API-553 Build 3 band with switchable frequencies

[Spencerleehorton]

Bit too complicated for me! I'm just gonna keep mine nice and simple.

 

[iprovlek]

You right Spence!

Isnt be good to put 2520 opamp instead that opa604 chip!!!


That would be great!!!

What you think Spence!!!

 

[Spencerleehorton]

Yes that's what I've done I've used the 2520, but I think that other design uses opamp as input buffer/gain.

 

[Spencerleehorton]

This is what I'm picking up tomorrow

RM8 N48 Al400 (Epcos)

RM8 3H1 Al630 (Ferroxcube), 3H1 is an equivalent material

Need to confirm winds next, I think I read  1260 winds for the 1H and also read to overwind a little.
And 400 winds for the 100mH.
Could anyone help confirm this and know how much to overwound? (1280 for 1H and 491 for 100mH)

 

[Spencerleehorton]

It is announced as Al630, so you need 1260 turns for 1H. Cross-section is about 28mm², which indicates a maximum square-section of wire of 0.022 mm² resulting in a diameter of 0.14mm.
Mean Length Turn is 42mm. Closest gauge is 0.125mm (AWG36), resulting in a DC resistance of about 75 ohms.
You would need only 400 turns for the 100mH, for a DCR of about 25 ohms.
Beware that adjusting the final value needs to be done in-circuit, checking the actual circuit's response. Most inexpensive LC-meters give very inaccurate values. If you need super-accuracy, you should wind a few percent more turns than the calculation and adjust for teh final value. Also beware that properly setting the two halves of the core is important; there could be as much as 5% variation between an not-too-well seated core and one that's properly set. You have to rub them against each other.

 

[Spencerleehorton]

right,

I've wound a few inductors now and got some 1H and 100mH, what sort of tolerance is acceptable for these inductors? 3-5%
if so that would give 95mH - 105mH and 950mH - 1050mH, mine at the moment ive wound at 103mH and 1025mH.
should this be ok?

regards

Spence.

 

[Spencerleehorton]

from another source these first figures look really good, so im going to put it all together and do some testing inside a Neve 1290 preamp.

 

[nielsk]

Very easy to use a center off toggle to have 2 freqs per band with a center off...

 

[Indecline]

this i think, is more on the money:

MF

3Khz      2,7nF
2,5Khz  3,9nF
2Khz      6,3nF

LF

150Hz    1µF
220Hz    0,5µF

HF

10Khz    370pF
12Khz    300pF

With the values being so close with such a wide Q, you wont hear that much of a difference when you switch frequencies. I modified my 553's with a decade smaller capacitor (I think!) on the switches. You'll lose gain and the Q tightens a lot, but it's a decernable difference that has come in handy a few times.. at least now my 553's get used more often after the modification 

 

[Spencerleehorton]

could you suggest what figures you think maybe which would work better?

 

[Spencerleehorton]

Also as the winding of the inductors went so well, i went back to my supplier and have done another deal which could put these inductors out professionally wound at £15 each!! would need to be a fairly big order for this to happen though.

Anyone interested?

 

[Indecline]

could you suggest what figures you think maybe which would work better?

I'll check over the weekend what values I used 

 

[Spencerleehorton]

thanks very much!!!
i just gotta build a stable psu for this as having problems altering this ssl 9k psu to try and accomodate 48v, 24v, 15v and -15v.

 

[Spencerleehorton]

this is going to be my psu.

 

[Spencerleehorton]

This is what i will be making for this and the Neve Preamp.

 

[Spencerleehorton]

Thought I'd put up a pic of the inductors.

 

[Spencerleehorton]

Had another little look at this today and will be building +15/-15v Psu to see if I can see how these sound.

 

[Spencerleehorton]

Thinking of using a 4 pole lorlin for the bypass switch so I can wire off the pcb, rather than get a 4pdt switch, but might order a couple as it’ll be easier.

 

[Spencerleehorton]

Making the +\- 15v pcb, hopefully populate and test tomorrow!!!

 

[ruffrecords]

|I see you ended up with simple toggles to select two frequencies for each band. There is a simple way to make this three frequencies using toggle switches with a centre off position.

You wire the first cap right across the switch so when the switch is in the centre off position this cap determines frequency. This will be the highest of the three frequencies. Then you use the other two 'on' positions of the toggle to add two different value caps in parallel with the first one. Both these frequencies will below the first because the total capacitance is increased. I use this method in my new REDDPLUS EQ to get three frequencies on each of the three bands.

Cheers

ian