More Range Master questions

[1wahfreak]

I'm building a ranger master with an original OC44. It's a perfect piece, Hfe at 90 and leakage at ~50uA. I used the tuning methods described by RG by substituting 100K and 10Kpots respectively for the 68K and 3.9K resistors. When I measure the voltage at the collector I only got about 2.5V. So I tweaked the pots to get to 7.0V. So far so good, but when I disconnected the pots and measured them, they are both outside the range the RG states in his article. He said that if the pots are out side this range that I have a high gain trannie or a leaky one which is not the case. Does it really matter what the resistence is at those two points or just that the voltage at the collector is ~7.0V. It sounds pretty damn sweet the way it is but I just want to make sure it as close to the original as possible.

[R.G.]

It sounds pretty damn sweet the way it is but I just want to make sure it as close to the original as possible.

What will you do if "as close to original as possible" turns out not to sound as sweet?

Sound is a very personal experience, and your own personal ears are what matters there. Believe me, "original" is not particularly something to be pursued at the expense of good sound. About one in twenty real, no fooling, original fuzz faces sounded good. The hyperselected, tuned things coming out of the work on the web is far better than the originals.

So far so good, but when I disconnected the pots and measured them, they are both outside the range the RG states in his article. He said that if the pots are out side this range that I have a high gain trannie or a leaky one which is not the case.

So how far out are they? I'd like to calculate a bit with what you found with an hfe=90, 50uA leakage transistor that didn't fall in the range. Always possible I made a mistake.

My issue with changing the resistors too much is that is that changing the input resistors too much changes the input rolloff frequency, and that's where your treble boost comes from. This is no tragedy as almost everyone who builds one of these wants to tinker the input frequency a bit, but you have to know where you are to figure out where you're going.

Let us know what resistors you came up with.

R.G.

[1wahfreak]

First off I miss-marked my pot for the original reading at the collector. With everything at nominal settings I get 1.5V at the collector not 2.5V as previously stated.

If I leave the 68k at nominal, I get 645 ohms at the 3.9k while still maintaining 7.0V at the collector. I also lowered the 68k down to 40k just to see what happens and I got 324 at the 3.9k.

What will you do if "as close to original as possible" turns out not to sound as sweet?

I will probably keep this set up seems as how it sounds good, but I always feel like I want to start as close as possible to the original. Because most of us (me) don't have the originals we don't have a reference to start from. The sounds I'm currently hearing from my frankenstien pedal might not even be close to a Rangemaster.  Thanks for your input RG.

I really appreciate the forum here.  I never thought it would be this cool, or that people would be so helpful. I'm total addicted!!  Thanks guys! [/quote]

[R.G.]

First off I miss-marked my pot for the original reading at the collector. With everything at nominal settings I get 1.5V at the collector not 2.5V as previously stated.

If I leave the 68k at nominal, I get 645 ohms at the 3.9k while still maintaining 7.0V at the collector. I also lowered the 68k down to 40k just to see what happens and I got 324 at the 3.9k.

Wow. That's strange. Can I ask a favor - or a number of them, I suppose? Can you measure each resistor, including the fixed ones, and let me know what they measure? Also, could you check for DC coming out of the input/output caps?

Finally, could you check to see that you were mesuring between ground (which is the *positive* battery lead in this circuit) and the pins? And that you measure the power supply as -9V?

R.G.

[1wahfreak]

I'll see if I can spell this out so it makes sense.
I'm using GGG's PNP negative ground layout, so I thnk I was measuring right. Attaching the neg. lead to the "-" side of the battery and measuring with the positive lead.
The resistor (measured) values are 469k, 3.90K and 68.0k. (the 3.9k and 68k are the pots). Also using no pulldowns.
I'm going to take back my "mis-measured pot" statement from the last reply. It looks like one of my leads had a short giving the low voltage reading. This time I measure 2.345V at the collector. (2 out of 3 must be right)
I get 8.34V at the "out" side of the input cap.
I'm not really sure what is the "out" side of the output cap but I get 0.00V on the switch side and 1.103V on the pot side that is attached to lug #2 of the boost pot.
Supply is 9.48V.

Mike

[R.G.]

I'll see if I can spell this out so it makes sense.
I'm using GGG's PNP negative ground layout, so I thnk I was measuring right. Attaching the neg. lead to the "-" side of the battery and measuring with the positive lead.

Actually, that's 99% of your problem. Using a negative ground version of this circuit means that you are measuring voltages from what would be the power supply of the Rangemaster circuit at GEO. That means that you want a collector voltage of 2V, not 7V on a 9V battery.  With your 9.48V battery in the negative ground circuit, you ought to see maybe 2.2V on the collector. Try that.

What you call ground does make a difference.

R.G.

[Andy]

rg,   how do you check for DC?  do you take your scope and put the grounding clip on the circuit ground and simply touch the probe on the back-side of the cap?  or is there another way to do this?

I am new to using an oscilloscope

[R.G.]

When I'm looking for DC levels, I usually don't use a scope at all. I use a DMM. But yes, you clip the reference lead to circuit ground.

Where you decide "ground" is matters. That's the problem we're dealing with here - using a reversed ground arrangement has caused the DC voltages to read different from my original article, although there may be no particular difference when you pick "ground" to be the same as I did.

[1wahfreak]

Thank you R.G. U da man!!!