Programmable Active Crossover/Pre-Amp *PIC*

[robertcottiers]

This is two of my recently completed projects.The unit on top is a 2-way Digitally controlled Active crossover(Linkwitz Riley 24dB/Oct).This unit has a useable range of 2khz to over 10Khz in approx. 100hz step increments.All of the frequency determining resistors in the circuit(16 total)have been replaced with software programmable Digital Potentiometers(Analog Devices AD5263).A PicMicro handles all of the communication with the crossover.

I wrote a Visual Basic application that allows a user to download new crossover points to the unit via the hardware serial port on the picmicro and the serial port on a PC.I can also use a rear mounted potentiometer to change the x-over point.

The performance of the unit is quite good,I can download new crossover points during live listening with no audible switching transients.

Next step is to add 1 or 2 parametric EQ sections (also with digital pots),this will allow notching or peaking to correct for driver irregularities.This is a hand wired prototype which was difficult to build.After the EQ sections are added,I will need to have some PC boards made up.To be perfectly honest I have just been too damn lazy to learn PC board layout!!..If there are any seasoned PC board developers out there e-mail me....

The bottom unit is a four channel Pre-Amp.I used an Analog Devices SSM2164 Quad VCA chip.The circuit I used is pretty much right from the datasheet.For those interested in more details on this chip you can search the AD website(SSM2164).

Regards Bob C.

[donparsons]

[shawn_a]

Will you stop making such ugly pieces of equipment!?! .

Once again, you have just blown me away with your workmanship and knowledge. Way outta my league for sure. It's astonishing at how you can make great equipment and put it in a case that outclasses anything out there. Amazing.

shawn

[killerkowalczyk]

So, when do you want to build me a 300WPC class A into 8ohms and stable down to a 2ohm load amplifier?

[robertcottiers]

Shawn:Most of this was made with scrap pieces of veneer and MDF.I built this in 8 hours(minus finishing time).The four posts are solid wood with a light chamfer on top.The front consists of 2 thin pieces of solid walnut glued on with a bevel on one edge.The top front and sides are just veneered MDF.The front panel is screwed into the front posts with pocket holes from the inside....I think this would be a very nice project for your new workshop....I look forward to the photos..

Bob C.

[robertcottiers]

> So, when do you want to build me a 300WPC
> class A into 8ohms and stable down to a 2ohm
> load amplifier?

Killer:I don't have any heatsinks big enough for Class A...I'm a chip amp kinda guy!!...BTW the pre-amp is switch selectable from Class A/B to full Class A just by switching in a resistor.Check out the SSM2164 chip on the AD website.No reason you could not build the pre-amp,get some samples and GitterDone!

Just for your information.. I could not tell the difference between the 2 modes of operation...guess I'm gettin old!..

Take Care

Regards Bob C.

[shawn_a]

Oh I'm sure I could aspire to your level one day far down the road but I'm still in awe. I do want to do a chipamp project sometime so who knows what I will come up with.

As for the workshop, I will be doing a walk-through next week and see exactly what I'm getting myself into. I will be sure to take plenty of pics, if not just for insurance reasons but to share with everyone.

shawn

[robertcottiers]

> Oh I'm sure I could aspire to your level one
> day far down the road but I'm still in awe.
> I do want to do a chipamp project sometime
> so who knows what I will come up with.

> As for the workshop, I will be doing a
> walk-through next week and see exactly what
> I'm getting myself into. I will be sure to
> take plenty of pics, if not just for
> insurance reasons but to share with
> everyone.

> shawn

Shawn:Let me know when your ready for working with chip-amps,I have quite few working prototypes(LM3886)(Free of charge!). I can give you a pair already on a heat sink..just add a power supply and a case and your good to go...I can also provide a good supplier for Chip-amp PC boards,If you want to build your own from scratch.

CHeers Bob C.

[jimgutterman]

Nice work.

