Newsgroup: it.arti.musica.strumenti.chitarra
Titolo: Jrc 4558 e ts5 ibanez

Chiedo scusa per l'insistenza , ma scrissi un po' di tempo fa per chiedere
informazioni riguardo le istruzioni per la modifica del ts5 . Ho cercato in
giro su diversi siti americani (analogman, fuzzcentral .....) ma non ho
trovato nulla; ho spedito e-mail ai curatori dei siti , ma non ho ricavato
informazioni apprezzabili, se non altri siti da visitare che, a loro volta,
non mi hanno dato informazioni utili. Sempre e solo schemi e instruzioni per
il Ts9, Ts10. Nessuno del NG ha mai modificato (o fatto modificare) il Ts5?
é possibile trovare istruzioni per la modifica di questo pedale  che (almeno
io) ritengo sottovalutato?
Grazie in anticipo a chiunque mi risponda
Saluti
Luca

Cosa? ma guarda Luca cosa ha osato scrivere...

A te... devo farlo anch'io...
http://www.geocities.com/SunsetStrip/Vine/6655/tubescreamer.htm
Ciao...
PS vieni sul forum di Fennec a parlarne: 
manuelconti.supereva.it
Ola

 ha scritto nel messaggio
news:i4wnc.167680$hc5.7...@news3.tin.it...

atk mi ha battuto sul tempo........ ;-))
io l'ho modificato seguendo quello schema.
occhio alle saldature, levare l'IC non è semplicissimo se non sei un minimo
esperto
ciao
rude

Cosa? ma guarda rude cosa ha osato scrivere...

E ora come suona?
Ho letto sullo schema che posso sostituire il chip anche con un TL072...
Fa lo stesso?
Ola

 ha scritto nel messaggio
news:i4wnc.167680$hc5.7...@news3.tin.it...


 Fa lo stesso?
ennň, che non fa lo stesso ;-)))
La tradizione vuole il JRC4558D, altrimenti non si suona come SRV,
ecchecazzo! ;-)
Io ho il JRC sia sull'SD1 (originale, non ho fatto modifiche neanche alle
resistenze) e sul TS5 (modificato).
Il TS5 č un pň piů "aperto", ma ha meno volume dell'altro, che uso
sostanzialmente come boost ai miei due RAT.
ciao
rude

