Build Report - Plexiser

[mydementia]

Hi guys.
I just finished testing out the new Plexiser circuit (from this thread: http://www.diystompboxes.com/smfforum/index.php?topic=50207.0).
Built from Mojotron's schematic: http://www.mojotronics.com/images/plexizer/Plexizer_s.JPG
And Buck's Layout: http://www.4thlevelmedia.com/stompboxes.html

My initial impressions (thru my SS test amp...):
The good:
Nice tone - very similar to my Thunderchief.  Tonestack adds a lot of flexibility.

The not so good:
It's noisy... Initially, I set all the drains to 4.5V (~1/2 supply) and it had a lot of 'hiss'.  So I followed MartyMart's advice and messed with the Q5 trimmer to quiet it down.  When I added voltage it got a little quieter, but also more shrill - when I lowered voltage the hiss went away, but strummed notes 'farted out'. 

FYI: The layout is huge!  I sized it for 0.1" centers on the JFET's and it barely fits in a 1590BB!  I shrunk it a little more and etched away.  I know Buck was concerned with how crammed in the Dr. Boogey layout was...just be warned!


I'm going to put it in a temp 1590BB and try it in my main rig (once everyone is awake) to see how it compares to my Thunderchief.  If the results are dramatically different, I'll add to this post. 

Anyone have ideas on how to tame the hiss?

Mike

[RedHouse]

Where'd ya get those 50v axial caps?

[mydementia]

Local surplus store in Boulder, JB Saunders... I thought they were pretty cool too!
Mike

[nightingale]

plus saunders has loads of tropical fish caps, and super good PNP germanium for fiftly cents a pop!

i am one of the amp techs at robb's music. i pretty much have to go to saunders every day.. not a bad way to break up the day a little.

[dano12]

Regarding the hiss, those are pretty long runs on the input wiring. Shieled wiring from the input jack to the 3PDT and from the 3PDT to the board will help quite a bit.

[MartyMart]

Mike, your wire runs are about twice the length of mine = possible noise addition.
I have retuned Q5 by "ear" with gain pot set to max and have found an optimum
bias for lowest noise.
You are correct, there is a trade off of tone/volume when doing this, but there is a
happy medium which still gives the pedal a decent vol boost etc/
Still some "hiss" - but at high gain , pretty much every OD/Distortion will be making
a similar amount of noise, TC and DrB also "hiss" when cranked.
I have a "non tone stack" version, which sounds great and matches the original with
all tone stack pots at 12 o'clock, however, when gain is low, the overall tone gets quite
thin and "scratchy" !!

MM.

[Gary]

Marty,

Clip that bright cap!  The scratchies will go away.

If you lose to much sparkle, consider switching the first DC blocking cap to 2n2.

[stm]

Anther option to try with the bright cap is to place a series resistor to limit its action at low gain settings. You may start with a 100k resistor in series with the cap and then adjust accordingly.  This is similar to what it's done with the bright cap in electric guitar wiring.

[mydementia]

Hi Marty.
When I boxed this circuit, I used new I/O wires that were cut to length and soldered in place (to the switch)...still has more hiss than my first Dr. Boogey.  I diddled with it some more after boxing, but didn't max the gain and adjust Q5...to be continued...

I did solve one problem...
I used the same box that I had my second Dr. Boogey build in (other thread - squeels like a banshee).  Aside from squeeling when it was 'on' - the Dr. was squeeling in bypass.  Since I always use JD's 3PDT grounded input bypass switching (from GGG) I was really confused...  When I put the Plexiser in that box (reusing the switch and jacks) I realized that I hadn't hooked up the ground wire to the switch - wasn't thinking...didn't think I needed it 'cause I wasn't bothering with an LED...stupid me!!  ...but it still squeels WAY too much when it's 'on'!!  I etched a board for Gringo's Dr. Boogey layout...will give that one a go soon.  The major difference I see in that one is the pots all come out of one end and don't cross the circuit... we'll see if it makes a difference.

I'll try diddling with the Plexiser more tonight...

Mike

PS> Hi nightingale - good to meet a neighbor!! 

