Designing the biggest, most euphonic set of transformers?

[bcarso]

Yes, I am entirely in your camp about coloration/effects.

Another somewhat-off-topic thing on the subject of "natural" IM is the work done by some guys Cerwinski hired in at Cerwin-Vega some years ago, I believe émigrés from the former Soviet Union, who were experts on various things acoustically nonlinear.

They gave an AES paper I heard which wound up with advising that, for lower distortion in performance the seating arrangement in big bands should be changed, and the various section players distributed all over rather than sitting together!

I don't think it caught on :razz:

 

[TomWaterman]

[quote author="Gus"]I built the c800g type microphone with a 7903.[/quote]

I think I remember that...just tried to find it in the META but no luck. What did you think to the LL7903 in that application...I know its totally different but interesting none-the-less?

[quote author="JohnRoberts"]My personal opinion is if you identify a nonlinearity that you believe sounds so good that it is merchantable (people will pay for it), put it in it's own black box, with a bypass switch.[/quote]

I have seen you mention this very thing before and I actually agree with you on many levels. You are definitely not the only designer who thinks that way. I'm sure Rupert Neve sees things in a similar way, hence his silk function. I have had chats about similar things with a friend of mine who works at Audient here in the UK and it seems the designers there have exactly the same outlook as yourself. So their new Black series products have optional colouration devices in circuit, switchable - called HMX. Similiar in idea to SSL VHD.

I guess my thinking is, if I want pristine don't use transformers..if I want transformers - why not use the best sounding (to me), most colourful ones I can find to give something some subjective character (maybe)!

ioaudio - Max has a good point about science vs art in design.
I read a thread here yesterday in which Soundguy (Dave - who has left here) made some great comments about transformers and their sound in application. Although technically lowest distortion THD or IM, flattest freq response and lowest noise should be the 'best' on paper - the best subjectively is so much more different.

What I was getting at in the original question was the barrier between designers/manufacturers and sound operators (not engineers).

You'll have to humour me. But if somebody describes a sound to you - could you invision a way to make that work technically?

CJ's research and dissections show that things sound different for a reason.

If one wanted to achieve a certain sound - there should be some technical guidelines about how one may go about achieving that, right?

I am not expecting answers from you guys...just stimulation to go and read some more and keep learning.
I have done a whole load of learning the last two nights to catch up with my idle mind and now am aware of a few ways to achieve certain performance within a transformer and design compromises RE winding structures, core material, permeability etc.

Radiotron and the Handbook for Sound Engineers has some really good info, as do a few of the papers lurking on the web. I have the Lee, Carter, Wilson book as a PDF and that is an amazing resource.

I agree with John , IM distortion is pretty unpleasant but 2nd and 3rd harmonic is pretty damn nice in reasonable levels - I use it a lot when mixing in the box. Brads notion of musically relevant IM is great. Now I wish I hadn't given up playing the recorder in primary school!

How many of you guys sit there and dream of the sound in application first before thinking of the design?

Is that a bad question? :green:

-Tom

 

[emrr]

Tom,

I'll be in the minority here by saying that I am not after tranparent linear reproduction, I'm after making the source (which is usually amateur, and not very good) sound better than it is. In rock music, that usually means some sort of color imparted by the signal chain.

Most audio people seem to approach sound recording as photography, when it is equally legitimate to approach it as painting. The photo is no more reality than is the painting.

To get back to your question, I don't think what you ask is that easy, or even possible. I have a large collection of restored antique audio gear that I use for its various colorations, and the differences between the pieces is enourmous in certain contexts, tiny in others. There is no across the board solution, other than a larger box of crayons.

Motorcycles aren't cars; we might as well not wish they were, nor vice versa. Get one of each. Or his and hers, in seasonal colors. We're up to 16 now, aren't we?

As I understand it, when you wind single section non-interleaved iron you get a certain type of possible response curve, with a corresponding distortion component. When you go for high numbers of winding sections you can get better high frequency response, but at the expense of having increasing numbers of resonant points and their effect on distortion.

Sometimes you want low freq. phase and harmonic distortion, sometimes you want high freq. phase and freq. distortion. This is usually two different transformers wound two different ways. What's your recording source? your mic? The operating level? They are all BIG BIG pieces of the end result.

Best answer is a bigger box of crayons from which to pick. Pairs of everything.

Though it doesn't hurt to dream about the ultimate version of something.

