Transistor type, which is bestest?

Tone-Bending electronic fuzz unit, harmonic generator with 20 second sustain.

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Transistor type, which is bestest?

Post by The Captain » Fri Dec 11, 2009 10:27 pm

Hmmmm okay, seems like a good a time as any to finally make some words about this topic and try and make sense of something.

The OC81D

The bestest evar, right? Jimmy Page used these, right? All the early Tone Benders had these, yes? No. Probably not, and no again. Yes the Mullard OC81D is a very cool transistor and I don't just mean for its mojo factor.
Good well kept examples are very nice to work with and by that I mean the specifications fall into certain pockets that make it a little easier to tailor for use within a MKII circuit. That said, so are many other Mullard devices. If we cut through the shit the OC81D’s desirability really is a mojo thing that has bloomed on the internets over the last few years. It does not guarantee anything. You could quite easily assemble a MKII circuit with OC81D's and it could sound like total dog shit. If the specs ain't right and the thing is not put together in a certain way all you really have is some magic numbers.

I've done my fair share of placing the OC81D on a little throne over the last few years. Its cool shit right, there is no denying that. It is a rare part to obtain but certainly not the rarest, green jacket OC82D anyone? The original Vox and the Rotosound MKII's that used the OC81D's do, on whole, sound very good indeed. So, we can say that the OC81D has it going on but it’s not the be all and end all of getting a MKII circuit to sound good.

Old shit is old

As I understand it right now Sola Sound produced the MKII with only three transistor types. The Mullard OC75, IMPEX S3-1T and the Mullard OC81D. The main bulk of the MKII's, this includes the variants made for other companies, used the OC75's. I've as yet never seen a Sola Sound badged MKII with anything other than OC75's and have only seen the IMPEX'S in the (prototype?) Vox MKII and the Marshall Supa Fuzz. The OC81D only in the Vox MKII and the Rotosound's. Just saying that as it may be of interest and it was rattling around in my head.

Does exactly what is says on the tin?

So, what I was actually getting too. Transistor type and tone. Does it guarantee anything? The short answer would really have to be no. Of course certain transistors were designed for certain jobs. Sola Sound obviously used the Mullard OC75 as a staple for a good reason. It’s a high gain pre-amplifier. Makes sense right? Its specification makes it ideal for use in an audio circuit and would offer a good all round performance.

You can take a random OC75 MKII and a random OC81D MKII and they could sound quite different. Not hugely, it’s still the same pedal and circuit at the end of the day, but they could sound and behave differently. This has to be the different transistors at play right? So what I just said is the ramblings of a mad man then? Well I'll still say no. We could also take two OC81D or two OC75 MKII's and they could sound different. We could also take two MKII's and do a blindfold test and you may think because one does a certain something and the other doesn't do it as well or does it differently that one is one and one is something else but they could in fact both be packing the same transistors. Confusticated yet?

Okay a little example. I’ve got 8 original Sola Sound MKII's here right now. Pretty much one of everything. Small board Sola Sound MKII, A Rotosound, couple o' Vox MKII's, a bunch of Supa's and even a transitional MKII in a MKI.5 box. It’s a pretty bad ass cross section of what was made from '66 to around '68 MKII wise. Here's the thing. They all have OC75's but they do not all sound the same. The Rotosound gates like fuck with some insane raspiness on the go and offers you little in the way of clean up. The small board Sola is as smooth as butter, cleans up way easier and slurs into feedback quite readily.
But, with the above gibberish said certain transistors will and do display certain characteristics. Come on, man! You're going around in circles here. No, no, I just wanted to emphasize that its not a clear cut case of chalk and cheese from one to transistors type to the other. An OC75 does not always guarantee mucho rapsiness....and so on.

We need an anchor here so I'll throw something into mix for that purpose. This only relates to the original MKII's and what I hear. These are also the extremities that I hear. As in, at the most extreme I'd say an OC75 could be gated. Very basically....

Mullard OC75 - Compressed, gated, raspy, dense.
Mullard OC81D - Open, fluid, soupy, dynamic.

The little thing up there with the IMPEX is to note that these kinda sit squarely in the middle. These things are spooky cool. The few IMPEX loaded MKII's I've seen are really awesome sounding pedals. One in particular was actually my all time favourite MKII. The behavior of the Attack control was the main thing I wanted to incorporate on the new Sola Sound models. These are based upon those IMPEX loaded MKII's. Oh, I'll quickly mention that nature of the OC81D seems relates to any driver device. OC78D, OC82D etc.

The Conclusion

So the type of transistor does bring something into the mix but I personally think that the quality and condition of the parts, gain selection, biasing, understanding the biasing, understanding the circuit and having some kind of handle of the nature of the original circuit is far more important. Which I why I say no, transistor type does not guarantee anything especially Rock God like status or sonic bliss.


