Mic Pre Designs - A Discussion

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kornowsd

Member
Joined
Dec 31, 2004
Messages
15
Location
TX
Hey Everyone;

All right... my second post and this may be a long one. I want, overall, to stimulate some discussion, clarify some of my understanding and just, overall, get some ideas for a DIY mic preamp project I'd like to embark upon. This project stems from a direct need to have a very configurable mic pre that really does what I want it to do. :) Of course, that's what we're all looking for, in the end, I think.

In reading through all of my documention, including the Radio Designers Handbook (F. Langford Smith), Mullard Tube Circuits, Handbook for Audio Engineers, The Art of Electronics, and various other volumes covering tube and solid-state design as well as various schematics from the industry I've sort of come to an impasse with regards to mic pre's.

Let's start w/ the 10,000 foot view of these things. All camps scream "accuracy" in the mic pre. They gain this component aspect of the pre by various designs - high impedance inputs so that there is no "loading" of the mic, differential amps all the way through the signal path for high CMRR, fully "balanced" signal path from input to output, DC-coupling between stages to minimize/avoid low frequency phase shift, minimal component circuits to avoid coloration by multiple stages of active devices, high amounts of negative feedback to increase entire pre linearity, high quality components, etc.

Let's drill down... there seem to be a few different camps, in the world, with regards to inputs. The first camp says that transformers inherently color the sound of the mic and, in some cases, unnecessarily "load" the mic down. So DC-coupling, direct to your first preamp stage is the way to go. Others say that the transformer allows for better CMRR, and "proper loading" of the mic. So, the first "confusing" part of the mic pre starts here.

Personally, I like the idea of a multi-tapped transformer, at this stage. A linear unit, like some of the Jensen's that can pick up and translate signals from nearly DC to a couple hundred kHz without phase shift or amplitude distortion. But, of course, Jensen doesn't make a multi-tap transformer for this... so, who does?

The second question is: Does the transformer step up the voltage/impedance, or step it down to the amplification stages, or do we achieve better results with a 1-to-1 transfer? And how does this impact the tonality of the pre after that stage?

Once the signal is removed from the transformer and into the mic pre's active stages, there are a ton of different considerations. If you're looking for accuracy, then a higher impedance input to the first gain stage is a must to pick up all the transient information, etc. at that stage. Secondarily, there are other things to look at. In order to be totally accurate. From the higher level design references that I have, they note that this first input stage "balances" best at about 10K ohms of input imedance. Much less than that and you load the input stage. Much more than that and you increase the EIN, random noise of the stage, etc.

So the question, here, really becomes what type(s) of input impedences are we looking at to really optimize the stage, here. There is one thing that I've noticed about all the mic pre's that I worked with (Focusrite, Groove Tubes, Avalon, Millenium, etc) is that when the higher input impedances are used (both on the input transformer and on the first gain stage) the mic loading may be somewhat less, but man, they get "edgy" and "harsh". Is it just that the "noise" I create to record has that much "noise" inherent in it? In other words are the mic's picking up all the environmental noises and really transferring them to my pre's?

In all of the gain stages we should be designing to several things: 1) Frequency linearity which requires some sort of feedback to keep the stage linear, 2) Slew Rate - to be able to accurately capture the transient information WITHOUT changing it's frequency reference, 3) Phase accuracy - control of stray capacitances, inductances and the proper matching of caps, etc. when/where needed through the signal and feedback paths, 4) Amplitude accuracy - the ability to handle inbound transients without compromising the actual signal envelope, etc.

To me, if you're going to focus on the signal path, in this way - and I could be wrong, it would require several things: 1) High voltage supplies on the active elements in the circuit. The higher the supply voltage the more we can put the signal swing in the "middle" of the transfer curve for that element (whether it be a tube, transistor or FET) where the device is the most linear. Also, in the tube world, this allows for enough electrons to be built up in the device ready to move at a transients notice so that slew rate is at is level best. 2) High quality signal path components (i.e. very tightly toleranced resistors, caps, etc.) so that the contribution to overall signal "degredation" is at a minimum. 3) Either really HUGE coupling caps between stages or no coupling caps, at all to eliminate any potential low-frequency phase shift on the input.

Finally, the output stages of the thing require a few elements, as well. The first part, again, is how to couple the output of the active device(s) to the actual output terminals - do we use transformers, do we couple via caps, etc? The goal, in the better audio equipment, is to build an ultralow impedence output so that any load can be put on the thing and not have to worry about "loading" the output of the pre. What considerations would we try to account for, in this stage.

