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Author Topic: Frackel Guitar Preamp/Processor  (Read 14182 times)

Bob Leonard

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Re: Frackel Guitar Preamp/Processor
« Reply #20 on: August 23, 2015, 11:29:59 pm »

I'm in no way trying to promote digital is better.....but back to the original post....the axe fx is an outstanding modeler, and sounds amazing in the right hands.



I can agree to that. Most of my amps and guitars are asleep, so not in the picture, and there are others on the bench for customers. What you see are my working amps and a few of my favorite guitars, specifically the custom shop 60 LP historic reissue my wife gave me.
« Last Edit: August 23, 2015, 11:36:02 pm by Bob Leonard »
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Bob Leonard

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Re: Frackel Guitar Preamp/Processor
« Reply #21 on: August 23, 2015, 11:46:12 pm »

OK you made me look... I found a schematic of the "Ross Compressor" and found nothing remarkable...  No bucket (?) chips (bucket brigade delay?), and I don't know what a clown fish cap is (please don't tell me).

From input it is a simple emitter follower with relatively high input impedance (470k). Good for lead guitar pick-ups. 

The gain element is relatively common ca3080 OTA (operational transconductance amp). While common this is a somewhat premium approach for a guitar compressor that more typically use a cheap JFET shunt design.   

The important thing about dynamics is the side chain. The Ross uses full wave rectification for faster reliable attack from either polarity signal. It is generally very fast attack (as fast as a transistor can discharge a 10uF cap) with a slower fixed release time.

The 3080 OTA is cleaner than a JFET shunt, but not as clean as a VCA. In that application the side chain manipulations will be more audible than than the OTA distortion, which isn't 0%, probably a few tenths percent THD.   

I don't see anything that couldn't be modeled with a little effort.

JR 



Sorry John, I was thinking of an Ibanez AD-9 delay I was working on just before the post. Many have tried but only a few have come close, and this I can't explain. Clown caps are those little square ceramics with the colored stripes on them. You don't see many anymore, but I have plenty to last until I'm gone. I would doubt they make a difference in all actuality, but once again it's the sum of the parts and not any one part in particular. Analog Man and Keeley have come very close, but both of them have modified the original circuit to "make it better".
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Andrew Broughton

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Re: Frackel Guitar Preamp/Processor
« Reply #22 on: August 24, 2015, 01:20:26 am »

Clown caps are those little square ceramics with the colored stripes on them. You don't see many anymore, but I have plenty to last until I'm gone.
If they're the ones I'm picturing, they're actually metallized film capacitors, made by philips. I had piles of them when I was younger.

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Bob Leonard

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Re: Frackel Guitar Preamp/Processor
« Reply #23 on: August 24, 2015, 08:18:55 am »

Clown cap it is.
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David Buckley

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Re: Frackel Guitar Preamp/Processor
« Reply #24 on: August 24, 2015, 08:34:13 am »

You gotta hear Bob, and his fuckton of amplifiers, and he's right, of course.  But there is an increasing body of people who will settle for 98% of the tone and 85% of the feel because that is what gets the job done.  People who are mostly younger than us, of course :)

Wasn't so long ago that a "serious" level guitar rig would be mostly valve.  There's lots now that all solid state, even if the 4x12s are still there, being driven by QSCs or whatever.
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John Roberts {JR}

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Re: Frackel Guitar Preamp/Processor
« Reply #25 on: August 24, 2015, 11:26:23 am »

Sorry John, I was thinking of an Ibanez AD-9 delay I was working on just before the post. Many have tried but only a few have come close, and this I can't explain.

OK now your getting into my wheel house... back in the '70s I worked with the still experimental Bucket Brigade shift registers (invented by Phillips and later licensed to Matsushita, aka Panasonic). For some BBD trivia, they are light sensitive. We got a batch of test pieces from Phillips with open top cans, and the bench light would trash the audio flowing through the analog shift register... We didn't figure that one out right away.  ;D

The BBD (actually a subset of the larger CCD charge coupled devices) was a remarkable technology for back in the '70s. By the '80s digital delay that started out very crude and very expensive had pretty much eclipsed the analog delay market. I made some hay while that sun was shining. I designed consumer delay for Bozak (the speaker company) and professional studio delay/flanger for Loft, not to mention selling a kit delay/flanger through my kit company that was actually used on records back then.

