Diode shootout - Zeners and transistors on a Marshall JMP comparison video.

[RedPlated]

Had my JMP opened up to compare various diodes on the SAT switch. I tested 20v, 16v and 12v zeners, as well as MPSA06 transistors.

This clip will give you an idea of how lower values affect the tone. Basically, the lower you go in voltage rating, the more perceived gain, more compressed, saturated and darker. For this amp, I preferred the 20v. They offered the least gain but also the most seamless transition from clipping on and off. They were clearer, more defined. Just better for this particular amp and what I want it to do.

The MPSA06 were also really good in this amp. They fall somewhere near the 12v Zener in volume and saturation.

I used an iRig Pre HD with SM57. Charvel Nitro Aged with EVH Frankenstein pickup. Cameron 4x12 with G12H30 anniversary.

 

[thenine]

Tough call. The sizzle on the transistor wins for me. I’m surprised I’m saying that. LP might make me think different.

 

[RedPlated]

I agree with you on that. It was probably my favorite overall. It is saturated and gainy like the 12v Zener, but more open and defined.

I would have left the transistors in, but I want this to be a less gainy sounding amp and maintain the core tone as much as possible.

 

[controlled_voltage]

if i wasn't watching i'd say they all sound great with minimal difference
is the feel different?

 

[harddriver]

20V zeners tend to stay crunchy with more headroom, that's why I prefer them with a Jose or JCM800 master setup. Unless you really want alot of saturation say in the 10 to 12V range, some like that.

 

[psychodave]

I like the 16 in your video. I believe Fortin mixes values like a 15 and 20, or a 10 and 15.

Of course different brand diodes/transistors will sound different and add their own “magic” to the sound.

 

[RedPlated]

if i wasn't watching i'd say they all sound great with minimal difference
is the feel different?

The feel is definitely different. If you listen to the fatness of the individual notes and the overall compression between the types in the video, you'll pick up on the difference in dynamics.

I need to do some testing with mixed values. I'm sure there's some great tone to be found that way. I have some Zeners that are below 10v that I really like A LOT. I didn't test those here, but they'd be too low voltage for this setup anyway. There are so many types, brands and voltages that you could spend an infinite amount of time testing. Luckily they're cheap. I've been buying them 100 at a time in each value.

 

[blackie13]

I would put the 20v zener and the MPSA06 in a switch...

Actually I have already done this...!!!!

 

[harddriver]

Thanks for posting that vid! It was cool hearing a back to back comparison between all those diodes. Your vid helped me confirm what I thought I was hearing with the zeners voltage thresholds when I experimented quite a few years ago and landed on what I liked.

Anyway... thanks for taking time to record and post that video!

I liked the 20V in your vid and the 16 was cool if you wanted more saturation but it starts to round out the low end but that's the saturation coming into play as you reduce the threshhold voltage lower in the zeners.

You could also try two IN5400 diodes (oriented assymetrically) I'd have to pull the chassis. I read Dave Friedman liked those as well. I'm pretty sure I used those for a plexi saturation switch in my Jose/2203 build just off of the standard JCM800 master and it really adds alot of sag to the feel/tone when switched in. I'm running 20V zeners off of the Jose Master pot on a switch on that amp, and I added the plexi sat switch off the standard JCM800 pot that I left in that 2203 build.

I just looked up the voltage clipping threshold on the IN5400 and it is 50V. The IN 5408 was 1000V so it was the IN5400 that I used in the plexi switch. the IN5408 would be used in the mains rectification circuit in for B+ and bias supply. You'd have a hard time clipping 1000V diodes. I think the 50V IN5400 soaks up quite a bit of current giving a really saggy effect.

 

[RedPlated]

I

I would put the 20v zener and the MPSA06 in a switch...

Actually I have already done this...!!!!

I use 6 way rotary switches in my other amps with 5 values and one position with no diodes. I just really don’t want to go further than I have with this amp. If I had to I’d add another push pull to switch values.

 

[RedPlated]

I liked the 20V in your vid and the 16 was cool if you wanted more saturation but it starts to round out the low end but that's the saturation coming into play as you reduce the threshhold voltage lower in the zeners.

You could also try two IN5408 or IN5400 (oriented assymetrically) I'd have to pull the chassis. I read Dave Friedman liked those as well. I'm pretty sure I used those for a plexi saturation switch in my Jose/2203 build just off of the standard JCM800 master and it really adds alot of sag to the feel/tone when switched in. I'm running 20V zeners off of the Jose Master pot on a switch on that amp, and I added the plexi sat switch off the standard JCM800 pot that I left in that 2203 build.

Thanks man, I appreciate that info. Always good to learn something new !

It’s so hard to shut an amp off for a second, switch diodes and 100% accurately remember the A/B comparison. Recordings help a lot.

 

[scottosan]

We’re you implementing them fireman style with a parallel resistor or true Jose style. I’ve found the the friend an technique is less sensitive to differences between values.

 

[RedPlated]

We’re you implementing them fireman style with a parallel resistor or true Jose style. I’ve found the the friend an technique is less sensitive to differences between values.

1 Meg parallel. It’s a non-pre-tone stack MV.

 

[fusedbrain]

Cool vid! Thanks for posting.
20V and the MPSa06's sound great
I love MPSa06 for a SAT circuit. It can be a bit much gain-wise. but the tone is always killer.
I hate the feel of zeners lower than 20V or 18V.
Actually, I usually do 20 / 18V zeners and MPSa06 on a switch. The asymmetrical zener clipping sounds better to me than 2x 20V's.

Ya want to talk about a rabbit hole.... start playing with which end of the zener's you connect together, or shoot out 4 different brands of MPSa06.......

Amp sounds really good though, nice work

 

[psychodave]

I thought the MPSA06 was around 10 volts? I know that it clips less than 5.6v zeners…

 

[RedPlated]

I thought the MPSA06 was around 10 volts? I know that it clips less than 5.6v zeners…

In my testing, they clip just a bit more than the 12’s and less than 8’s. So they’re somewhere between there. Around 10-11v seems about right.

 

[RedPlated]

Cool vid! Thanks for posting.
20V and the MPSa06's sound great
I love MPSa06 for a SAT circuit. It can be a bit much gain-wise. but the tone is always killer.
I hate the feel of zeners lower than 20V or 18V.
Actually, I usually do 20 / 18V zeners and MPSa06 on a switch. The asymmetrical zener clipping sounds better to me than 2x 20V's.

Ya want to talk about a rabbit hole.... start playing with which end of the zener's you connect together, or shoot out 4 different brands of MPSa06.......

Amp sounds really good though, nice work

The lower value diodes do start getting a bit round with less attack as you go lower. I think I have some 18's. I should test those as a compromise between the 20 and 16. I will try the 20/18 combo as well.

I have had MPSA06 and 20v on a switch before. the volume drop from the 20v to MPSA06 is significant. A lot more clipping. But the transistors seem to retain the cut and attack better than equal voltage diodes. It's definitely a "feel" thing too.

 

[SpiderWars]

I thought it was the base-emitter breakdown voltage that is listed on the data sheet. MPSA06 is listed as 4v minimum. It doesn't correlate to a 4v zener but at least you can gage different transistors against each other.

 

[Mark Skid]

16v Zener FTW.

 

[psychodave]

Didn’t go back to look, but are you using a depth circuit? If so a little tweak here, can really help the final tone… meaning if you get to a time where you really like a specific part, let’s say it’s a zener/transistor, you can use the depth (obviously other areas as well) to fine tune. An added resistor in the depth can really focus the frequency of the depth. Or you can add another pot like Cameron’s “Q” pot.