 

[ioaudio]

low frequencies & operating level are limited by the given primary inductance, the core-size and -alloy.
high frequencies suffer from winding capacitance and leakage inductance, which can be overcome by winding techniques such as sectioned coil structures, interleaving layers and bifilar windings, sometimes fighting against each other, then there´s the phase issue...
chapter 5 - radio designers handbook is a great start, also search for some of the above keywords here on the forum for prr´s fantastic explanations.

again, i think accuracy in audio is just a matter of definition - to some degree colouration happens as a matter of fact in every aktive ciruit - without a bypass switch - and as designers we have possibilities to control some of the quantities & qualities of such colouration.

-max

just to clarify - i dont like the sound of e.g. a starved plate tube squeezed into a forrest of chips for colourful sound and sound enhancers and such stuff either.

 

[Dan Kennedy]

I dunno, I kinda like transformers myself. I am well aware of the colorations, the imperfections of the iron, the imbalances that seem to manifest themselves, all that, but, at the end of the day, I prefer transformer circuits for mic preamps.

I've built all types of transformerless ones. For years, trying to develop one commercially. I haven't found one I'm willing to put my name on.

My special little project this winter is going to use up some iron I've got laying around, plus the last two old MP-2 boards. I've got a pair of Muirhead 600 to 20K input transformers that sound better than anything else I've ever been able to find, and a pair of WE 111 repeat coils for outputs.

It should sound glorious. F*&k accuracy.

 

[emrr]

Ah, a nice thick sounding WE 111C in a completely impractical footprint. Sounds perfect.

I keep a pair on the output of my mixes 99% of the time.

I've always thought there'd be no way to make one of the classic period AC/DC records sound like they do without a bunch of iron in the path.

 

[mikep]

[quote author="JohnRoberts"]
Again if ever desired that could be a separate black box effect with a bypass switch, so we're not burdened with the distortion the rest of the time when it's undesirable.

JR[/quote]

As an Electrical Engineer, I agree with you. But Ive spent enough time in studios to know that recording "engineers" don't work that way. Any button or knob labeled "tone" or "color" will be discriminated against as being a gimmic, regardless of the validity of what it does. IMO It just won't sell. For whatever reason, this is the world we live in: Recordists like to pick and choose mic amps based on their non-adjustable nonlinearities. They want a bunch of them with different characteristics at their disposal.

this is a sore subject for me right now, as Ive spent the last 6 months or so trying to figure out what constitutes "good sounding" nonlinearity, and trying to figure out a way to tastefully do just what you propose, put a bypass button on the nonlinearity. Now that I've got something usable, none of the in-the-trenches engineers Ive talked to think it is a good idea. dismissed on concept. Im still trying to figure out how to make it fly, but I assure you the problem here lies in politics, not the electronics!

mike p

 

[JohnRoberts]

The customer is always right, even when he's wrong.. :roll:

I chose to walk away from the high end hifi market due to what I perceived as a disconnect between real performance and perceived value.

My suspicion is what you are talking about is similar to the fashion business... "This season the XYZ sound is in".. There seems to be a mass of plug-ins available to mimic "classic" efx. I guess the next step is to mimic other classic designs, warts and all.

I don't have the proper political skills to operate in such a market, while I have a friend who does quite well. It is very much about the customer's perceptions. I prefer a marketplace where the product really does do something useful and different.

JR

 

[bcarso]

There's something about appearance and sheer physical presence that carries the day in studio and home environments, no doubt about it. To have a certain sound available via emulation of whatever variety (DSP likely to be the most expeditious if you are good at that sort of thng) will simply not do.

My friend was advised that his electronics have to look really cool if he expects them to sell in the high-end market. He really hates this and hates to spend unnecessary money (his own industrial design skills/creativity are essentially nonexistent). I need to persuade him that it is necessary money if you are going to play in that arena.

 

[Larrchild]

Here's what I think. Back in the day, gear had imperfections. Design engineers removed most of them over the last 30 years. I remember the push, in studio gear, in the late 70's, to remove all the transformers from the consoles and tape machines.

Then, years later, when our signal paths were as transparent and neutral as they can be now, we needed some flavor in our spice rack to cook with, to avoid bland flavor. And also, to get a period sound, if desired.

So there is a place for both transparent and "colorful" gear.

The problem that design engineers face is that it is easy for them to understand "transparent". But colorful is less quantifiable by their gear and training, so they can be dismissive at times.
It's funny to watch.

 

[recnsci]

[quote author="JohnRoberts"]

I have never heard IM distortion that I found remotely euphonious. Harmonic distortion that mimics natural musical overtones can in some cases be good sounding, but that is subjective and depends on the content of the original source, not something I would be comfortable making intrinsic to any accurate audio path.