So, where do these final D*A*M MKII's fit into the picture? AC125's an all....what's all that about? Without going on to much longer. These are the last D*A*M MKII's but the first made as a 'Tone Bender' I wanted to go out using that name for one because I own the trademark for it, and two I'll have made close to 400 MKII variants over the last few years and wanted to leave at least a couple of D*A*M Tone Benders out there.
I have been into the idea of the 125's for a while. I made a bunch of hi-gain and bass MKII's with em before and they were pretty cool and I wanted to make these more of a 'D*A*M' pedal than a replica so seemed a good candidate. I also wanted these to be a different creature to the Sola Sound pedals I'm making. I guess on the above reference thing you could place the AC125 between the IMPEX and the OC81D. Angry soup would be a good way of putting it. I guess it’s also a culmination of the research I've done over the past 5 years on the original Sola Sound pedals. The last as it were.

Shit! That was a little long winded. Anyways, for what its worth that's my take on this transistor shit at the moment. btw - this only relates to the above mentioned transistors within the MKII circuit.

I surely earned myself a drink after all that...
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Post by Moods » Fri Dec 11, 2009 10:57 pm

Great read Cap. Lots of good education in there. I don't know shit about whats what with tranny's (unless they are in an amp) :hihi: Thanks for the clarification. I just listen to 'em fuzzes and go from there. I want Philips Impex!

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Re: Transistor type, which is bestest?

Post by Austintrax » Sat Dec 12, 2009 12:50 am

Hey, thanks for takeing the time for that Dave ...good stuff :tu:

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Re: Transistor type, which is bestest?

Post by JP30 » Sat Dec 12, 2009 2:14 am

I have one of those 125 hi gain MKII from last year.

my bestest MKII ever. I honestly like it better than OC75 now.
more hair than OC75.
mine does not clean up as good at full tilt and it's bit gated, but I roll off attack a little and it get's smooth yet texture rich gremenium fuzz.

you all gonna love it. I found a few MKII clones that does D*A*M OC75ish sound, but never 125 .. yet.

((that said, if any of you want to trade my OC75 to your 125 let me know. :hihi: ))
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Re: Transistor type, which is bestest?

Post by garyrogue » Sat Dec 12, 2009 5:05 am

Yes a very good read and it is what is contained in your conclusion that is the essence.
thanks for sharing your thoughts
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Re: Transistor type, which is bestest?

Post by psycho*daisies » Sat Dec 12, 2009 5:26 am

The D*A*M Tone Bender™ MkII :chaos:

now, that has mojo written all over it!


cheers, Dave
a great read, as always
this is an exciting time to around here...history in the making
Last edited by psycho*daisies on Sat Dec 12, 2009 2:41 pm, edited 1 time in total.
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Re: Transistor type, which is bestest?

Post by Bobby DEE » Sat Dec 12, 2009 6:54 am

GREAT post david.......very informative, and great to read something that detailed from one of a HANDFUL of people on the planet who knows transistors THAT well.


the art of working with vintage transistors is becoming a lost, esoteric art. thank you for keeping the flame alive!
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Re: Transistor type, which is bestest?

Post by cubba » Sat Dec 12, 2009 7:22 am

Like the guys said here Dave,
that was a great read and thanks for taking the time to jot it all down!
To date I've tried 3 of your D*A*M MKII circuits.
One had 3 OC75's and two having a trio of OC81D's.
They all sounded pleasantly similar to each other,
which is a good thing since when one invests in a D*A*M MKII
it's nice to know you are getting a certain level of quality and consistency of tone from it.
But... each also sounded different from the other.
The OC75 had a little less gain and less cleanup ability that the one OC81D unit had,
while the other OC81D had even more gain, less cleanup,
but an incredible, forward sounding midrange that any other MKII could only dream of having.
The last "MKII" I heard was an original Marshall Supa that was a fucking animal!
Look out when you step on that one, it can take you places only a MKI can,
but still with that characteristic MKII sound.
So in the end (and with my somewhat ltd. experience) I agree with your conclusions.
It is mostly about the builder's ear and how they can translate those conceptions of tone into reality,
via the pedal, that matter most.
You can have the right components but it's a crap shoot if you don't acutely know what you're doing with them
in order to get the magic out of the device.

Vive la AC125!!!
What gets me is all the tweaking,
just crank that bitch and be done with it! -- duende
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Post by Philip » Sat Dec 12, 2009 7:48 am

Wow, cool read!

Thanks for taking the time to type it all out!

A big thanks should also go out to folks like Graham and Stu etc for loaning you their rare pedals.

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Re: Transistor type, which is bestest?

Post by Philip » Sat Dec 12, 2009 8:03 am

The Captain wrote:Very basically....

Mullard OC75 - Compressed, gated, raspy, dense.
Mullard OC81D - Open, fluid, soupy, dynamic.

All things considered, it's most likely 0C75's(possibly an early small board version!?) that Mr James Page has in his MKII(s).

The branding - Sola Sound MKII Professional on his pedal, the sound - Compressed, gated, raspy, dense etc. Also, I think those early small board versions don't have the inupt cap thingie which stops MKII's from working with Vox/crybaby wahs.

Anyone ever seen an actual Sola Sound MKII Professional with anything other than 0C75's?
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