'Blue Magic' build report

[Ge_Whiz]

I've just completed (and debugged) a stripboard build of Jake Nagy's (Nagey's?) Blue Magic. Thirty years of stripboard construction experience didn't stop me from putting the MOSFET in the wrong way round and then wiring the JFET stage to the MOSFET gate rather than the drain. I didn't have the exact parts to hand, so I substituted a ZVN0535A for the MOSFET (I bought 50 of these for £1 some years ago in a Zetex clear-out), and a 2N5457 for the JFET. It still sounds just like the samples - very nice. When carefully set up, the oscilloscope clearly shows the emphasis on the second harmonic, just like the textbooks say.

However, I still can't make any sense of the 'Mid boost' section. I thought that the 470pF and 530pF capacitors would be too small to do anything, and the switch has no audible effect nor does it change the appearance of anything on the oscilloscope. The wiring around the mid-boost switch looks a bit weird to me - as with the rest of the schematic, where wires cross they are supposed to be connected at a junction, right? Or does anyone know of an error here?

However, no good deed goes unpunished - just as I got the Blue Magic up-and-running, the volume knob on my recently rewired Burns died, albeit in the full-on position - oh well, another repair job for the weekend.

If you tranny amp users want a 'tube-like' sound, this is definitely where it is.

[Paul Marossy]

I built that one, too. Nice sounding little circuit. I noticed that the mid boost switch on mine seems to be very, very subtle. Maybe I have mine wired wrong? I used Jake Nagy's PCB layout, though... I dunno.
Anyhow, yes, it's a very tubey sounding circuit.  

[Stef]

After a little tweaking the blue magic can really dial in a sweet range of OD tone. Nice subtle warm break up all the way to some really sticky crunch. Here's what I swapped out.
For the boost: C13a,b- socket one of the caps and then bring the total in the range of 780pF. This really sounds great for leads (use a SPST stomp) and can be bumped up higher but keep in mind as the overall gain is turned up, the difference between the ‘without boost’ and ‘with boost’ decreases (ie, the boost won't take the circuit beyond gain at full throttle). I thought the sound was a little dark for my rig, so mine has a .0039uF in C12 and C8a has a 4.7uF- makes it a little livelier- your call per your amp/guitar. Lastly I dropped a 50k lin in R11 and call it the ‘tightness’ adjustment- this one is really key and can bring the sound from gritty and open to teflon smooth. I call mine the ‘blue magoo’.

Stef

[Ge_Whiz]

Thanks for the comments and advice. Obviously, there's still some tweaking to be done this weekend.

Being from the London area, I thought I'd call mine "Tube Station".

[Gary]

Mind the gap!

[bettycat]

The "Blue Magic" is my current DIY project too. The box is finished and I will populate the PCB during the weekend. I´m VERY curious how it will compare to my other overdrive boxes.

@Stef: thanks for the great suggestions, I will give them a try.

[aron]

It's a fantastic circuit. Very responsive. I think that switch was very subtle for me too.

Jake can hear things us mere mortals cannot  

[Aharon]

Same here,the switch is subtle but that's the way it is on the SupaNova too.I think he did mention that you were going to find it less pronounced depending on the pick ups you use and a resistor had to be changed for a more pronounced effect,didn't he?.
Take care
Aharon

[Stef]

As a mid boost in a band setting, I found it was getting lost in the mix, but if the caps (C13) are bumped up from 530pF to the range I was mentioning (700-800pF), you get a really nice to pronounced boost (depending on how great the total cap values are). With this change it is a mid boost but also a gain boost as well (you will hear the difference btw off/on) and works really well for accent. The box is a permanent fixture on my board.

Stef

[Thomas P.]