If I understand you correctly, you have an analog active XO using digitally controlled resistor arrays instead of fixed resistors - essentially digital pots.

If this is the case, I am very interested in your circuit. I have an L-R 4-way active XO currently residing on a breadboard and it is very noisy now due to degredation of the BB. If you have built PCBs for this critter I would be very interested indeed.

I am torn between rebuilding my XO and using the true digital XO the company I work for is developing. The problem with the true digital XO is that I would prefer not to resample the signal and we may not be able to correlate all the channels from a digital input. Another issue which is debatable is the quality of the components; the product is not an audiophile quality unit. Our company is run by a highly skeptical friend of mine that often can shred any argument regarding the effectiveness of high quality components as opposed to good components or similar arguments, so I will not be able to convince him to use top-shelf bits. It may or may not make a difference, but I figure the better the components, the better the chance there is good sound. I believe that the use of higher quality op-amps in my XO - I originally used NS5532 op amps (IIRC) and replaced them with some BB OPA 2134s - made a sidnificant difference. My friend thinks I am hallucinating, and he may well be right, but I maintain I heard a noticible difference. The only way to tell would be to A/B/X the two and see if I can identify one or the other reliably, but with a 4-way XO this is not easy.

At any rate, if you have anything useful in the way of PCB masks or the like I would be quite interested.

Keep up the good work, and enjoy the hell out of the system!

> This is two of my recently completed
> projects.The unit on top is a 2-way
> Digitally controlled Active
> crossover(Linkwitz Riley 24dB/Oct).This unit
> has a useable range of 2khz to over 10Khz in
> approx. 100hz step increments.All of the
> frequency determining resistors in the
> circuit(16 total)have been replaced with
> software programmable Digital
> Potentiometers(Analog Devices AD5263).A
> PicMicro handles all of the communication
> with the crossover.

> I wrote a Visual Basic application that
> allows a user to download new crossover
> points to the unit via the hardware serial
> port on the picmicro and the serial port on
> a PC.I can also use a rear mounted
> potentiometer to change the x-over point.

> The performance of the unit is quite good,I
> can download new crossover points during
> live listening with no audible switching
> transients.

> Next step is to add 1 or 2 parametric EQ
> sections (also with digital pots),this will
> allow notching or peaking to correct for
> driver irregularities.This is a hand wired
> prototype which was difficult to build.After
> the EQ sections are added,I will need to
> have some PC boards made up.To be perfectly
> honest I have just been too damn lazy to
> learn PC board layout!!..If there are any
> seasoned PC board developers out there
> e-mail me....

> The bottom unit is a four channel Pre-Amp.I
> used an Analog Devices SSM2164 Quad VCA
> chip.The circuit I used is pretty much right
> from the datasheet.For those interested in
> more details on this chip you can search the
> AD website(SSM2164).

> Regards Bob C.

[bill]

Bob,

I'm interested in the chip-amp board supplier. I can take care of the rest, but my board-making skills are from back in the days of tape and Sharpies.

I bought a Pic trainer kit from Rat Shack, but I haven't had a chance to play with it yet. Time to get back to Basic!

As usual, your casework is gorgeous. One of these years I hope to get my skills up approaching your level.

Best regards,
Bill

> Shawn:Let me know when your ready for
> working with chip-amps,I have quite few
> working prototypes(LM3886)(Free of charge!).
> I can give you a pair already on a heat
> sink..just add a power supply and a case and
> your good to go...I can also provide a good
> supplier for Chip-amp PC boards,If you want
> to build your own from scratch.

> CHeers Bob C.

[robertcottiers]

> Nice work.

> If I understand you correctly, you have an
> analog active XO using digitally controlled
> resistor arrays instead of fixed resistors -
> essentially digital pots.

> If this is the case, I am very interested in
> your circuit. I have an L-R 4-way active XO
> currently residing on a breadboard and it is
> very noisy now due to degredation of the BB.
> If you have built PCBs for this critter I
> would be very interested indeed.

