Maxon Phase Tone

[MAO]

I love anything Maxon, definitely want to give this Phaser a go.

Maxon PT999 Schematic



Need some help though, having trouble getting this one to fit on a 22 wide layout.

I was hoping to use this arrangement for the jfets so either DSG or DGS could be used. But if needed, I'd settle for DSG :0)

Hoping someone can take a crack at this as I seem to be layout blind at the moment.

Thanks!

[Alex]

Hi Michael!
Do you want it max 22 rows large to fit it in a 1590B size box?
With 3 op amp and 5 transistors I think it may come out too large.
Maybe 22 x 28 or something like that.
How would you make it true bypass?
Jump Q5 (eliminating all "footswitch" components) and eliminate C24 & R28?
Using a TL074 instead of 2 1458s?
What about a daughter board for the matched transistors in case the final layout would be too large?
Let me know what you think so I'll give it a try.

[MAO]

Hi Alex,

Thanks for the quick response!

And yes on all suggestions, sorry I should have mentioned those.

A 1-knob 1590BB just seems wrong :0)

I'm embarrassed to admit I didn't even consider using a daughterboard even though that's pretty much what I posted in the request :0)

Don't waste you time on it, I'll give it another go with the daughterboard in mind.

[Alex]

Already started one!
I'll see how it goes.
I think you need to eliminate R29 too.

[MAO]

Agreed on R29

I'll leave the layout to the expert then :0)

Thank you!!!

[MAO]

I know we have different layout styles, but in case it helps here is/was my updated jfet daughterboard with trimmers and wire routing holes.

I eliminated the extra socket intended to accommodate the original DGS jfets, which I do not have. I'm assuming 2n5457 SMDs will be ok.  

[Travis]

MAO you got me wanting to build this now!

Except I would rather use the original buffer and switching. With LFO pedals buffers tend to be my best friends for resolving ticking noises.

I wonder how important the LM1458 is here. I know there are some effects which won't work properly if you sub the 1458 like the Meatball/other Mutron III derivatives. I'm guessing the application here is less sensitive but slightly wary

[MAO]

It looked similar to the MXR Phase 90 I wasn't thinking much about the ICs or jfets, but now you have me wondering if that's where some of the mojo is coming from.

[Travis]

It would be cool to do it with dual op amps so you could try the original parts vs subs but it could make the layout pretty big. The 1458 is supposed to be a dual 741, and I think there's a quad version but can't think of it. They probably all have minute differences anyway

[MAO]

It's funny, I watched the video again and now I'm really starting to wonder if the 1458s are part of it's character.  I can almost hear the 741s character :0)

Looks like the LM324 is the quad 741, so if the layout ends up with a 14 pin IC, we'd have that option.

I do prefer the 741s in certain overdrives and distortions, but have never kept one in a clean effect...other than the EHX Bass Balls (couldn't get the effect to work without the 1458s)

Makes you wonder if Maxon chose the 1458s for the re-issue as a tone necessity, or just to market a "true re-issue".

I guess we will find out soon enough :0)

 

[Travis]

I was thinking LM324 but couldn't find anything to confirm that. Got some of those ready to go too :P

[MAO]

Travis, you inspired me to keep working on the layout, against my better judgement

I'm sure Alex's version will be much better as I really struggled with this one.

But I managed to get it on a 22 x 27 with one external jumper wire. The yellow wires need to be connected together. I'd route the wire through the board and run it underneath on the copper side.

I did omit the switching circuit, but maybe that can be added as a daughterboard if needed.

Also, the JFET sockets are laid out for DSG (2n5457) rather than the original DGS (2SK246).  Probably will use a MPSA18 or 2n5088 for Q5.

And note the stomp switch is wired slightly different for use with the added LED PCB.

Proceed with caution as I'm seeing double

Update - Found typo 430R should be 470R, corrected layout.  

[Travis]

Nice work Mao. The transistor type shouldn't be important but the 2SC1815 is super cheap to stock up on. Check eBay. The ones that I have mostly have an hfe ~150 so MPSA18 and 2N5088 would be much higher hfe, again not that I think it would matter much.

I'm considering having a go at hacking up a version with the original switching. 3 wires to the stomp switch, one pot, what's not to love? Might as well include the dry out too I guess

[MAO]

Good point on Q5 (TR1), I didn't check the datasheet for those...it was a late night.

I do have some 2n3906s in that hfe range.

If going with a daughterboard for the switching, I'd remove the 47n (C11) on the right edge of the board and tap into the top and bottom of where that cap was.

Referring to the schematic. the switching board would start with C11 and end with the source of Q5 & R29. And would "plug" into the main pcb at the removed 47n (C11).  Would have to tap into vbias too, which is the next row down.  

Maybe expand the LED PCB to do both? Should be plenty of room to tuck it under the main pcb since there is only 1 knob.  

Guess I know what I'll be doing tonight...

 

[Alex]

It's just an Output buffer. 2n5088 should be fine.
2n3906 is PNP and wouldn't work.
I don't think there's a Dry Output jack here.

[MAO]

Sorry, I meant 2n3904.

I threw this combined switching/LED daughterboard together quickly, with the intent to line up with the connecting points on the main pcb.

Should be able to wire the boards side by side and flip the daughterboard underneath. Component side facing down.

C11 would need to be removed from the main pcb which will also make room for the connecting points.

LED could also be tapped off SPDT Stomp switch lug numbers 1 & 2 or even board mounted if preferred.

[MAO]

About half way done...

Also, I found a typo in the 1st layout, the 430R should be 470R.  I updated the layout.

[MAO]

12/15/2016 Note - These JFET and LFO readings are not valid. I will post the corrected readings once I have the lower trimmer sorted out. That trimmer doesn;tseem to be doing anything at the moment.  

Good new..bad news...

Fired right up, passes sound, however the phasing is extremely weak.

No time to troubleshoot tonight, but here are the voltages.

Speed maxed, Trimmers dead center

jfets (matched 2N5457)
G= varies 4.58 - 4.64, S=4.77 and D=4.77 (Gate voltage is affected by either trimmer)

lfo
pin 7 4.9 - 6.36
pin 6 4.97 - 5.04
pin 5 4.99-5.09

Non LFO ICs
pins 1,2,3,5,6,7 4.78

VCC 9.01V
VB 4.51


Going to try J201s tomorrow.

[MAO]

She's alive!

The 10u tantalum was shorted. Replaced with an electrolytic for now.

The top trimmer is very sensitive, it's a small adjustment window to get the phasing. For mine it was about 1/3 turn.

I would like to say the main layout is verified, but the lower trimmer doesn't seem to be doing anything. I was assuming this trimmer would either even out the upper and lower phase shifts, or adjust the height of the sweep, but I can't hear it changing anything. I may swap it out with a larger value to see if that makes a difference.  

I used 3 1458s and matched 2n5457s. Will checkout some other ICs too.  





   

[MAO]

Forgot to mention, the Speed connections are lugs 2 and 3 (not lugs 2 and 1)

I'll post the updated layout once I have the lower trimmer sorted out.