"(...) '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, Dec.2006

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Scroll down for a choice of people and studios trusting in our work...

Jorge Avendano, Mexico - Angelic Record Productions, UK - Apes on Tapes, Belgium - Audio Unity, Japan - Baba Music, France - Boom Room Studios, Austria - Anouar Brahem, Tunisia - Henrik Cederblom, Sweden - Bunnyco, Belgium - Canorus., TN - Capitol Records, Hollywood CA - Edwyn Collins, UK - Coral Sound Inc., NY - Donagh Long, Ireland - Vlado Dzihan, Austria - Eastside Sound, NY - Electric Productions, Romania - La Fémis Film Academy, France - Goran Finnberg/The Mastering Room, Sweden - Fox Music Company, Germany - Antoniano dei Frati Minori, Italy - Paul Giger, ECM Switzerland - Koen Gisen, Belgium - Gismo 7 Studios, Spain - Studio Syrland, Iceland - Hawaii Institute of Marine Biology - Helicopter, Belgium - Helter Skelter, Sweden - Hickorystreetstudio, NY - Hochschule der Kuenste Bern, Switzerland - Jolly Roger Recording, NJ - Justin King, OR - The Kodak Theatre, CA - Labomatic, France - Luckymusic, Switzerland - Madooma , Germany - Magnanimous Recording Studio, Greece - Mammoth Sound, CA - McDonnell Productions, Netherlands - Doug McKean, CA - Guido Martens, Belgium - Bart Mombaerts, Belgium - Shinichiro Murayama, CA - MUSE United Kingdom - Nelldal Productions, Sweden - NoHype Studio, Belgium - Gunnar Norden/EMI, Sweden - Officine Meccaniche , Italy - Opera Prima Italy - Organic Music, Germany - Paraktio Studio, Athens/Grecce - Peermusic, Germany - Piano Salon Christophori Berlin - Benoit Piccand , Switzerland - Playground 571 Switzerland - Porgy & Bess, Austria - Power Sound Studio, Netherlands - Prolyd, Norway - Regime Studios, CA - Qubitt AB, Sweden - realsound.it  Italy - Matthias Reim, Spain - Rising Sun Studio, Belgium - Riverbend Studio, IL - Rock Town, Netherlands - Rohrklang, Germany - Oddvar Ruud, Norway - Silent Sound Studio, Canada - Silver AB Martin Hedström, Sweden - Silverstone Studios, NY - Soundpark Studios, Germany - Soundspur Records, Austria - Soundtrack Studio, Sweden - State University of New York - Studio de l'Arrosoir, France - Sonic Pump Studios Nino Laurenne, Finland - Studio de la Grande Armée, France - Studio des Aviateurs, France - Studio des Forces Motrices, Switzerland - Studio Intonato Ted White, CA - Studio Lakanal, France - Studio Syrland, Iceland - Sutton Sound Studios, CA - Svenska Grammofon Studion , Sweden - TELEFUNKEN USA - The Audioplex, Singapore - Theater und Philharmonie Essen, Germany - Eventkoordination M.Vetters, Austria - Tonstudio Solle Everswinkel - Tucan Studio Germany - Tucton Audio Service, Switzerland - Tuerk Technologies, South Africa - Caglar Türkmen, Turkey - Tundra Records, Denmark - University of Texas Dept. of Music, TX - Hrolfur Vagnsson, Iceland - Paolo Vinaccia, Norway - Voltart, Romania - Wavebase , AZ - Martin Westlund, Sweden - Wildplum Studio, CA - Wonderlust Productions, UK - Yleisradio Finland - Zack Studio, Switzerland - Zurich School of Music, Drama and Dance, Switzerland - (t.b.c.)

Some of our clients' appreciated feedbacks:

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 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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...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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Ein wunderschön klingendes Instrument... grossartige Arbeit - und nochmals herzlichen Dank!
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Ich bin nach wie vor entzückt über diese hervorragende und wunderbar verarbeitete Lösung.
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Die reskinnte Kapsel klingt hervorragend. Ich kann keinen Unterschied zum Original feststellen. Tolle Arbeit! Vielen herzlichen Dank!
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Vielen Dank für Ihre tolle Arbeit! Wir sind sehr begeistert von unserem 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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Ich bedanke mich sehr herzlich für ihren absolut grossartigen (und von mir in der form bisher noch nie erlebten) service!
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Your Power Supply looks brilliant,
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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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Danke für den guten Service. Das U87 funktioniert wieder bestens!
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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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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.