"Red Star Drive"

[frequencycentral]

"Red Star Drive"

This is so simple stupid I can't believe I didn't try it sooner. Last week I breadboarded a few different fuzzes and drives using some newly acquired Ge trannies and Ge diodes. One of the circuits I did was the Trotsky Drive, I used one SFT353 and two 1n67a – I was amazed at the great sounds coming from such a simple circuit.

It got me thinking how it would sound if I replaced the transistor with a 5672 submini pentode. So I breadboarded it – sounded good, but could be better.

Over the last few days I've played about with the 5672 biasing in an attempt to get more gain from what is essentially a PentaBoost with clipping diodes. I came to the conclusion that it won't deliver any more gain at low voltage. So I started playing about with different combinations of clipping diodes until I stumbled across the perfect pair – a back to back 1n4148 (Si) and 1n67a (Ge).

The result is good IMHO – nice clipping, a good amount of gain, and excellent boost too. This is not a massively saturated gain pedal by any means. I find it nicely gritty and fattening, while preserving the character of the original signal. More bluesy than metal – but sometimes oatcakes go down better than brownies right?

Turn the 'Clip' to minimum and you effectively have a clean boost pedal, turning it up increases the clipping.

I think it should work equally well at 9 volts or 12 volts. I'm a 12 volt guy myself.

So:

Red - influenced by the Trotsky Drive.....
Star - uses a pentode.....
Drive - it's an overdrive.....

Cool name huh?

Soundclip #1 (dry): http://www.aronnelson.com/DIYFiles/up/Red_Star_Drive_Dry.mp3

Soundclip #2 (cab sim): http://www.aronnelson.com/DIYFiles/up/Red_Star_Drive_+_Cab_Sim.mp3

[ConanB]

When all the 5672's arrive I'll have to breadboard this one up and compare it to my trotsky.

[mth5044]

Rick you are KING OF SUBMINI'S!

Very Nice.

[Jered]

  Very nice Rick. Your going to crack up at the PM I sent you before I read this post. Oh well.

[Jimmy-H]

Nice little design Rick! 

I did something like this in a 10 watt tube amplifier of mine but with a switch to disconnect the diodes.
But with one diode the volume drop was rather big.
So I placed 3 diodes in series on each side.
And also placed a 10K pot in series with that.
The pot works like a kind of blend this way.
Did you also tried multiple diodes in this design?

[sweetwilly]

Nice one Rick.  Think all my remaining 5672s have found future homes and might need to look into getting some more!

btw, how do the Raytheon sound compared to the Valvo - any other differences in noise, construction, etc?

[frequencycentral]

Nice little design Rick! 

I did something like this in a 10 watt tube amplifier of mine but with a switch to disconnect the diodes.
But with one diode the volume drop was rather big.
So I placed 3 diodes in series on each side.
And also placed a 10K pot in series with that.
The pot works like a kind of blend this way.
Did you also tried multiple diodes in this design?

I tried a few different diode combinations:

2 x 1n67a - too much of a drop in gain
2 x 1n4148 - not enough crunch
2 x red LED - no crunch
2 x amber LED - no crunch

Some other (unidentified) germaniums I have performed identically to the 1n4148.

What i haven't tried yet is zeners.....

I also played about with some diode warping ideas from the AMZ site, but finally decided that this arrangement was the simplest and the best, added crunch but preserving gain. I don't have every diode type available - it would be interesting to find out how it performs with 1n34a for example. I'm sure there are other multiple diode combinations that would sound good.

Nice one Rick.  Think all my remaining 5672s have found future homes and might need to look into getting some more!

btw, how do the Raytheon sound compared to the Valvo - any other differences in noise, construction, etc?

I replaced a Valvo for a Raytheon as soon as they arrived - there doesn't seem much difference. The soundclip was using the Raytheon.

[frequencycentral]

I'm justs in the middle of putting my build together, just waiting for the clearcoat to dry...............I changed a couple of things:

I opted to use a 220 ohm / 1 watt voltage drop resistor instead of the LM317. It's a big fat sausage of a resistor and gets nice and warm! I'm measuring 1.275 volts at pin 3 of the 5672, which is just fine, well within tolerance.

I changed the 'Clip' pot from 47k to 100k. Strangely, the one on my breadboard only needs 47k to get clean boost with the 'Clip' pot turned all the way down, whereas my build is still dirty with a 47K, so I changed it. The only thing I can guess this is due to is slightly different tolerances in the clipping diodes - maybe?

[mth5044]

That resistor is almost as big as the tube 

Can't wait to see the finished product.

[ConanB]

Box of 10 raytheon 5672's finally arrived on my desk this morning, so time to start testing out these designs!   

[asfastasdark]

Just a question, but wouldn't a 100K log pot be better as a volume control?

[frequencycentral]

Just a question, but wouldn't a 100K log pot be better as a volume control?

My background is modular synth building, where Lin is used for audio and Log for control voltages. The range seems smooth enough to me. Just do what you're comfortable with!

[asfastasdark]

OK, cool. This might very well be a future build for me. 

[Jimmy-H]

Really nice layout again Rick!
I'm looking forward to your final result!
I'm convinced that it's a typecal frequencycentral design again.

Great work so far

[asfastasdark]

I made a layout for Version 2, I think it's pretty nice and compact, and I think it's one of my best so far.    I represented the 5672 by a blue switch. See what you think, and this is completely unverified, of course.

[frequencycentral]

I made a layout for Version 2, I think it's pretty nice and compact, and I think it's one of my best so far.    I represented the 5672 by a blue switch. See what you think, and this is completely unverified, of course.

Cool looking layout, I can't see any errors. I should do a layout myself of the build I just finished (I'll post photos of the finished build tonight!) , although I used 'Tripad' board which is not widely available. I could translate it to perf, it's pretty neat because the pots are also on the board, so the off-board wiring is minimal.

I should mention that I use a 10uf electrolytic decouling/smoothing cap on all my builds between +ve and ground. I usually mount it onto the  2.1mm DC input socket.

Also, iif anyone plans to build Version 2 for a 9 volt supply, the 220 ohm / 1 watt resistor should be changed to 150 ohm / 1watt. With only 50 ma current draw it's quite feasible to run this circuit from a 9 volt battery

[frequencycentral]

[kurtlives]

I made a layout for Version 2, I think it's pretty nice and compact, and I think it's one of my best so far.    I represented the 5672 by a blue switch. See what you think, and this is completely unverified, of course.

Really quickly looking over this...
Out is lug 2.
Clip should be 2 not 3. If it was 3 then the pot would not function as a variable resistor.

[frequencycentral]

Ok, here's an UNVERIFIED layout for stripboard. It's my first time using DIY Layout Creator. It's very close to my finished pedal, just a few changes I made to suit stripboard as opposed to the 'Tripad' board that I prefer. A couple of long jumpers on there, but pretty much everything is on the board including the pots, so off-board wiring is minimal. The red dot on the 5672 should be at H7. I mounted my tube on 'the wrong side of the board' in my build, which worked well for me but was a little fiddly to solder. I would be obliged if someone could check it!

[Jimmy-H]

A real great build Rick.
It fits with the other pedals you've build.
I like it very much.

As for the vero layout: I think there's a mistake with D1 and D2.
Now they are connected to the middle lug of P1.
But they have to be connected to the lower lug.
The middle lug and the upper lug should be connected to ground.