PLUTO-2 parts ordering at Digikey

[roehrig]

I played around a little with SL's spreadsheet pz-eql.xls (see the Pluto+ page, in the "Frequency response equalization section"). I filled in the target values in block 1 with
f0 = 66
Q0 = 0.85
fp = 41
Qp = 0.71
C2 = 100

Set M = 1

The calculated values come out as
R1 = 8.25
R2 = 11.84
R3 = 21.42
C1 = 851.3
C3 = 328.5
C2 = 100

The chosen standard values for this circuit in the Pluto 2.1 are
R1 = 8.25
R2 = 12.1
R3 = 21.5
C1 = 860 (= 470 + 390)
C3 = 330
C2 = 100

These give calculated values for the poles and zeros that are spot on; that is, the values in block 3b exactly match those entered in block 1, with gain Adc = 8.3.

The 330 nF capacitor in question (C61 in the Pluto schematic) corresponds to C3 in the spreadsheet. If you get a 3% tolerance capacitor and it turns out to be 3% low (i.e., 320 nF), the spreadsheet shows that the values of f0 and Q0 change almost not at all, while fp goes down to 40 Hz and Qp goes up to 0.72. These will surely be far less than the unit-to-unit variation in the driver parameters. With the low value of 320 nF, the gain Adc goes up to 8.6, but this is also well within the range that the tweeter adjustment pot can handle.

If the capacitor you end up with is 3% high (340 nF), the story is much the same. f and Q change hardly at all, while Adc goes down to 8.1, again within the range of variation that the pot can handle. You can play around with the spreadsheet yourself to see what other out-of-tolerance parts will do to the response of the equalizer.

I don't think you'll have any problem with a 3% part for C61. If you can still get it!

Steve

[JimB]

Good answers!

Don't forget to look here before chasing alternatives to the original parts: http://orion.quicksytes.com/viewtopic.php?f=12&t=1018&start=17

But, as of today, following those instructions will leave at least 4 values unavailable in the desired series at 2% or 1%. In some cases, 5% parts are available and will be fine. This is true for the PS and input cap examples for 0.33 uF. Steve has addressed the remaining concern there (C61).

For the other parts, where tolerance is important, a little network scaling can solve the problems. My Pluto schematic is out of date (bought plans but never built, so I have not kept up). From my parts list, here are the other values that are no longer available from Digikey, in 1% or 2%:
P3905, 2.2 nF
P3919, 33 nF
P3921, 47 nF

That 33 nF part is used a lot. Taking it as an example, where it is used 10 places for the 980/1000 Hz XO (C22-25 and 51-56), you could choose to drop to 30 nF (the 1% part is P3859-ND, $0.84@, with 616 available today). In this case, you would raise the corresponding R values to match, such as:
R24, 26, 51-54 from 3.48k ohm to 3.83K (3.83KXBK-ND); and
R25, 27 from 6.81K ohm to 7.50K (7.50KXBK-ND).

I don't have the time to do more on this now, but likely the others could be resolved, similarly. This is how I would approach it if I were building a set today. I would certainly do this before I would compromise on part quality (series).

[londonorion]

For what it's worth, I've fount the LCR series of 1% Polystyrenes stocked by Farnell ( www.farnell.com ) to be very useful when I've needed a close tolerance capacitor. They're axial leads and as such can be "convinced" to fit just about any PCB spacing. The farnell SKU for a 33nF 1% unit is 9520449. The UK product page is: http://uk.farnell.com/lcr-components/fs ... dp/9520449. The US product page is http://export.farnell.com/lcr-component ... dp/9520449

[kmorgan]

I asked SL the following during Pluto construction

I've nearly finished the electronics now. I have one concern though. Having found 330nF polyproplylene caps hard to find here, I ordered some polyesters instead. I reasoned that there should not be a huge difference (but what do I know?). Now I find that these are tiny compared to the ones in the photos and the spaces provided on the pcb. Do I need to source some correct ones?

And got the following reply

Keith,

There should be no problem with the polyester caps.

SL

The polyesters in question were actually 5% ones, I think. I didn't have the means to measure them so bunged them in and hoped for the best. I had noticed that only one position seemed critical in audio terms. From the above it seems that any effect is just on tweeter gain, which is adjustable via VR1. I have one VR a half notch higher than the other to make the pink noise sound the same. Both are pretty much in the neutral position to make the Plutos sound sweet.

Keith

[koonce]

After reading all this, what I'm getting is that it may not be THAT important for the tolerance to match precisely. Can I assume a 5% tolerance capacitor will work instead of 2% as specified? There are many options at the 5% level. Are there any caps that require the closer tolerance.

The above is assuming the proper type of capacitor is used, ie PP or PPS and not PET (polyester)?