Ultimately, after having really torn down the middle section of the mic pre, here's what I'm looking for. I want a mic pre that will "capture" the depth of the low-end on my mic's. I know it's there. I can, sometimes, here it. :) I want a mic pre that will accurately capture, and translate, the high-end frequencies coming from the mic's without sounding overly aggressive, or harsh. I want to be able to select different input impedences from 150 ohms to 10k ohms, or there abouts in some usable steps. I want to be able to change, possibly, the slew rate of the device, as a whole (probably just the final output stage, rather than the whole device as this seems to make the most sense).

Anyway... there starts the discussion. I'd love to get into the technical details of some of the mic pre designs and start really sussing out the cooler aspects of each. Sometimes, I get the feeling that recordists, in general, are in the "vintage is better" camp without really focusing on the engineering aspects that make "better" actually better. I'm really wanting to focus on the contributory elements that really separate a great mic pre from a poor one.

Also, if folks have some designs, other than the G9, to share, that would be great. While I've worked w/ the Avalon and Millenia's, in the past, I haven't had a chance to open them up and see how they were put together - although I have enjoyed some of the sounds that come out of them. I just got a Groove Tubes VIPRE, recently (at well below cost, for a new, in box, unit). I'm going to be spending some time, when I get off the road, for work, and taking that thing apart and really evaluating how they did some of their work, as well.

Thanks for listening, would love to have some discussion come out of this.

Thanks.

Dar
 
there is a thread here some place that alot of stuff is talked about. CJ had some Gordon preamp pictures etc. anyone remember the title on the thread?
 
Dar

Alot of ideas that are not always true.

"All camps scream "accuracy" in the mic pre" Not true some designers look to add some distortion.

Transformers can be as clean or dirty as designed more "how much money do you want to spend" I have spent up to $250.00 for a tube microphone transformer.

Loading down an input with a transformer would be because the design is bad or it was made to work with something esle than what you used with it.



Your post reads like you are looking for FREE design work.
Why would anyone here want to help you then?
And if we did someone else might go and make it and call it there own.

The G9 the only pre here?
 
Actually,

I'm not looking for free design work. I can get that by going to Guitar Center and reverse engineering a few of the devices I like and bring them back within my 30-day time limit. A few digital photos, some minor work w/ a photo editing program and I've got PCB masks ready for etching.

My goal, as is the goal of this site, (at least that was my impression) was to stimulate some discussion on various approaches to mic pre design, to sort of go beyond the "I have to build a UA 610", or whatever. I'm not asking for someone to sit down, create a series of schematics, PCB layouts, gerbers and net lists to meet some of the things I layed out, in the prior post... I'm merely looking more for discussion points, viewpoints, opinions and approaches.

Money, really, isn't much of an object. $250 on a transformer is not a lot of money if you're getting something out of the end-result. Again, the approach, why use transformer "x" for $250, versus transformer "y" which costs $850. What "advantages" are you getting? Does transformer "x" yeild a more "clear" or "open" sound, as opposed to transformer "y" which has some phase distortion... you sort of get the idea.

I'm not asking for engineering design, I'm asking for approaches, methods, concepts, discussion. Very different things, overall.

Dar
 
http://www.sweetwater.com/store/detail/LiquidChannel
In five years most decent mic pres will follow the foot steps of the LiquidChannel. They will get cheaper by the year as the novelty wears off. Digital processing becomes more powerful by the month and gets cheaper by the day.
Of course, like many, I am always up for a brisk round of mental masturbation.
My favorite fantasies are devoid of input transformers and revolve about circuits like the AES paper 2106 circuit, or the Forssell version of it.
Usually I have more of a lack of time problem instead of a lack of ideas issue.

Cheers,
Tamas
 
Dar,
Welcome! I think some of these guys are giving you a hard time becaues it seems like you are just kind of coming in with a huge ammount of questions-many of which have been answered. Check out the Meta's as mentioned already, and then why not jump in and build something? You'll soon see that every project has it's own thing. THere is no one mic-pre for the job-otherwise, we'd all have that one.

Take care,
joel
 
I agree, there is no one "right" pre for the job. I guess one of the things I'm really looking for, in a professional DIY-type forum is a somewhat engineering-based approach / discussion.

