Rochester has been around a very long time.
It used to be that manufacturers manufactured and distributors held stock to sell. It's really two very different businesses and usage of capital.
Sometimes very old stock lingered in distribution. And then US tax law changes eliminated the "asset value" of old stock. Book publishers' back catalogs vanished, and a lot of electronics distributors mergered or vanished.
Yet there IS demand for small lots of odd parts. The B-52 has been flying for 60+ years (with a couple updates). Thousands of industrial machines designed in the 1970s are still running, and an occasional vintage repair part is far cheaper than an all-fresh re-write.
IIRC Rochester used to be a mid-line distributor but fell into the role of old-parts broker. They knew where dusty parts were, could do you a deal for a few, and sometimes bought-out bulk stock when they could predict a profit. Essentially they took a long view of the market. After some years in that game, some critical chips became totally sold-out.... and being "obsolete" technology Rochester could buy foundry time or machines at yard-sale price and produce brand new vintage chips.
How they work with Mouser is news to me but not new business. Popular parts, the distributor (Mouser) will buy and hold inventory. (Heavy parts like tube transformers, Hammond's drop-ship connection saves money in inventory and single-shipping.) Rochester's parts are NOT popular. Mouser would not want to hold them for possible buyers. Rochester clearly has faith in buyers, and the storage cost for chips is trivial. The capital cost can be large but it is more per-wafer than per-chip, so again Rochester would logically take that investment. Mouser is of course the best order-taker in the business, and cross-connecting their order fulfillment is logical.
It used to be that manufacturers manufactured and distributors held stock to sell. It's really two very different businesses and usage of capital.
Sometimes very old stock lingered in distribution. And then US tax law changes eliminated the "asset value" of old stock. Book publishers' back catalogs vanished, and a lot of electronics distributors mergered or vanished.
Yet there IS demand for small lots of odd parts. The B-52 has been flying for 60+ years (with a couple updates). Thousands of industrial machines designed in the 1970s are still running, and an occasional vintage repair part is far cheaper than an all-fresh re-write.
IIRC Rochester used to be a mid-line distributor but fell into the role of old-parts broker. They knew where dusty parts were, could do you a deal for a few, and sometimes bought-out bulk stock when they could predict a profit. Essentially they took a long view of the market. After some years in that game, some critical chips became totally sold-out.... and being "obsolete" technology Rochester could buy foundry time or machines at yard-sale price and produce brand new vintage chips.
How they work with Mouser is news to me but not new business. Popular parts, the distributor (Mouser) will buy and hold inventory. (Heavy parts like tube transformers, Hammond's drop-ship connection saves money in inventory and single-shipping.) Rochester's parts are NOT popular. Mouser would not want to hold them for possible buyers. Rochester clearly has faith in buyers, and the storage cost for chips is trivial. The capital cost can be large but it is more per-wafer than per-chip, so again Rochester would logically take that investment. Mouser is of course the best order-taker in the business, and cross-connecting their order fulfillment is logical.
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I presume Central Semiconductor works similarly to Rochester. I've looked for obsolete jelly-bean BJTs and Central shows up as an in-stock manufacturer for a couple dollars each.
Richardson is now part of Arrow. i've purchased from them and RfParts (rf eqpt and new tubes)
Newark still has very broad industry coverage.
prr did you mean digikey or mouser?
Newark still has very broad industry coverage.
prr did you mean digikey or mouser?
Back on topic, the following images show the output waveform and frequency spectrum of a single J112 JFET gain stage, biased to about 0.3 mA, powered by 18 volts, and with the collector resistor value tweaked for maximum output headroom.
The input signal was set so that the output was just short of actual clipping on either half-cycle.
The circuit was simplicity itself, with a 1M gate resistor to ground. The JFET source resistor was, I think, 8.2k, and was fully bypassed with an electrolytic capacitor.
I have never seen this much soft nonlinearity from any other JFET family I've used in the past. LTSpice doesn't predict this much nonlinearity from its J112 model, either. My guess is that the J112 (and probably its relatives, J111 and J113) have non-uniform channel doping or channel geometry, and don't quite follow the usual JFET square-law I/V characteristic; they appear to be even more non-linear than that.
-Gnobuddy
The input signal was set so that the output was just short of actual clipping on either half-cycle.
