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0C3 Guitar Amp Controlled Smooth Sag
One of the non-linear characteristics that SS and especially digital can't do well is to deal with/model/emulate smooth and progressive edge of breakup transition revolves around analog sag that is powerfully affected by extremely slight differences in string gauge, EQ, power amp overdrive and especially pick attack and fingering.  This characteristic of tube power amps is responsible for a very "human voice" type of nuance creating inflection and expressiveness. 

Granted some players, especially Metal and Shred lovers want the exact opposite, extreme consistency that lends itself to speed articulation but passion players tend to prefer singing lead work and much of that comes from tube analog sag.  This thread is about a severely unrecognized design that improves sag by creating an especially sweet balance between predictable and serendipity that every player that I've known immediately hears and feels.

This design is only a very small step removed from common design since "all it does" is regulate screen grid voltage by tracking plate current and maintaining a constant voltage difference between plates and screen grids so the grids are never positive relative to plates (a distinctly disastrous effect on harmonics) and maintains a constant relationship between the business end of power pentodes in relation to input signal.  While this does tend to improve high end response as well, apparent headroom goes way up especially in high current demand caused by low end frequencies that naturally require more power.  The result is that lop end never "farts" but still generates pleasant and articulate overdrive harmonics.

The design difference that creates such dynamic response is the 0C3 "regulator" valve that is still rather cheaply available as NOS devices (was never very popular among the bean counters that chopped design costs fort instrument amplification back in the day).  AFAIK this tracking regulation has no single element counterpart in solid state electronics and we all know (or should know) that in general simple is better where instruments are involved.  This is because of one long overlooked perspective that

INSTRUMENT AMPS ARE NOT REPRODUCTION DEVICES BUT INSTEAD PART OF THE INSTRUMENT OF ELECTRIC GUITAR!  IOW, one important view is that very few players want an electric guitar to sound the same as a non-amplified strum only louder.  Most want "color".  Especially these days where very few venues allow the volume levels that allow that incredible feedback loop where volume makes a guitar system, including the air in between speaker and strings, makes an electric guitar "come alive".  I'm not going to insult anyone's intelligence by saying this amp design negates that physical attribute that only comes to that degree with sheer SPL, but it does indeed reduce the levels at which the effect begins at more reasonable levels.  You can't possibly know this without experiencing this for yourself and as noted, this design has been all but non-existent in guitar amps so how could you.. with the vaguly possible exception of one playing through an old Leslie rig (that depended  on the 0C3 to get extreme headroom for extreme frequency response, especially in the low end for bass pedals on a B3) ?  Most players who actually played through a Leslie like model 147 simply thought the sound came only from rotating speakers since they generally only switched a Leslie on when they wanted the modulation, never hearing the effect for straight clean.

This is the design schematic of a similar setup modified to be more aligned with guitar needs than organ that can very easily be tried out, even temporarily and in some cases with no newly drilled holes, in existing amps just to get a glimpse of the improved dynamic and tracking response that sounds so sweet and human.  It works with either SS bridge rectifier systems or valves like 5AR4.  Naturally an amp with a 5AR4 or similar rectifier amp can easily be temporarily rewired to employ SS diodes so the 5AR4 socket can be used for the 0C3, and put back if one doesn't like the results before one is faced with the decision of adding an octal socket to make the mod permanent OR just build one from scratch.

Without any further explanation, here it is, but with some coupling cap values left out for personally desired EQ response characteristics....BTW worthy of note one doesn't need to buy a Leslie 125/147 Output Transformer since any OT with a dual output secondary like 16 ohm and 8 ohm, or 8ohm and 4 ohm can do the job.  Also one could simply ignore the local feedback loop to the cathodes and eliminate the need or use another NF geometry.

[Image: 0ZKrFaU.jpg]
Hi Guys

An interesting thread showing a method for a fixed level of power reduction that would be aesthetically pleasing to many guitar players using tube amps. The mod is simply the cathode-bias version of PS-TT (Power Scaling Two-Thirds) where the plate voltage is not controlled. Output power is reduced and the high-power output stage effects are achieved at lower power and lower loudness.

