Made a Rangemaster clone, and need some help.

[johnny pop]

Hi, First post here.
I built an old school Rangemaster clone from my parts stash today.
I wired it up using a terminal strip. Used a Mullard OC44 transistor with the yellow dot warhead.
Used carbon comp resistors, and all other parts with correct values. I also used the old on/off switch instead of the stomp box switch.
So this is a table top unit rather than a stomp box.

So I plug it in and it sounds great! But when I quit playing, there is an ongoing crackling. So,I go grab a bite, come back later and plug back into
the RM clone. No more crackle!? Just the somewhat normal Hissssssss.  Later still, I plug it in again, and the crackle is back!?!

So I'm wondering, is it the carbon comps? the transistor? a cap? maybe the layout?
I would like get rid of the crackle, and the hisss is louder than I would like.

Any of you pro builders have a tip or two?

Thanks.

[LucifersTrip]

that actually sounds like a leaky transistor...or bad solder joint.

[johnny pop]

that actually sounds like a leaky transistor...or bad solder joint.

Thanks,
I'll check that tommorrow.

[LucifersTrip]

that actually sounds like a leaky transistor...or bad solder joint.

Thanks,
I'll check that tommorrow.

i'm betting on the leak...a leaky one will cause hisssss, shhhhh, or breaking up crackle like you described. a bad solder connection prob won't cause hiss.

[Strange]

Did you bias the transistor? Using the 'correct values' of the RM circuit (3k9 and 68K) are not necessarily going to dial that transistor in for you. If your transistor is not biased propely it could easily be your problem.

RG has written the gospel on many topics - the Rangemaster include.

[Strange]

I know it is a dead horse, but metal film resistors could not hurt to clear up some of that hiss.

[darron]

Strange is spot on.


I've made lots of circuits like the rangemaster with PNP germanium transistors similar to your OC44s


I use a bias trimpot and find there is a range where i can get a rolling crackling noise which can also come and go a little bit (maybe with temperature or 'warming up' the transistor?). With a trimpot I can avoid that area and also find the quietest area with optimal output.


How do I adjust bias? The 470K and 68K resistors between +/- form a voltage divider making a DC voltage. These nearly add to 500K together so I use a 500K trimpot with +/- hooked to the outside lugs and the wiper connected between the input cap and Q1. This does the same thing as the two resistors but lets you change the bias voltage without changing the input impedence.



Hiss though... If you can work out a way to make the GE rangemaster less hissy let me know ASAP! Other than using low leakage, high quality transistors...


Edit: Oh! and don't cheap out on the trimpot! Use the best quality one you can find, like a cermet sealed multi-turn one... It seems like the cheaper ones have been a source of aditional noise for me in the past. All the tracks in them are carbon after all and inject DC straight onto your signal.

[Strange]

How do I adjust bias? The 470K and 68K resistors between +/- form a voltage divider making a DC voltage. These nearly add to 500K together so I use a 500K trimpot with +/- hooked to the outside lugs and the wiper connected between the input cap and Q1. This does the same thing as the two resistors but lets you change the bias voltage without changing the input impedence.



Hiss though... If you can work out a way to make the GE rangemaster less hissy let me know ASAP! Other than using low leakage, high quality transistors...


Edit: Oh! and don't cheap out on the trimpot! Use the best quality one you can find, like a cermet sealed multi-turn one... It seems like the cheaper ones have been a source of aditional noise for me in the past. All the tracks in them are carbon after all and inject DC straight onto your signal.

Neat - I am going to try your biasing method out. What difference do you hear in the circut as the impedence changes? I have been satisfied so far by starting out using RGs method and placing a 100K trimmer in place of the 68K resistor and biasing to -7V. From there I adjust with my ears. It works but I will definitely try your method out if that impedence issue makes an audible difference.