I have had the problem that even the tone control was so subtle that I can hardly say it's working at all :wink:
But he said (J.) it depends on your setup - I'd rather go with aron and say he has super-human ears :wink:

[JN]

Glad you guys are getting some fun out of this.  I've sort of been out of the loop, but feel free to ask here or send me a message if you encounter problems or want a couple tips.  Based on the comments here, you could try removing C9 and playing with the tone stack values to create a wider range.  I leave D2 out because I think it dulls the sound a little.  In case you are wondering, those empty pads next to C8 are provided to add a bypass cap to C8.  Use a high quality .1uF film cap there in addition to the 10uF electro to bring out more articulation.  While on the subject, make sure to experiment with different electros for that byapss cap.  Since this is a relatively low parts count circuit, the quality of the parts can make an audible difference.  On this point, you are better off using two 3.3uF caps for C2 instead of a single 6.8 electro.  Also, the suggestion to alter the values/ratios of the mid-boost switch is a good one!

Jake

[bettycat]

I´m about to collect all the parts I need for my Blue Magic and I wonder if anybody knows where to find silver mica or film caps with the values 470 and 530 pF without using two caps in parallel - there is not much space left on the PCB for such experiments

[Peter Snowberg]

I don't know about 530, but you can find 470 and 510 here:

http://www.mouser.com/catalog/615/434.pdf

-Peter

[Craig V]

I was going to build a TS808 clone, but after hearing the clips on GGG, I think I might do the Blue Magic instead.  Was that direct or miked through an amp.  It sounds way too good to be direct, but if it is, I'm sold.  That is about the best Strat tone I've ever heard

How do the TS and the BM compare head to head?  

Thanks.

[JN]

I was going to build a TS808 clone, but after hearing the clips on GGG, I think I might do the Blue Magic instead.  Was that direct or miked through an amp.  It sounds way too good to be direct, but if it is, I'm sold.  That is about the best Strat tone I've ever heard

How do the TS and the BM compare head to head?  

Thanks.

I don't remember exactly how I recorded those clips.  I'm pretty sure I miked them with the amp set clean at bedroom levels.

The TS probably has a little more low end rolloff, might be a tighter distorion (which can be good, but can also sound more artificial and less amp-like) and has a more pronounced mid hump (again, which can also be good).  The BM sounds a little more clear, with less coloration of the guitar, is more amp-like, and can be very loud.  They really are apples and oranges.  Build both!

Jake

[Craig V]

Thanks for your reply.


I think I need to build both.  Those sound clips just blow my mind, especially the second one.  

Great playing btw.

[petemoore]

cna't remem what exactly it calls for the tone pot [some taper pot] but I just hacked mine into functionality by adding r's to the pot to get it where I wanted it [only a small amount of tone knob influence]
 My BM has more output than the TS [both have alot] and less grind/more snoothy.

[HellStorme]

Hi, I've built the Blue Magic but i can't get it to work, i 've trying to debugit without success, i found that  i have signal in some parts of the circuit but nothing on the drain of the J201, nothing on the gate or s also, so basically i'm very frustrated, i'm no electronic expert so I was wondering if someone here had the same problem or the solution, or even some idea of what can be causing this problem, I think is a human error (mine of course) but I seem to be to dumb to figure it out.
Any suggestions?? any one?? Should I choose another hobby???  :shock:

[Doug_H]

The mid boost control works pretty well at low gain levels. It is a way of tweaking the "treble-leakiness" of the treble-leak caps. It functions like a typical "brite switch" where it affects it at low gain by leaking high frequencies at full gain. As you turn it up, all frequencies get passed so the difference is less apparent.

Doug

[george]

Hi, I've built the Blue Magic but i can't get it to work, i 've trying to debugit without success, i found that  i have signal in some parts of the circuit but nothing on the drain of the J201, nothing on the gate or s also, so basically i'm very frustrated, i'm no electronic expert so I was wondering if someone here had the same problem or the solution, or even some idea of what can be causing this problem, I think is a human error (mine of course) but I seem to be to dumb to figure it out.
Any suggestions?? any one?? Should I choose another hobby???  :shock:

as a first step I would recommend checking the pinouts on the J201 - they're different from that of other JFETs eg the MP102 ... and check the pinouts on the MOSFET too.

and I assume you've checked the "What to do if it doesn't work" sticky?

cheers