tester. 

See latest Chameleon info


Your  Chameleon preamp with mother and daughter tube board concept has transformed my system.  A Solid State crust has vanished, something

whose presence was unknown until removed.

With the 6H30pi board option, your preamp produces minimal -- if any --classic tube coloration: Softness and caramel coating, for example. Paradoxically, my system now sounds tube based, maintaining neutrality while exerting  the characteristic spatial rendering and ingratiating  characteristics of tubes.  Extreme listenability and ease. Jane Monheit makes me liquefy and pour off the couch.  Great bass!

If I find myself longing for a classic tube lushness fest, I'm sure one of your 4 other boards will accommodate.  NOS Mullards, that type of 'phile indulgence

I find myself wanting to listen more than ever: The ultimate test. It becomes redundant to mention the exceptional non-fatiguing qualities of this circuit.

Brilliant concept and realization John.  Congratulations.

David A. Hartwick

Chambersburg, PA    717-263-0128

[System: MC PA-3D based monoblocks,  MD DAC-1A Platinum Plus Ultra,  MC SuperConnects throughout, Intuitive Design Gamma Summit speakers, Modded Denon transport]

—-------------------Since this comment Dave has added other tube boards, Teflon coupling caps and experimented considerably–––––––––––-


Chameleon Preamp with PC-1T and PC-4T

Very pleased with the sound - Fantastic value.  10+

John N., Anacordes, WA

[ John N. is using our PC-1T configured for 6N23P(6DJ8 type) tube and PC-4T configured for 6N6P at high current ]


New>> Elite Power Amp Modification - DH-200 amp

Dan has our PA-3 Signature series boards, one PS-200J board(4-10,000uf/80V Jensen four-pole caps), TP-200 dual-wound toroid transformer, 'single-current' Exicon mosfets, more

Dear John, I have followed your products and their progression for many years. You have always impressed me with your ability to consistently provide musically satisfying amps and preamps. Dollar for dollar they outperform most of the market offerings. In fact you could say that they are real over achievers. Your recent redo of my Hafler DH 200 is however in a class of its own. The combination of Jensen B + capacitors and the Exicon mosfets are, simply put, amazing. You could say that this is a kind of breakthrough in two-channel audio. The presentation of good recordings is striking. It’s all there, the controlled bass, the harmonics, the overtones, dynamics, pacing, the sound stage, you name it. I am using one of the new Fried loudspeaker systems and the combination with your amp is very compelling. If there is anyone who is searching of good music and needs an great amp, look no further. I don’t know of a better value in audio than to send you an old Hafler to transform or invest in one of your new amps. This is to say bravo John! Daniel, Co

Our NOS 6922 vacuum tube 

Hi John - you modified my Music Reference preamp about a year and half ago, with great results - in fact, I haven't bought any stereo gear since! An unprecedented situation - but it really sounds beautiful.

Now it's time for new tubes and I wanted to get 3 of those old  NOS 6922s from you at $49 a piece (if they're still available...). 

Thanks, and thanks again for such great work - Dock Boggs is pouring forth as I write, and he sounds pretty darn good.


Neal S.



THE TUBES ARE GREAT!  You were right.   From top to bottom it blew the Svetlana 6N1P's away.  Things that sounded like noise in the background before, are present and articulated like never before.  Thanks.

James W.


Musical Concepts modifications

Hi John, just wanted to let you know that I updated the Hafler P500 with the PA3 boards this week and they are awesome along with the new filter caps I just received.  Excellent design.  I’m driving a set of UREI 813s (came from Fantasy Studios in Oakland ) or a set of Quad ESL 63s that have been fully restored.  What fun!

  Thanks! Cheers,    David


Eight year-old Enigma 7 with Berning Microzotl and Grado RS-1 sounds terrific. Excellent bass, eerie vocals and maximum ambience retrieval are just a couple of sonic virtues. Smooth, detailed blah blah blah. Your eight year old design kicks some SERIOUS MUSICAL ass.

I am thinking of adding a tuner. Do you do any mods? Which brand and model? How much?