For the most part, I'm relatively new to the field of audio engineering. I've spent the better part of 10 years in the black magic world of high frequency RF design where a 1/100 pF capacitance misplaced somewhere in a circuit can cause an entire design to destroy itself in a matter of seconds. I'm finding that some of the rules that we hold near, and dear, to our hearts in RF don't always hold true in the audio realm. It's an entirely different animal, in some ways, and very much the same in others.

Basically, I'm looking for a starting point, some insights from the experience(s) of others, etc... something to get me grounded... and then move out from there.

I did try, as suggested, a quick search for "META" and didn't really find anything other than some banter about whether Sowter is better than Jensen... type of thing... really not a lot of depth or detail regarding approaches...

A quick topic - do most audio transformers step mic impedence up, or down to the first stage pre-amp? Or are they just a 1:1 ratio? What makes more sense in the end result? Actually, what are the end result(s) to each approach? I, generally, understand the signal path, the elements of it that cause phase shift, phase distortion (although that one is getting a bit more attention in my research these days), amplitude distortion, IM, TIM, THD, etc.... there are some elements of this topic that elude me...

Dar
 
With regards to the comment: "If I wanted engineering design I'd go to Guitar Center, take apart a few pieces of gear and copy those..." No, that's not something I do. I was using it as an analogy to note that I'm not interested in "taking" the hard work of others and just copying it for my benefit. I was using to illustrate a point. Being an engineer, myself, I can certainly appreciate the amount of time, effort and energy that goes into a finished product and I strongly believe that the folks that do the work should get the credit.

Dar
 
from tx? the only things from texas are streers and q... well you guys know how that goes. :grin: anyway to get back your question. alot of that has been discussed here b4 just read the metas. Now on a more personal note look in design to a groove tubes Vipre here you have a unit that can be trasnfomer or transformerless and have a varity of ohms. take one mic and record with it. change settings and then record again. transformer VS transformerless,eetc,etc,etc. You will find there is not one answer for everything and each sound has it's own aplication. looking to the liquid channel it has a transformer in it. a 1:1 I belive which according to fuckusright, yields the puriest/ceanest in sonic qualities thus allowing the convolution to audiable. so it's basicly mic pre with a huge trafo in it and then goes through the convolution tec of different mic pres to alter the sound emulating the different pre's. it's amzing how they did it and yet at the same I am like what is the point. If I wanted 1073 I will use a 1073 from a rental house. it's not the gear but how you use it.

If your real serious about any of it. read read read.
 
[quote author="kornowsd"]A quick topic - do most audio transformers step mic impedence up, or down to the first stage pre-amp? Or are they just a 1:1 ratio? What makes more sense in the end result? Actually, what are the end result(s) to each approach?
Dar[/quote]

Input transformers are usually from 1:2 to 1:10 ratio. They provide low noise gain, high CMRR, gentle signal compression and an infinite lifespan compared to electrolytic capacitors
The higher the turns ratio the more defects (regarded as character) are added by the transformer.
Transformers often simplify microphone preamplifier circuit design and most of them have a likable character. For tube circuits they are almost a must to achieve acceptable noise levels.
There is a tendency to adore them on this forum, most of the time with good reason. You can build a mic pre using really good transformers for less than commercial products.

Don't worry about the crap people give you. As soon as you bring some interesting information to share they will be having a brew with you. :sam:

I hope this helps,
Tamas
 
> I'm really looking for, in a professional DIY-type forum is a somewhat engineering-based approach / discussion.

You are in the wrong place. (There may be no right place.) 90% of the folks here don't really know Ohms Law. I do, but 90% of the folks here know a LOT more about music than I ever will. So the emphasis is on practice and prejudice, not always rational engineering.

> do most audio transformers step mic impedence up, or down to the first stage pre-amp?

I'll speak as if I knew a little of RF and you know a lot.

In audio, gain is cheap, reflections negligible, and power-matching is rarely done. That is very different from RF, especially cutting edge RF.

You know what an RF preamp Noise Figure is. You may also know the concept of effective noise resistance. In audio mike preamps, gain is cheap but S/N sometimes has to be very-very good. So transformers are used to "match" the mike source impedance (typically taken as 150Ω, though varies 100-300Ω) to the input device's noise resistance.