The circuit was simplicity itself, with a 1M gate resistor to ground. The JFET source resistor was, I think, 8.2k, and was fully bypassed with an electrolytic capacitor.
I have never seen this much soft nonlinearity from any other JFET family I've used in the past. LTSpice doesn't predict this much nonlinearity from its J112 model, either. My guess is that the J112 (and probably its relatives, J111 and J113) have non-uniform channel doping or channel geometry, and don't quite follow the usual JFET square-law I/V characteristic; they appear to be even more non-linear than that.
-Gnobuddy
Attachments
the problem is input range where the nonlin is seen.
its a sweet 'spot'.
there is little headroom just above then hard clip is seen.
its a sweet 'spot'.
there is little headroom just above then hard clip is seen.
I agree. To some degree, this is a problem with all simple solid-state nonlinear circuits. Note that exactly the same problem applies to the circuit in post #1 of this thread, and that circuit is considerably more complicated.jfetter said:
This particular circuit (a J112 common-source stage biased to 0.3 mA) is better than most simple solid-state analogue distortion circuits in this regard. The J112 has a lot of nonlinearity just before clip, as you can see in the images I attached in my previous post. This means there is still an audible amount of low-order distortion at much lower drive levels. There is a reasonable range of input levels during which you hear progressively increasing amounts of distortion; it's not a sudden harsh onset of distortion like the ever-popular clipping diodes found in a thousand guitar distortion pedals.
Also, the JFET circuit is so simple that it is easy to cascade two or three identical stages. Put resistive attenuators in between each gain stage, so that the output signal is cut back down to an amplitude suitable to drive the next stage into gentle nonlinearity. Each stage contributes a bit more smooth, progressive distortion.
It won't be the same as a good tube guitar preamp. But it is a simple circuit that provides smooth, low-order harmonic distortion in audible amounts, without the harshness that plagues diode-clippers, or the complexity of an assymmetrical long-tailed pair like the one Bucks Bunny shows in post #1 of this thread.
-Gnobuddy
Oddly enough, I have. A friend had one, given to him by someone else, dusty and faded on the outside, but working as well as ever. I don't know my Jazz Choruses, so I couldn't tell you what year or version it was.PRR said:
IMO reverb, delay, and chorus all help to cover up the cold-steely-thin, too-clean sound of a very low THD solid-state guitar amp. But it is not quite the same thing as whatever it is that goes on in a great tube guitar preamp set to nearly-but-not-quite clean, with just a few percent low-order THD, gentle squashing of transients, and whatever else might be going on.
I know the Jazz Chorus was popular with jazz guitarists, who probably loved its light weight, solid bass response, and lack of audible THD; those guys love to play bizarrely complex chords that already have all the "colour" built in, I think, so they wouldn't want any audible tubey distortion. But I would guess the Jazz Chorus was not at all popular with, say, blues or rock guitarists, even the ones who were "comping" chords on the track.
I'm not suggesting that there is magic pixie dust in tubes by any means - I think some of the digital modelling amps and preamps are starting to sound convincingly good of late. But I don't remember the Jazz Chorus appealing to me significantly; it sounded less-good than my budget-priced, hybrid Fender Super Champ XD, set to the clean channel, once you turned it up far enough for the tube power amp section to start working a little.
This video contains several currently-available solid-state amp-in-a-pedal devices, designed to plug straight into your computer, and make your guitar sound as though it went through a great tube guitar amp. I think the Ampli-firebox is particularly good: The Ultimate Preamp Pedal Shootout! - Creating GREAT Guitar Tones Without an Amp - YouTube
-Gnobuddy
JFETs begin to seem less "simple" when one has to consistently build one circuit after another.
I think that with proper circuits one can achieve tubey sounds with all devices and - like with tubes - there isn't a magic device that always guarantees a "tubey" tone. Jazz Chorus is a great example how one can employ (supposedly tubey) cascaded common source FET gain stages and build a very sterile, hifi sounding preamp with horrible distortion tone. Then we can take circuits with very generic overdrive schemes such as FlexWave (diode clipping) and TransTube (overdriven bipolar transistors) and achieve very "tubey" performance simply due to clever bias shifting they employ in addition to clipping. (Peavey designers figured it bares more importance than using FETs instead of more consistent BJTs).
