SLOB project

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Ray P
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#226 Re: SLOB project

Post by Ray P »

Nick wrote: Sat Dec 05, 2020 10:14 am Simply put, I don't know, as its inside the feedback loop.
Just goes to show, what do I know...
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#227 Re: SLOB project

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ed wrote: Sat Dec 05, 2020 11:20 am Here's the cheapskate's approach.
Good stuff Ed, hopefully B&Q will oblige :thumbleft:
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#228 Re: SLOB project

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So how's this for a crossover plan...

Master volume control will be in the digital domain using the excellent HQ Player software control.

For the full range driver, driven by the 6C33C SE-OTL amplifier, I'll bandwidth limit the amplifier to have -3dB point at around 180-200Hz. Given previous discussion about this, the simplest option seems to to use a simple cap on the input - something like 9100pF (silver mica or polystyrene) with the 100K input impedance will give the right sort of result.

For the bass unit, I'll need a volume control to set the correct level and follow that with a simple low-pass filter and then a buffer stage - I've been looking at the JG buffer that's available from JL Sounds as it seems to be a good option;

http://jlsounds.com/buffer.html

http://jlsounds.com/uploads/JGbuffer.pdf
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#229 Re: SLOB project

Post by Ray P »

Having mentioned the JG buffer, I remembered that I still have a few vintage BUF-03 devices so maybe that might be a good buffer option after the lo-pass filter - the BUF-03s worked very well in the buffered passive pre that I built earlier this year;

https://www.stereophile.com/images/arch ... can35.html

http://www.audio-talk.co.uk/phpBB3/view ... =11&t=7788
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#230 Re: SLOB project

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Regarding the lo-pass filter for the bass amplifier (I already have a couple of chip-amps to power the bass drivers), I was looking on ebay and saw these and thought a couple of them (one per channel) might suffice as a starting point - any experience/thoughts? I assume the bass frequency control just sets the corner frequency.

https://www.ebay.co.uk/itm/Low-Pass-Fil ... 0005.m1851

They're available in kit form too so easy to ensure the parts are up to scratch.
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pre65
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#231 Re: SLOB project

Post by pre65 »

Interesting.

I have thought about separate amps for my 18" bass units, and I have a 50w stereo chip amp in the office, so a pair of those boards may be worth experimenting with.

There are a few different types on Ebay, some have two ICs.

I must check my transformer stock and see what's about in the 12v - 18v range.
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#232 Re: SLOB project

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I imagine the boards with one opamp will be first order filters and those with two will be second order - but maybe not!
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#233 Re: SLOB project

Post by Ray P »

This one has a schematic...

https://www.aliexpress.com/item/3266400 ... 5196435618

and here's an alternative complete with onboard chip amp

https://www.ebay.co.uk/itm/HIFI-Low-Pas ... 1438.l2649

Still keep coming back to thinking that getting hold of a DSP unit might be a better way to experiment though, use it to get a good balance and then try to replicate it with an analogue lo-pass filter.
Last edited by Ray P on Thu Dec 31, 2020 12:20 am, edited 1 time in total.
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#234 Re: SLOB project

Post by IslandPink »

It would be nice to know what they do, before buying one !
Certainly a 2nd-order low pass would be useful for a lot of bass drivers.
Most sub amp modules have a filter and controls built in, though don't they ?
i am thinking about this subject myself, now, but I'm no expert.
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#235 Re: SLOB project

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IslandPink wrote: Wed Dec 30, 2020 10:56 pm It would be nice to know what they do, before buying one !
Hard information is a bit lacking Mark but I guess they're all going to be active op-amp based filters - in my last post I included a link to one with a schematic - I've had a look and I think it's a third order lo-pass - should be able to model it in a filter designer package, though component values are obscured so would have to do some guess work.. That said, they're mostly less than a fiver each so not much of a risk.
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#236 Re: SLOB project

Post by pre65 »

I thought about it for a while, then I just ordered a pair. These ones take a DC input, and as I have a couple of SMPS 12v supplies (from Ray ?) they will be good enough to test the process.

By the time they arrive I'd have forgotten what I ordered them for. :wink:

https://www.ebay.co.uk/itm/Low-Pass-Fil ... 0008.m2219
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#237 Re: SLOB project

Post by jack »

The schematic looks like a fairly standard NE5532 setup from one of the application notes.

At first look, there's a first-order low-pass passive input filter on each channel, Ic1a is a preamp configured as an adder for both L & R channels, ic1b is a second order Sallen-Key unity gain adjustable low pass filter, ic2a is a 0 or 180 degree phase shift and ic2b is a unity gain buffer to give low output impedance.

So, over all a third order filter i.e. 18dB/octave

I've probably missed something in there but will try to look properly later.
Last edited by jack on Thu Dec 31, 2020 11:51 am, edited 7 times in total.
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#238 Re: SLOB project

Post by ed »

not sure if it's of any benefit but this is what I'm going to use...when I get round to it...Rod also has a xover calculator for the circuit.....

https://sound-au.com/project09.htm

At the moment I'm not sure if I want 2 or 3 way. If I go 3 way I'm going to use the Fostex tweets because I really don't care for the Monacor ribbons I have on the shelf. They are absolutely horrible in the horizontal plane....beam in a razor sharp line.
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#239 Re: SLOB project

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ed wrote: Thu Dec 31, 2020 9:11 am not sure if it's of any benefit but this is what I'm going to use...when I get round to it...Rod also has a xover calculator for the circuit.....

https://sound-au.com/project09.htm

At the moment I'm not sure if I want 2 or 3 way. If I go 3 way I'm going to use the Fostex tweets because I really don't care for the Monacor ribbons I have on the shelf. They are absolutely horrible in the horizontal plane....beam in a razor sharp line.
As they say in the text - this is just a collection of standard second order Sallen-Key high- or low-pass blocks daisy-chained. There are calculators all over the place for these filter blocks, so you can tailor the 3dB points for whatever frequencies you like, just choosing the closest E24 or E48 values for the resistors. Not that "precise" is important in this application.

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#240 Re: SLOB project

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