> The higher the turns ratio the more defects

This is NOT true, except when there is some standard source impedance. In audio terms, it is easy to wind for any low impedance, but very hard to wind for impedance 10K and up. In electric terms: scaling impedance scales leakage reactance, but capacitance is pretty much the same for any impedance. Capacitance for mike-sized transformers runs 100pFd-300pFd. So nominal impedances from under 1Ω to over 1KΩ can ignore capacitance: bandwidth is just the ratio of primary to leakage reactance. This depends first on the iron (and audio iron has very high permeability) and second on the interleaving. 1,000:1, even 10,000:1 bandwidth is no great problem. But up over 10KΩ the capacitance can't be ignored, resonates with leakage inductance, peaks-up the top of the band.

Specific cases:

A vacuum tube has voltage noise but very-very little current noise (remember: in the audio band; at AM frequencies you get current noise you can't ignore). Voltage noise is similar to a 3KΩ resistance. Mike source resistance is 150Ω. The ideal step-up would be 100K, 500K, or more. But the diminishing returns point is 3KΩ. And the ringy-tranny point is 10K. So we traditionally use a 1:10 step-up, to bring source resistance voltage noise well above tube voltage noise, yet not go so far as to get intolerable ringing. Also to get free gain, because vacuum tube gain isn't THAT cheap.

JFET noise current is even lower, but we are limited by transformer flaws. OTOH a $2 JFET can have lower voltage noise than a $20 tube, so we can use lower step-up ratios without much rise in Noise Figure, and get less tranny ring. (But some folks like a ringy top.) (I mean few-dB ring, not some Q=10 ring-a-ding.)

Bipolar transistors is where it gets real fun. More so than tubes or JFETs, you can select BJT current and area to make the noise resistance about anything you want. When we used small-area low-current devices, the old 1:10 transformers worked OK, despite the high noise current. When good clean large-area devices came out, and when designers thought about extreme gain-bandwidth products for huge negative feedback, we got noise resistance below 1KΩ. 1:2 to 1:4 transformers optimize noise, and tend to be very flat across the audio band. But take this a little further and you can get noise resistance below 300Ω, a pretty-good N.F. with 150Ω sources. There were single-ended amps using a 1:1 transformer just as a balun (balanced/unbalanced). But the extreme is the transformerless differential input: two large-die transistors worked very rich.

In much commercial gear, transformers are "bad": the price of low-production transformers rose while the price of generic transistors sank, so it is a $50 versus $2 decision, critical to a large board that needs dozens of mike amps. Also the weight of a decent hunk of iron, soldered to a PC board, and dropped off a truck, will break the PCB; transformerless weighs nothing. But everything that goes old becomes new again: Bell-bottoms and paisley are back, and so are transformers.

Specific objections: a wide-range multi-tapped audio transformer is a real expensive beast. For best performance you must fill the window with copper. For low-Z a few turns of fat copper, for high-Z a lot of turns of skinny copper. A tapped winding over a wide range is a bad compromise: the low-Z end will have excess copper resistance (not such a problem in much RF work), or the high-Z end of the winding just won't fit at all. Yes, you can change gauge at every tap and it is not so bad. But tapping, much less changing spools, costs radically more than just letting the winder spin. Lundal's "volumed control" transformer with a couple dozen taps is very expensive, I'm sure due to wind-time and hand-tapping, and line-level work like that is not so critical about keeping copper resistance very low.

High input impedance does not increase EIN when working with the nominal source impedance (it actually improves N.F.). But there is diminishing return above about 2KΩ, maybe 10K if you are very fussy. For BJT with significant base current noise, a high input impedance leads to high noise level when the mike wire gets yanked out: not normal operation but a factor in live work.

Essentially all mike makers suggest load be several times rated mike impedance. 2K seems to be safe for anything with an XLR on the end. Some are fine with 1K or 500Ω. Many (not all!) condensers have such stout internal amplifiers that performance is unchanged (except output voltage) for any load down to or even below 100Ω. Yet though the makers say "over 2K", the latest fad is for some sort of "variable impedance". Some mikes have very flat impedance: load just reduces output. (This may be good if you were clipping and refused to admit it.) Some mikes have very lumpy impedance; loading changes the frequency response (but an EQ will do it better). Condensers have buffers so loading will not affect the mechanical system. Most dynamics are so inefficient that loading can't do much to the mechanical response. Ribbons could be mechanically loaded by electrical impedance, but I don't see how that must be good (and ribbons are not so widely used). Not sure what to make of this vari-Z fad. My instinct says to make a good low-noise hi-Z input, and add a dummy load resistor if a mike is known to work "better" with heavy load.
 
here is the thread


http://www.groupdiy.com/index.php?topic=3291
 
[quote author="PRR"]A vacuum tube has voltage noise but very-very little current noise. [/quote]

[quote author="PRR"]Voltage noise is similar to a 3K resistance.[/quote]

PRR, can you explain how you arrived at the 3K value for the typical vacuum tube voltage noise figure? How is tube voltage noise calculated?