JR[/quote]

Well... I have read quite a few times , from pens of very knowledgeable
people, about merits of circuits that have low IMD, compared to
"nice-and-cheerfully-euphonic" harmonic distortion. Problem that
bugs me: even simple square law circuit (like, imagine textbook
perfect JFET without any source degeneration) will have 6dB higher
IMD than THD. So please, could somebody provide me with a link
to magickal circuit that has substantial enough THD to be called
euphonic but is almost IMD free. (not that I belive I will ever see
such a monster).

cheerz
urosh

 

[CJ]

Transformers kind of "peaked" out during the "golden age of audio" when people were really fussing over the details.
Audiophiles had a wealth of voodoo to explore, turntables, tubes, transformers, money meant nothing to the high end nuts.

But now, everything is on a chip, so it can be small, light and cheap, and quiet and better sounding.

So the first component the engineers had their murderous eyes on was transformer.

"If we could just get rid of that....."

Well. they did. Slowly but Shirley, UTC, Peerless, Triad (although still in bizness) they went away.

And now, anybody who wants to recreate the past, will have a lot less options to work with, unless he's a millionaire and wants Mag Metals to do an old school run of lams.


So laminations is one limitation, next would be winding equipment.

Apparently, UTC had some real specialized custom made equipment for winding those A-10's.
They use foldback winding on the secondary, becuase they wind two pies at the same time. And when you switch directions to add another layer, and only one wire wants to track properly, you have a problem.
So what you do with that fine hairwire, is to bring then Both all the way back over to where you started, that way you can put a cam in the machine which will increase the pulley angle so much, that both wires have no choice but to come back over at the same time to start another layer.

So, I don't know if Magnetica inherited any of this equipment, but that is another problem you will have with the UTC stuff.

Ever wonder why nobody takes the time anymore?
It's a pain in the ass! And if the money does not justify, ...

So lams, winding machinery, what else is in our way?

Wire is not the same. The old insulation was improved upon, so now the insl to copper ratio is all different, this means that the coil build will be slightly different, which will change capacitance, and thus the resonant peak frequency of the transformer. UTC had to use interlayer insulation in order to provide enough space between layers in order to prevent breakthru.
Nobody is going to bother with 0.0005 paper anymore. How would you cut it, anyway?
You don't. You wind 24 coils side by side and cut them apart with a band saw. This way, you do not fuss with 24 strips of paper every layer, just one.

You will probably not be able to afford enough copper wire to spin 24 coils at once, so you will have to find a machine to cut 0.0005 paper accurately.

OK, lams, wire, paper, machinery, what else?

Mu cans. You will need three telescoping mu cans to get the same shielding. Maybe shielding isnt a problem nowdays?
No more AM transmitters around the studio.
Maybe we can use 1 nested can in an forged outer can for B max protection?
OK, but will that influence the sound?

Then the potting compound. Every xfmr I took apart had a different smell.
I heard that they use to dispose of chemical wastes at the factory by putting all the stuff in a big holding tank, adding some PCB's and polycrystaleine wax for good measure, and mix it up for potting compound.
Langevin had the weirderst smelling stuff. Peerless was the cleanest. Triads was some in between. UTC did not use wax. Just black tar, to hold the lams. The wires are free to vibrate at high frequencies, specially after dryout, when the 0.0005 paper becomes 0.0004 thick, providing more space to rattle, which is a form of mechanical feedback, which will effect the high end.
No wonder I am so weird, all those fumes!
So different recipes for wax means different dialectic constant means different sound..
Good idea, though. Ship all your waste out in tiny little packages, all over the world.

So big deal. Whats potting compound gonna do anyway?
Well, it gets in between the windings during vac impreg, and forms a dialectic. This changes the capacitance>res freq>sound of the transformer.

So we have lams, wire, machinery, mu cans, and potting compound.

OK, I will just go ebay and save the hassle.
Well, all that stuff inside the xfmr, all these years, and the loosed lams i see in half the utc's I pull apart, hard to say if they sound the same and won't break from high voltage, due to erosion of the insulation of the wire and paper.