The mod is not actually one that enhances sag per se; rather, it allows the output stage effects to be experienced at a lower power level / loudness.

Note that all guitar players realise that their instrument is only really "half an instrument" inasmuch as an amp or other electronics is required to produce The Ultimate Tone the player wishes for, just as has always been said in the TUT-series since 1994.

The OC3 is essentially a zener diode with an "ionizing heater" rather than the usual filament or heater+cathode. This allows it to be a 2-terminal device, but it has an octal base. The single component sub is a 100V zener. The OC3 is rated to conduct 4-40mA while maintaining 105V across itself. At 40mA there is a dissipation of just over 4W. As a zener we would want to use a 10W device if it is available, or go to series-connected lower-voltage 1W diodes.

The alternative is to use a low-wattage zener, such as 1N4764 and a pass element such as a BJT or mosfet bolted to the chassis. Yes, more than a single component BUT affordable, compact and available components. Certainly, for the aesthetic of "all tube" find an 0C3 or equivalent. Note the first digit is zero, not a capitol "o".

One advantage of using the series string of zeners is that a rotary switch could be added to select the reduction level. Of course, it can also be made fully variable as our kits allow.

We know that the tube is cathode-centric and in a tetrode / pentode there is an intrinsic triode comprised of k, g1 and g2, where g2 is the "plate". If you change the screen voltage (Vs applied to g2) then the idle condition of the tube changes in step. Assuming we are modifying and amp as the OP suggests, then we consider these issues:

In the case of a cathode-biased amp, the tube finds a new place to settle working against Rk in the new voltage environment. With conventional Rk biasing, the idle condition will no longer be as stock, as lower plate current flows and the supply voltages will be slightly unloaded, rising as a result. Maximum output power is reduced, which means the compression and clipping will be at a lower loudness level. Above the class-A transition, the single driven tube is working against Rk on its own which linearises what it does but ultimately restricts the output.

All cathode-biased guitar amps (except my own) have a bypass cap Ck in parallel with Rk. This allows a smaller number of tubes to produce a given output power and/or for more output than the full idle dissipation of the tubes otherwise allows, usually because there is a transition to class-B.

In fixed-bias, the drop in Vs reduces Ik as above. Without an adjustment of -Vg1, the tubes will likely be in cut off (zero current), and what is needed is a proportional reduction of -Vg1 to set the world back in order. As with the cathode-biased situation, these conditions for the output stage will produce lower output than stock.

In cathode-bias, we should note that adding the Vs reducer is only half the required mod. The supply will unload and the preamp and driver stages will all have higher voltage and have a brighter overall tone. To restore the stock conditions, a voltage regulator should be added for all those voltages. Really, the voltage needs to be clamped or restricted to not rise higher than the stock values, rather than adding hard regulation. Our VCK Voltage Clamp Kit does exactly this function for cathode-biased amps being Power Scaled.

There is a misstatement in the OP post regarding keeping Ea (plate signal) from falling below Vs. In every conventional output stage, the plate voltage swings close to ground at peak drive, never getting all the way because of the tube's internal resistance and Rk if the latter is present. Long before this point in the signal cycle, the plate voltage dips below Vs and everything is fine. Things are working as they should.

I believe it may be coincidental that when the OP's amp was modified to reduce Vs by 100V, that the signal swing on the plate "just happened" to never go below the reduced Vs value. This is normal in PS-TT since Va is left as stock.

Also, please attach the schemo as an attachment rather than inline if you want the text to be legible. Thanks Smile
Thank you K O'Connor for your points and suggestions however I don't think I even implied that signal voltage was being directly controlled or tracked, so I disagree this was a "misstatement", It is the supply voltage conditions between Plate and Screen Grid that tracks and remains a fixed distance apart. It's not perfect as it is a difference not a percentage but the effect on sag is in fact quite noticeable.