> I am torn between rebuilding my XO and using
> the true digital XO the company I work for
> is developing. The problem with the true
> digital XO is that I would prefer not to
> resample the signal and we may not be able
> to correlate all the channels from a digital
> input. Another issue which is debatable is
> the quality of the components; the product
> is not an audiophile quality unit. Our
> company is run by a highly skeptical friend
> of mine that often can shred any argument
> regarding the effectiveness of high quality
> components as opposed to good components or
> similar arguments, so I will not be able to
> convince him to use top-shelf bits. It may
> or may not make a difference, but I figure
> the better the components, the better the
> chance there is good sound. I believe that
> the use of higher quality op-amps in my XO -
> I originally used NS5532 op amps (IIRC) and
> replaced them with some BB OPA 2134s - made
> a sidnificant difference. My friend thinks I
> am hallucinating, and he may well be right,
> but I maintain I heard a noticible
> difference. The only way to tell would be to
> A/B/X the two and see if I can identify one
> or the other reliably, but with a 4-way XO
> this is not easy.

> At any rate, if you have anything useful in
> the way of PCB masks or the like I would be
> quite interested.

> Keep up the good work, and enjoy the hell
> out of the system!

Yes Jim..That is exactly what I have.I used the OPA627 op-amps for both the input and output buffers,the filter section used OPA4134,which is the quad version of what you used.Like yourself,I prefer to use good quality components in the signal path,whether or not these are the "BEST"parts to use,I will leave up to the discretion of the builder.I usually stay away from subjective evaluations regarding the Sound of a particular component.Each person is entitled to his/her opinion on what sounds best to them.

The NS5532 chips have been around a long time and still used quite frequently.I agree with you regarding A/B/X testing and the test setup required to do this,I'd rather spend my time doing other things!!

At the present time I do not have any gerber files or such for my design..I am pursuing these as quickly as I can.

Regards Bob C.

[robertcottiers]

> Bob,

> I'm interested in the chip-amp board
> supplier. I can take care of the rest, but
> my board-making skills are from back in the
> days of tape and Sharpies.

> I bought a Pic trainer kit from Rat Shack,
> but I haven't had a chance to play with it
> yet. Time to get back to Basic!

> As usual, your casework is gorgeous. One of
> these years I hope to get my skills up
> approaching your level.

> Best regards,
> Bill

Bill:I sent you an E-mail...Thanks for the positive comments,I think your nipping at my heels with respect to woodworking...that nightstand you built made me very nervous!!!

[envisionelec]

>..If there are any
> seasoned PC board developers out there
> e-mail me....

Seasoned in mixed signal layout. I have a sample for a never-built kit for the three channel National Semiconductor ICs. Maybe someday. Anyway, let me know if you want a board laid out.

[rudy]

[neildavis]

I think I still have about 7 PWB's with the circuit below. I started going this analog route for a project and then shifted gears to a digital approach. I used a couple of the boards in an active 3-way and they worked fine. It's not an ideal layout since there is no ground plane, but I didn't have a problem with noise. There are a number of jumpers that allow configuring this in different ways, and most of that caps are drilled for both 5mm and 7.5mm lead spacing (4 holes per cap), so it's fairly "universal". I've got a picture of a built-up board somewhere, but it would take some time to dig it up. There is also a "Thor" Linkwitz transform circuit that isn't shown (it's on page 2 of the schematic).

You can have one for free but after that I'd appreciated getting what I paid for the boards (they were probably about $15-$20 each). You can have the schematics and layout files (ExpressPCB).

[bill]

> Bill:I sent you an E-mail...Thanks for the
> positive comments,I think your nipping at my
> heels with respect to woodworking...that
> nightstand you built made me very nervous!!!
>

Bob,

Thanks. I haven't been able to get near the e-mail machine tonight.