So you can change winding structure, but everybody is stuck with the same alloy from MagMet, so this leaves one other option: lam shape.
There are a million lam shapes and stacks, and they influence sound.
When UTC picked a lam, they designed the hell out of it. Why?
So they only had to stock a few part numbers.
When Ersel B Harrison did something weird by using nickel for the Peerless 217 output, lord have mercy, well, he probably used that lam a lot of other places. This saves redesign time also, since you use the same insulation and tooling to build the thing.
He also used the same geometry over and over again, the 5-4 sandwich.
5 secondaries-four primaries, for the high dollar 20-20 series..
Do anymore layers, and its diminished returns due to leakage-layer build up.

So these guys were lazy. And pressed for time. So time Is on your side, since it's not your job to knock out transformers.
So experiment with different lam shapes.
Use the 5-4 layering, it don't get much better than that.

Get a MagMet catalog.
Or go online.

 

[JohnRoberts]

[quote author="recnsci"][quote author="JohnRoberts"]

I have never heard IM distortion that I found remotely euphonious. Harmonic distortion that mimics natural musical overtones can in some cases be good sounding, but that is subjective and depends on the content of the original source, not something I would be comfortable making intrinsic to any accurate audio path.

JR[/quote]

Well... I have read quite a few times , from pens of very knowledgeable
people, about merits of circuits that have low IMD, compared to
"nice-and-cheerfully-euphonic" harmonic distortion. Problem that
bugs me: even simple square law circuit (like, imagine textbook
perfect JFET without any source degeneration) will have 6dB higher
IMD than THD. So please, could somebody provide me with a link
to magickal circuit that has substantial enough THD to be called
euphonic but is almost IMD free. (not that I belive I will ever see
such a monster).

cheerz
urosh[/quote]

I am probably the wrong person to ask I generally try not to add distortion to any of my audio paths.

My one experience of (some) customers preferring distortion was in an old studio delay line flanger. I had improved the companding noise reduction used around a BBD delay line, from a pretty dirty CA3080 OTA to a much cleaner NE570 series compander chip. While that audio path was still plenty distorted by the BBD, running the CA3080s pretty hot to get good S/N generated lots more. The distortion mechanism in an OTA is from input LTP run open loop. I suspect it had plenty of IM to go along with THD. FWIW, I was never tempted to go back to using the old OTAs, even in an effects unit. (Note: the customer's didn't say it was distortion they liked, just my best guess from what was changed and what wasn't. At the same time I changed to a newer longer BBD, but it was from the same vendor and same technology so I expect only slightly lower distortion from that with similar characteristic).

Here's another story perhaps showing my personal bias (or SH__ for ears). Years ago back when I had a real job (Peavey), I was being a good engineering manager and trying to sell some slow moving inventory. Long story short(er) we had an excess of simple one rack space 4x2 (? actually I think they were 2x4x1) vacuum tube mixers. They were level only, and dirt simple, just a clean, simple audio mixer path. This was designed for MI use (with guitar level signals) so it was all 1/4 ins and outs. I had my tech make me up some RCA adapters and took a unit home with me so I could listen for the "tube magic" on my home system. We had a pretty low cost basis in these and studio types were paying big bux at the time to be touched by a tube (late '80s). Well after a lot of listening I heard absolutely nothing... nothing good, nothing bad, nothing... I heard just what I was sending through it. I didn't give up, I then had the tech change some resistor values to increase the mix gain, so I could easily overdrive the tube path. That should surely release some tube magic. Noooooh. I had zero success raising any interest for this "real" tube path, while other companies out there were pretending to involve tubes in some pretty high selling products.... go figure.

OK, last distortion story (I promise). I was advising on a Tube mic preamp, VMP-2, that was designed by PV's top analog guy for the AMR (recording division). I was concerned that the unit might be too clean. After all, people don't buy tube units to get a straight wire with gain, they want some tube in their audio. I had the designer include a jumper on the PCB so we could reduce the amount of negative feedback. This would leave more of the open loop "tube" transfer function in the path. I didn't tell anybody we did this, just kept it in reserve, waiting for the first customer complaint that it sounded too clean.. Never got those complaints and we removed the jumper in a later cut. I was impressed with the low NF (down around 1dB IIRC) as good as solid state. It used a big honkin input transformer, I think it was a Reichenbach ( ? less $$) version of a popular Jensen, and the gain knob went up to 11. :grin:


So I guess my (almost) attempts to add distortion were dismal failures.

JR

 

[CJ]

I wonder if the ear is less sensitive to distortion in the bass region, because this is where transformers really barf up the wave form.
.
.
.
I just figured out > Waveborn is just Waveform, but the poor guy missed the F and hit the B , which is one space over and a row down.
Toke me long enough.

