My M800 is apparently a bust
- Thread starter PKRPedals
- Start date
griff10672
Active member
Interesting ...... I used Siliconix J201's in my M800's as well .... got them from Smallbear I think ... they have the white dots on top ... they sound amazing ...
PKRPedals
Active member
My M800 has been put on the shelf. I'm still not getting it. I think I've tweaked it as much as it can be tweaked and to be honest, it just doesn't sound great. The gain control is pretty much useless when trying to turn down the gain. I pretty much have to have the gain wide open for it to sound half way decent. It still has that sort of fizzle out on some of the notes. It does have more sustain but not what you would think it should have. I guess this one is just a bad build. I'm sure everyone has had one from time to time. Maybe I'm just expecting too much.
griff10672
Active member
really sounds like you got some " reject " J201's .....
the more I research obsolete chips and transistors ...... the more I see " beware of fakes and rejects "
I've read that a lot of obsolete components out there for sale are also " factory rejects " that work ... but were scrapped for some kind of quality issue ..
but who knows ...... I try whenever possible to get the obsolete parts from Smallbear ..... have never had a problem with anything from there
griff10672
Active member
hmmmmm I've never heard of Pedalhacker ... have to check them out
griff10672
Active member
sucks when a pedal doesn't work ... or worse ... works half ass .... drives me crazy actually .....
I rechecked Smallbear for more Siliconix after I did my build last weekend..... was already sold out
PKRPedals
Active member
I ordered another M800 today. I’m gonna give it another run. Maybe the first one was just not going to work. I am going to use 2N5457’s this time, ordered from smallbear. I’m also going to use Cermet trimmers as opposed to the ones I have now. Hoping for a homerun this time
griff10672
Active member
interested in hearing how it turns out
Chuck D. Bones
Circuit Wizard
J201s have very low Idss and that translates to low gain and cold bias. Spec for J201 is 0.2mA to 1.0mA. I have to believe that by now all of the good ones have been cherry-picked and the ones still on the market are the runts of the litter. Or fakes.
Here's an easy way to test JFETs:
Short the Source & Gate together and connect them to the minus side of a 9V battery or pedal power supply. Connect a 1K resistor from the Drain to the positive side of the battery or power supply. Measure the voltage across the 1K resistor. Whatever you get in volts, that's Idss in mA. If Idss is less than 0.5mA (0.5V on the DMM), then you probably don't want to use it. If you get 9V across the resistor, then Idss is greater than 9mA. Won't happen with a J201. For P-channel JFETs, reverse the battery.
By comparison, Idss is 1 to 5mA for 2N5457, 5mA minimum for J112, 4 to 20mA for PF5102 and 5 to 30mA for MPF4393 or PN4393.
I have built a few pedals using MPF4393s and they all work great. I built one pedal using J201s (Corduroy) and it works great. Small Bear sold me some good J201s, but now they're out of stock.
Here's an easy way to test JFETs:
Short the Source & Gate together and connect them to the minus side of a 9V battery or pedal power supply. Connect a 1K resistor from the Drain to the positive side of the battery or power supply. Measure the voltage across the 1K resistor. Whatever you get in volts, that's Idss in mA. If Idss is less than 0.5mA (0.5V on the DMM), then you probably don't want to use it. If you get 9V across the resistor, then Idss is greater than 9mA. Won't happen with a J201. For P-channel JFETs, reverse the battery.
By comparison, Idss is 1 to 5mA for 2N5457, 5mA minimum for J112, 4 to 20mA for PF5102 and 5 to 30mA for MPF4393 or PN4393.
I have built a few pedals using MPF4393s and they all work great. I built one pedal using J201s (Corduroy) and it works great. Small Bear sold me some good J201s, but now they're out of stock.
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Just finished mine and i got rid of most of the fizzing out by turning the gain all the way up. Turning the guitar volume down and lightly picking the strings and adjusting each trimmer to where i thought it sounded best. Those settings seemed to really exaggerate it “choking” out which helped in adjusting it. It sounds pretty good now. I think spending more time with the trimmers could probably get it 100%
Chuck D. Bones
Circuit Wizard
Can you do us a favor and once you have it dialed in to your liking, measure the drain voltages on Q1, Q2, Q3, Q5 & Q6 and report them here? Might make it easier for the next guy to dial it in, at least get a good starting point.
PKRPedals
Active member
I absolutely will. I’ll be starting over on a new board and going on vacation at the end of the week so it may be a bit. I got a tester today and tested my J201’s. They appear to be good, they are reading around .5mA and 366mV or is that low. I have some 2N5458’s that are reading 1.5mA and 1.6V. Would the 5458’s work. I’ve got some 5457’s on the way, they may be better.
PKRPedals
Active member
Got the second M800 built. I used 2N5457's instead of J201's. It sounds a little better than the first one but still not great. The notes still sputter off instead of ringing through. I measured every component that went into it. I bought new pots for it and it still doesn't sound really good like others have reported. If anybody wants to take a look at it and see if it can be good, I will send it out. As for now it is on the shelf.
PKRPedals
Active member
Update: I had a little time to go back to this one. I soldered up some SMD J201's and installed them. I set the drain at 4.5 and there it is. Sounds good now. Still have a little tweaking I want to do but it's there, I just want to see if I can get it better. I guess I can chunk those other J201's and just go with SMD from now on. Thanks everybody that replied.
