Tube + State Variable filter

Hi I found Stephen J. Conner's site AKA Scopeboy,

and found this circuit that fits some of my needs,
but seeing as this page was last updated in 1999,
I though some comments of what is possible today
might be in order before I start building something.

New parts and even a single unit doing the whole SS job,
might have been developed since '99.

The whole page is here:

http://scopeboy.com/peq.html

and the circuit in particular is here:
http://scopeboy.com/hybrid3.gif

I love tubes by themselves, but I also like unique sounds
that you can create no other way but by experimenting.
This is for a specific stereo amp sound I hear in my head,
but haven't found the interface of solid to vacuum to make happen yet.

Interesting not a single comment!

Test

Hi Ethan
Great forum site. I have been learning a lot.
Blame PRR for my presence he told me about it. :razz:

Since there is NO ONE with a clue about studio electronics
within 500 km and most of those not knowing that much useful to me,
I have to do it all. So back in the tech woodshed.

I am lucky that there is one tech for consumer crap and computers
who speaks english and isn't an arch-nationailstic, anti-foreigner ass,
has a pretty large stock of parts and is rather bemused with
my tube building antics.

Most are not blending tubes and SS, which might explain;
the lack of comments, but 100+ views. Maybe I am mixing
ancient greek and modern sanscrit here. :grin:

PS There has been interest in attracting NewYorkDave back,
maybe you can drop him a note. hint hint

I have nothing to add about glass design

I'm currently pushing 1's and 0's around and figuring out pointer offsets.

Good Luck

JR.

Hi John,
you've been helpful in other threads about the filters themselves.
I know what I want to do, just not sure on the interfacing issues
of specific components etc. HAy, ein't that engineering!
Time for more coffee!

[quote author="Animatic"]
Most are not blending tubes and SS, which might explain;
the lack of comments, but 100+ views. Maybe I am mixing
ancient greek and modern sanscrit here. :grin:

PS There has been interest in attracting NewYorkDave back,
maybe you can drop him a note. hint hint[/quote]

I've actually been playing around with tubes and SS for a number of years, I've tried every configuration I could think of. Blending is loosely used here and as such makes little sense to me. If you so called "blend" SS with tubes it must be done to acheive a specific requirement and please don't say "sound".

I don't think Dave likes to blend sandstate with his tubes, brother.

analag

Hi Analag.
Yes I have noticed your mix topology work.
Some very cool stuff.

I have two different needs for this.

One double amp guitar amps with single preamp and TMB
feeding both SE and PP outputs.
But I want a semi parametric bandpass for EACH of those two output stages.
3 EQ's, the regular one feeding another inter stage for each output.
And a pan pedal to blend between the two power amps.

I am thinking like a recording head , not like the typical amp builder.
And I don't give a hoot about what's been done,
I hear a sound and want to build it.

Secondly I need some tube preamps like the Gordon system
controlroom gain control and monitoring, but the pteamp staying
as close to the mic as possible. The rub there is making the preamp
controlable and not a lot of excess noise running both ways.

Sure I could run a cable and a pot back right out of the circuit
and then tweak from afar, but that sounds like noise source big time,

so I am looking at DC controled opamps, or JFET with along control voltage run.
I really don't want digital control, just a low voltage DC that adjusts the gain.

Another idea is just run it flat out, and adjust the return,
but that's not so good for overload at the preamp,
and lowering the gain to avoid that also raises noise.

I could do LED monitoring back at the control room
at the end of the line run before the patchbay.

I understand tubes better than the recent advances in SS tech parts.
I know what I want to do, but have few resources to get the
engineering side done. There are good engineers in Thailand,
but thinking out of the box is not a local trait encouraged by the school system.
So I have been dredging up my dormant, 30 year old, electronics school info
and trying to update it.

I'm for adding EQ to tube stages in guitar amps
without changing too much the tube tone, unless I want to,
and remote control & monitoring of tube mic pres.

I am like NYDave in that I would prefer one or the other,
but can't see how to really do what I want without mixing the two.

A few more Mila's have been built and no doubt a few forumites
would be interested in his feedback.

I plan on two Mila's now, and I am wondering what he would find
LEAST objectionable in mod'ing his circuit for remote gain control.

If I can find a some basica starting places, I can bread board
and test a few designs before building 12 units for myself etc.

[quote author="JohnRoberts"]I have nothing to add about glass design

I'm currently pushing 1's and 0's around and figuring out pointer offsets.

Good Luck

JR.[/quote]


:green:
haha

try


for a vacuum tube- transformer coupled sound. Don't forget to oversample for the aliasing!

:grin: :grin:

[quote author="noulou"]


:green:
haha

try




:grin: :grin:[/quote]

A little more cryptic than that...