I also disagree that a simple SS Zener Diode will directly sub for the 0C3. The characteristic of tubes/valves differs from SS in that SS has an extremely sharp knee while valves are softer. This is even true for rectifier type processes and can easily be measured and compared by scope'ing the output of a Full Wave Diode Bridge vs a common FW Tube/Valve. Yes the "DC" output voltage of the tube/valve is less than that of the SS "equivalent" but so is ripple and not just to the degree of the voltage difference but substantially greater. For trained ears it can also often be heard.

I'll post some photos and clips soon as well as the preamp schematic..
I suppose I should give a reference point so here is a live clip of two (2) Fender Deluxe Reverb Amps I modded for channel switching 30+ years ago in an open mic jam session.  It's somewhat long but annotated so you can FFWD if you like but it shows a similar preamp design to tyhe New Amp just with AB2 power section asnd with only 6L6s. 

Then when I link New Amp clips it should demonstrate the difference that occurs with Direct-Coupled Cathode Follower Tone Stack and 0C3 regulation.  The basic architecture and parts values are nearly identical, with only those 2 exceptions... that and the New Amp maintains the Overdrive stage always connected. not switched, just controlled by the "Volume - Gain" controls.  This is made more usable Live by the expanded range of edge of breakup possible to some degree with the Tone Stack but especially because of the dynamic range characteristics possible with the 0C3.

Oh yeah I should mention that although the recording was originally done quite well for the time it was copied onto cassette and badly stored for 30+ years before I attempted to salvage what I could.  I couldn't dismiss all of the tape noise but I think I did a pretty good job of restoring the lost and muddy extremes.  You can definitely get a feel for the amp sounds.
Hi Guys

Below is the statement that is incorrect, particularly the section beginning with "so". The part prior to that is also inaccurate inasmuch as the 0C3 is not tracking plate current; rather, it is following plate supply fluctuations that result from signal-dependent variations of that supply.

""all it does" is regulate screen grid voltage by tracking plate current and maintaining a constant voltage difference between plates and screen grids so the grids are never positive relative to plates"

Otherwise, what you did is as I described but using a tube instead of solid-state. That is a nice variation of tech but gives few options for setting loudness since Vs has been reduced by a fixed amount. You can get lucky with things (fixed loudness reduction) and maybe you have for your needs?

A simple way to make this full variable is to have a voltage divider across Va that has a variable portion (a pot). The pot wiper ties to a mosfet gate that has D to filtered Va and S to ground via a high-value resistor, and also ties to the screen-stops. The screen voltage will be any amount lower than Va that you need for loudness adjustment and it tracks the sag of Va. Again, this is just a PS-TT variation that works with cathode-bias. Add a tracking bias reg for fixed bias.
I'd like to take a moment to discuss what is very commonly, and again here, is the thousand pound gorilla on the basketball court, the boundaries between Art and Science, or more exactly the scaling, not of amplifiers, but of data and design considerations.  The way I see it the only realm where actual "proofs" exist (or should) is in pure Mathematics.  This is because at it's most fundamental Mathematics is an abstract construct where variables are commonly eliminated, the "Black Box" realm if you will.  This is exactly the source of the extreme precision possible in Mathematics. 

Only slightly removed from Pure Math, is Science, because in actual practice it is indeed possible to remove or ignore as many variables as humanly possible to get precise results, or extremely close to a "proof".  This is where the Sigma scale comes into play such as the highly desirable 5 Sigma for extreme statistical probability.  Next comes Engineering, and please notice that in this progression and hierarchy all employ Mathematics because being an abstract construct Mathematics has Universality and consistency as well as precision when used under strict conditions of Logic and is careful to avoid an invalid conclusion no matter how precise one's mathematics is if the axiom or premise is faulty, even nonsensical. 

In Engineering abstractions are reduced in importance in favor of what works in real world conditions where all variables cannot be controlled, and sometimes, even considered for various reasons, not the least of which is the "at odds" conditions where extreme simplicity is desired but assuming such simplicity is in conflict with inherent, and often badly understood real world conditions,  The deeper we go the more room for complexity is revealed, so Engineers must include redundancy and fault tolerances to create designs that actually function under varying condition.

