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Author Topic: Any DIY EQ interest?  (Read 40842 times)

dcollins

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Re: Any DIY EQ interest?
« Reply #30 on: July 20, 2004, 01:52:12 am »

JLaPointe wrote on Thu, 15 July 2004 11:47
Quote:


Please tell more! What's the premise here? A DC bias on the inductor to put it into saturation earlier?  How was it implemented as a de-esser?      



Yes, an external bias is applied.  That's about all I know of it!  Why doesn't someone research this and get back to us?  I still like the idea, but if was that great, why so rare?

An Ortophon de-esser worked like this but the I've never seen the actual guts, just the schema.

DC

bblackwood

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Re: Any DIY EQ interest?
« Reply #31 on: July 23, 2004, 03:33:37 pm »

Still trying to keep yup here, so little has been done, though I am bouncing ideas off of our own DC (and I'm dragging Dave Hill into it...).

Updates as available.
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Brad Blackwood
euphonic masters

dcollins

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Re: Any DIY EQ interest?
« Reply #32 on: July 24, 2004, 01:39:04 am »

bblackwood wrote on Fri, 23 July 2004 12:33

Still trying to keep yup here, so little has been done, though I am bouncing ideas off of our own DC (and I'm dragging Dave Hill into it...).

Updates as available.


Ooh, I've got it!  Baxandall with a "color" knob.  Or should that be "colour?"

Google "three band baxandall schematic"  Or?

DC

malice

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Re: Any DIY EQ interest?
« Reply #33 on: July 24, 2004, 08:19:10 am »

bblackwood wrote on Fri, 23 July 2004 21:33

Still trying to keep yup here, so little has been done, though I am bouncing ideas off of our own DC (and I'm dragging Dave Hill into it...).



Dave who ?

kidding

If Dave Hill is in, all I can say is : wow !

this is getting better and better

As an STC-8 user, I take this opportunity to state that Dave has made my life considerably more comfortable Wink

malice

moogus

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Re: Any DIY EQ interest?
« Reply #34 on: July 24, 2004, 10:20:23 am »

I cant help myself from responding here.  

We just finished 2 mastering pultecs the other week, that are pretty darn close to what youre describing.

2 bands, with sepperate freqs (12) for cut and boost, in 0.5db steps to 5.5db.

Switched bandwidth on high boost (inductive) from, well, fairly narrow to very very wide.

Using the JLM instrument opamp from the mastering console to give fully balanced i/o and provide the makeup gain, which runs on +/-24V, has +36 headroom, bandwidth from DC to above 10meg and plenty of zeros in the THD%.

Theyre certainly useful little beasts, and we found the matching between the two units to be extremely close, just with normal 1% resistors.

This version also drives 6db more level thru the inductors than the old version, and reports suggest this has improved the eq's utility on program material.

It would certainly be worth experimenting with making the gain up before the eq, based on these results.

Good luck with it.


M
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bobkatz

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Re: Any DIY EQ interest?
« Reply #35 on: July 24, 2004, 11:28:56 am »

moogus wrote on Sat, 24 July 2004 10:20



This version also drives 6db more level thru the inductors than the old version, and reports suggest this has improved the eq's utility on program material.




The drive to the inductors can be an interesting form of distortion generator. I'd make it variable.

BK
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lucey

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Re: Any DIY EQ interest?
« Reply #36 on: July 24, 2004, 01:51:30 pm »

moogus wrote on Sat, 24 July 2004 09:20

I cant help myself from responding here.  

We just finished 2 mastering pultecs the other week, that are pretty darn close to what youre describing.

2 bands, with sepperate freqs (12) for cut and boost, in 0.5db steps to 5.5db.

Switched bandwidth on high boost (inductive) from, well, fairly narrow to very very wide.




sounds good, is this something you can help us DIY or are you a manufacturer?
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malice

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Re: Any DIY EQ interest?
« Reply #37 on: July 24, 2004, 01:56:26 pm »

lucey wrote on Sat, 24 July 2004 19:51

moogus wrote on Sat, 24 July 2004 09:20

I cant help myself from responding here.  

