OC 44 biasing in Rangemaster (and other minutiae)

[SCP]

I wish this was to contribute, but again it's to ask. Though I guess expert answers become someone else's (and mine of course) gainings. As it's often said, check the forum, someone has asked that before... I received a Mullard OC 44 from Small bear today (for a Rangemaster project). I read in a few postings here that the bias point that some of you prefer is not necesarily what R.G. Keen suggests (6.6 to 7.2V). My question is:
Small Bear's transistor says that Re and Rb1 for my specific device ought to be 3K9 and 56K for it to bias according to R.G Keen. How detrimental to the project would it be for me to use nominal 4K7 and 68K instead? out of the question? no big deal? In other words, how delicate are these numbers. Also, would using nominal values bias my transistor closer to what some of you say you prefer? And lastly, please understand that I don't understand much about this as I wished, that I have with me the resistors in their nominal values and would like -if it's posible- to use them (ie not wait for the suggested ones to arrive should I order them so that I can build this thing in the next few days and use it in a very nice concert in which I have wanted to 'inaugurate' the clone), and that I ask humbly: please bear with me if my question has missused technical terms. And one more small question: How have any of you attached a terminal strip to the enclosure?? Thanks and more thanks to any help
Sebastian

[caress]

not knowing the sonic significance of this change personally, i think it would probably be in your best interest to simply breadboard the circuit, try the different values and come to your own conclusion about how it sounds.  the "suggested" range, in this case the bias point, is a general and possibly historical(?) preference, but certainly not what's right for everyone.  you might like it a little under- or over-biased, darker or brighter, etc... than the next person...  i know this is pretty obvious and it didn't really answer your question, but i think it's important to remember with this effect among others.

[hellwood]

oh, well the last guy beat me to it and said pretty much the same thing:
start on a breadboard. use trimpots to bias and when you like what you hear, WRITE DOWN ALL OF YOUR MEASUREMENTS, then see how close you are to RG's #'s. then you can try it w/ the suggested bias voltages and if you dont like it you can put it back to where you had it.
next , yank the trimpots and measure them and get the closest resistors you can to match your results, then commit to solder. done!

[frankclarke]

Assuming Small Bear has breadboarded it for you, you can parallel standard value resistors to get Steve's suggested values. Try it with the standard values, it will probably work. There is no absolutely correct biasing value for the Rangemaster. R.G's method will give you more consistent results if you are building more than one.

[Solidhex]

Yo, if its really eating you up just build it with the 3.9k and put a 100k pot for the 68k. I don't find an external bias on a Rangemaster as "fun" as the one on a fuzz face but hey...then you can always let your ears be the judge.

--Brad

[SCP]

Thanks a lot for the responses, they're really very helpful. I am still not very clear as to what aspect of the sound does the biasing affect. My guess is that the amount of added 'color' or distortion of the transistor varies with the Bias. So if my thinking isn't too off, then higher resistor values to bias the transistor mean that the effect of the transistor on my sound would be more subtle? Is my thinking somewhat accurate? Then, external Bias would somehow increase/decrease amount of distortion added by the thing, and since it's much less about distortion than a fuzz, the less fun it is?, meaning, the less noticeable or dramatic? Thanks a lot again. Also, How has any of you attached the terminal strip? screws? glue?
Gracias
Sebastian

[hellwood]

I am still not very clear as to what aspect of the sound does the biasing affect.

How has any of you attached the terminal strip? screws? glue?
Sebastian

the bias is required to get the transistor to work or not work. without getting scientific, its usually the difference between a gated honky barky broken sounding pedal or one that has sustain and behaves the way it should.

teminal strip? im assuming you are referring to the pc board. some people use stand-offs but i use foam and cut it perfectly to suspend the components so they cant short.

[DougH]

Here's an idea to try. If you have a breadboard, wire the circuit up. Then in place of the 56k, put a 33k in series with either a 50k or 100k pot. Hook the wiper to the 33k and one of the end lugs to 9v (where the other end of the 56k goes). Now you can adjust the bias with the pot and find the setting you like the most. Once you find it, pull the pot and measure the resistance between the wiper and the end lug that you used. Add 33k to that, and find a resistor that is close to your final value. Then use that resistor instead of the 56k.

Remember that adjusting that resistance will also affect the cutoff frequency of the high pass filter on the input. That frequency is determined by the parallel combination of the two base resistors and the size of the input capacitor. So if you reduce the resistance from 56k significantly, it will raise the cutoff freq of the filter and it will sound "thinner". You can compensate for this by trying a bigger input capacitor. And vice versa...

Have fun!

[SCP]

Great ideas, you guys made my project more ambitious and interesting. Thanks a lot.
I literally meant terminal strip, as opposed to PC board. It's the old fashioned way or something. Not quite sure, but it's described in R.G.Keen's article. The strip comes without screws or anything, so I am just wondering if people using them drill little holes to screw the terminal strip to the enclosure.
Thanks again
Sebastian

[hellwood]

I literally meant terminal strip, as opposed to PC board. The strip comes without screws or anything, so I am just wondering if people using them drill little holes to screw the terminal strip to the enclosure.
Thanks again
Sebastian

JB weld