Since this is a guitar and HiFi forum, please allow me to use examples that fit in the form of pickups and speakers.  An electromagnetic sensor like a guitar pickup in it's simplest form is "merely" a coil of wire around a magnet. So why, given such apparent simplicity, do no two PAF clones sound the same?  One reason is that "wire", "coils" and "magnets" are not specific terms in this context. Slight variations can accumulate and alter the results.  More importantly cloning implies what sample is being cloned and in the case of PAF pickups, also non-specific since no two of those are identical especially after decades of exposure to impact and environment. So, at best, "PAF Clone" is only a moderately useful "ballpark" label.  Speakers suffer the same varieties and flaws.

In addition, speakers are not standalone devices.  The are driven by amplifiers and in wildly varying environments.  We can calculate that given a specific output power and speaker efficiency, while also including signal frequency and various resonances, what the resulting Sound Pressure Level should be.  However what if the system is stereo and the 2 speakers face each other and are out of phase? and by what degree? or in an anechoic chamber or a vacuum?

This brings us to the last category, Art, which is closely related to Engineering because it's concerns emphasize "what works" in a complex environment above precision in an abstract "Black Box" environment and this complexity with Art includes the wildly varying and often fooled Human perceptions.  There is even a term for this in Audio and it is Psychoacoustics since human hearing is not linear, varies with individuals to some degree, and can involve emotional concerns and effects leading to subjective evaluation.

An acoustic guitar is just a wooden box with strings attached under tension, but not only is there variations in types of woods, geometry, types of strings, etc but it is even utterly common that not all Martin D-28s with the exact same string set, under exact same tension, even with the exact same human player,  in the same room sound the same.  Whether or not you understand the Math, Science, and Engineering if you've ever tried out a dozen D-28s (or any guitar model) to pick "the one that speaks to you" you know this intuitively "in your bones".  This is an inherent nature in Analog devices.

I like to sort of reverse a wise old cliche and view it this way -

Wise Old Cliche Wrote:  If all you have are nails, everything starts looking like a hammer, even wrenches, screwdrivers and rocks

Thank you again K. O'Connor for your deep understanding and obvious training and experience in electronic audio and your contributions to this thread.  It is my understanding that you are long involved in this forum as well as "London Power" in some capacity and are potently involved in Power Scaling and the long list of associates involved in such amplifier concerns are also a litany of the "cream of the crop".  Kudos! 

However, K. O'Connor, although it is natural given your background and focus that you would view this 0C3 controlled design through the eyes of Power Scaling, that is only a small part of what this design does and how humans perceive it. It's not at all the "Why". Although somewhat modified for guitar amp service, the basic power section design is adapted from Leslie 122/147 design.  Mr. Leslie was not at all concerned with power scaling.  He began his research for it's design in the 1930s desiring to attempt to reproduce on portable electronic organs the massive and formidably awesome sound of HUGE Pipe and Theater organs.  These devices take up cubic yards of space and weigh many tons.  The volume and pressure of the air that drives such pipes (basically Helmholtz resonators) is FAR beyond what lifts your car or truck at the shop.  Mr. Leslie was not looking to scale down power. If anything he was looking to maximize it.

Leslie was after both power and phase relationships that mimiced the awesome power of such pipe organs at substantially less size, weight and expense.  At this point I need to ask, and anyone reading this should ask themselves, have you ever experienced the sound of a multi-ton, multiple cubic yards pipe organ? Then for comparison have you ever heard a Hammond B3, especially with the Bass pedal accessories, through even one Leslie 147?  If you have experienced the latter I think you might agree that it does not sound like a mere 30 watts, scaled or not.  It sounds more like 100 watts.  It sounds utterly massive and also massively pleasant, articulate, but rich and warm as well.

THIS ^^ is what I'm after with this design incorporating the fixed regulation via the 0C3 and it does deliver as you may soon experience for yourself as much as that can come across when not in-the-room but limited by digital reproduction and bandwidth compression... OR grab an 0C3 and build one!  I suspect you will be delighted. If you can unlock the mojo with SS devices, it could add to your reputation and wealth.  I'm too old for such things.  I just love the sound.
Progress -  Some photos

Note:  If I didn't already mention it I suppose I should point out before anyone has apoplexy (and no, that's not a Steve Jobs built Marshall clone  Wink  ) I'm building this amp in a rescued Blackface Princeton chassis and cab  salvaged from a dumpster where the owner had tosses it after a fire.  Not much was left.

