Un Hobby: ricostruzione, recupero, ammodernamento di antichi sistemi HiFi, valvolari e non

  Ho deciso, su richiesta di vari amici, di aprire questa pagina con la storia della ricostruzione di vecchi, antichi, introvabili sistemi di Alta Fedelta' HiFi, quasi esclusivamente valvolari, ma anche giradischi e casse acustiche e qualche transistor HiEnd. Ho scelto di presentare anche gli apparecchi piu' economici, piu' facili da trovare che pero' forniscono un suono meraviglioso una volta ricondizionati, ma non vi risparmio qualche Audio Note, Krell, ARC, Quad e Jadis su cui ha avuto l'onore di mettere le mani.

  Questo hobby mi ha permesso di ascoltare apparecchi stupendi e qualche volta difficili da raggiungere per un comune audiofilo. L'approccio e' quello del restauro di una opera d'arte, in cui si cerca di preservarla senza cancellare tutti i segni del tempo ma cambiando la cornice di un quadro ormai diventata mangime per gli insetti (attenzione anche la cornice fa la storia del quadro).

  Please note that all the work presented herein this site is non-commercial. This is my hobby and I am doing this in my spare time. Some restoration project run for a month, some for one year! Through this page I freely share my knowledge with you. But if you like my work, please consider to donate some bitcoin to me (see code at the end of every project).

  As already said repairing HiFi is not my main job. I have a full-time job, in fact I have two. Since I don't depend on repairs for my regular income, I can enjoy wasting time on restorations whose commercial cost would far exceed the valuation of the equipment itself. The downside is that sometimes my time is a bit long (a year for the Quad II, and almost another for the PX-2). Not doing it as a job though, my friends know that I choose what I like to study first, then restore, and finally listen to!

  Please note that I'm not affiliated with the people or companies from the links in all of those pages. I just find them interesting or good sources of components/schematics/suggestions.

  I should begin by saying that working on Audio Equipments presents a very big health hazard. There are lethal voltages inside (as example the Type 845 tube run up to 1250V to produce 75 Watt). Not knowing what you are doing might result in severe accidents and possibly death by electrocution. I am very skilled in electronics repair and I have been doing such repairs for almost 50 years! This qualifies me, a little, to work in this field. But if you do not have experience, please take this information just as a knowledge base. Do not attempt to repair something that you cannot handle as there is a big probability to completely destroy the equipment, and further you also suffering accidents. (text extracted and modified from here)

BBC EL34 tube amplifiers (Sound Sales, LSM/10/133)

  Introvabili, ne ho visti solo una coppia. Venduti fra due persone che conosco. Sono due monofonici costruiti in Inghilterra, nel Surrey forse negli anni 50.

  Domandando, domandando ho scoperto che la Sound Sales Ltd aveva sede proprio in West Street a Farnahm, nel Surrey e costruiva per gli studi di registrazione con schemi e specifiche della BBC (cosi' mi hanno detto!).

  Seguendo questo link potete trovare alcune foto, lo schema elettrico, un piccolo suggerimento per l'aggiornamento. PRIMA di continuare a leggere queste sono le istruzioni. Read these instructions BEFORE start reading.

H.H. Scott, Stereomaster, 299C

  Questa e' una vera ricostruzione. Esiste tutta una serie di piccoli amplificatori valvolari integrati da 10W fino a circa 30W, degli anni 50 e 60, che sono molto apprezzati sia perche' ben costruiti sia perche' ben suonanti.

  Lo Scott 299C e' un magnifico apparecchio, monta come finali delle 7189 che sono considerate dagli audiofili valvole ben suonanti. Come quasi tutti questi integrati la sezione pre (oppure la sezione tuner-pre) e' spesso sacrificata ed invece la sezione finale e' buona e/o ottima.

  Questo apparecchio era danneggiato e nelle pagine seguenti potete trovare alcuni cenni alla sua ricostruzione ed anche aggiornamento (tipico per questi integrati).

  Seguendo questo link potete trovare alcune foto, lo schema elettrico, molti suggerimenti per l'aggiornamento. PRIMA di continuare a leggere queste sono le istruzioni. Read these instructions BEFORE start reading.

Electronic Instrument Co. Inc, Eico ST-40

  Anche per questo apparecchio qualche problema specialmente nel reperire le valvole ed i condensatori.

  Anche l'Eico ST40 e' un magnifico apparecchio, usa come finali le 7591 che negli anni 50 furono progettate appositamente per HiFi.

  Dobbiamo ringraziare la JJ Electronic, nella Repubblica Slovacca, una volta conosciuta come Tesla e poi rilevata da un industriale forse lungimirante per la possibilita' oggi di trovare ottime valvole HiFi e appositi condensatori ad alta tensione.

  Seguendo questo link potete trovare alcune foto, lo schema elettrico, il manuale di montaggio e di manutenzione (gentilmente fornitomi da un appassionato). PRIMA di continuare a leggere queste sono le istruzioni. Read these instructions BEFORE start reading.