Re the nightstand, while it's an amazing ego boost every time I look at it (or my wife proudly shows it off), one project does not a portfolio make. When I can consistently crank out work of the quality you do, I'll consider myself competent. It's not just your joinery skills, either; it's your eye for design.

Meanwhile, I wound my first inductors tonight, using a drill press and a small homemade coil-winding form. It's pretty easy and much cheaper than buying the Jantzen coils. On the other hand, I could see where you could lose a finger if you're not careful.

I'll check out your e-mail tomorrow. Thanks again.

Best regards,
Bill

[robertcottiers]

> Seasoned in mixed signal layout. I have a
> sample for a never-built kit for the three
> channel National Semiconductor ICs. Maybe
> someday. Anyway, let me know if you want a
> board laid out.

It Sounds like a nice offer to me..I will be in touch to discuss the details.

Bob C.

[Adrian]

Have you called your local patent attourney? I think you should. . .

> This is two of my recently completed
> projects.The unit on top is a 2-way
> Digitally controlled Active
> crossover(Linkwitz Riley 24dB/Oct).This unit
> has a useable range of 2khz to over 10Khz in
> approx. 100hz step increments.All of the
> frequency determining resistors in the
> circuit(16 total)have been replaced with
> software programmable Digital
> Potentiometers(Analog Devices AD5263).A
> PicMicro handles all of the communication
> with the crossover.

> I wrote a Visual Basic application that
> allows a user to download new crossover
> points to the unit via the hardware serial
> port on the picmicro and the serial port on
> a PC.I can also use a rear mounted
> potentiometer to change the x-over point.

> The performance of the unit is quite good,I
> can download new crossover points during
> live listening with no audible switching
> transients.

> Next step is to add 1 or 2 parametric EQ
> sections (also with digital pots),this will
> allow notching or peaking to correct for
> driver irregularities.This is a hand wired
> prototype which was difficult to build.After
> the EQ sections are added,I will need to
> have some PC boards made up.To be perfectly
> honest I have just been too damn lazy to
> learn PC board layout!!..If there are any
> seasoned PC board developers out there
> e-mail me....

> The bottom unit is a four channel Pre-Amp.I
> used an Analog Devices SSM2164 Quad VCA
> chip.The circuit I used is pretty much right
> from the datasheet.For those interested in
> more details on this chip you can search the
> AD website(SSM2164).

> Regards Bob C.

[robertcottiers]

> Have you called your local patent attourney?
> I think you should. . .

Adrian: These devices are used in all types of equipment nowadays,my circuit as viewed from a Hardware standpoint is quite simple.I think most people would like the fact that you can hook up a serial cable from either a laptop or a PC and quickly evaluate different crossover points during the design phase of speaker building.This crossover is a far cry from a "Behringer",but still quite useful in it's simplicity.

I will update as the project advances,thanks for the comments!

Bob C.

[Adrian]

Bob,
I know these types of programmable crossovers are ubiquitous, but yours simply seemed unique to me. I guess my assumption that it was indeed uniqe (outside of the inherent uniqueness of any DYI project)might have been premature. I have worked for several companies that have profitted from a new or different way of doing something "old." That's where I was comming from. In either case what you have produced is quite an accomplishment for an individual who doesn't have a team of engineers at his disposal. Good job and I look forward to seeing and maybe reproducing more of your work. Not this one though. I am too lazy and am simply saving up for a Behringer Ultradrive Pro.
Once again, Good Job!
Adrian

> Adrian: These devices are used in all types
> of equipment nowadays,my circuit as viewed
> from a Hardware standpoint is quite simple.I
> think most people would like the fact that
> you can hook up a serial cable from either a
> laptop or a PC and quickly evaluate
> different crossover points during the design
> phase of speaker building.This crossover is
> a far cry from a "Behringer",but
> still quite useful in it's simplicity.

> I will update as the project advances,thanks
> for the comments!

> Bob C.