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PostPosted: Tue Aug 01, 2017 10:47 am 
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Just finished up the germanium boost, went very smoothly and seems to work flawlessly. I felt the bias pot needed to be turned all the way up, otherwise it sounded really farty to me, almost like speaker distortion.

I'm pretty happy with it, sort of feel that it's either on or off in the touch sensitivity department though - you really have to dig in to get it to break up unless you have it turned all the way up. Curious if anyone knows any good mods for this pedal to change up the sound, maybe reduce some of the fatness? I'd be willing to try any tweaks for fun.

As always, any feedback on my work is much appreciated!


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PostPosted: Tue Aug 01, 2017 11:22 am 
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If you have to run the trimpot at the extreme end of its sweep to get the tone you like best, you may benefit by replacing it with one of greater resistance range, i.e. a 250K. Dialing in a bit more resistance could improve the tone further. These NOS germanium transistors vary widely and some need more resistance than others to bias correctly.

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PostPosted: Tue Aug 01, 2017 3:04 pm 
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duhvoodooman wrote:
If you have to run the trimpot at the extreme end of its sweep to get the tone you like best, you may benefit by replacing it with one of greater resistance range, i.e. a 250K. Dialing in a bit more resistance could improve the tone further. These NOS germanium transistors vary widely and some need more resistance than others to bias correctly.


Awesome, I can totally do that! Is this the part you're talking about? I'd assume I select the 250k one? https://buildyourownclone.com/collectio ... ot3306trim


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PostPosted: Tue Aug 01, 2017 5:45 pm 
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terrible_soldering wrote:
Awesome, I can totally do that! Is this the part you're talking about? I'd assume I select the 250k one? https://buildyourownclone.com/collectio ... ot3306trim

That's the one.

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PostPosted: Tue Aug 01, 2017 5:49 pm 
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I love how the germanium transistor is plug and play. Any other ones I should try?


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PostPosted: Wed Aug 02, 2017 9:14 pm 
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You can always pick up another germanium transistor or two online. I would suggest dealing with a reputable seller who pre-tests their trannies, since the supply of good (i.e. reasonable gain and low current leakage) NOS germanium transistors continues to dwindle, though I have heard reports of some new production starting up recently. I'd stay off of eBay for these, since I've heard a lot of horror stories of bad product being passed as good. For reliable NOS Ge trannies, I'd recommend Small Bear.

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PostPosted: Sat Aug 12, 2017 10:05 am 
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duhvoodooman wrote:
If you have to run the trimpot at the extreme end of its sweep to get the tone you like best, you may benefit by replacing it with one of greater resistance range, i.e. a 250K. Dialing in a bit more resistance could improve the tone further. These NOS germanium transistors vary widely and some need more resistance than others to bias correctly.


So I removed the 100k trimpot and installed a 250k and I noticed that I'm able to dial it in way grittier with this one if I dime the trimpot and when I back it off, I seem to find a happier medium. I also bought a 500k to potentially try in the future, but I was curious if you could explain what exactly I'm doing to the circuit when I go from a 100k to 250k to 500k trimpot for example? Is this cutting and boosting the current to the germanium transistor?


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PostPosted: Sat Aug 12, 2017 10:34 am 
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I'm no theoretician when it comes to how transistors work, but it has to do with getting the bias voltage at the collector of the transistor within a certain range. Somewhere around 7.0VDC (assuming a 9.0VDC power source) is where the effect sounds best to most ears. The issue with achieving this bias voltage is that old production germanium transistors tend to be extremely variable, and the best ones have often been "cherry-picked" out of remaining stocks. So there is often a wide range of gain and current leakage found in these transistors, which affects how they bias. Consequently, you will sometimes need more resistance from the trimpot than the standard 100K version gives. At least, that's how I understand it. Perhaps someone with a stronger theoretical understanding can explain this in more depth....or correct me if I got anything wrong!

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PostPosted: Sat Aug 12, 2017 12:26 pm 
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duhvoodooman wrote:
I'm no theoretician when it comes to how transistors work, but it has to do with getting the bias voltage at the collector of the transistor within a certain range. Somewhere around 7.0VDC (assuming a 9.0VDC power source) is where the effect sounds best to most ears. The issue with achieving this bias voltage is that old production germanium transistors tend to be extremely variable, and the best ones have often been "cherry-picked" out of remaining stocks. So there is often a wide range of gain and current leakage found in these transistors, which affects how they bias. Consequently, you will sometimes need more resistance from the trimpot than the standard 100K version gives. At least, that's how I understand it. Perhaps someone with a stronger theoretical understanding can explain this in more depth....or correct me if I got anything wrong!



