What to do with all these urei inductors?

[Vyvyan]

Just got a bunch of nice inductors ranging from a few MH to 63H!

Trying to find some decent EQ projects where I can work out RC values with my given L values.

Anyone want to point me in the right direction? Already working on an API 553 with some home etched pcbs, but would like something with switchable frequencies and possibly a 4th band

 

[user 37518]

If you don't know what to do, sell them!

 

[Vyvyan]

If you don't know what to do, sell them!

I like learning

 

[user 37518]

I like learning

Fair enough

 

[TwentyTrees]

API 553 topology but with extra bands and switchable frequencies sounds like an excellent EQ to me!

I use these calculators all the time for RLC filter calculators. If you know your target Q and your L, you can brute-force the rest (or use a reactance nomograph to get in the ballpark).

 

[Vyvyan]

API 553 topology but with extra bands and switchable frequencies sounds like an excellent EQ to me!

I use these calculators all the time for RLC filter calculators. If you know your target Q and your L, you can brute-force the rest (or use a reactance nomograph to get in the ballpark).

Thanks!

The Q factor is the one thing I'm lost on and can't seem to find any useful info on.

I'm not Shure what a good Q factor is for a simple bell curve?

And doesn't it effect the overall impedance of the circuit? Giving me a limited range to choose from?

Would adding a switch for a high q on the mid bands be simple?

Been looking at ian bells universal EQ as well and fell I could probably use some veroboard to make that up, but wanted to start with something simpler like the 553

 

[TwentyTrees]

When it comes to the Q of a filter, "good" is entirely down to the designer's intent. Do you want a broad, gentle lift or something tight and pointed? What EQs do you like? A little research into bandwidth of other EQs may help figure out what general range you want to target. I also found that playing around with a parametric plugin EQ was really helpful in dialling in what I was looking for from a particular build.

I pulled this together a few years back when looking into this for myself. It shows the minimum and maximum bandwidth & Q factor for a mid band in a variety of EQs.

EQ filter bandwidths	Broad		Narrow
	BW - oct	Q	BW - oct	Q
Sontec	1.8	0.75	0.6	2.5
Knif Eksa	2.5	0.5	0.3	5
GML 8200	3	0.4	0.4	4
Massive Passive	0.9	1.5	0.5	3
Knif Soma	2.5	0.5	1	1.5
Speck ASC	2.5	0.5	0.4	3.8

In terms of the impact of the characteristic impedance of your circuit, as I understand it that's not such a huge factor in an active swinging input design such as the 553 (happy to be told otherwise!). It is absolutely something to be concerned about with a passive EQ. If you did want to go passive, one of Ian's designs would definitely serve you well.

You could certainly have a high / low bandwidth switch on any given band. At a given impedance, bandwidth of an RLC filter is determined by the relationship of the inductor and capacitor, so you'd need a different LC pair for each target Q value if you want to keep the centre frequency the same.

 

[ruffrecords]

I would not worry too much about the Q of the inductor.

Q is defined as the resonant frequency of the RLC circuit divided by the -3dB bandwidth of the bell shaped response it produces. So if an RLC has a resonance at 1KHz and a 3dB bandwidth of 500Hz, then the Q is 2. As you probably know the resonant frequency depends only on the values of L and C. However the Q depends on L and R and the frequency in the following formula:

Q = (2 * PI * F * L) / R

If you measure the inductance and dc resistance of an inductor you can work out the Q of the inductor on its own at any frequency. Modern ferrite inductors have fairly low resistance which means their Q values can be very high much higher than you want in an EQ. However, once you use the inductor in an EQ circuit, the value of R is the sum of the inductor's R and the other resistances in the EQ circuit that create the final RLC. As a rule, an EQ designer wants his circuit to define the Q so as long as the inductor resistance is small compared to that of the circuit resistance the Q is controlled by the circuit. You can alter Q deliberately by adding resistance in series with the inductor. This is exactly how the Q control in the Pultec EQ works.

Cheers

Ian

 

[andia]

I recently did a 553 in 500series format, mainly because I wanted to test my new winding machine and I wound my own inductors. Great eq and it worked out really well, this was the first project I did without having to order any of the parts besides the pcbs. I also have the idea to extend the possibilities of the eq with more frequencies.
Really nice collection of inductors you got there.

 

[Vyvyan]

I recently did a 553 in 500series format, mainly because I wanted to test my new winding machine and I wound my own inductors. Great eq and it worked out really well, this was the first project I did without having to order any of the parts besides the pcbs. I also have the idea to extend the possibilities of the eq with more frequencies.
Really nice collection of inductors you got there.

I've got more than I know what to do with hahaha. I've also been sourcing some from Yamaha pm-1000 and pm-430 channels, realistic 31-1988/1987's and some ADC sound shaper one's. Going to experiment with some line amps/EQ's and eventually put a 12 channel 4 buss board together

 

[AtticMan]

I like learning

Or sell just a handful to fund other projects?

 

[Vyvyan]

Or sell just a handful to fund other projects?

That thought has gone through my head, I buy lots of old broken or untested gear so I'm kind of drowning in parts