Thanks for the links scopeboy but the only one interesting to me was the Atomic product line. Since an FX box is putting out a usable signal with sufficiently low impedance why wouldn't a unity gain power buffer work well here (think Firstwatt F4)? This should make a pretty decent output device coupled with a durable full range speaker given the nature of the source it would be coupled with. Anyone see any negatives to this pairing?
White Bread and Sonics
I think you may become very dissatisfied with a strictly clean PA and effects boxes. I've been that route and the tone gets to be quite boring after a couple of days. I'm working on an emulator amp at the moment and I think a basic preamp stage with an EQ and the ability to get a little bit of high gain crunch out of the unit will give you a great deal of variety.
Another plus is to use another EQ unit just prior to the PA to dial in the final tone coming from the effects units. If an amp emulator is of sufficient quality you can forego the second EQ. play a variety of styles for my own amusement and get a great deal of use out of the amp emulators. Lots of variety to keep me interested.
Ccat.
I think you may become very dissatisfied with a strictly clean PA and effects boxes. I've been that route and the tone gets to be quite boring after a couple of days. I'm working on an emulator amp at the moment and I think a basic preamp stage with an EQ and the ability to get a little bit of high gain crunch out of the unit will give you a great deal of variety.
Another plus is to use another EQ unit just prior to the PA to dial in the final tone coming from the effects units. If an amp emulator is of sufficient quality you can forego the second EQ. play a variety of styles for my own amusement and get a great deal of use out of the amp emulators. Lots of variety to keep me interested.
Ccat.
I couldn't even play one song with every single preset on a typical FX unit in two days let alone playing with any custom variation on each one and when you add in the additional parameters of the instrument tone controls, your comment seems highly cynical. I would have tried harder to look for my tone. I am thinking, instrument>FX unit>power increase>loudspeaker. Anything else should be superfluous. The Pass F4 mentioned above would seem to be fairly impervious to environmental changes and pretty durable but I'm unsure about the stability for this use. Any thoughts about my proposed configuration are welcome.
Happy New Year to everyone!
Some thoughts on the proposed configuration:
F4 has a damping factor in the range of 30, no global feedback, the harmonic distortion content being mostly 2nd order and gently increasing with watts. The complementary pair are not exactly matched for P and N type and that is deliberate to the design. Decent input impedance should present no problems for a well designed preamp. The preamp is gonna do the heavy lifting voltage wise, so care to be taken on noise specs..
Terrence, do you have access to an F4 to test this out? Maybe you would want to work on a smaller wattage scale, say for example an ACA?
Some thoughts on the proposed configuration:
F4 has a damping factor in the range of 30, no global feedback, the harmonic distortion content being mostly 2nd order and gently increasing with watts. The complementary pair are not exactly matched for P and N type and that is deliberate to the design. Decent input impedance should present no problems for a well designed preamp. The preamp is gonna do the heavy lifting voltage wise, so care to be taken on noise specs..
Terrence, do you have access to an F4 to test this out? Maybe you would want to work on a smaller wattage scale, say for example an ACA?
Bonne année shanx! No, I don't have the F4 and parts scarcity make it an inconvenient build but it does fit my needs pretty well. I'm not up on the numbers for the Amp Camp Amp. Did it have a similar THD harmonic profile to the F4? How much worse than the F4 was its crossover distortion?
a lot of commercial tube guitar and bass guitar amps used output transformers smaller than hifi equivalents, and with reasonably low primary dc resistance - primary inductance was also less than a hifi equivalent so LF cutoff of the transformer was higher - in a way I think this could sound better for sound production than the hifi output transformer. Also, there was a subjective liquidity to the midrange of amps like the old Traynor YBA-3. Maybe its good only to have loop feedback from the output transformer's secondary back to the driver and let the rest of the circuit do without loop feedback (?)
I'm a big fan of accurate reproduction - in hi-fi amps. Instrument amps aren't about accurate reproduction, however. They're about dynamically inaccurate reproduction. I'm not sure you can capture the quality in a single, or even multiple DSP functions. I think you're barking up the wrong tree, but you might show me to be wrong...
There is one outlandish DSP gadget in a vintage-looking head box that claims to capture the tone and feel of your vintage amps and speakers. I forgot the name of it, but I believe it works with Volterra kernels, basically a more general version of convolution that can handle nonlinearity.
I would question the need for such complexity, as I've seen good guitarists play well and get great tone from all sorts of simple and cheap amps, both tube and solid-state. I guess it keeps mathematicians with body piercings off the streets.
What is the rated output power of the F4? Do you plan to gig this thing with a drummer?
I would question the need for such complexity, as I've seen good guitarists play well and get great tone from all sorts of simple and cheap amps, both tube and solid-state. I guess it keeps mathematicians with body piercings off the streets.
What is the rated output power of the F4? Do you plan to gig this thing with a drummer?
The ACA is a different design, but in some key elements remains similar to design goals of F4, in smaller watt "package". The harmonics again favour 2nd, build gradually with output. Of course there is some 3rd harmonic that increase as well at high outputs. Not a bad thing for guitar. I would not worry about crossover distortion because of the biasing point:
Mostly operating in Class A and transitioning that to AB at higher watts, like the F4.
Low damping factor, again this is an important consideration.
You can build it with a classic power supply, or try with the SMPS.. the parts count is low on this one.
Recommend reading articles by Nelson Pass for ACA, F4 F5 F6.
The ACA is 5watt rated, I think you could push a bit more out of it. The F4 will do 50 watt into 4 ohm.
Mostly operating in Class A and transitioning that to AB at higher watts, like the F4.