[mydementia]

Just plugged the Plexiser into my rig...VERY nice. 
At high gain settings, the hiss is pretty bad...but, as in the Dr. Boogey, I don't really see a need to go beyond about 10:00 on gain.  Tone is good - very similar to the Thunderchief but a lot more flexibility due to the tone stack.  I think my volume pot has a problem - or this circuit has TONS of boost... I get unity around 8:00 (6:00=0).  Also, the presence pot doesn't seem to do much...similar experiences?

Bottom line - this is a great sounding circuit with excellent flexibility.  Even at low gain (which is stil a LOT of gain), the thing rocks.  It's a good compliment to the balls-out Dr. Boogey. 

I'm excited to see more build reports on this.  I'm especially interested on hearing from the folks who socketed the 'Miller' caps...wondering who notices what...

Thanks to mojotron for his work on the circuit...and, as always, to ROG for emu inspiration...  Anyone shooting for a Diezel VH4 Heavy Channel?  Bogner Uberschall? 
Mike

[mojotron]

Thanks Mike - glad you like it. I did not have a hiss problem on mine, I'm guessing as we pool our experiences we'll figure that one out. I thought that having a Plexizer, Dr B and a TC on the same pedal-board was really the a great combo.

I have the same experience with the volume pot and the presence control - these are design issues that I am working on. The presence control will require some time to work out - for now I would suggest using a 1uF cap - it will give you a lot more than the .1uF in the schematic. For the volume - you can try a 50kA pot instead of the 100kA or bridge the outside lugs on the 100kA pot with a 100k resistor. What I really want to do is use an output buffer like on the TubeScreamer for the out put to isolate the output impedance from the LPF off of the last FET- perhaps it will not make a difference.

ROG brought a great deal of great ideas to the rest of us - I can never say THANKS to ROG enough!

[MartyMart]

My "volume" experience is a little different, Unity at about 11 o'clock and boost there after, but
only with some decent gain.
With gain at 8 o'clock, vol unity is around 2 o'clock, this seems fine , plenty of scope available.
I'm quite liking version 2 - without the TMB tone stack - this is a gain MONSTER ! - could perhaps
be a little thinner, I dont like too much low end "mud" , this is easily adjustible, as I kept a couple
of drain caps socketted.
There are some great "tones" between all my Jfet builds ( 12 ! ) but once you get into higher gain
settings they all seem to get "similar" other than some bass/treble content.
Distortion decay on a few gets kind of "farty" but on this one and the TC it's quite smooth !

MM

[mydementia]

Just an update...
I built the little power regulator Xavier recommended (Here: http://www.diystompboxes.com/smfforum/index.php?topic=50776.msg380245#msg380245) and tried it in my multi effect box (Dr Boogey, Matchbox, Phase90) and got strange results - only 3.5V...wtf?  Tried battery (9.3V) and wall wart (9.1V)...  The raw circuit puts out ~8V outside a circuit...hmmm...

So I yanked the regulator out of that box and put it in my Plexiser (still in the temp enclosure).  Here, I get ~8V (still not sure why I'm not seeing 9V...) - so I biased all the drains to ~4V and plugged in.  This eliminated the hiss almost completely...  I can now max the gain without gritting my teeth. 

Maybe Xavier is on to something here... now if I could just figure out what the hell was going on in the multi effect box...
Mike

[Xavier]

Just an update...
I built the little power regulator Xavier recommended (Here: http://www.diystompboxes.com/smfforum/index.php?topic=50776.msg380245#msg380245) and tried it in my multi effect box (Dr Boogey, Matchbox, Phase90) and got strange results - only 3.5V...wtf?  Tried battery (9.3V) and wall wart (9.1V)...  The raw circuit puts out ~8V outside a circuit...hmmm...

So I yanked the regulator out of that box and put it in my Plexiser (still in the temp enclosure).  Here, I get ~8V (still not sure why I'm not seeing 9V...) - so I biased all the drains to ~4V and plugged in.  This eliminated the hiss almost completely...  I can now max the gain without gritting my teeth. 