[darron]

well. the way that i was talking about shouldn't really change the impedence i ment.

i haven't tried R.G.'s way but it sounds like that's the same principal, but will give you less range to play with. it will probably give you ranges that are all useable though unlike the way that i do it. i use the 500k pot because it eliminates one resistor too, so no need to complicate things.
'

how does it change? here's the sort of range that i find from end to end:


NO signal   >   quiet signal and noisy   >   loud optimal volume signal and noisy   >  loud optimal volume and less noise (no rolling noise any more at least)     >    starting to missbias (maybe farty/splattered and/or clip depending on setup) but noise at lowest point    >      volunme dropping    >    no signal.

[Strange]

I think your method definitely provides a wider range. RGs method - when employed by yours truly - seems to give a range of nothing - useable - minorly tweakable - useable - nothing. There seems to be little of the misbiased sounds available. I usally stick with a 3k9 or 4k7 resistor whereas RG specifies a 10K pot along with the 100K. With the trannys I select there seems to be no need to use both trimmers as I can dial it in pretty quick at +/- 7V.

[Strange]

+1 on using a solid trimmer. The extra control is worth it alone.

[johnny pop]

Strange is spot on.


I've made lots of circuits like the rangemaster with PNP germanium transistors similar to your OC44s


I use a bias trimpot and find there is a range where i can get a rolling crackling noise which can also come and go a little bit (maybe with temperature or 'warming up' the transistor?). With a trimpot I can avoid that area and also find the quietest area with optimal output.


How do I adjust bias? The 470K and 68K resistors between +/- form a voltage divider making a DC voltage. These nearly add to 500K together so I use a 500K trimpot with +/- hooked to the outside lugs and the wiper connected between the input cap and Q1. This does the same thing as the two resistors but lets you change the bias voltage without changing the input impedence.



Hiss though... If you can work out a way to make the GE rangemaster less hissy let me know ASAP! Other than using low leakage, high quality transistors...


Edit: Oh! and don't cheap out on the trimpot! Use the best quality one you can find, like a cermet sealed multi-turn one... It seems like the cheaper ones have been a source of aditional noise for me in the past. All the tracks in them are carbon after all and inject DC straight onto your signal.

Wow! Thanks Darron, that was the deal! I dialed it in with the 500k pot. Then I measured the resistance on each side of the pot and went through a bunch of
resistors to find the values I needed.

One other question I have.
I tried another OC44 in the circuit and got nothing anywhere on the 500k sweep. I measured both OC44s with a mulimeter (base to collector and base to emmiter) The working one
read out at 9 ohms, the non working one was only .5ohms.

I don't know much about this stuff, but I would hate to throw out an OC44 if it can be used.

[darron]

ahm.. i've never measured them that way?


well... i just pulled out some yellow dot ones to give it a go. they seem to read between 3.6k to 4.2k from base to collector and base to emitter.

[Toney]

 My quick way is simply to leave the standard 470/68k as is and replace the 3.9K a 5k trimmer.
Dial the collector voltage in. Done.

I like your pot trick though Darron - guess you could tack a 39k resistor on to the "high" end lug for even more precision, then replace with the appropriate resistors.

[johnny pop]

ahm.. i've never measured them that way?


well... i just pulled out some yellow dot ones to give it a go. they seem to read between 3.6k to 4.2k from base to collector and base to emitter.

Well, yeah, But I have no idea what i'm doing
What is the proper way to measure these?  I'm wondering if my other OC44 can still be used?

[Toney]

This is your best bet.
http://www.geofex.com/Article_Folders/ffselect.htm

[Strange]

To go with Toney's post, here is RG's gospel on the Rangemaster:

http://www.geofex.com/article_folders/rangemaster/atboost.pdf

[Strange]

My quick way is simply to leave the standard 470/68k as is and replace the 3.9K a 5k trimmer.
Dial the collector voltage in. Done.

Same, but I like to swap the 68K with a 100K - I find the 5K trimmer in palcement of the 3k9 doesn't give you the range and control the 68K/100K swap affords.