The differential of the OP... It's indeed nice for soft clipping (and because of that the circuit was featured in triangle-to-sinewave converters already in the early 1970's) but one must use it without feedback and at few millivolts of input signal range maxim. So it can and probably will get noisy. It will clip very nicely and softly (and without the tilted emitter degeneration very symmetrically as well) but in reality that is very different from how a generic common cathode triode gain stage clips. And as said, without any DC offset shifting (and dynamic shifting in harmonic content) the distortion will be lacking all complexity and dynamics we typically associate with tube distortion.
I think that with proper circuits one can achieve tubey sounds with all devices and - like with tubes - there isn't a magic device that always guarantees a "tubey" tone. Jazz Chorus is a great example how one can employ (supposedly tubey) cascaded common source FET gain stages and build a very sterile, hifi sounding preamp with horrible distortion tone. Then we can take circuits with very generic overdrive schemes such as FlexWave (diode clipping) and TransTube (overdriven bipolar transistors) and achieve very "tubey" performance simply due to clever bias shifting they employ in addition to clipping. (Peavey designers figured it bares more importance than using FETs instead of more consistent BJTs).
The differential of the OP... It's indeed nice for soft clipping (and because of that the circuit was featured in triangle-to-sinewave converters already in the early 1970's) but one must use it without feedback and at few millivolts of input signal range maxim. So it can and probably will get noisy. It will clip very nicely and softly (and without the tilted emitter degeneration very symmetrically as well) but in reality that is very different from how a generic common cathode triode gain stage clips. And as said, without any DC offset shifting (and dynamic shifting in harmonic content) the distortion will be lacking all complexity and dynamics we typically associate with tube distortion.
I used to look for stuff like this, however a 12AX7 or 6922 cost a few bucks each and can be used to provide the tube sound to SS amplifiers.
A 12AX7 and 6922 pure triode output section with MJE13007 current boost provides 30w from a 150v B+. fantastic little amp
A 12AX7 and 6922 pure triode output section with MJE13007 current boost provides 30w from a 150v B+. fantastic little amp
Sure. What is optimum for mass-production is not the same thing as what is optimum for one-off DIY construction. The latter is what this forum is all about.teemuk said:
It's easy to see why digital modelling has been the focus of mass production (for "tubey" solid state distortion) for some time. Costs come down with large production runs, results are consistent from unit to unit, upgrades are a firmware change away.
It's also easy to see why analogue nonlinear circuits have been the focus of DIY. For a one-off, the cost of the digital circuitry exceeds the cost of the analogue, and then there is the additional (and enormous) complexity of developing the appropriate software.
From clips I've heard, both Flexwave and TransTube sound decent once cranked deep into distortion, with the dynamic bias shifting contributing some complexity to the distorted sound. But clean tones are still thin-steely-sterile-clean, and the all-important smooth and progressive transition from cleans to distorted tones is lacking.teemuk said:
John Murphy seems to have been the originator of the "duty-cycle modulation" concept back in the early 1990s, and the sound clips I've heard of his products from 25 - 30 years ago had exactly the same problem. Reasonably rich distortion once deeply overdriven, but thin and steely clean tones, and lacking the crucial gentle progression between the two.
Mediocre guitarists (like me) tend to dial in one level of distortion and stick to it through the entire song; great guitarists, like session master Tim Pierce, vary the level of distortion continuously, by setting signal levels in that transition range where the guitar amp can go from clean to distorted simply by varying picking intensity on the guitar.
As an example, notice how there is this sort of dynamic variation in almost every single phrase in this Tim Pierce video (i.e. in a group of three or four notes, one will be picked much harder than the others to alter the distortion level within the phrase): I WORKED with one of my HEROES | My Guitar Session - Joe Cocker | Have a Little Faith in Me - YouTube
For a really bad guitarist, none of this is necessary, and a couple of clipping diodes producing a static and unchanging buzzy noise will be sufficient. Here is "Turnip Farm" by Dinosaur Jr., with a terribly overplayed lead guitar part that sounds like a kazoo: Dinosaur Jr. - Turnip Farm (bonus track) - YouTube
-Gnobuddy
The classic fuzz face circuit is a nice example of how common transistors can generate a progressive and harmonically rich distortion , with some duty cycle modulation. And yes they do clean up well once you roll back the guitar volume, the good ones anyways. It can be much more "alive" sounding than just simple diode clipping.