I can think of several reasons that an analog delay based effect might be difficult to model.  The analog shift register has a modest operating range with different saturation effects at the top and the bottom of its voltage range. (So two units side by side might not sound alike if bias trims are set differently).  Further the optimum operating point (bias voltage) can change with clock frequency. Since you vary the delay time by changing the clock frequency the path would need to modeled slightly differently vs delay. The noise floor changes with clock frequency, at lower clocks and longer delay the path is noisier and that noise is not simple Gaussian. When going for deeper delay effects a common technique, is to recirculate a fraction of the output signal back to the input. The result from this is very affected by frequency response of the the recirculation path, and even the polarity (that affects where comb filter bumps and notches land), Finally since the delay is a sampled system, it will also suffer from Nyquist criteria. The inputs will require anti-aliasing filters and output will require reconstruction (smoothing ) filters. At best you will get extra roll-offs from marginal sampling rates, for extreme (long delay) low clock frequency you can experience aliasing artifacts as the HF audio folds down into the passband .

I believe this all is possible to be modeled, but there are a lot of moving parts that will interact requiring a complex model and lots of computation. There are still people using that old studio flanger I designed back in the '70s for the unique sound. If I was smart i'd design a plug-in for it (that actually sounds like it). But that would be a whole new programing environment  to learn... nah.   

The old BBDs that I used back then are long since obsolete. Rather than component development making better and better BBDs, it looks like somebody in China knocked off the old Matsushita parts (that they licensed from Phillips). So there is apparently still a market for BBD chips in guitar efx...   
Quote

Clown caps are those little square ceramics with the colored stripes on them. You don't see many anymore, but I have plenty to last until I'm gone. I would doubt they make a difference in all actuality, but once again it's the sum of the parts and not any one part in particular. Analog Man and Keeley have come very close, but both of them have modified the original circuit to "make it better".
Didn't I say I didn't want to know about clown caps...  8)

JR
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Bob Leonard

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Re: Frackel Guitar Preamp/Processor
« Reply #26 on: August 24, 2015, 12:35:08 pm »

I guess these are the things I'm talking about John. You can get close, but certain things just can't be modeled and sound like the original. I hate it when the Chinese take a chip and replicate it, and I hate it when the tolerances for older chips are "tightened". It takes away the character of the original much in the way a 1% resistor doesn't react the same as a 10% old school carbon comp. It's all these unknown variables that add to the character of older hardware.

I didn't know you were that involved with BBD, I'm impressed, especially since I never really got deep into the world of IC. The link below will take you to a good schematic of the AD-9. Can we make it better?

http://www.dirk-hendrik.com/Ibanez_ad9_analog_delay.pdf
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Stephen Kirby

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Re: Frackel Guitar Preamp/Processor
« Reply #27 on: August 24, 2015, 01:49:20 pm »

The main complaint that guitar players have against modelers (even as good as the AxeFX) is the same reason that soundpeople and studio engineers love them.  The feel, dynamic and timbral response is homogenized.  A good musician can create a lot of subtle nuances in their playing.  But for the same reason that engineers put compression on everything to "normalize" it and keep it in a consistent place in the mix, all that expressiveness of a Dumble or whatever good amplifier makes notes sound different.  Which is their reason for being.  But outside of the Baked Potato or other small jazz club, makes it harder for the engineer to "control".
I know people who play very responsive amplifiers live, but have done innumerable sessions using fairly cheesy modelers.  Not as much fun to play though, but makes the engineers job easier and makes the producer happy.  These guys get the session work because they know how to give the producer what they want.  Then they'll pull out the vintage or high end amp for a local gig and play for themselves.
So back to the OP's question.  From a soundperson's perspective, the modeler will make your job easier if the levels are worked out well.  Once in a patch, the sound won't change as much as if they were playing a /13.
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Andrew Broughton

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Re: Frackel Guitar Preamp/Processor
« Reply #28 on: August 24, 2015, 01:58:21 pm »

The main complaint that guitar players have against modelers (even as good as the AxeFX) is the same reason that soundpeople and studio engineers love them.  The feel, dynamic and timbral response is homogenized.  A good musician can create a lot of subtle nuances in their playing.
That may have been true in the past, but not so with the Axe-FX. It can be as dynamic and expressive as you like, but to get it to match a regular amp takes some tweaking.
It comes down to whether the convenience of having an infinite number of amps and fx in a 2u rackspace is worth the (possible) fiddling required to get the tone you're looking for. If you typically use 1 amp and a pedalboard for all your songs and don't mind dragging it around, then there'd be no reason at all to buy an Axe-FX. Just like the guy mixing just one band on an analog board with an outboard FX rack. If he doesn't need the size and flexibility advantages of a digital console, then why buy it?
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Luke Geis