We just finished 2 mastering pultecs the other week, that are pretty darn close to what youre describing.

2 bands, with sepperate freqs (12) for cut and boost, in 0.5db steps to 5.5db.

Switched bandwidth on high boost (inductive) from, well, fairly narrow to very very wide.




sounds good, is this something you can help us DIY or are you a manufacturer?


Moogus works with a nice manufacturer in OZ, but maybe he is willing to participate ...

Moogus ?

malice

dcollins

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Re: Any DIY EQ interest?
« Reply #38 on: July 24, 2004, 08:03:44 pm »

moogus wrote on Sat, 24 July 2004 07:20

I cant help myself from responding here.  



Quote:


We just finished 2 mastering pultecs the other week, that are pretty darn close to what youre describing.



What are you using for input, interstage and output transformers?

Iow, just cause it has an inductor, does _not_ make it a Pultec!

Quote:


Using the JLM instrument opamp from the mastering console to give fully balanced i/o and provide the makeup gain, which runs on +/-24V, has +36 headroom, bandwidth from DC to above 10meg and plenty of zeros in the THD%.



That sounds interesting.  I'm a little scared about the >10MHz response though.  I tend to go for something around -3 at 300kHz just because there is so much RF noise out there today.  Arguably the recordings I have that sound the most "open" were done on gear that was positively struggling to be flat at 20k!  But that's a story for another day...


DC

bobkatz

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Re: Any DIY EQ interest?
« Reply #39 on: July 24, 2004, 08:15:03 pm »

dcollins wrote on Sat, 24 July 2004 20:03



Quote:


Using the JLM instrument opamp from the mastering console to give fully balanced i/o and provide the makeup gain, which runs on +/-24V, has +36 headroom, bandwidth from DC to above 10meg and plenty of zeros in the THD%.



That sounds interesting.  I'm a little scared about the >10MHz response though.  I tend to go for something around -3 at 300kHz just because there is so much RF noise out there today.  Arguably the recordings I have that sound the most "open" were done on gear that was positively struggling to be flat at 20k!  But that's a story for another day...


DC




DC, I don't know the JLM, but would you be satisfied with an opamp with feedback compensation so resulting frequency response was around -3 dB at 300 kHz?
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dcollins

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Re: Any DIY EQ interest?
« Reply #40 on: July 24, 2004, 08:34:06 pm »

bobkatz wrote on Sat, 24 July 2004 17:15

Quote:


DC, I don't know the JLM, but would you be satisfied with an opamp with feedback compensation so resulting frequency response was around -3 dB at 300 kHz?


That's a good place to start the rolloff. When I'm calculating the feedback R/C it's always something from say 150k to 300k.  For audio that is.

That JLM stuff looks interesting, but I don't know how anyone can use that kind of output level.  90% of stuff is on +/- 15V rails so if your opamp is really swinging +/- 60 Volts, there's gonna be padding somewhere. The A/D converter chip wants to see like 2 Volts....

Since low noise is so easy to achieve nowdays, why not just run your system at low levels and get the headroom that way?

DC

moogus

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Re: Any DIY EQ interest?
« Reply #41 on: July 25, 2004, 12:16:32 am »

[quote title=malice wrote on Sun, 25 July 2004 03:56]
lucey wrote on Sat, 24 July 2004 19:51



Moogus works with a nice manufacturer in OZ, but maybe he is willing to participate ...

Moogus ?

malice



Id love to help as much as I can, although you already have some real designers on board.

If youd like me to I can foward some questions on to Joe.


M
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moogus

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Re: Any DIY EQ interest?
« Reply #42 on: July 25, 2004, 12:22:14 am »

dcollins wrote on Sun, 25 July 2004 10:03



What are you using for input, interstage and output transformers?

Iow, just cause it has an inductor, does _not_ make it a Pultec!