Here it is now,....

[Image: XCa2iLS.jpg]

and inside

[Image: PEIqgpa.jpg]

I have to find a new silkscreen service or try to muddle through some sort of masking template myself as the service I used for years is apparently defunct.  The actual Front Panel layout is "Gain" (parallel) in #2 Input, Volume, Treble, Middle, Bass, and Master.  FX Loop is on the back panel and if anyone decides to build something like this if you are a heavy high gain guy, like if you have both channels dimed a lot, you'll need a voltage divider at FX Send somewhere between 50% and 80% reduction should work for the most Metal.
New Preamp Schematic -

[Image: eStCVar.jpg]

If you have any trouble with size for reading values please just Rt Clk and Open in New Tab.
I can't tell if anyone is still accessing this thread but FWIW here's an initial clip of simple chords at very early edge of breakup with single coil pickups.  It's a Lipstick Tube Silvertone on neck pickup.

Early Edge of Breakup

I'd love to hear any comments.  Tolex, Genalex KT-77s, octal tube retainers and rubber feet arrive in a few days.  This clip is with 2x10s from a Bassman 10, 2x32 ohm speakers in parallel for 16ohms, mounted in a modded Deluxe Reverb Amp. Next month I get a Celestion Type A 12 incher. Cab and baffle should be complete by then.
Hi Enorbet2

Your amp draws from a variety of vintage sources to combine as one that provides safe, warm tones most seasoned players (eventually) strive for.

The front-end gain is the same as early Mesa amps, although a similar method was used in a later circuit point in the Mk2 amps. Randall took Howard to task as they both developed the same circuit at the same time; Randall lost his argument. Where mesa hung the gain stage across a mixing resistor as you do, Dumble did it better without the mixing aspect.

The CF-driven EQ is standard Marshall ripped from Fender with Bassman values. The gain stage values are generally "Fendery", which one could say are very similar to most guitar amps up to the 60s. Low-value coupling caps reign in fatness to make low-frequency distortion tighter.

The FX loop is like the Dumblator: series jacks with a high-gain free-running stage after. It is easy to run into a noise penalty here, as Fender and Peavey both did, but the goal is to be able to use pedals between the preamp and power amp.( The London Power loop does this without a noise penalty.)

The PA has not been described apart from the use of KT-77s. These are a "muddy" or "creamy" tube depending on your taste. They are what makes a significant part of the Hiwatt tone.
Overall, the amp should have a warm clean sound that rolls through overdrive into a fat distortion. The speakers can make or break that sound as they heavily filter the signal coming from the amp.

Old-school players usually want to work a bit for their tone. Amps that roll into breakup through pick attack and/or use of the guitar volume control (yes, that is what that control does) are very satisfying to play through provided the loudness produced is controllable. The most amazing sounds from the pre-digital age were created by players pushing their gear and themselves to the limit. I still prefer doing it that way.
Hi Guys

Anyone who solders as well as plays guitar knows well that the ultimate arbiter of tone is your ear and personal taste. It is art, and as the TUT-series shows, there is science behind that art to explain what you hear and how specific circuit elements change the sound.

There is no separation of art , science, engineering and math - they are all part of the same spectrum and are part of the same quest. In general terms, an ancient view of science was that it is a search for god, or a way to understand the mind of same. For our purpose of tone creation, we use the tools at our disposal and the knowledge we acquire through our own observation and those of other people to help our quest.

For example, a voltage regulator can be viewed in many ways. An ideal form has absolute rigidity of output regardless of input and load variation. This is called a "voltage source", and is unattainable. We can get very close, and within the Human Scale of requirement / ability, it has been achieved. This would be "hard" regulation.

Real-world components have tolerances and there are countless circuit variants one can use to regulate voltage. In guitar amps, I only use "soft" regulators as this works better in a tone creation system. I do not select the circuit for its sound per se, but realise that there are aspects of component understanding and circuit design that are overlooked by the mass of engineers primarily because their focus is not the same as mine. Our views are more in line for hifi design.

