Hi, I've been building a '73 ram's head clone during the last two weeks and I just finished soldering everything but the switch and the led. To me it sounds like a whole gain stage isn't working properly. When I turn the sustain pot all the way up it sounds like its at minimum and if I turn it all the way down, it goes completely clean! I'm using this layout: http://effectslayouts.blogspot.com.es/2014/12/electro-harmonix-rams-head-big-muff.html (http://effectslayouts.blogspot.com.es/2014/12/electro-harmonix-rams-head-big-muff.html) replacing the components with the ones in this schematic: (http://www.bigmuffpage.com/images/schematics/KR_1973_V2_Big_Muff_FS36999_schem.jpg)
I've used two 15k resistors in parallel for R19 and R12 and I haven't put the 1M resistor which appears in the layout. Which component(s) could be the responsible for this if they weren't soldered well?
welcome to the forum, Rolan. do you own a multimeter?
you have three transistor amplifiers, all with the same resistor values. this means the transistor voltages will all be very close to the same. go thru with your meter, measure/record/post here the DC volts at the B-C-E of each, find where there is a discrapancy.
what's that? they all measure the same? well now you know it must be one of the interstage parts doing something silly. or your feedback diodes/caps aren't quite right.
also, post up some pictures of what you have built, copper side, parts side, and off board wirings, and we'll have a look at what we might find.
[edit :] oh, yes, now I see the unscrolled bit of circuit, and remember four transistors for a big muff, the last one w/ different voltages ....... silly me.
I've been out all day and I just measured all transistors with the multimeter.
Battery Voltage: 8,64 V
*Transistor names according to schematic (not layout)
Q4 C: 7.03 V
Q4 B: 0.550 V
Q4 E: 0.010 V
Q3 C: 6.84 V
Q3 B: 0.560 V
Q3 E: 0.010 V
Q2 C: 6.97 V
Q2 B: 0.550 V
Q2 E: 0.010 V
Q1 C: 7.16 V
Q1 B: 0.980 V
Q1 E: 0.430 V
I know Q1 has to be different from the others, and they all seem to match perfectly so i checked the diodes with the multimeter (diode testing mode) and they all say 1.2 V
Here are the photos of my build: https://drive.google.com/open?id=0B7D9iKLWiY8_LTA2U1JneVFncjA When i finish im going to mount the pots off board but its more comfortable like this for testing. I've also bought an oscilloscope online and should arrive on wednesday or so, so i should be able to tell better where is the problem. Thanks for the help :icon_biggrin:
Edit: Btw im using BC239 transistors
Since I'm tinkering with a BMP myself at the moment:
1. Are you REALLY sure there are no unwanted solder connections? The solder side of your build looks mighty crowded ... I thought I saw at least two iffy "neighbours" touching each other in an inappropriate way
2. The BC239 has a minimum Hfe of 120 - some say you should at least aim for 400 (e.g. 5088, 5089, BC549 etc.). But it should clip the hell out of the 239, too.
3. You sure that you haven't mixed up resistor values - most of all R10, R12, R19, R21 and R22?
Although your measurements aren't quite accurate (voltages & currents diverge from theoritical values but we may put the blame on your multimeter..) I vote for wrong R12/R19 values.. :icon_wink:
Those shield wires are making me nervous.
..... and because you checked the transistor pinout on your datasheet, you already know the transistors are all in barseackwards.
Quote from: duck_arse on September 11, 2017, 10:38:39 AM
..... and because you checked the transistor pinout on your datasheet, you already know the transistors are all in barseackwards.
As duck sorta already stated, the 2N5088 is an EBC @ 123, pinout while the BC239 is CBE @ 123 pinout. They are most definitely backwards and the main cause of your issue. I hate perf, vero, etc. So the back of that board frightens the hell out of me too. Swap your trannies around first and see what that gets you.
Quote from: duck_arse on September 11, 2017, 10:38:39 AM
..... and because you checked the transistor pinout on your datasheet, you already know the transistors are all in barseackwards.
Quote from: bloxstompboxes on September 11, 2017, 11:05:06 AM
As duck sorta already stated, the 2N5088 is an EBC @ 123, pinout while the BC239 is CBE @ 123 pinout. They are most definitely backwards and the main cause of your issue. I hate perf, vero, etc. So the back of that board frightens the hell out of me too. Swap your trannies around first and see what that gets you.
Yep, im so dumb i didn't worry about checking transistor pinout directions, it's my first build and pretty noob at soldering so some silly fails are justified :icon_rolleyes: The pedal sounds amazing now, just what i was going for, i may do the flat mids mod sometime cause i don't like my tone being so scooped. Thanks everyone for all the help! :icon_biggrin: :icon_biggrin:
if you want mids, you can replace R5 with a 100K pot
Why in the @#*%$ would anyone want to add mids on an all-time-classic mid-scoop pedal..?? :icon_mrgreen:
Schematic says R22 = 100 ohm. That's brown-black-brown.
I don't see those colors at on the Q1 on the left of your photo. I do see them on the other 3 Q though.
Did you miss out a part of sub a different value for R22?
come back, Rolan - you can't leave without first posting the good voltages you are now getting.
don't worry about backswarding the BC's on yr first build, there's people round here been handling them for 40+ years, still doing it.
I did the unspeakable and spliced the venerable ROG tonemender into where the standard BMG tone "control" should not reside. Lots of Parts, lots of violent over the top EQ fun