 Fa lo stesso?
ho trovato qualcosa (non quello che ti dicevo nel post precedente, però)
copio e incollo
***********
The Opamp
The TS808, the TS9, most TS9 Reissues, and some of the 10's and perhaps a
few 5's came with the "JRC4558" dual opamp. Most 10's, almost all 5's and a
few 9 RI's came with other opamps. The JRC4558 is a dual opamp with
"industry standard" pinouts which means that there are perhaps fifty
different dual opamps from different manufacturers that will fit in the same
holes and work.
There seems to be a difference in sound depending on what opamp is actually
in the circuit. In fact, this may be the single biggest effect on the sound
of the TS circuit. The JRC parts were undoubtedly chosen by the design
engineer primarily because they were cheap. During the time the 808 was in
production, the JRC was oneof the cheapest dual opamps on the market with
acceptable audio performance. As such, it was used in huge volumes of
Japanese audio equipment. The opamp is described in some Japan Radio
Corporation (JRC...) literature as "an improved dual 741 type opamp with
better noise, drive capability, and slew rate than the original 741 type
opamps". Note that this is not saying much, as the 741 is a fairly abysmal
audio part.
For some reason, the JRC4558's seem to be well suited to duty in the TS type
circuit. JRC later changed its name to New Japan Radio Corporation and made
parts titled "NJM4558". By most reports, these sound abysmal. So do the
NJM4558's, 72558A, and several other types reported in the 10's and 5's.
From the brave souls who took the suggestions in the tube screamer clone
section over on GEO and put in a socket to swap parts, the following types
of opamps DO seem to sound good.
LM833
RC4558, made by a couple of US firms
TLC2202
TLC2272
OP275
LT1214
What makes for a good opamp versus a bad one? I dug through the data books
on the ones that people told me sound good, and came up with a common
factor. The ones that sound good seem to all make a point that they recover
from overdrive gracefully. I can hear you asking "what the devil does that
mean for opamps?" It's like this - in a feedback configuration, an opamp's
enormous gain keeps both inputs within a few millivolts of each other all
the time, every nanosecond. When the opamp is driven to the point where the
output is near a power supply voltage and cannot swing any further, the
feedback is no longer keeping the inputs together, and one input is driven
further toward a power supply than the other. This can cause some ugly
things to happen. In some opamps, the output inverts polarity for a few
microseconds. I'll leave it to you to imagine how ugly those little "blatts"
sound. In other opamps, the recovery time from overload is slew rate
limited; the output does not follow a multiple of the input, but "slews" at
a fixed rate until it catches up to the amplified input. This also sounds
bad.
While the clipping opamp is not driven into overload, I theorize that the
sudden change of gain every time the diodes go into and out of conduction
can cause a similar although briefer recovery period at each "corner" of the
clipped waveform. In this period, you'd get non-harmonically related
artifacts that would neve be very big (all that lowpass filtering, remember)
but which would be audible as a harshness or edginess.While this is just a
theory, it does seem to meet the only observed facts, and has predicted a
couple of opamps that did sound good. You're free to come up with your own
theory, of course, but I like this one. It has worked so far.
There is some confusion at present over what is a true or "vintage" JRC4558.
Several electronics suppliers list the JRC4558, but reports are that you get
the NJM4558 when you receive the order. This is probably because New Japan
Radio Corporation, the maker of the original and the NJR part, insists that
the NJR part is a valid replacement for the JRC. And it probably is, for the
things that an electronics supplier wants to see. Subtlties of tone in a
distortion pedal are not even on the opamp maker's radar screen. Some direct
calls to NJRC and some distributors produced an offer to sell "JRC4558" in
5000 unit lots for $1.58 each, a flat denial that they could be had any
more, and a company representative saying that NJRC probably wouldn't
consider starting up the old process line for fewer than 50 million parts.
What is happening here is that all semiconductor processes mutate with time.
As the silicon and photolithography gets better, the semiconductor houses
optimize their fab processes to make more parts that are still within the
spec. In general, this means smaller chips, and more chips per wafer. The
improved performance of each part lets them make the chip smaller, more
chips per wafer, and ergo more money per unit of work, since the unit of
work in a semiconductor fab is the wafer. Therefore, there aren't going to
be any more "vintage" JRC4558's. Does this matter?
Probably not. There were zillions of the real "JRC4558" made when it was
current. They are still available in isolated caches of parts, although they
can sometimes be hard to find. John Greene did some detective work, and
received indications that the original JRC4558 was marked "JRC4558D" and did
not have a date code on it, the date codes happening later. However, another
company rep indicated that the date codes started about the time the TS
series was being made, so the date code is not conclusive. Also, the
JRC4558D was used in tons of Japanese audio equipment at about the same
time, so a junky cheap Japanese stereo or clock radio could have several
hidden inside it. Can you say "Goodwill"? I thought you could.
The best thing to do, I believe, if you're hunting the Tube Screamer Holy
Grail is to stick in an 8 pin socket on the board, noting the orientation of
the original chip carefully, and then just plug in various dual opamps until
you find one that conjures up images of your own personal guitar deity.
************
per altre notizie:
http://www.geofex.com/Article_Folders/TStech/tsxtech.htm#opamp
ciao
rud

 pedale...... da qualche parte dovrò pure cominciare! o no?
se fai qualche errore, rischi di rovinare un pedale pagato qualche decina di
euro.
Ad esempio, se usi il saldatore sbagliato rischi di bruciare le resistenze,
oppure rischi di fare qualche saldatura "fredda" e il pedale non funziona
più.
Sei in grado di capire l'errore fatto?
Sei in grado di valutare se e dove il circuito si interrompe?
Non voglio spaventarti, le cose elencate sono facilmente risolvibili,
ma..... valuta tu se questa è la strada giusta per fare pratica, tutto qui.
Personalmente, da un pò di tempo a questa parte, considero meno affascinante
il tempo dedicato alla modifica di un pedale rispetto a quello dedicato a
suonare. ;-))
ciao
rudy