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Re: Frackel Guitar Preamp/Processor
« Reply #29 on: August 24, 2015, 03:01:25 pm »

I have been playing guitar for about 23+ years and prefer high gain amps. I like them because I can get a lot of gain, or a little, with the twist of a volume knob and go from full compressed saturation to a more dynamic bluesy growl. I do not like pedals, I repeat, I DO NOT LIKE PEDALS............. I use a static FX unit in the amps loop for verb and delay if i feel the need for it, but otherwise the signal is dry. I have cloned a ZVEX Superhard On, and even built an AMZ mosfet clean booster as well. I like the BS170 designs, what can I say. I don't really even care for clean boosters though. So what does this have to do with modelers?

I have a neighbor friend who has a nice AXE FX II XL ( not the latest plus version ) and he even suited it well with the Atomic CLR powered speaker! To say the least, it is one killer ( and very expensive ) rig. I have owned a L6 POD HD unit and ended up selling it. I have had and still own a ZOOM 2020 that I got about 20 years ago. I re-acquired it in an interesting way. I sold it to a guitar shop, It went through about three hands before I go into a studio to do a session. I see it sitting there and tell the owner about it. He gave it back to me. It was out of my hands for about 5 years and it still works! It sounds like absolute ass though; I can't believe I used that thing in live shows...... In either case I just can't totally embrace the modelers yet. I have had my fair use of them, but to no avail. I even owned a Digitech GNX 3 for a while, it just couldn't do it.

So here are my thoughts on them. The FX and the cool spatial and otherworldly things you can do are far and beyond amazing! The modeling of the amps themselves are really amazing too, but they still have not gotten the touch thing figured out. They can do all they want with input impedance or whatever they do to try and make it react like a real amp, but they just haven't yet. It is one thing to have a stellar sounding model, but it's the touch. I use the volume knob a lot and want the amp to clean up a little and growl instead of scream and the modelers just have not got that figured out yet. They are not touch responsive in the way a tube amp is and they do not clean up and react like a tube amp does when you roll the volume back on the guitar.

Another thing the modelers have not gotten yet is the noise floor. I'm sorry, but a high gain amp does not necessarily have hiss and noise. I have a Peavey 6505+, A Peavey XXX and a Jet City JCA50H and none of them have noise when set for realistic gain settings. The fractal, and other modelers always seem to model in too much noise when set for even modest gain settings. I don't like high gain amps because they have super saturation, I like them because when set for modest levels of gain, they are ( most of them anyway ) quiet with more than enough gain on tap. Other high gain amps I have owned exhibited the same thing. If you crank the gain, yes there is hiss and noise, that is a given. The amps modelers just have too much noise for any given setting and I don't think I should have to use a gate to clean it up.

I think if running the modelers more like conventional tube amps, you could get a more in touch feel from them? It still won't be a tube amp and may be better in a lot more ways, but it is not a practical and cheap answer at that point. Lets imagine a $3.5k modeler ( the basic retail price of the Axe FX II XL+ ), an amp which could set you back another $600+ and a speaker cab which for a decent one is yet another $600+. This puts you almost $5k in the hole to come even with a real tube amp. I just assume get a Diezel VH4 at that point. To me running a modeler in a conventional way is a pure waste of the technology. The idea is to get away from having to mic a guitar cab and simply send the signal to the PA ready to go. I have not had a chance to try the newest Fractal unit or the Kemper Profiling amp, so perhaps it has been figured out? Mark DV also has a neat unit that follows a more conventional route.

I have had three instances where a modeler was used and the signal sent to me was only from it. In one case the band was more rock and the other two were metal. The metal groups of course had no problems and sounded very good. The rock group sounded fine as well, but he did mostly distorted sounds and did not roll the volume back much. In either case I found I had to do very little to get an acceptable sound and honestly I was hard pressed to tell the difference once the band was up and running. I think the hardest thing is as a guitarist to embrace the technology and simply trust it. Obviously some styles of music require less touch response and are more suited to the higher level of production capable in the modeler. I think that hard rock, metal and experimental music best suits the current modelers ability. County and blues require something that the modelers can't quite do yet very well. Those are two genre's where modelers have not taken much hold yet incidentally. My bet is that within 5 years it will be figured out, cheap enough and superior to current tube amp design to have no excuse to not use a modeler.
« Last Edit: August 24, 2015, 03:04:31 pm by Luke Geis »
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Re: Frackel Guitar Preamp/Processor
« Reply #29 on: August 24, 2015, 03:01:25 pm »


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