Low damping factor, again this is an important consideration.
You can build it with a classic power supply, or try with the SMPS.. the parts count is low on this one.
Recommend reading articles by Nelson Pass for ACA, F4 F5 F6.
The ACA is 5watt rated, I think you could push a bit more out of it. The F4 will do 50 watt into 4 ohm.
Coupled with the right loudspeaker(s), the F4 would be adequate for just about any live venue. Why tweak up an ACA when the F4 is pretty much there already? I've found crossover distortion is one of the more sonically detrimental distortions. Please remember that I want to isolate all my FX on a separate unit and add flavor only with my choice of loudspeaker, the amp should be hifi capable.
50W into 4 ohms should be adequate. I've done gigs with 40W of solid-state power into an Eminence Beta 8. 🙂
However this was with an experimental power amp designed to sound good overdriven. To stay true to the design goal of being clean and leaving all tone shaping to the FX, you might want more headroom. Maybe 100W into a 12" driver, like the Mini Brute and Henriksen jazz amp.
However this was with an experimental power amp designed to sound good overdriven. To stay true to the design goal of being clean and leaving all tone shaping to the FX, you might want more headroom. Maybe 100W into a 12" driver, like the Mini Brute and Henriksen jazz amp.
You might be thinking of the Kempler Profiler amp. It is extremely clever - it connects to the input and output of any classic amp and it can 'identify' the nonlinear transfer characteristics. It comes with a 'library' of classic amps already stored.
I went to a very professional concert by a superb band with 3 guitarists. One had the Profiler, one had another DSP 'modeller' (couldn't make out which one) and the third had an old Laney valve head with a 4x12. I'm not at liberty to reveal which sounded by far the best, because I'm worried that those mathematician's with body-piercings might come after me. 🙂
Another amp design was brought to my attention that may fit my criteria but it needs a closely matched, quiet, high current drive front end. Something like a 2SA970BL/2SC2240BL. I need candidates with >360mA of drive so an MPSA18 won't do here.
Yes, that was it, the Kemper Profiler! 🙂
There are so many devices like this on the market nowadays, there is definitely demand for a "guitar PA" with a flat response. However, a guitar PA is always going to struggle to compete with a dedicated guitar amp. The fundamental reason is that guitar speakers are designed for efficiency over flat frequency response. They have a huge midrange peak and a 12" driver might have 100+dB sensitivity at this particular frequency.
On the other hand, PA and hi-fi speakers with a flat frequency response achieve it by damping down the resonant peaks. The modelling amp or FX unit would then have to recreate the peaks of a guitar speaker by driving more power into the speaker at the relevant frequencies. You can enter a vicious circle where you need to use a bigger voice coil to handle this extra power, then the extra mass of the bigger voice coil makes the speaker even less sensitive and duller sounding, so you need even more power, and a horn tweeter, and so on. This is probably why the Atomic cabinets use 500W into a dual concentric PA driver.
There must be a middle ground where the speaker is sensitive enough to play loud, but strong enough to handle some electronic EQ, and sounds bright and lively without being massively coloured. I remember a while ago, a few people were claiming that the Tone Tubby hemp-coned guitar speaker made a decent full-range hi-fi speaker.
I believe these issues, plus a bit of latency, are the reason why the old Laney can still kick ***. 🙂
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That's it. Also tube guitar amps invariably have pentode output tubes. (Sometimes a triode/pentode switch is provided but players tend not to like the triode option.) Pentodes, with no (or very limited) global negative feedback, behave almost like current sources (or in other words they have high output impedance). The effect of this is that the voltage sent to the speaker tends to track the impedance variation (with frequency) of the speaker. This gives extra output at any resonant peaks, in particular the low frequency resonance. It also gives a brighter high frequency output as the speaker impedance increases at high frequencies (due to the voice coil inductance).
Again, all this kind of thing can be modelled using DSP, etc. and presents an interesting technical challenge. It is an attractive option for a guitarists to be able to bring along a small effects unit and plug in to the PA. It would save lugging heavy tube amps and speakers around.
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Hi Terrences,
I just want to say ref your original post, that I don't necessarily accept or believe that an MI amp which is integrated would be better than a preamp to power amp setup. As we are discussing, I think that the power amp having certain considerations in mind such as damping factor, and overload response can work very well together with a good preamp. The F4 is going to be a good candidate, it's a very live sounding amp and very detailed, so if you are willing to give it a try as a musical power amp, I suggest going for it. Please keep us up to date on your progress!
I just want to say ref your original post, that I don't necessarily accept or believe that an MI amp which is integrated would be better than a preamp to power amp setup. As we are discussing, I think that the power amp having certain considerations in mind such as damping factor, and overload response can work very well together with a good preamp. The F4 is going to be a good candidate, it's a very live sounding amp and very detailed, so if you are willing to give it a try as a musical power amp, I suggest going for it. Please keep us up to date on your progress!
Thanks shanx (there's a tongue twister for you) 🙂
As modeling pre-amps and computer audio evolves, I suspect this will be the way to go. I put out some feelers for an F4. It looks like there may be a GB coming up for that one but the active parts are not readily available and that sours me slightly about building it. I'm also looking at the SKA line because they also have a strong 2nd harmonic character but they may not be as resilient as the F4.
As modeling pre-amps and computer audio evolves, I suspect this will be the way to go. I put out some feelers for an F4. It looks like there may be a GB coming up for that one but the active parts are not readily available and that sours me slightly about building it. I'm also looking at the SKA line because they also have a strong 2nd harmonic character but they may not be as resilient as the F4.
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