Platinum modified Hafler preamp and power amp

Hello John,

      I know you are very busy and get lots of emails, but I just have to share some of my thoughts with you and hope you have time to listen a bit. As I'm sure you remember, I have your Platinum  MC-3 modified Hafler DH-110 preamp, as well as your Platinum modified PA-3B boards in my Hafler DH-500 with all of the other Platinum mods that go with it. I also have a pair of Arius speaker cables. What I am going to tell you in these next few lines you probably already know. I have been listening to your modifications in my equipment for a couple of months now and am very satisfied, but it wasn't until I listened to other manufacturers gear that really makes me appreciate it more than ever. Basically, your stuff is far superior to what I have heard at some of these high end shops. I have listened to some of these systems that cost nearly as much as the house I am living in, and in a nutshell, your gear sounds BETTER!!!!! . I have listened to names like Krell, Audio Research, Mark Levinson, Macintosh, B&K, and some other amps and speakers that I have never heard of, and some of these components each cost more than the new car I drive. I used to think that you offered us blue collar people with the closest to a white collar sound that we will ever have in out living rooms on our blue collar budget, but after listening to these HIGH DOLLAR systems, I realized most of them are just overpriced, overrated electronic trophy's for egotistical people that just have way too much money to spend on HI FI. Heck, I even listened to a system that had a pair of speaker cables that cost $29,000.00. I don't know how good these cables were if you were to rate them alone, but overall the system in my living room you designed sounded better. Maybe the beauty is in the eye of the beholder, but I think I am being honest with myself when I say these things, because I haven't heard a single piece of music anywhere that I honestly preferred the sound of more than either in my living room or in your listening room on the Innersound ISIS speakers you had set up. I'm sure you know of the places I listened to some of these systems at, and I won't mention their names, but for honest sound quality, and not the status symbol of some of the overpriced crap out there, your equipment and mods stack up higher than they do!  I am dead serious about that! As I said, I am sure you already knew that, but I thought you might enjoying hearing it from someone else. Thanks again for the great sounding hardware.  I love it!

Scott  M.


PA-3B versus some well known amps

John,  I really want to thank you for your prompt response on sending the PA-3B. I installed it this weekend. I was really surprised (pleasantly) by how simple it was to install and calibrate. But...I was *shocked* at the sound difference! The Hafler went from a somewhat gritty transistor amp to one of the sweetest sounding amplifiers I've *ever* heard. I'm including my VTL Tiny Triodes, Audio Research D-75, and a borrowed ARC VT100 in that comparison. Amazing. And you don't even change the power stage. Congratulations! The biggest improvement/dollar I've ever seen. Now I have to upgrade the ARC D-75. Any ideas? :-)

Eric J., Chief Technologist



John,Hey! The unit sounds awesome! I have a Mercury Living Presence CD of Appalachian Trail that sounds horrid on just about anything I’ve played it on. Bad tape hiss, screechy sounding violins on track 2. Now, you can still hear the tape hiss, but it sounds like reel to reel tape hiss - i.e.. more bearable, and the violins are very liquid. I used to hear very subtle differences between my Sony DVP7000/Link DAC combo and the PD-65. I wasn’t really sure which one I liked better, but thought the PD-65 had just a little more bass and was maybe a tad smoother. Well, not so subtle anymore! The PD-65 smokes it! There is more air, and I can actually hear the hall! Piano notes have a nice "round" quality to them and I don’t have some piano notes jumping out at me and others recessed. It is now a very, very rock solid soundstage. Very cool!




PA-3B mod for Hafler DH-500

Had an old Hafler Dh500 from 1982 I decided to bring back to life since I wasn’t entirely satisfied with my Denon 5700 on music. I purchased Musical Concepts PA-3B mod kit consisting of 2 new stuffed boards and some misc parts such as caps and gold rca jacks. The install was pretty straightforward and taking my time consumed about 4 hours including adjustments with a DVM. It didn’t work the first time (due to my error) and I had to call John Hillig at Musical Concepts who was very gracious and helpful. It’s nice to find out a company actually has great customer service. Anyway, last night I was able to listen for the first time using the Denon as a preamp and a Pioneer PD-65 as the source, I started with Dave Brubeck’s Time Out. All I can say is wow! The drums and horns just came alive with so much more definition. The lower bass is now so tight and solid and the upper bass just sweet. I swear I hear music I never heard before. Switching to Brumeister CD#4 I was anxious to hear vocals. Boy I was not disappointed! The female voice is now so clear and just so DEFINED like never before. I had to break off early to do some chores and my son came along and popped in some new CD from ATC, la la la or something. I ran back into the room to

hear it. It was actually quite pleasant with super strong, tight bass and wonderful high freq notes along with another fantastic female vocal. (The CD is pure bubble gum pop but I nor my son could believe how good it sounded). My son kept commenting it sounded like a different cd.

Any of you with an old Hafler around, try Musical Concepts. I think I now know what people are talking about with tube amps. The Hafler is now so much more musical.