Hobbyists often have difficulty reading component data sheets, specifically in mining out nuances of performance that are there if you know what to look for. For example, a zener diode (just like every other diode) has internal resistance that can be taken advantage of for use in audio, even in a regulator. Remember - the power supply is the other half of the signal path, so it needs a bit of love and attention. Zeners are tested at 5mA - sometimes other values depending on the rating of the device - and if they are operated at a lower current, their performance is not guaranteed. What you will see is a higher voltage than rated, up to the rated voltage tolerance.

Readers of the TUT-series know that we can increase the dynamic resistance in the circuit to provide soft clipping, for example. The compliance value (resistor) can be anything we find that sounds good to us. The science is there to show what happens. The art is in selecting it simply by empirical means. No one will die if we choose the wrong value. Nothing will blow up.

So, your experience can be that solid-state as a whole sounds terrible, or that some of it sounds good, or that all of it has its own place. Your opinion is not wrong even if it is uninformed. If you have only ever experienced the sonic impact of zeners used for hard regulation, then you cannot know what else they can do.

Everyone keeps re-inventing the same things. We live in isolation and experience the world uniquely despite the general Human experience being the same for the most part. We each invent happiness, sadness, fear, sex, creativity. When it comes to guitar amps, there is a safe common tonal range where every player begins or ends up in, with occasional excursions into varied realms. "Safe" is not a bad word here. It just represents a widely accepted sort of tone that most other players acknowledge and accept, and that audiences accept, for example a Fender clean tone with a touch of reverb.

When I design an amp, I usually want it to at least be able to provide that safe Fender clean sound. The rest is ear gravy.
Hi Guys

enorbet2: Your use of the 0C3 is very cool and innovative Big Grin

I did not mean to imply that it was anything other than that by pointing out that the method is a form of PS-TT. I apologise if I came across in any way belittling.

The fact is, parallel development and independent innovation and invention happens all the time in every industry and every area of interest. Two famous guys invented calculus but only one is revered. There might have been others who had the idea but did not have an outlet to disperse the knowledge. Two guys invented the telephone but there were likely others and again only one guy got the fame. Many people invented rockets of a modern form but only a few are recognised.

When techs see the Power Scaling circuits, they say, "Oh, that's just a regulator. I knew that". But they did not know to apply it for the purpose of loudness control. Once you are shown something, or hear about it, it will seem obvious - the definition of "patent". Most of Smith's patents are obvious things that were already public domain but the USPTO is profit-oriented and will take his money for truly worthless patents. Part of my goal with my books is to make as many cool ideas as possible public domain so people like Smith cannot interfere with small builders and hobbyists.

So, when I say the alternative to the 0C3 is a resistor plus a zener, it is merely to help others understand what is going on in your amp, and to show that there are readily attainable alternate components that allow other amounts of voltage and power reduction. The 0C3 is a cool "hot" device. Kudos on using it.
Thank you K. O'Connor for clarifying your goal and the gentlemanly manner in which you did it.  I'm pretty excited today because while building I use a Variac and old tubes just to avoid damaging anything really decent.  I'm nearing completion now and just got a matched pair set of the Chinese Gold Lion KT-77s.  They bought the name Genalex and perhaps they understand how high end Genalex was back in the day because these tubes/valves are excellent.  They didn't slack on these bad boys. They test strong and they sound superb.

So I have 2 clips for your audio enjoyment and critical listening.  The first one is at the very earliest stages of edge of breakup with single coil pickups.  The guitar is a vintage Silvertone "Lipstick Tube" and the quick 'n dirty phone recording cycles through Neck > Both (parallel) > Bridge.  The amp is playing through an open back cabinet with 2x10 inch speakers from a Bassman 10.  Check out the clean sustain and low noise floor at the end. They are 32 ohm speakers in parallel.