Maybe Xavier is on to something here... now if I could just figure out what the hell was going on in the multi effect box...
Mike

Mike, I still don't know what may be happening to your circuit. I've built another of this small regulators for the flipster I made for my bass player, with identical results (very good ones).

Being such a small circuit it should be easy to figure out what's happening. I still bet is the diode you are using

[Bucksears]

Well, I'm glad to know a few things:
A) my PCB works
B) the circuit sounds good
C) there are some buzzes about the sound, but there are some possible fixes.

I hope to start on this one by this weekend. It's taken a while to get around to building pedals again with so much going on at home.
- Buck

[343 Salty Beans]

The regulator I use is an L7809 IC...I got the idea from...I think it was RG  . A 220uF cap across 9V+ and ground, then an L7809 power regulator, then a 100uF cap across the output of the L7809 and ground. It keeps most of the noise out of my paralooper, at any rate. I also tied a diode bridge on the front of it and can use these 12V AC adaptors I found at the thrift store that have the right size plugs.

[mydementia]

I built another regulator (using another 1N4739A 9.1V Zener and a 1.2k resistor - I'm out of 1k!!) and get just under 9V.  Cool...  When I added the circuit to my multi-box - the output dropped to 3.4V... WTF?  I think I'm going to yank my Dr. Boogey out of the multi-box and try the regulator alone... we'll see what happens.  I'm contemplating just giving up on my second Boogey and using my SansAmp - man are there some AWESOME tones in that thing!!!  (...and mine has very little hiss - lucked out on that one!!)

Buck - thanks for another great layout.  The circuit DOES sound good...very good, in fact... When you build yours, do you plan to socket the Miller caps?  I'm still curious how much they are 'helping' the performance/tone of this circuit...

Mike

[Bucksears]

Buck - thanks for another great layout.  The circuit DOES sound good...very good, in fact... When you build yours, do you plan to socket the Miller caps?  I'm still curious how much they are 'helping' the performance/tone of this circuit...

No problem, it's my pleasure to give something back as I'm not a circuit designer. Yes, I'll socket the Miller caps as I want to try them out on this and the Dr. Boogey circuit. It will be interesting to have all of the caps socketed, then take them out one by one and hear a difference in the sound. I'll post a report as soon as I have them done.

- Buck

[mojotron]

Buck - thanks for another great layout.  The circuit DOES sound good...very good, in fact... When you build yours, do you plan to socket the Miller caps?  I'm still curious how much they are 'helping' the performance/tone of this circuit...

No problem, it's my pleasure to give something back as I'm not a circuit designer. Yes, I'll socket the Miller caps as I want to try them out on this and the Dr. Boogey circuit. It will be interesting to have all of the caps socketed, then take them out one by one and hear a difference in the sound. I'll post a report as soon as I have them done.

- Buck

Great idea, I've done something like that while assembling this design. I did not socket the caps, and used 150pF parts; I really like the approach you guys are taking much better to evaluate the Miller caps. From my experience the one's on Q1 and Q2 make 90% of the difference - and C17 does about 9% of the rest (with it's biggest contribution being lowering hi-fr. There's a couple of things to think about too:

1) C9 is not really a Miller cap, or at least does not function really as a Miller cap normally would. It has more of an effect on Q2's transfer function than it does on Q3's. I thought this one could be taken out as it's all pretty minor in my simulation experiments.
2) Although it seems like a bigger cap then you might think of using, you might try a 220-250pF cap on Q2 or Q1 or both. I thought that 220pF did some wonderful things for the EQ on the Dr B.

[slacker]

I built another regulator (using another 1N4739A 9.1V Zener and a 1.2k resistor - I'm out of 1k!!) and get just under 9V.  Cool...  When I added the circuit to my multi-box - the output dropped to 3.4V... WTF?

The reason the voltage drops is probably because the resistor is too big. The current through the resistor will be the same as the circuit it's attached to and with a 1K resistor each milliamp that the circuit draws will drop the voltage by 1 volt. If you're getting a 5.6 volt drop across the resistor then that means your multi box is pulling about 5.6 milliamps which sounds reasonable.
Try changing the resistor to about 100ohm that should reduce the voltage drop to about half a volt.