-- from Jim H. –




I received my PA-3Bs on 2/23/01. They were of such high quality that I just couldn’t install them inside my dusty old Hafler DH-200. I wound up completely stripping the chassis, cleaning it and reinstalling everything. I put in new binding posts and I even put in new FET sockets! After I reassembled everything not only does it look beautiful, but the sound with my new PA-3Bs is wonderfully clear and transparent. The modified amp has brought new life to my Magneplanar speakers. Great job! You certainly deserve congratulations on this one.


Another PA-3B modification


3 things. First, one word on the PA-3B mod - WOW! I finished it last night and plugged it in (recall my preamp has the 110 mod installed). The sound is fantastic - I’m hearing music on my discs and LPs that I didn’t know was there. Detail, space, etc,  all great.

Jim M.


Extensive Hafler DH-500 modification

Dear Mr. Hillig;

I recently purchased a set of modifications from you for my 17-year-old Hafler DH-500. These mods were as follows: 2 PA-3BK replacement circuit boards, 2 TP-500, 500 watt toroidal transformers, 2 LC-500 pairs of 39,000uf/100 volt power supply caps and Signature upgrade for PA-3B that includes 2 hyper-fast rectifier bridge kits.

This was not a stock amplifier. I had installed your MKH-500 mod in it when I originally built it in 1984. At the outset, I was very happy with the MKH-500 mod and enjoyed many years of use without any problems or repairs whatsoever. Recently, I upgraded the rest of my system and I felt that the DH-500 was lacking in the tight, well-defined bass that  matched the performance of the other speakers in my system. At this point, I need to mention that this is a 4-way multi-amplified system utilizing an electronic x-over and 3 other stereo amplifiers (McIntosh Tube-type) besides the DH-500

which drives the bass channels.

I was somewhat reticent to make such a large purchase without ever hearing what your modifications would do to improve the sound of my amp. I thought it over and I recalled that I had used your mods on a DH-101 and a DH-220 in the past and was very happy with them. (Especially the DH-101) A few of my Hi-Fi friends scoffed at my idea of spending almost a thousand dollars on an old amp that I only paid $600.00 for new in kit form, but I felt that I should trust my gut feeling that I would get an improvement commensurate with such a large outlay of cash to Musical Concepts.

I have finished installing the mods following your excellent directions and I have had a few days to listen to various types of music played back on the DH-500. These are my observations:

1. This is literally the quietest amp I have ever heard. The music leaps out from total silence that is almost uncanny. You can even put your ear right in the woofers and not hear any noise or hum at all. This is something I have never heard ANY amplifier do.

2. Originally, the bass was somewhat fuzzy and indistinct. I (and some of my audiophile friends) attributed this to my listening room and I was planning to use a pair of McIntosh MQ-104 environmental equalizers to compensate for this problem. It wasn't the room. I was very shocked to hear perfectly clear, pure bass coming out of my woofers (4 JBL 2215H's) when I first fired-up the DH-500. I could actually hear the differences in kick-drums, something I couldn't dream of doing before.

3. It is very hard to put into words, but there is something else about the way this amp sounds. I would categorize it as effortlessness. There is nothing strained about the sound of the DH-500 with your mods. What's there is pure musicality. I use McIntosh Vacuum-tube amplifiers on all my other channels for this exact reason. Tubes are more musical than transistors or FETs, or so I thought until I heard this amp. All the best sonic characteristics of tubes without the drawbacks are embodied in your

modification of the DH-500. Simply put, this amp sounds at least as good as the very best tube amplifier!

4. (Value) What this mod has done is to transform a mediocre, somewhat dated kit amplifier worth at most couple of hundred dollars used into something that people expect to hear from an amp costing ten thousand dollars or much more. No hype here. I would not be the least bit surprised to find that this amp sounds much better than those legendary "Audiophile" products from Mark Levinson, Threshold, Krell, etc. John, I thank you for a far more than equitable purchase and I sincerely hope other people out there in Audiophile-land will discover Musical Concepts and enjoy your amazing products.

Paul H.


PA-3B Circuit Boards, Schottky Diodes

Hello John,

     I finished installing the Platinum PA-3B boards and Schottky diodes in my DH-500 over the weekend and I have just one thing to say to you,..............WOW!!!!!!..............I am most impressed!....I spent the weekend listening and it seems the more listen, the better it sounds .....I just wanted to let you know everything went well with the installation and thank you again for all of your help.     Now that my amp and preamp are fully modified to the platinum level, I guess now it is time to work on the digital part of my system.

Scott M.


PA-3B Circuit Boards with Dual-Mono Power Supply

The work is done! Great improvement in the dynamics and imaging. A well worth while addition, I now have dual mono, new boards and great sound. Thank you for the really great amplifier, and the quality of the parts. Maybe now I’ll listen for a while and plunge for the Platinum!