Thanks,

E.
 
[quote author="kornowsd"]Hey Everyone;[/quote]Hey Dar, welcome! I'll gladly join in here, for what little my comments and opinions might be worth. :green:

All camps scream "accuracy" in the mic pre.
Sorry to start off with a negative, but this isn't really the case. Lots of mic amps are known and loved for a lot of things that really aren't "accuracy" at all.

...The first camp says that transformers inherently color the sound of the mic...Others say that the transformer allows for better CMRR, and "proper loading" of the mic. So, the first "confusing" part of the mic pre starts here.
To make this more confusing, there really are transformers that are more "accurate" and ones that are not. Sometimes its a matter of $, sometimes not. If you are an experienced engineer, then you know firsthand that "everything has compromise and tradeoffs".

Slew Rate - to be able to accurately capture the transient information WITHOUT changing it's frequency reference
Perhaps you could expound on this idea as I am not really following you.

Sometimes, I get the feeling that recordists, in general, are in the "vintage is better" camp without really focusing on the engineering aspects that make "better" actually better. I'm really wanting to focus on the contributory elements that really separate a great mic pre from a poor one.
It would seem from your proposals and questions that you are after something specific. "Hammers and wrenches" - different tools for different jobs. Lots of "recordists" don't give a flip what is inside the box, just that it works for them... or it doesn't. But this forum is about DIY! but I have picked up some very handy recording tips as well.

...if folks have some designs, other than the G9...
If you haven't found any other mic preamps here, you have not looked very long at ALL.

I just got a Groove Tubes VIPRE...taking that thing apart...
Don't forget to post pics!

I'm reading the other looong thread that someone pulled to the top. I missed this before. Can't read all of this STUFF! Its all good, though!

Peace!
Charlie
 
> explain how you arrived at the 3K value for the typical vacuum tube voltage noise figure?

Equivalent noise resistance (not noise figure).

For any good clean well-used device, BJT, FET, or VT, the main source of voltage noise is the cathode impedance 1/Gm where GM is transconductance. In effect, the cathode (emitter, source) is a resistor and has thermal noise.

(A rigorous derivation says 1/2Gm, but in practice it is often higher so omitting the "2" is conservative.)

Gm of a typical tube used as mike input after a transformer (12AX7, 12AY7, etc) is 1,000microMhos. 1/Gm is about 1,000Ω.

BUT this is thermal noise. And the cathode-space of a thermionic vacuum tube runs HOT. Relative to Absolute Zero, a VT cathode runs 3 times hotter than a BJT or FET working near room temperature.

So the equivalent noise resistance is about 3K ohms.

For best signal to noise, you want to transform the source impedance to a value higher than 3K. We typically transform to around 20K, which gives a Noise Figure around 1dB.

Tubes do have current noise but the equvalent resistance is hundreds of Megs. We want to keep transformed source impedance much lower than this, but that's not a problem since we couldn't wind a transformer that hi-Z if we tried. (It is an issue in condenser mikes.)

High transconductance tubes will have lower equivalent noise resistances. Run a lot of milliAmps through some tuner tubes, Gm approaches 5,000 uMhos, Rk is like 200Ω, equivalent noise resistance is under 1K. That eases the design of the grid transformer, but makes power supply design harder (more expensive).
 
FIRST PRR THANK YOU VERY MUCH.... your response inspired me to actually figure out what I needed to research, on my part, to get to where I want to be going. It was the initial approach-based process that had all the parts that I was missing. Thanks again.

SLEW RATE Slew rate is an amplifiers ability, at its output, to follow changes at the input. The slew rate parameter is presented as Volts Per Microsecond (V/uS).

Slew rate "controls" several elements of your amplifiers ability to track dynamically changing input signals. First, it "limits" your overall gain AND frequency response together. Higher frequency signals "slew", or change, faster than lower frequency signals. Thus, the higher the frequency that you want to reproduce, the faster the slew rate must be, for a given gain.