Thanks, that makes sense but definitely open to anyone who has anymore info. Sounds like it might even be worth trying the 500k trim pot, shame their a bit of a pain to remove and replace.


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PostPosted: Sat Aug 12, 2017 12:40 pm 
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Personally, if a 250K doesn't optimize it, I'd try changing the Ge transistor before I'd go to a 500K trimpot.

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PostPosted: Sat Aug 12, 2017 12:42 pm 
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Good to know, was thinking of ordering 2 or 3 different kinds from that website you shared with me.


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PostPosted: Sat Aug 12, 2017 12:48 pm 
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I'd be interested to know what voltage you're seeing on the collector of the transistor. Do you have access to a multimeter and know how to measure DC voltage with one?

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PostPosted: Sat Aug 12, 2017 9:58 pm 
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duhvoodooman wrote:
I'd be interested to know what voltage you're seeing on the collector of the transistor. Do you have access to a multimeter and know how to measure DC voltage with one?


This is a bit embarrassing, but I bought the BYOC starter kit and it came with a multi-meter, but the instructions are almost all in Chinese and I have no idea how to use it... any tips are welcome!


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PostPosted: Sun Aug 13, 2017 11:29 am 
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Nothing to be embarrassed about--we all need to learn new things sometimes. Heck, I didn't learn how to use one until I started building pedals when I was nearly 56! Who says you can't teach an old dog new tricks??? ;)

There are several useful videos on YouTube about how to use a multimeter. Just type "multimeter tutorial" into the YouTube search box and check out a couple of them.

For this particular test, you need to be able to measure DC voltage at a test point--in this case, the collector of the germanium transistor. Refer to the image below of the multimeter that BYOC sells. Here's what to do:

Power up the pedal with the rear cover removed. Remember that you need to have a cable inserted in the input jack for the circuit to be energized. Prepare your multimeter by inserting the black probe plug into the COM port and the red one into the port immediately above it. Turn the meter on and set the selector to 20 on the DCV scale. Ground the black probe by inserting it into one of the corner screw bosses of the enclosure--now you're ready to take a measurement. Touch the red probe to the collector of the transistor--that's the leg closest to the edge of the PCB, adjacent to the eyelet labeled "OUT". Hold it there for a few seconds until you get a stable reading (it's fine if it fluctuates by a few hundredths of a volt). That's all there is to it. If it's more than a few tenths of a volt away from 7.0V, adjust the trimpot while holding the probe in contact with the collector until you get it into that range. But also keep in mind that the final judge of the correct setting should be what sounds good to your ear...

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PostPosted: Sun Aug 13, 2017 9:18 pm 
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Awesome! The mulit-meter supplied to me was a bit different, but I got it working. So I measured the ranges and when I have the bias pot (250k trimpot) turned all the way down it reads 0.05 when I turn it all the way up it reads 6.35 and the sound I felt was the best by my ear was 4.75. This is using a 9V Fulltone noiseless wall-wort power supply (not switching).

This is fascinating any thoughts, it gets really gritty and almost fuzz like when I dime it to what turned out to be 6.35, which is why I had backed it off a more over-drive like 4.75.


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PostPosted: Mon Aug 14, 2017 8:34 am 
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Sounds to me like you've just got a germanium transistor that needs a lot of resistance to bias correctly. Nominal for the classic Rangemaster treble booster circuit is a fixed resistor of 68K. You're up to nearly 4 times that resistance and the collector is just getting into the "nominal" voltage range. But if it's sounding good to you around 4.75V, that's what to go by.

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PostPosted: Mon Aug 14, 2017 11:37 am 
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Sounds like it's time to try some other GE transistors.

Any you recommend starting with off of here? http://smallbear-electronics.mybigcomme ... gemasters/


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PostPosted: Mon Aug 14, 2017 11:53 am 
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The Texas, the Newmarket, or anything in the middle row should do the job. You don't want any of the NPN trannies or the ones sold in pairs, since they are for different versions of the pedal than you have.

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PostPosted: Mon Aug 14, 2017 3:51 pm 
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Cool, just ordered both of those, will see how this helps.


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