I will write a review of the mods and the kits when I get time.

Thank you, Alastair


Hegeman Hapi One preamp modification

Editor note: If you remember this one you may have a few gray hairs! Stu Hegeman was a well respected designer who designed many products including tubed products, I believe some of the HK Citation tube gear too! The Hapi One was an early IC based preamp.

Hi, John:

Thought I’d let you know that the Harris diodes and changes to some of the power supply caps made a significant improvement in the sound from the Hegeman Hapi 2 preamp. Not only is the sound smoother on female vocals, the soundstage is notably wider and more detached from the speakers, and the bass is really improved, much more solid, quick and detailed, and even a bit deeper. It was the best $120 I’ve spent on sound equipment. It was a lot of bang for the buck. Thanks much. I really appreciate your work.





I installed the LC-500 kits and Schottky diodes last Friday without any problems.  I waited until I reviewed your cut sheet that came in the mail on Saturday before I powered everything up. 

The Adcom 555II amp is a different animal now.  The mods actually improved some aspects that I was not expecting it to.  What I expected, due to the increased capacitance, was a more controlled and definitive bass (which I

have in spades). But, I also got a larger sound stage and what appears to be a "quicker" amp that seems to enhance transients allowing more resolution.  What aspect of the mods produces this effect?  Is this due to the Schottky?

The triple bypass caps (2.2uF+0.1uF+0.01uF)?

Unfortunately, my normal digital front end is awaiting a new power supply, so I did not get the full impact of the upgrade yet (hopefully by next week).  However, I hooked up my cheap Panasonic A110 DVD/CD which normally I cannot

listen to because it is very digital and 2 dimensional.  The mods to the amp have made this player listenable and definitely more 3 dimensional.  I was not expecting this and still puzzled how an amp mod could accomplish this. 

Makes me think I am missing a whole lot of resolution that my normal digital front end provides.  I can't wait to find out!

How much is your circuit mod to remove the servo circuitry?  What areas of performance would this increase? (more natural reproduction? better soundstage? depth?).  How long does the mod take to complete?


Jeff H.

Modified Adcom GFA-5500

Hi, John it’s Frederick W. from Columbus Ga. Thank you for the mod to my GFA-5500 Adcom amp. I am looking forward to Platinum. After John’s LX-Signature mod to my Adcom GFA-5500 amp, I begin to love listening to music again. 

The ups driver dropped the amp off at 5 o’clock and five minutes later I had to stop everything and call John to say, Thank You! Right out of the box, not even broken in yet it sounded fabulous, but just in case you don’t understand what 

I mean by fabulous. For about two years I have been from dealer to dealer trying to figure out why I didn’t like my fourteen thousand dollar system with music. Some said it was the speakers, some said it was my Lexicon. So for two years 

I was about to go crazy trying to find a solution. I found my solution in Musical Concepts mods, and I am so happy I just had to Tell!!!!!!!!!!!!!


Custom modified Dyna PAS-3 with single 6H30Pi tubed line stage. New transformer installed on back panel and massive internal power supply.

Hi John,

The 6H30Pi is amazingly quiet and has a linear sound, meaning that in my system, it’s very well-balanced top-to-bottom. And whisper quiet. Let me also say that I am awed by the sound of the preamp.

And awed by the design. So simple! It sounds wonderful! Such imaging and dynamic range! Great job!

Thanks,  Stuart


Musical Concepts finished products

Signature DVD/CD player(DV-48)

Good Morning.  I wasn’t prepared for the sound, truly a quantum leap this time.  Holographic all over the house, sixty foot  plus sound stage from the listening position, lightning speed  and perfect decay, not to mention wonderful clarity and naturalness.  I am so amused to see my Labradors jump up and race out of the house to bark at something they heard on a disc; the sound is that real.  In short, we love it.  

Al A.


Enigma VII CD player

Editors note: We always have tried to stress that our digital products sound very musical regardless of the underlying technology, bit rates and such! This customer e-mailed us about his 8 year-old Enigma CD player.

Eight year-old Enigma 7 with Berning Microzotl and Grado RS-1 sounds terrific. Excellent bass, eerie vocals and maximum ambience retrieval are just a couple of sonic virtues. Smooth, detailed blah blah blah. Your eight year old design kicks some SERIOUS MUSICAL ass.

I am thinking of adding a tuner. Do you do any mods? Which brand and model? How much?



SuperConnect IV Interconnect Cable

Dear John;

Well, you did it again. You underrated one of your products by saying that times!)

4. Perceived spatial differences between instruments was dramatically time I have gotten more value than for my dollar spent than anywhere else.

Thanks John.

Paul H.