The second clip I think even as nasty as a quick phone recording is, demonstrates the extremely gradual transition into overdrive  which makes this design especially "vocal" according to touch and guitar controls settings.  This clip is wide open in the preamp, both gains dimed, and the Master Volume (which doubles as an FX Return level control) a nudge below "2" out of 10.  It's not loud in the room, likely under 90db.  With this Tone Stack the gain and where overdrive occurs first (in which frequency band) varies wildly with controls this interactive.  However I left the tone controls close to midway throughout and this clip is the single coil bridge pickup only.  Ultimately it's to demonstrate max distortion with single coil pickups but the fist chord you hear is with the guitar Volume Off, then advanced in steps.  It's easy to hear how the transition is wide and gradual.

Anyway my playing skills are horrendous from severe nerve damage but this was just a basic test, so here goes...


and all out...

DIMED (master less than 2)

I can't wait to hear it with the Jensen C12N.
Hey man

Sounds cool.

90dB not loud? I used to guess at loudness numbers then I got a SP meter. Boy was I way off. Im a metal guy and 90dB is frikken LOUD !!! I didn't realize that before.

I power scaled my marshall with KOCs help and did some other mods and I can get sounds loike yours at really low volume and save my ears. I used to just be cranked distortion but maybe my playing is getting better cuz the amp sounds so good at low volume I can just play soft or play hard and not touch any controls and go from clean to death zombies without thinkin about it and it goes smooth from one extreme to the other, not sudden like it used to.
Hey nauta, thanks for the reply.

I gotta admit it's been a long time since I used my SPL meter but I do have literally decades of experience onstage and behind desks, both recording and live, and at least at one time (who knows how much it's atrophied after neglect) could quickly identify sound pressure levels within 2-3db. Now it's also possible my hearing in general has taken more hit than I know or recent tests reveal but I'm a child of the 60s and I played LOUD for decades. I've never been a Metal fan so averaging around 100-103 db with peaks around 110db was an everyday event, so I don't relate to 90db as being particularly loud. Personally I am upset by and can't stand even the thought of Rock 'n Roll at 85db. That sounds to me like a Bill Hicks "Corporate Approved Rock" joke to me except the joke is on us.

That said I will have to break out my db meter and do a brain and ear check to see how far off I might be. These clips were recorded in an 10 foot x 12 foot shop and at the beginning of the "Dimed" clip the first chord is totally acoustic, zero amplification, so that might be a clue as to actual SPL. Also my shop has lots of tools and stuff on shelves, on the walls, all over the floor, and just hanging about and none of it was rattling around. The "Clean-ish" clip was a bit quieter but both were "volume normalized" in Audacity in order to give consistency for comparison and to protect peoples ears, especially those using headphones.

Anyway I'll check with a meter and write back and later I'll publish a real studio recording and hopefully a live band shot. BTW and maybe a heads up, while I don't regret in the slightest bit the constant volume levels I perpetrated on myself (it was worth it!) recent professional testing surprised me. I thought for years the first sign of hearing loss was first noticeable in the extreme highs and since I can still hear out to ~16K i figured I had been lucky and avoided all damage BUT the tests revealed some not insignificant loss in high mids so I can hear women speaking clearly but some deep voiced men I have to be line-of-sight to get any articulation as their voices obviously lack energy in the high mids.

Anyway thanks for the reply and the vote of confidence. KEEP PLAYING!

Addendum: Oh yeah do you check out any That Pedal Show or recent Anderton's YouTube clips? I think it is brilliant they keep an SPL meter clearly visible during all demos and tests. It's a great way to get a feel for what actually works.
UPDATE - Progress Photo

Heya all,

Got a ways to go yet but we are getting close now.  Still have to make the 1x12 baffle and clean the Grille cloth, add nickel corner protectors and seal seams, but it's close.  I was pretty sold on the Celestion Type A but I've changed my mind and think the Jensen C12N would be a better fit musically.  I'm waiting to hear back with a quote on an actual name plate.  This one is just a print on paper for testing.

[Image: bBRy1QC.jpg]
I changed my mind on the speaker.  I had initially decided on a Celestion Type A, which Celestion bills as their "American Voiced" model and I do love Celestions but I decided that Jensen was the original that created much of the American Voice and that jensen was bought out/moved to an Italian firm only improves on that in my mind... or at least I hoped so since I ordered a Jensen C12N.

