"(...) 'Peter does incredible work on all vintage microphones. One of our favourites is a Neumann/Gefell UM57 totally rehabbed and outfitted with his solid-state multipattern power supply,' Holtzman says."

MixOnline on Les Paul's latest, grammy-awarded album (Eastside Sound NYC)

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"The DN221 is beautifully made(..). The Tubelife-257 and the Gefell supplies sounded fabulous, with strong mids and deep lows, but the DN221 was quite different. (...) Transients seemed quicker and fine details were enhanced. "

MusicTech Magazine

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A small selection of artists and studios trusting in our work:

Atlantico Blue Studios Portugal - Advanced Audio Microphones Canada - Anouar Brahem Tunisia - Phil Caivano/Monster Magnet USA - Capitol Records Hollywood CA ´- Billy Cobham - Coral Sound Inc. NY - Eastside Sound NY - ECM Records Germany - Estudio del Sur Chile - La Fémis France - FLEA Microphones Slovakia - Galaxy Studios Belgium- Paul Giger Switzerland - Gismo 7 Studios Spain - Hawaii Institute of Marine Biology - Helter Skelter Sweden - Hochschule der Kuenste Bern Switzerland - Idee und Klang Switzerland - Institut für Musik und Medien Germany - The Kodak Theatre CA - Kool Savas Germany - KORE Studios United Kingdom - Labomatic France - Luckymusic Switzerland - Madooma Germany - Magnanimous Recording Studio Greece - Mammoth Sound CA - The Mastering Room Sweden - METALLICA CA - Midilive Studios France - MUSE United Kingdom - Musica Divina Belgium - NoHype Studio Belgium - EMI Sweden - NRK Norwegian Broadcasting Corporation - Officine Meccaniche Italy - Pannonia Studio Budapest Hungary - Paraktio Studio Athens/Grecce - Peermusic Germany - Piano Salon Christophori Berlin - Playground 571 Switzerland - Porgy & Bess Austria - Power Sound Studio Netherlands - Powerplay Studios Switzerland - Prolyd Norway - Radio Television Suisse RTS Switzerland - realsound.it  Italy - RED BULL Studios - Matthias Reim Germany - Rock Town Netherlands - Robert Schumann Academy Germany - SEEED Germany- State University of New York - Sonic Pump Studios Finland - Sonogramme France - SRG SSR Television Switzerland - Staatstheater Darmstadt Germany - Studio Dealers Paris/France - Studio de la Grande Armée Paris/France - Studio des Aviateurs France - Studio des Forces Motrices Switzerland - Studio Lakanal France - Studio Syrland Iceland - Stephan Sulke Switzerland - Sunset Sound Studios Hollywood CA - Sutton Sound Studios CA - Svenska Grammofon Studion Sweden - TELEFUNKEN USA - Theater und Philharmonie Essen Germany - Tucan Studio Germany - Tuerk Technologies South Africa - Caglar Türkmen Turkey - Universität für Musik und darstellende Kunst Vienna/Austria - University of Texas Dept. of Music TX - Hrolfur Vagnsson Iceland - Viennabackline Austria - Paolo Vinaccia Norway - Voltart Romania - Wavebase AZ - Wisseloord Studios Netherlands - Wunder Audio USA- YLE Yleisradio Finland - Zack Studio Switzerland - Zurich School of Music Drama and Dance Switzerland - (t.b.c.)

Some of our clients' appreciated feedbacks:

I don't know what to say!  I just setup the SM69 and I have never heard such a beautiful sound come out of this microphone before.  Whatever you did, is magic!  Thank you a million times!
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We will name the mic after you. The 57 is really getting a lot of repeat requests and is satisfying many clients. Great on Chico Freeman's sax on his latest CD. I always let everyone know who brought it to life.
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The PSU definitely gives a huge leap in the sound! Now my U67 sounds more clear, punchy, fat and in detail.  And the case looks totally beautiful and is built like a tank!!
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The mic sounds excellent and is in the condition you described. Great power supply!
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I would like to report that the U67 is working (sounding actually) perfectly after the service you did. Thanks.
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How happy I am with the work you've done on these two mics. They sound fantastic. Thank you !
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What a detailed mic. Blew away our akg's.
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The mic sounds incredibly smooth, especially on the top end. I really love it.
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The power supplies are some of the most beautifully made and beautifully finished pieces of electronic gear that I have ever seen.
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I never heard anything like in my life
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The UM92 has just come back to life! Night and day difference from before we sent it to you.
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Just received and tested the power supply. Perfect ! Our Neumann has no noise at all !
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We are very happy with your work, and I have used the M49 on several live TV broadcasts.
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...never I would imagine that a CMV563 could sound this way. (...) It is now one of the best sounding mics I have ever heard. And I heard a lot of the best sounding "classics" and also new stuff. Biggest compliments.Your work is great and I am really happy with the sound...
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A beautifully sounding instrument... great work - and again, cordial thanks !
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The M269 sounds significantly more open and balanced than I can remember. Many thanks for your awesome work.
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The reskinned capsule sounds amazing. I can't hear any difference to the original. Great job ! Many cordial thanks !
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Many thanks for your outstanding work ! We are very amazed by our matched U87 pair !
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I received your PSU DN 221 and i used it immediately during a recording in the afternoon. The microphone doesn't lose the warm and typical bass... I am very happy to work with you!
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I thank you very much for the absolutely magnificent service. Never experienced anything like this anywhere else !
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You made my studio a much happier place !
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Thanx for the excellent business on the power supply.
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The mic (and power supply) is awesome. Thanks once again.
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Thanks doctor !
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My 87 is now close to perfection!
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My U87 sounds lovely by the way. Thanks again!!!
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I luv your work...
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Many thanks for an excellent product & your very efficient service.
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It's wonderful to have one of my favorite mics finally without "tube frying" noises. I really appreciate all of your good work!
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I always use those mics on EVERY session. They have a certain something...
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Thanks for the good service. Our 87 is at its best again !
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Your support has gone above and beyond any I have experienced anywhere, from any manufacturer or retailer.
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The Brauner you modified for us is... how shall I say... absolutely dynamite !
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Your power supply arrived a few minutes ago. I plugged in the C24 and it is WONDERFUL. No hum, no RFI, nothing but clean sound. THANK YOU!!!!!
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The mic sounds fantastic! Really happy to have it back and performing well. The power supply is excellent. Of course it is VERY well made! I'm glad I decided to buy it.
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You are helping to keep alive the craft of making great sounding recordings! I bow in the direction of Konstanz !
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I tested the KM254 today, and the sound of an acoustic knocks me off my feet. Thanks for your amazing work !
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Many thanks for the microphone !!! I received it completely safe back and it works like it never worked before :)
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The result is amazing: the definition is at its best and noise has gone completely ! A miracle...
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I am so appreciative of your work and help, it is the best on earth! Old world craftsmanship and new world friendliness, what an unbeatable combination !