fOXX Phaser Stages

[nickbungus]

Can anyone help me with a few questions that have been nagging at me?

1)  Does the values of C16 and C21 matter too much?  The schematic asks for 10nfs, the reverse engineered model had 100nfs.

2)  Does it matter if C3 is polarised or not?

Thanks in advance.

[njkmonty]

1)  Does the values of C16 and C21 matter too much?  The schematic asks for 10nfs, the reverse engineered model had 100nfs.

try both but keep both the same?

2)  Does it matter is C3 is polarised or not?

dont think so

[njkmonty]

Can anyone help me with a few questions that have been nagging at me?

1)  Does the values of C16 and C21 matter too much?  The schematic asks for 10nfs, the reverse engineered model had 100nfs.

2)  Does it matter if C3 is polarised or not?

Thanks in advance.

[anotherjim]

Those caps set the low bass roll off. Into the 100k resistors, 10nF give a roll off around 160Hz. This might just be ok on guitar but would be too bass light for other instruments. Raising them to 100nF gets you full audio range.

Now I think about it, this has implications for feedback. Generally, I find that feedback rarely sounds good if there is too much bass content. It can get into a howl too early and sound congested and "blocky" if there's a lot of bass. Since the original took feedback after everything else, the signal fed back got treated to the 160Hz low cut - every time it went around the loop.
I would experiment with the value of the coupling cap added in the feedback loop - it might be best if pretty small, 1nF or under.

[ElectricDruid]

+1 agree with Jim - a bit of bass cut on feedback often helps.

When I was doing the Flangelicious design, I found that cutting the bass enabled me to get the overall feedback level higher before it became a runaway howl. So the filtering improved the sound by allowing a more resonant sound without feedback. I used even more cut, with a rolloff below 460Hz, so perhaps some experiments are in order - it's a question of taste at some point.

Tom

[nickbungus]

Wow - Cheers guys.  The first time when I was messing around with 6 Stage, I didn't understand much but this time round I'm really learning something.  (Setting myself up for some more stupid questions).

I would experiment with the value of the coupling cap added in the feedback loop - it might be best if pretty small, 1nF or under.

Brilliant. I'm playing with the feedback tonight.

What about Q2?  Does it matter if C3 is polarised or not?  I think whats really confusing me is I would expect the polarity to be the other way round. 

[anotherjim]

C3? Sometimes, the caps between stages have no best polarity, because the DC voltage either side is identical.
In this case, the first amp outputs its reference DC of 1.8V, however, the second amp input is biased around the feedback from the FET supply of 6V. So it looks like the DC to the left of C3 is the lower voltage and so the negative plate faces that. If I were going into production with this, I'd like to think I would measure the voltages on either side of C3 or any other polarized cap in similar circumstances just to prove it is the right way.
That said, I've seen cases where polarized coupling caps have been the wrong way, but probably because the voltage difference was small or a large resistance is in series, it hasn't made the slightest difference for years and years.

[nickbungus]

Anyone got an idea what these might be?  I'm trying various combos on here and cant get anything that looks right (standard values).  Bonus points for the resistor between the cap and the trimmer.



1.  6M2? (Blue/Red/Green) I mean it looks more like Blue/Red/Blue) 62M
2.  6k2?  (Blue/Red/Blue)

Did 62 used to be a popular range?  Wouldnt  you just use 6M8 and  6k8

[duck_arse]

the bottom and middle show gold band, so that narrows the choices down somewhat - for bottom I'd guess 820R or 8k2, can't tell the multiplier, and the middle I'd guess 100k.

the top one looks like it might be a silver band on the left, but the other bands don't make a lot of sense.

[anotherjim]

Top. If it's gold band then multiplier might be yellow, so I'm saying 820k.
Middle. Deffo 100k.
Bottom. I go with 820R.

[nickbungus]

Ducky, you're up late!  Thank you for your assistance

I've adjusted the brightness on the image and the middle is clearly a 100k

[nickbungus]

Thanks Jim and Ducky

So what I'm seeing as blue is more than likely Grey - gotcha

[nickbungus]

Well....

I've been looking to buy a new guitar and visited reverb.com.  Then a thought occurred to me to look for Foxx Phasers that have sold and check out the images.  Well I wasnt disappointed.  I managed to find these:







Along with the original I might have enough to try and reverse engineer (and some guess work + usage of the v2 schematic).



I also pulled this from another source, but the quality isnt there:



What the hell is that daughter board thing and what is it hiding?

[Mark Hammer]

Those pics make me thankful for how capacitor sizes have been shrinking over the years.

[duck_arse]

Anyone got an idea what these might be?  I'm trying various combos on here and cant get anything that looks right (standard values).  Bonus points for the resistor between the cap and the trimmer.



1.  6M2? (Blue/Red/Green) I mean it looks more like Blue/Red/Blue) 62M
2.  6k2?  (Blue/Red/Blue)

Did 62 used to be a popular range?  Wouldnt  you just use 6M8 and  6k8

6M2. deffo.

the daughterboard isn't hiding any 15k resistors, that's for certain.

[nickbungus]

6M2 - very specific!

What is that daughter board?  Its not present on the other one I have an image for.

Also, on the same side as the in and out jacks, on the board there's these copper strips (remind me of cartridges on my old Commodore 64).  Some just have holes with nothing connected, some have wires connected and some seem to be connected to copper tracks but they dont seem to serve any purpose.  WTF?!

[duck_arse]

during production, do you:

a) test the assembled but unwired board by plugging a test rig on a card-edge connector,
or
b) swear because you've wired an untested board into that mess, and now it doesn't work?

[nickbungus]

Thanks Ducky- Seems like a good Idea for testing .

Any ideas on the weird daughter board?