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Active filter board GB

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#482
There seems to be enough interest to justify another order of Active Filter 4 boards.

I'll buy a batch of boards and try to keep them available through my website. The price increased to $5.50 per board due to expected smaller lot sizes. Any excess will be donated to the forum.

You can pre-order boards now for early December shipment. I'll add a bunch to however many are ordered in the next two weeks.

I'll try to keep PSU kits in stock, too.
 
#484
Have at it, if you are so inclined.

The advantages of the inter-stage buffers is that they allow setting the filter Q independent of the effective crossover frequency. Without them, as the Q is changed the levels must be matched elsewhere in the system to prevent unintended over or underlap.

For example, if you need a slight peak in the bottom of the tweeter transfer curve to compensate for a rising tweeter response you might choose a filter with a Q=1.1. Without the inter-stage buffer and its associated attenuation, the 3 dB down point would be lower than expected. A couple of high Q filter sections could result in overloading the following stage.

There are lots of ways around the buffers without performing board surgery if you don't want them.

As I have mentioned before, you can always take your output from pin 1 or 3 of JP8/JP15. this will give you a fixed buffered output. If you need to tweak the levels and can do without an output buffer, you can just take your output from pin 3 or 5 of IC9.

Using a second order slope and want variable attenuation and an output buffer? Connect the IC4A/IC7A end of C11/C21 to JP8/JP15 pin 2. Sure, you'll have an extra opamp loading the filter, but if you are using FET input chips the impedance is high enough not to matter.

Want a 4th order filter and get rid of the inter-stage buffer? Bend out/clip off pin 7 of IC4 or IC7 so that it doesn't contact anything. Now jumper pins 1 and 7. The same would apply to getting rid of the IC5 or IC8 buffer.

Sure, I'd like to have another all-pass section. With a couple of jumpers and cutting the connection from IC2B pin 5 to ground (top and bottom) you can make an all pass section out of the Linkwitz transform section. I'll leave it to the reader to figure out how that would work.

All in all, I like the flexibility of the current design and don't have the ears/system to distinguish any extra distortion caused by the buffers. 😉
 
#485
I'd like to sign up for a couple of boards, I'm just afraid it's a total overkill for me. All I'm trying to do is switch out the passive filters between a side-mounted 10" bass (SEAS H1305) and an MTM top on a dynaBel S33. The high-pass on the mids is a simple 12dB, and the bass filter is a 12dB with an extra 5.5ohm-22mH-268uF circuit in parallell. I'm kinda new at this, so I don't even know what that's for... The filters between mids and highs will stay, atleast for now.

I'd love to just run a pair of very simple 12dB filters with adjustable gain in either direction, but if this board can do it better without five years of education and experimentation to figure it out, I'm all for it.
 
#486
Lars,

This board is very flexible - none of the extra stuff (EQ, LT, All-pass) is there unless you jumper it in. It is quite easy to get a 2nd order adjustable gain buffered output. You'll just have some unstuffed board space.

Schematic, filter calculation spreadsheet and user's guide Here
 
#488
Subwoofer EQ?

Firstly, Thanks Bob and Jens. Quality boards.

Please excuse my limited knowledge here, not my forte. Im wondering if these boards are practical for general sub EQing. I would like to make a steep high pass at say 15Hz (rumble filter), perhaps a notch or two for some room eq and a 24dBL/R Low pass at 80Hz to mains.
I have plugged in figures into the spreadsheet and of corse it calcutales the values, but Im not sure if they are sensible values/frequencies for this design.

Am I stretching the rules here, or is this application do-able for these boards?
Thanks.
 
#489
Joe,

The boards can do what you want, sensible values is sometimes the tough part. If your filter resistor values are in the range of 5K to 100K and the caps fit in the spaces provided, great.

You'll probably find that the notch filter resistor values will be out of this range, especially if you need them to be deep. My Cauer filters use 200K and 800R. The other issue with notches is finding values that allow you to use standard capacitor values. I've ended up adding a cap in parallel on the bottom of the board.

The tradeoff with resistor values is noise and distortion. Higher values of resistance tend to lead to more noise, too low and the load on the opamp leads to increased distortion.
 
#491
Ok, four boards and a heap of caps ordered and paid for. Looking forward to playing with them!

Just got 14 Jensen 4-poles today, which go well with a couple of 1300VA audio trafos from Noratel. Now all I need is for Lars Claussen to get his finger out and send me four NewClassD units 🙂
 
#493
I don't see any reason why you couldn't use the LM4562. Avi mentioned earlier in the thread that he has successfully used the LM6172, which is even faster. Reading about the 4562 almost makes me wish I didn't have so many OPA2134s.

Avi paid special attention to bypassing, which may or may not have been necessary. (I don't remember that he tested without special treatment. I think he just used his favorite configuration.)
 
#494
I will order AF4 boards this Friday. Orders have just been slowly trickling in, so I don't think I will order too many extras.

If you want AF4 boards, get your order in by Friday or at least let me know.

EDIT: I only have 6 PSU2.2 boards left after filling existing orders. These are also available with the parts kit.
 
#495
BobEllis said:
I don't see any reason why you couldn't use the LM4562. Avi mentioned earlier in the thread that he has successfully used the LM6172, which is even faster. Reading about the 4562 almost makes me wish I didn't have so many OPA2134s.

Avi paid special attention to bypassing, which may or may not have been necessary. (I don't remember that he tested without special treatment. I think he just used his favorite configuration.)
Click to expand...


Hi Bob,

Since this time I've tried:

AD8065 for the input buffer on Brown-dog adaptors- (the 0.1uF connected directly to his legs, 10uF on each rail on the other side of the PCB for extra decoupling)

The AD8065 sound very good but first time I connected it, I forgot that it can handle up to +-12v (I had +-14.4V)- one AD8065 had damaged and the LM6172 got so hot that it burned my finger.

LM4562- is now fitted in my HP section. Very different op-amp from all other I tried- it is very, very clean sounding, and the OPA2134 sounds veiled in comparison. - But, IMHO, it can be in some combinations cold and maybe sterile for some; it is very analytical sounding op-amp, and it is the opposite for a tubby sound character.

I've ordered LM6172 from Digi-Key to put all over the crossover since I liked this op-amp the most from all I tried here.

But, I must say I have some troubles with the LM6172- its sound is superb, but every time something is a bit wrong in the circuit- the LM6172 can be damaged- I lost few of these during experimenting the board.

The LM6172 may perform better with lower values for the feedback resistor- I want to try say 1k ohm in this possition, it may help for the stability issue.

There is some hiss comming from the speakers when the LM6172 or the LM4562 is connected to the HP (Not with the OPA2134)- but I hope it is due to the sockets I use in order to make the op-amp changing more comfortable, I do hope the LM6172 without the socket will behave more nicely.

I wouldn't go for the OPA2134 anymore. The LM6172 (and LM4562/AD8065) are much more open sounding and detailed op-amps. However, using the LM6172 properly it's, well how to say, more challenging 😀

Best Regards,

Avi
 
#499
Ah...I must have missed that part of the discussion. The link for the PDF schematic is similarly busted, though. Anybody got that one?

Despite being part of the Round 1 GB, I haven't touched these things 'til now. It now appears I'll have some time to play with these, since my employer decided it didn't need the services of 11 of us anymore. (Closed the entire office.) :bawling: :bawling: :bawling:

--Greg
 
#500
Greg,

Sorry to hear about your job situation. Been there, but it worked out for the best. Hope yours does, too.

I haven't used any of mine either. Ive been too busy with speaker boxes and other priorities.

I have the schematic on my page - www button below.

Bob
 
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