I am interesting in the "transition zone" at the moment. I have studied the high end and how winding structure affects it, I have seen distortion from overdriving an input transformer with 20 hz, but I have never gotten into what happens when the frequency reaches a point where the core quits, but still provides enough inductance to pass a signal.
This will be somewhere in the midrange, where most of the program material is, so I think its worth investigating.

Put an xfmr on the bench, run 20 KC thru it, then pull the lams and watch what happens.

 

[JohnRoberts]

[quote author="CJ"]I wonder if the ear is less sensitive to distortion in the bass region, because this is where transformers really barf up the wave form.
.
.


[/quote]

It depends on where the distortion lands... Harmonics above 20Hz fall where our hearing is more sensitive, harmonics above 20 kHz, fall where we can't hear them (but IM goes both up and down).

WRT transformer LF saturation, my patent (5509080) was for a bass boost circuit clipper. This was designed for use in the fixed install market where all those constant voltage 70V and 100V audio transformers live, and every speaker has another step down transformer.

Clean bass takes more iron which cost money, and the issue isn't sound quality, it's reliability issues with audio power amplifiers trying to drive into a bunch of saturated windings.

My bass clipper, only clamped the bass that was being boosted, and only when it was above threshold. It actually sounded OK, because the unmolested HF content masked the bass path clipping.

The customer could crank in all the bass boost they wanted, get all that boost at low level when they need it for loudness correction, then at high level the boost goes away so magnetics wouldn't saturate.

I don't think I'd go so far as to call it hifi but it worked well for that application (background music and voice announcements).

JR

 

[CJ]

They need that at the drive in movies.
:thumb:

Altec made these speakers for 70.7 lines that fit between the wall studs.
Big magnets, so I figured I would sneak them into the car doors, with that low profile and all.
Sounded like shit!
:twisted:

Boy, wireless is everywhere, now speakers.(ipod, etc)

But wait, didn't they have that back in the 50's?

A detachable wireless speaker that would allow the record player to be anywhere?
I think Les Paul did something with that.

 

[TomWaterman]

[quote author="emrr"]I'll be in the minority here by saying that I am not after tranparent linear reproduction, I'm after making the source (which is usually amateur, and not very good) sound better than it is. In rock music, that usually means some sort of color imparted by the signal chain.[/quote]
Yeah Doug, thats exactly what I mean. If all preamps were to designed to sound totally transparent by the book, wouldn't they sound very very similar? This is not my experience, but I do not think that one needs lots of choices to pick for each source.

[quote author="emrr"]Best answer is a bigger box of crayons from which to pick. Pairs of everything.[/quote]
Most of my favourite records were made with one type of preamp and not a 'transparent' one at that. Mostly either Neve, API or Spectrasonics in the case of some Stevie Wonder.

After going through a bunch of different commercial preamps - I'm looking for ways to spice up the one I'm working on so that I consider it to be great sounding for most all sources...sort of like how I consider a 1081.

So that its larger than life sounding in a really musical way. And then back it up by building 4channels of Forssell transformerless JMP/992 pres to get some purity as a choice. But thats it. I need a smaller rig to carry around.

Am planning to shoot out the following mic TXs.

Lundahl LL1530 1:3.5
Lundahl LL1576 1:3.5
Lundhal LL7903 or 7905 wired 1:2.8
Cinemag CMMI-3.5C 1:3.5
Sowter Calrec Remake 1:3
A custom 1:3 that I might get made with the info I am learning now.

I will pick the best one.

[quote author="Dan Kennedy"]I've built all types of transformerless ones. For years, trying to develop one commercially. I haven't found one I'm willing to put my name on.[/quote]
And that says a lot coming from you Dan.

That WE111C seems to garner a bit of love for sounding great. I think CJ suggested a reason why in another thread I stumbled across somewhere...

[quote author="mikep"]Any button or knob labeled "tone" or "color" will be discriminated against as being a gimmic, regardless of the validity of what it does. IMO It just won't sell. For whatever reason, this is the world we live in: Recordists like to pick and choose mic amps based on their non-adjustable nonlinearities.[/quote]
Well I guess the cheap products like Focusrite platinum etc didn't help, as most often the distortion adding feature is a crappy way to enhance crappy gear. So it gains a poor rep.

Sometimes a piece of equipment can have too many controls. Engineers..sorry Sound Operators - are often tweakers and giving them lots of knobs and options (OK so this would only be one more but) its one more thing to slow them down when making decisions on a session.

Also (and myself included) - a lot of us younger guys didn't have the privilege of learning about what sounds good in context under somebody who really knew their shit for a long time. Most modern sound operators (from amateurs to pros) are likely self taught in so many ways.