Gain, of course, controls your overall output level/voltage. With a lower gain setting, the output of the amplifier doesn't have to change as much so, you can reproduce higher frequencies with lower gain (same slew rate).

This one parameter is VERY important if you're designing a preamp/power amp that is going to very accurately track the input. Secondarily, when high gains are required (like in mic preamps where you're doing 50-70dB) slew rates are ABSOLUTELY critical... the higher the amp gain, and the higher the frequency you want to reproduce the faster the slew rate must be.

Some Preamp Design Thoughts - From My Reading My goals are pretty simple, now...

1) Create a mic preamp that's as absolutely "clean" as possible - with no coloration, at all.

2) Create a mic preamp that has some variable input impedances. I have to admit I really love that part of my VIPRE pre-amp. It does some amazing things to many of the mic's that I own.

In reading up on various mic pre's, there seem to be only a few that "boast" no coloration (Millenia Media and Grace Designs). I haven't been able to get hold of Millenia Media's design approach but TI has most of Grace's mic-preamp on their site under the INA103 Instrumentation Amplifier.

To me, the above approaches require several things:

1) Very good signal path circuitry, especially capacitors. In reading a TON of engineering references about these little gems I have stumbled upon some very interesting elements of caps that seem to impact audio circuitry more than not;

* Dielectric Constant - there's a great site called "The Sound of Caps" where the engineer who produced it has a bunch of Lissajou (spelling) patterns on the o-scope showing the capacitors ability accurately track input signal voltage. In some cases, the pattern isn't always what it should be.

The dielectric constant acts sort of like a small bank of capacitors and resistors all together, each with their own little RC time constant. If the signal through the cap is "stable" (i.e. unchanging) then all is well with the signal path world. However, as soon as a transient goes through (a guitar string plucked, a violin bow moved, etc) the cap begins to charge. The "capacitor" nearest the terminals dischanges first pushing the transient back out... the other absorbtive parts of the cap are still charging and will eventually discharge their part of the transient, as well... causing a "smear" in the upper frequency range... I used to call this "problem" group delay. It's now "Phase Distortion" in audio.

There are several capacitor types, out there, that greatly reduce this little issue. If you only have 1 capacitor in the signal path, that's great you probably won't hear it unless the cap is so bad it's causing other issues. However, if you have a bunch of these cascaded together, and you have little active devices after them, it's going to make a difference.


Resistors - Resistors come in various shapes and colors... as well as stability ratings. Accuracy requires two things in a resistor - value stability (tolerance) and temperature stability (measured in PPM / degree celcius). Both tolerances are important as your units will heat up, internally, from operations... secondarily, signal transients, as well as RMS signal voltage will further serve to heat the resistors. All of these things, taken together, will cause resistors with poor temperature stability to drift quite a ways out of their nominal value shifting bias points of your circuits, and changing the feedback circuits... in differential amps, where "balance" is absolutely critical - this means that you're not accurately amplifying your input signal.

Active devices - for me the active device of choice is a high-precision instrumentation amplifier that has, virtually, no noise, no distortion, high slew rates (50V/uS or greater), incredibly high bandwidth (>5Mhz), etc. This means, essentially, that I can have very high-gain with no impact on signal resolution throughout the entire audio spectrum, and beyond.

My approach will be fully differential (for higher CMRR), transformerless input, RF-shielded, with current feedback. Output will, also, be fully differential and transformerless with RF suppression. The actual signal path will be minimal in its approach. The first stage of the circuit to provide gain for the signal, the second stage of the circuit to match input impedance on the mixers this thing plugs into. Simple, straightforward...

The input caps will be a combination of very high-quality electrolytic (for low-frequency coupling) and a parallel coupled poly-type (for accurate high-frequency coupling). This is very similar to the RF-world, where parallel capacitors are commonly used to ensure flat frequency/phase response with very few artifacts. The output circuitry will be handled in the same way.

Feedback / stabilization capacitors (a necessary evil with operational amps) will be high-quality COGS types (cuz of the small values you typically end up w/ ceramic)...

Now, I need to spend some time and study in ground-plane layout and design... that's like the last critical step in any design is making sure ground planes are done correctly... poorly laid out grounds end up creating parasitic oscillations that may affect your amplifiers stability, but many times, really affect the integrity of the signal path from the additive noise/effect that poor grounding adds.

Thanks again, for the start of some answers to my questions... as I progress/learn I will post what I've come away with... and probably ask a few more questions, too.

Thanks, again, for the support.

Dar
 
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