Krell KSA200b, KRS2

  Non sono amplificatori valvolari ma dopo averli ricondizionati con componenti assolutamente originali e seguendo scrupolosamente le istruzioni del costruttore per la taratura, bisogna dire che nonostante tutti gli anni di onesto lavoro suonano davvero bene, specie il finale.

  Per vari motivi posso mostrarvi solo qualche foto (.JPG ~50 KBytes), del finale, e del pre, ma vi assicuro un suono roccioso, nitido, con una microtrama complessa.

  Ascoltandoli non si puo' dar torto a chi dice che i transistor (solo quelli da magnifici in su!!) cominciano a suonare bene dopo dieci anni di lavoro onesto senza strafare. Forse e' proprio la struttura stessa della giunzione che si modifica ammorbidendo quella spigolosita' e quella durezza che li allontana, da nuovi, dai valvolari.

Conrad Johnson PV10

  Uno dei nomi mitici dell'HiFi valvolare. Questo e' uno dei suoi piccoli pre ma e' forse il piu' famoso nelle sue varie versioni. Lo schema non e' facile da trovare ed anche gli aggiornamenti descritti sono spesso lacunosi.

  Spesso questi vecchi apparecchi sono stati manomessi da grandissimi esperti o profondi incompetenti con risultati discutibili. Anche questo.

  Come al solito una pagina dedicata alla descrizione, agli schemi ad un'aggiornamento che non chiamerei modifica. PRIMA di continuare a leggere queste sono le istruzioni. Read these instructions BEFORE start reading.

Rebuild Woofer, Midrange, Tweeter

  Many of these components have a suspension that connects the moving part to the basket made of foam (in italian spugna but this is not a good translation). This soft, flexible material allows movement and acts as a centering device and mechanical support for the moving part, which is usually a cardboard cone.

  Over 10 to 15 years, the foam degrades due to radical oxidation caused by the oxygen in the air. First, the polymer chains shorten, then, the foam completely depolymerizes (crumbles) into a sticky mixture of dimers resembling bitumen. If the problem is noticed early, the component can be saved and rebuilt.

  Follow this link to see examples of reconstruction that often save original speakers that are impossible to find. The link also contains a discussion on restoring foam, voice coils, cones, spiders, and more for woofers and tweeters.

Audio Technica 1005II, turntable arm rewiring

  Many people may not believe it, but I assure you that high-quality cables (top brand silver cable) inside a quality tonearm make all the difference. When transporting electrical signals ranging from zero to a few hundred microvolts (as in the case of a true moving coil) or up to a few millivolts (for MM), even the slightest resistance due to soldering and/or the cable can cause problems..

  Manufacturers are not stupid; however, market forces often require them to cut costs in certain areas. If they haven't cut costs on the mechanics, we can intervene with rewiring, as in this case.

Audio Note M3 and M6 phono-line preamp(s)

  Sorry for Italians but I see readers of those pages from many countries in the world so I like to write in english (as italian!). I already repair one M3phone and one M6phone of AudioNote UK, very interesting equipments well-designed and well-built. Having time I write e web page with some photo and the solutions of the problems, wait please.

Croft Supermicro Limited Edition

  One of the simplest tube preamps, but also with a good sound. With difficulty you can buy used, when available if often badly modified to (according to them) overcome some of its problems such as low gain.

  But why denature a Croft Micro or even a Supermicro? There are many preamp with high gain, dozens of inputs and outputs, dozens of kilograms of material, and maybe even a good sound, maybe the cost a little higher.

  Following this link you can find some photos, wiring diagram, a small tip for the update. BEFORE you continue reading these instructions. PRIMA di continuare a leggere queste sono le istruzioni.

Ethernet CAT6 / CAT6a cables as speaker cable

  The new Unshielded Twisted Pair (UTP) Ethernet cable label CAT6, used in Level 6 environment, can be used as internal speaker cable with success. But there are 2 cable forms, 3 different sizes of cable, and almost (2 methods) to link the 8 wires!

VTL stereo 75/75 power amp

  The first VTL products were originally designed in 1980 in South Africa by recording and film engineer David Manley, immediately VTL are recognised for the musical sound quality and for the use of "old" but well know schematics. Here there is show the restoration of one (stereo 75/75) power amp. Read these instructions BEFORE start reading.

Tannoy HPD 385 crossover

  More and more web pages was devoted to describe or modify the xover of old Tannoy speaker, as Arden, Berkeley, GRF, Autograph, Cheviot and other. Having hobby of restoration of old HiFi tube equipment of course sometime I like to work on speaker, turntable, arms, or crossover to be rebuild. Please follow this link to HPD 385a crossover repair.