--snip---

sub w2, w0, w0
bra Z, no_change
bra N, ave_att

-----
neg w0, w0
mul.uu w4 , w0, w6
add w6, w3, w3
addc w7, w2, w2

--snip---

Modding the MILA for remote gain control can be done via optical control, simply modulate the LED voltage to control gain, though for the sake of simplicity some control should be done at the preamp, like the feedback thingy.
You have a lot of ideas and they should be addressed one at a time for the best result, both from personal comtemplation and in presenting them to the Drawing Board. Well that's if you want to sanction some ideas from these guru's or the threads gonna go down the drain with silly responses.

analag

What are you working with John, RISCs?

We ARE arcane here.

As I read it;
buffer over run as a running joke?
Nand Nor Nand Nor
Nork and Nindy

AH optical control I had forgotten about that one.

If you go up to my original post,
it is one question about a circuit.

http://scopeboy.com/hybrid3.gif

ie. any comments on, or likely good updates in reference to,
this 1999 webpage of his circuit design,
that I find useful and want to build.
http://scopeboy.com/peq.html

If putting these SS state-variable EQ components
in between two tube stages, are there any updates
of components since this time, does anyone see anything bad
or that may be done better.

For instance if, as it is designed, you really over drive the 1st tube stage,
will it go out of spec for the SS components following?
Or is all well and just build away and test.

8-9 years is along time with component design,
I figured there are better choices now,
so I am asking this forum of experiences techs.

[quote author="Svart"]What are you working with John, RISCs?[/quote]

My apologies for the thread hi-jack, and I didn't even get the FOR loop joke.

I don't know what you consider RISC, the micro (16 bit PIC), has 70 instructions with multiply and divide... my old 8 bit PIC had a lot less..

I am mostly self taught, so I'm not hip to terminology on the digital (dark) side, but manage to get them to do the tricks I want.

JR

I got the joke sort of
with ancient memories of programing from 1969 and 1975,
and an attempt to 'Learn Java in 21 days',
while sitting in a Paris garret,in 1997 that resulted
in me getting glasses permanently.

I have gotten a reasonable handle on tubes again,
and am working into actual SS design concepts now,
with the aim of adding SS to tubes as hybrids.
Maybe next year I will deal with digital workings.
Control circuits and ADA sample rate conversion, smoothing etc.
Too much on the plate now.

Still hoping for comments on the scope boy schematic.
It took a long time to find something like that,
but I suspect there are one or two things not properly labeled on the schematic,
and referenced a bit too little in the text.
I like to KNOW what I will build before I start.

I learned Fortran IV in '66, BASIC in '70s, C in '90s, but as an old discrete analog designer, I prefer working at lowest level when coding small micros.

JR

Personally I think tubes and IC's don't go well together if you use them between or after tube stages. If you place them before the tube(s) then you might get away with it, from a sonic and reliability standpoint. I like to use transistors in the plate or cathode circuit only when I go hybrid. For example if you're building a differential tube gain stage, the higher the resistance the cathodes are faced with, the better the performance of the stage. Now consider these three ways to achieve this (1) use an extremely high B- and similarly high value cathode resistor (2) use a pentode and the typical 250V B+ it normally requires or (3) use a solid state CCS with as little as 25V to arrive at the same impedance, but typically more than you could realize with the first two approach. That's how I feel about the hybrid thingy, individuals may vary.

analag

Ok I hear you.
At the moment, I can't think of any other way to get the sounds I am looking for.

So I will bread board up a few things and see what I get.
if it doesn't blow up or eat the dog I won't think it lost time.

I would be interested in seeing an example of your tube differential stage you mentioned.
Is the transistor stage able to control gain of the whole unit?

And also when you say " don't go well together", what reasons ot instasnces?

Thanks for any advice past present and future.

[quote author="Animatic"]Ok I hear you.
At the moment, I can't think of any other way to get the sounds I am looking for.[/quote]
That should be an interesting sound, then.

[quote author="Animatic"]So I will bread board up a few things and see what I get.
if it doesn't blow up or eat the dog I won't think it lost time.[/quote]
Why don't you show us your idea in the form of a schemo, so we may understand.

[quote author="Animatic"]I would be interested in seeing an example of your tube differential stage you mentioned.
Is the transistor stage able to control gain of the whole unit?[/quote]
I implement it to work "with" not gain control "of"

[quote author="Animatic"]And also when you say " don't go well together", what reasons ot instasnces?[/quote]
You must know that a tube stage can swing signal voltages in excess of +/- 50V under conditions like that you end with a lot of junk in the signal path just to accomodate the sand state devices. I could go on.

Thanks for any advice past present and future.[/quote]


analag

Been busy, but am still also thinking of me next response.
Sounds like the filter needs a filter before it. Metaphorically.