I've made my first (big!!) order with Digikey. The only ones that are completely out and discontinued with my order are:

P3900-ND
P3222-ND
P3333-ND
P3473-ND
P3334-ND
P10290-ND
P6946-ND (although this one appears to have an acceptable substitute with 338-1599-ND)

Thanks,
Tony

[JimB]

After reading all this, what I'm getting is that it may not be THAT important for the tolerance to match precisely. Can I assume a 5% tolerance capacitor will work instead of 2% as specified? There are many options at the 5% level. Are there any caps that require the closer tolerance.

The above is assuming the proper type of capacitor is used, ie PP or PPS and not PET (polyester)?

I've made my first (big!!) order with Digikey. The only ones that are completely out and discontinued with my order are:

P3900-ND
P3222-ND
P3333-ND
P3473-ND
P3334-ND
P10290-ND
P6946-ND (although this one appears to have an acceptable substitute with 338-1599-ND)

Thanks,
Tony

Tolerance DOES matter depending where it is used. I can't review all your choices, but have you at least considered these alternatives:
P3222 - how about PS1H222G-ND?
P3333 - how about P12067-ND?
P3473 - how about PS1H473G-ND? Or P12075-ND?
P3334 - how about P12195-ND?

[etoiledusoir]

Hi everybody,
Finally I ordered the drivers from madisound for my Pluto project.
I find another alternative for a more economical transformer:
http://www.antekinc.com/details.php?p=32

Now, I need to make a decision as to odere those above or the tranformer from Apex jr:
http://www.apexjr.com/images/AdireToroid.JPG

I will be glad to have input concerning the tranformers.

[Turpin]

etoiledusoir » Fri Feb 26, 2010 2:21 pm wrote :

I find another alternative for a more economical transformer:
http://www.antekinc.com/details.php?p=32

Now, I need to make a decision as to odere those above or the tranformer from Apex jr:
http://www.apexjr.com/images/AdireToroid.JPG

I will be glad to have input concerning the tranformers.

That second transformer you listed has both secondary windings rated at 21.5v / 2.7a and so is more than twice the power rating of what is specified.

Comparing the specifications of the Antek with the recommended Amveco model, the former seems more massively constructed and that is usually a good sign.

[etoiledusoir]

Hi everybody,

As the capacitor recommended for c105 and c106 (panasonic fc 470 uf) is backordered, I'm planning to use parts I already have in hand. I have some Elna silmic II 1000 uf 50v. I use those capacitors in my chipamp and they are great for my taste. Because c105 and c106 is at the power supply, is it critical to use the 470 uf value ? Can I experiment with more capacitance ? I have read from another forum someone mod is pluto with higher cap value at the power supply to get a more open sound for is taste.

[BrianL]

I have a larger value in these (and other) locations without any ill effects. Much better to use parts you already own, if they work. A bit of fiddling may be required if lead spacing isn't the same.

[excaliburst]

The large 22.000 uf Cap electrolytic is backordered at DigiKey until midsummer.... So I have tried to locate some locally. But I am completely out of luck. What I can get is larger voltage (100V) and this makes them much larger physically. This is a no no as I want my foot to encompass the PCBs. This is the only component that I lack to finish the boards.

Sad to wait until midsummer....

Anyone any ideas for me to get 4 22.000 uf caps..

Best regards

[etoiledusoir]

The large 22.000 uf Cap electrolytic is backordered at DigiKey until midsummer.... So I have tried to locate some locally. But I am completely out of luck. What I can get is larger voltage (100V) and this makes them much larger physically. This is a no no as I want my foot to encompass the PCBs. This is the only component that I lack to finish the boards.

Sad to wait until midsummer....

Anyone any ideas for me to get 4 22.000 uf caps..

Best regards

Try this:
338-1599-ND

only 5 avaible

[Bill Schneider]

Another option is to use 18000uF caps, P6945-ND (if they are still available), as SL noted back in 2006 when the 22000uF caps were unavailable.

[excaliburst]

Sad to wait until midsummer....

Anyone any ideas for me to get 4 22.000 uf caps..

Best regards

Try this:
338-1599-ND

only 5 avaible

Thanks alot. I ordered 4 of them...

Last night I finished soldering the boards, until I missed these mothers.... I think this concludes my scrunging for electronic parts. I should be able to finish them within a month from now.

Now I'll get on with the enclosures.

Greetings from Denmark

[jake9115]

Has anyone talked about the -15V regulator?

The following are out of stock from the digikey site:

-15V regulator - LM79M15CT-ND
820pF - P3900-ND
2.2nF - P3222-ND
33nF - P3333-ND
100nF - P3104-ND
330nF - P3334-ND
470nF - P3474-ND

I'm not sure what to do!