TDL, monitor studio 4

  One of the major speaker from TDL electronics, not the 4 way RSTL, not the 4 way Monitor, the 3 way Monitor Studio 4, equal to Monitor Compact. One of the more interesting transmission line speaker. The speaker was restore principally in crossover and in the rubber of the midrange.

TDL, BS2 BookShelf

  Incredible one, the TDL Transducer was product a bookshelf! One of my friend buy in internet those speakers, completely destroyed, woofer and tweeter "without" foam, with the crossover in ?? And so on. But the box is in good condition so is interesting make a tentative of restoring.

Acrosound Stero 20

  Probably you know the Acrosound as one of the best producer of tube output transformer, it is true, but the Company build and sell some tube power amp and preamp. Someone describe those amp as one of the better sound (for the age) but with a lot of problems in reliability and in tube life (by overload). Of course this Stereo 20-20 suffer a lot. Read these instructions BEFORE start reading.

A.C. Magnum MF125

  A.C. Magnum Limited was a small British audio component manufacturer, was started many years ago by the one of the founding fathers of the REGA Planar turntable. Magnum is famous principally for power amp using MosFet, an example is this MF-125 mono amplifier. Read these instructions BEFORE start reading.

The Ground Loop Problem

  How to use the pin n.1 of XLR? Probably there are 10.000.000 bad installations in the world. How to reduce the hum from ground loop? And how to protect safety? Some reply from me after reading the Major HiFi designer (of course after reading we discorver our incompetence in this field).

Thickness of PCB copper, a big problem

  Probably no one has any idea how thin the copper layer we see in any printed circuit board is. If this is used for an operational amplifier (as LME49713, AD811, or super expensive and impossible to find AD9610 metal) everything is fine but what happens in a filter where 10A passes or for an output transistor capable of driving 20A peak?

  Now between these two PCBs, thinner than a hair, we put a cable of 1000 euros per meter !!

Probably the best KT66 power amplifier

  With a pair of KT66 tubes we can get almost 20W. Probably the reader is thinking of the Heathkit W5M, or the famous Leak TL12.1, or at the RCA LM-32216A power amplifier (MC30 father?).

  No, we're talking about The Best sound amplifier, with the simplest scheme, with a spectacular transformer, capable of piloting electrostatic speakers without problems, who is it? Read these instructions BEFORE start reading.

One of the best japanese tangential tonearm, and turntable!

  No fuss and talk, to read a vinyl record you need a tangential arm. But producing a good tangential arm that mimics the factory engraving arm is difficult. Yamaha produced a turntable that some consider to be the best of the best, the PX-1, here we fix and remove some flaws from its little brother, the PX-2.

  There is the PX-3 but cut and cut to lower the price little is left.

Build a PX-1.7 from a perfect PX-2

  Already said, to read a vinyl record you need a tangential arm. In a previous web page we study, understand the working principle and finally resurrect a "dead" Yamaha PX-2, but ...

  Study of the PX-2 reveals some design choices that were perhaps useful in reducing the selling price but could have been avoided. Or else they did not want to get too close in quality to the magnificent PX-1. However, many design choices can be improved. Unfortunately, the wonderful tonearm of that cannot be copied.

Vintage Marantz 7C, recap

  Every 2 or 3 years I remove the wooden frame and the two metal covers and open my Marantz 7C (European model 234Vac) for a visual check.

  This time some capacitors have cracked, I have to work on them.. Read these instructions BEFORE start reading.

Correct measurement of the capacitance of an audio cable

  So much is discussed about the capacity value of an audio cable, an important number especially for turntable tonearm cables.

  But as always we hear a lot of chatter, let's try to shed some light on it with this webpage.

We design and build a PCB for Lundahl transformers

  Lundahl makes excellent transformers (as many audiophiles recognise) for all audio purposes, even transformers for moving coil cartridges, but does not produce the PCBs for their assembly so we can design (open source) a PCB for many Lundahl transformers.

Repair a Leak TL12+

  After the war, entrepreneur Harold Joseph Leak produced his first amplifier in 1945, claiming an astonishing 0.1% THD, but a few years later, in order to sell, compromises were made, reducing the power to 12W with the TL/12, also known as Poin One. However, a further cut was made to the circuitry (the guy drove a Rolls Royce) and the TL12+ was produced, which is here for repair.

TDL 3201 woofer

  While restoring a pair of TDL Monitor Studio 4 speakers, we discovered that the woofers' rubber suspension had hardened to such an extent that it severely distorted the frequency response of the low audio range. Action must be taken.

TDL Monitor Compact

  TDL had a production agreement with A.O.S. in Germany to manufacture the “Monitor” series. My friend Jacek from Poland bought a couple of them that need restoration.

Fixing a speaker driver

  To update a crossover or repair a driver, you have to dismantle and reassemble the woofer or banana panel, but the wood gets damaged and the screws no longer hold. better use the tee nuts.

Next one

  And this is the next rebuild.

         
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