More options are just a way of providing more means to ruin the mix with overuse IMO.
I personally like stuff that is simple and I know sounds good (to me) so I don't have to tweak. I like LA2As as there are only two knobs...what can go wrong? I don't like it - move on to the next. More often than not I like it!

Thats not to say that I don't know how to operate a compressor or pre with more controls but its just more to think about, when the balance and music are most important to me.

I don't know how all of these guys actually track anything when they have 16 flavours of micpre...I barely get time to shoot out 3 mics on a session let alone combinations of mic/pres etc

[quote author="mikep"]this is a sore subject for me right now.....Now that I've got something usable, none of the in-the-trenches engineers Ive talked to think it is a good idea. dismissed on concept. Im still trying to figure out how to make it fly, but I assure you the problem here lies in politics, not the electronics![/quote]
I think that's interesting - maybe you should start a new thread to get some discussion going on your device? I'm sure engineers here would be interested.

[quote author="CJ"]So we have lams, wire, machinery, mu cans, and potting compound.[/quote]
Bloody hell! Thanks CJ - amazing post on the differences between then and now. I checked out MagMetals and will try and get a catalogue. You must be one of very few in the world that has gained this kind of knowledge...goldmine. Thanks again.

[quote author="CJ"]So these guys were lazy. And pressed for time. So time Is on your side, since it's not your job to knock out transformers.
So experiment with different lam shapes.
Use the 5-4 layering, it don't get much better than that.[/quote]
I will look into the 5-4 winding structure for pri/sec. I think winding my own transformers is a little far off at the moment. But I am young, a Jedi I will become...in time.

Typically the ear is most sensitive around 1-5kHz depeding upon each individual. So it would take a lot more than 2nd and 3rd harmonics in the 20-100Hz region to reach there. IM and high order harmonics maybe?

-Tom

 

[CJ]

well, if you roll the bass, you boost the mids by subtraction.
i think thats how lundahl gets that defined mid range.

 

[Guest]

[quote author="TomWaterman"]
Like how did Rupert end up at his torroidal design for Amek? [/quote]
I would have guessed that would be a hangover from the Montserrat neve desk
All the RF cos of the huge radio transmitter on the island...

 

[emrr]

[quote author="JohnRoberts"]
Here's another story perhaps showing my personal bias (or SH__ for ears). Years ago back when I had a real job (Peavey), I was being a good engineering manager and trying to sell some slow moving inventory. Long story short(er) we had an excess of simple one rack space 4x2 (? actually I think they were 2x4x1) vacuum tube mixers. They were level only, and dirt simple, just a clean, simple audio mixer path. This was designed for MI use (with guitar level signals) so it was all 1/4 ins and outs. I had my tech make me up some RCA adapters and took a unit home with me so I could listen for the "tube magic" on my home system. We had a pretty low cost basis in these and studio types were paying big bux at the time to be touched by a tube (late '80s). Well after a lot of listening I heard absolutely nothing... nothing good, nothing bad, nothing... I heard just what I was sending through it. I didn't give up, I then had the tech change some resistor values to increase the mix gain, so I could easily overdrive the tube path. That should surely release some tube magic. Noooooh. I had zero success raising any interest for this "real" tube path, while other companies out there were pretending to involve tubes in some pretty high selling products.... go figure.

OK, last distortion story (I promise). I was advising on a Tube mic preamp, VMP-2, that was designed by PV's top analog guy for the AMR (recording division). I was concerned that the unit might be too clean. After all, people don't buy tube units to get a straight wire with gain, they want some tube in their audio. I had the designer include a jumper on the PCB so we could reduce the amount of negative feedback. This would leave more of the open loop "tube" transfer function in the path. I didn't tell anybody we did this, just kept it in reserve, waiting for the first customer complaint that it sounded too clean.. Never got those complaints and we removed the jumper in a later cut. I was impressed with the low NF (down around 1dB IIRC) as good as solid state. It used a big honkin input transformer, I think it was a Reichenbach ( ? less $$) version of a popular Jensen, and the gain knob went up to 11. :grin:


So I guess my (almost) attempts to add distortion were dismal failures.

JR[/quote]


John,

I've always heard good things about that VMP-2, and the problem IMO is that they weren't in the stores (and the were related to Peavey in the musicians's minds). I've never once seen that Peavey product line in a store, and I understand it was because of dealer purchase requirements. If so, not your fault. Blame it on marketing and branding.