It arrived today and I am even more stoked.  If it sounds half as good as it looks and I'm talking about heft and precision not mere pretties, it's gonna be the perfect choice.  It's very beefy for a mere 50 watter and I am particularly impressed with the gauge of the steel frame.

Here's a photo....

[Image: mMEiOOe.jpg]
I can't wait to hear it!
(06-06-2023, 07:57 PM)enorbet2 Wrote: I changed my mind on the speaker.  I had initially decided on a Celestion Type A, which Celestion bills as their "American Voiced" model and I do love Celestions but I decided that Jensen was the original that created much of the American Voice and that jensen was bought out/moved to an Italian firm only improves on that in my mind... or at least I hoped so since I ordered a Jensen C12N.

It arrived today and I am even more stoked.  If it sounds half as good as it looks and I'm talking about heft and precision not mere pretties, it's gonna be the perfect choice.  It's very beefy for a mere 50 watter and I am particularly impressed with the gauge of the steel frame.

Here's a photo....

[Image: mMEiOOe.jpg]
I can't wait to hear it!

Just a friendly word of advice: give that speaker a long break in period before judging it.  I'm a Jensen dealer and I've had rather mixed experiences with RI Jensen speakers---some I think are great (C12Q, C10Q)and others (their P10R) fall far short of the sound of the old Jensen speakers had.  Some is due to the fact they are new stiff but they also sound really different from an expertly re-coned vintage Jensen.  The C12N is one of the better RI speakers but it takes long time to smooth out and sound less constricted than it does out the box.
Thanks for the Pro tip, makinrose. It's good to get feedback on "clones". They seem to be like the little girl with the little curl right in the middle of her forehead..."when they're good they can be very good and when they're bad they are horrid". I've been thinking about connecting to a low power sweep oscillator for a few hours each day until the cab is completed just to get the process started.

Speaking of clones, I asked around as to the quality and value of the Chinese "Genalex" Gold Lion KT-77s and a studio owner, engineer and player I respect said he'd had excellent results on half a dozen sets so far. I have experience with real UK Genalex Gold Lion KT-77s and I'm happy to report either the process is very good or I've been lucky, too, since they are very close to UK versions and adjusting for inflation, well worth the price.

I also have considerable experience with vintage speakers including Jensens and I will follow your advice and hold off on judgment until a few dozen hours of break-in. FWIW, I'm old school, so I play a lot cleaner than most guys these days so I have no problem waiting until I feel I can hit 'em harder. Thankfully it will be on a 30 watt amp so almost half it's rated power handling so clean should be quite reasonably gentle for a few weeks.
Ping Nauta ---
I have no way of knowing if you're still following this thread but I did finally break out my SPL meter and did my best to match the 2 clips I already posted.  The one titled "Clean-ish" averaged around 86db C-weighted and never exceeded 89db.  Dimed, being more compressed varied less but averaged around 88db and hit a few very fast peaks of 90db.  I had to run several times to verify it ever hit 90db but on some runs it did. 

If you watch the YouTube channels for "Andertons's" or "That Pedal Show" both channels demo gear and have large display SPL meters clearly visible.  I don't know (maybe I should ask them) but hopefully they are both using C-Weighted instead of A-weighted because C-weighted is more accurate for musical audio whereas A-weighted is more for very wideband noise like from traffic or construction sites.  In any case, neither of them nor I consider 90-100db excessively loud and neither does Rick Beato.  It's worthy of note that symphonic orchestras commonly hit over 110db.

UPDATE/Correction: - While A-weighting displays lower SPL numbers than C-weighting does in general, and I strongly STRONGLY suspect that is what you have used to think that 90db is loud, especially for Metal, I've discovered that my testing was flawed for lack of calibration and apparent drift of my meter.  It's not exactly a linear drift but until I can setup a proper test environment you should add a whopping 6db to the numbers above.  Example - the peaks originally measured as 90db are actually closer to 96-97db BUT properly C-Weighted, NOT A-Weighted.

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