With all due respect, personally, I would pay money NOT to have to hear a fuzz face, and to me, it sounds awful at every setting.shanx said:
But there you go, other people have entirely different opinions.
Here is a good demo of a couple of Fuzz Faces by a good guitarist: Dunlop JIMI HENDRIX FUZZFACE side by side comparison Mini versus Standard version - YouTube
-Gnobuddy
my opinion only but pch jfets sound better both hifi and instrument.
https://www.diyaudio.com/forums/solid-state/290026-simple-discrete-sziklai-pre.html#post4684522
https://www.diyaudio.com/forums/solid-state/290026-simple-discrete-sziklai-pre.html#post4684522
I have a Crate FlexWave amp. If you dial the OD channel to very low gain settings it provides wonderful "clean" tone with moderate breakup on highest transients and "tubey" compression. So, no, I don't agree that it's only good for extremely high gain tones.
When one evaluates these things its good to keep in mind that clean and OD channels are usually designed from very different perspectives: Clean channel in some FlexWave amps doesn't feature any clipping circuits (and is sterily clean) whereas OD channel has entirely different voicing with distinct mid-emphasis. Good for high gain overdrive, Sometimes "thin" sounding with clean tones.
AFAIK, Murphy wasn't originator of duty cycle modulation et cetera. It was common feature of several amps and Murphy merely pinpointed it out when researching what made tube amps sound the way they do. Tube amps, and even several solid-state amps such as Randalls, behaved this was before Murphy devised his emulation and guitar magazines advertised his newest splid-state Carvin amps.
There's also more explaining amplifier tone than clipping, which is what Murphy has asserted as well. (He gave major importance to these details). Carvin amp technical documentations still censor parts of these important equalisation circuits, and equalisation is what really sets apart one distortion circuit from another.
When one evaluates these things its good to keep in mind that clean and OD channels are usually designed from very different perspectives: Clean channel in some FlexWave amps doesn't feature any clipping circuits (and is sterily clean) whereas OD channel has entirely different voicing with distinct mid-emphasis. Good for high gain overdrive, Sometimes "thin" sounding with clean tones.
AFAIK, Murphy wasn't originator of duty cycle modulation et cetera. It was common feature of several amps and Murphy merely pinpointed it out when researching what made tube amps sound the way they do. Tube amps, and even several solid-state amps such as Randalls, behaved this was before Murphy devised his emulation and guitar magazines advertised his newest splid-state Carvin amps.
There's also more explaining amplifier tone than clipping, which is what Murphy has asserted as well. (He gave major importance to these details). Carvin amp technical documentations still censor parts of these important equalisation circuits, and equalisation is what really sets apart one distortion circuit from another.
Yeah I know that it may not be to everyone's personal tastes, but it is an example of how a simple transistor distortion circuit can be very effective at creating and preserving a certain "liveliness" to guitar sounds. A good example is of Dave Gilmour's solo on Time (Dark Side of the Moon) using an Arbiter Fuzz Face.
Gilmour was as close to a sonic magician as I've ever encountered. He could take a nasty-sounding pedal or two, combine it with a couple of other very ordinary pedals, and tweak everything until suddenly this insanely glorious sound came out of the combination.shanx said:
Eric Johnson is maybe the only other guitarist I can think of who could do something similar, making glorious sounds out of ordinary pedals.
The rest of us? Honestly, 99% of the time, I think overdrive / distortion / "dirt" pedals make our guitars sound worse, not better.
This is one of the very, very few "dirt" pedals I've ever heard that, IMO, doesn't make a guitar sound worse (CE Pedals FET Dream): CEPedals.com FET Dream overdrive pedal - YouTube
If the schematics for the FET Dream ever showed up on DIYstompboxes.com I would probably try building one, but it was an expensive, low-production boutique pedal from a small manufacturer, so that's not too likely to happen.
-Gnobuddy
That CE pedal sounds pretty good. I built up a perfboard project with 2 jfets and a mosfet, so basically staged gain with some tonal shaping from associated caps..and it definitely can sound quite organic and "tubey"like that. Been a while since I played around with it. If you like that style of sound you could web search for Brunetti Mercury Box, there are a couple of vids that do show it doing the lower gain overdrive thing, but a lot of high gain/more distorted examples..