Quote:


Using the JLM instrument opamp from the mastering console to give fully balanced i/o and provide the makeup gain, which runs on +/-24V, has +36 headroom, bandwidth from DC to above 10meg and plenty of zeros in the THD%.



That sounds interesting.  I'm a little scared about the >10MHz response though.  I tend to go for something around -3 at 300kHz just because there is so much RF noise out there today.  Arguably the recordings I have that sound the most "open" were done on gear that was positively struggling to be flat at 20k!  But that's a story for another day...


DC





No xformers, Its not a Pultec copy, just a passive EQ.  I use that term rather loosely.  

The ones we just built have something like that bandwidth, because we havnt limited them yet.  Of course you can limit it to whatever you like.


M
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moogus

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Re: Any DIY EQ interest?
« Reply #43 on: July 25, 2004, 12:31:27 am »

dcollins wrote on Sun, 25 July 2004 10:34

bobkatz wrote on Sat, 24 July 2004 17:15

Quote:


DC, I don't know the JLM, but would you be satisfied with an opamp with feedback compensation so resulting frequency response was around -3 dB at 300 kHz?


That's a good place to start the rolloff. When I'm calculating the feedback R/C it's always something from say 150k to 300k.  For audio that is.

That JLM stuff looks interesting, but I don't know how anyone can use that kind of output level.  90% of stuff is on +/- 15V rails so if your opamp is really swinging +/- 60 Volts, there's gonna be padding somewhere. The A/D converter chip wants to see like 2 Volts....

Since low noise is so easy to achieve nowdays, why not just run your system at low levels and get the headroom that way?

DC



That particular device is designed to be as transperant as possible, hence the massive headroom, and it was designed for the mastering console, not the EQs.  It just happened to provide an elegant solution in that situation.

High output headroom is a feature of a lot of Joe's designs (as is low noise).  I guess you could say its one of his 'trademarks' as a designer.

Best of luck to yall with this,


M
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Terry Demol

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Re: Any DIY EQ interest?
« Reply #44 on: July 26, 2004, 05:37:27 am »

moogus wrote on Sat, 24 July 2004 15:20

I cant help myself from responding here.  

We just finished 2 mastering pultecs the other week, that are pretty darn close to what youre describing.

snipped

Using the JLM instrument opamp from the mastering console to give fully balanced i/o and provide the makeup gain, which runs on +/-24V, has +36 headroom, bandwidth from DC to above 10meg and plenty of zeros in the THD%.

M


Hi Moogus,

Is this with the JLM99V or as your instrument opamp description
suggests, a fully balanced instrumentation amplifier Bal IP ->
SE OP, or just the front end of an instrumentation amp ie;
CM gain = x1 bal in bal out, or lastly, a fully balanced VG
(current) IP such as Nelson Pass's "Supersymmetry"?
 
There are a few issues which may be relevant WRT BK's and DC's
comments of BW limiting but they don't aply to all topologies
and designs, lets make sure we are all talking the same
language first.

Some of the topologies are in effect current feedback, ie
feedback to the IP emitters and as such you need to be careful
using FB BW compensation (as BK suggested). However there are
ways around all this.

You mention BW of 10meg, just for the record, with devices these
days having Ft's in the 100's of megs that is pretty common.
Joe seems to favour very simple topologies (which I like too)
and high voltage rails (which I also like), as such the high
BW will certainly be a given.  

There were valid questions of the necessity of such high rails
(DC). I think one big advantage is that simple circuits can
be more linear without the need for cascoding to linearise
capacitances and early effect etc. The headroom issue as DC
suggests is a red herring IMO the benefits are elsewhere.
Check some BJT data sheets and look where the miller C gets
very linear WRT voltage across the device. You can really
measure this especially on simple low FB circuits and at higher
frequencies.

Another related issue is if the given stage is fed from a
higher impedance such as a passive vol control. In this case
there will be increased distortion due to IP device modulated
miller C and as stated before it will manifest itself at higher
freq.

Cheers,

Terry
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