Just gonna through this out there.......
I've got an annoying problem while turning/adjusting the volume on ANY instrument!... or volume pedal... or acoustic pickup with a volume....etc,. Looks like a classic sign of a dirty/worn volume pot on the instrument etc,.OR a bad cord...but not so. It all started when I successfully cleaned the Master Volume pot and all others on my 1991 Tube Works RT-2100 MosValve+Real Tube OverDrive 100 watt Combo Amp. Concept and Design by B.K. Butler. I used a can of Deoxit Gold G5 spray. It worked GREAT! Noisy Crack POT SOLVED!! But not so fast grasshopper...Now it's developed this annoying glitch while adjusting ANY volume going in to the input ...either channel. I have switched the Master Volume pot out of the amp...no diff. Cleaned guitar pots...changed cords...different power outlets...tried ANYTHING with a volume...to no avail. Still got the problem. What could be taking the input signal and making noise ONLY when it is being adjusted with a volume pot? Any suggestion? I have soldering skills and can work a multimeter. By the way...the amp works perfectly normal on both channels. All amp pots are clean and no noise.
Signed, Baffled
You have DC at the preamp input jack.
To confirm it, set amp volume to 0 just not to hear hum or noise, plug a known good cable at the jack input and measure the other end of the cable, at the free/unplugged plug, between tip and body.
Use the muktimeter DC scale, start with the 20V one and then go down (2V , then 200mV) to see which one gives you the clearest reading.
Post results here.
PS: I *think* you are using the guitar straight into the amp, no pedals involved, are you?
Correct. Straight into the amp. On my multimeter ( which I've included a pic of ) I have a reading of 13.70 DCV at startup and slowly climbs to 13.99 DCV in approx 5mins.
We'd like a schematic of your amp. That is beyond the "normal" up to a volt that some amps create. That sounds more like a real issue. If the input stage is solid state, many have a pair of clamping diodes to the +/-15v rails, and if one diode goes leaky, your symptom can result. An open ground at the input could allow a floating condition, but then you'd have a ton of hum. If the input stage is transistor, a leaky or shorted input cap could cause this. Tube input? Hard to imagine it making 13v there.
I know!!! I saw the volt reading and said WTF??? That's why I included a pic of my volt meter so there's no confusion on what setting I'm using. Gotta go to work for the day now....I REALLY APPRECIATE you guys helping me out. Keep throwing the ideas out there. I'll check back later today......
Oh boy would I like a schematic too!!! Can't locate anything on the circuit.
Here is the schematic...
Wow! Thanks a million for the schematic!!!
1) thanks drgonz for the schematic :dbtu:
2) 13.7V DC??? OUCH !!!!!!!!!!
3) I see you are sleeping with the enemy :o
Don't get the full picture yet, but the schematic shows what looks like an "input in use" sensor circuit, not sure if it's some kind of mute or it enables some function, but there you have 2 x 22k resistors connected straight to jack ring pin leaf contacts and on the other end to "CA" .
Said ring pins are grounded if nothing is plugged in, you'll have current passing through the 22k resistors.
If you plug into any of both inputs, one 22k resistor gets open and you halve passing current; if you plug in both, you fully stop current there.
That can be detected for some function I mentioned.
The only "CA" I find (you might find others) is on the emitter of "Y" 2N5401 , to the right bottom of the tubes area, which is also connected to the power supply node "C+" , which happens to be .... +13.7V :trouble
Now those +13.7V shouldn't be a problem because if:
a) nothing is plugged in, 22k resistors get shorted to jack ring legs , so 0V there.
To boot, jack tip legs are also grounded, as an extra security layer.
b) you plug into 1 or 2 inputs:
the jack tip contact gets ungrounded, and signal gets into the preamp.
c) the jack ring contact also opens, current through 22k resistors stops, some function is triggered.
You have +13.7V 2 mm away from signal contacts, but it "SHOULD" be no problem, meager 13.7V can (should) not be able to jump 2mm of air or PCB material .
I guess either the jack is damaged, has bent leads, whatever, or resoldering shorted nearby contacts or leaf switches are worn or bent or PCB is contaminated , and now those 13.7V cxan contact the *audio* pins.
They travel backwards to your guitar and make a scratchy mess.
So I would replace those jacks, while out clean the PCB area very well, I'd use Isopropyl alcohol because it dissolves both grease and salts (Big Brother does not let you USA kids to buy 94% ethyl alcohol ;) ) and recheck that DC voltage dissapears.
This is what tip and ring means, applies both to plugs and to matching contacts in jacks:
(http://i258.photobucket.com/albums/hh245/amp_surgeon/trs-explanation.jpg)
By the way the amp schematic has tip and ring jack contacts drawn the wrong way, tip (wherev 68k resistor go) should be drawn the furthest away from the sleeve/ground contact, and ring between them ... as it physically appears in a plug.
And the input sensing circuit is also wrong: as drawn, whether 22k resistors are grounded or not , voltage at 2N5401 transistor does not change, since it comes straight from the nominal "+15V" OpAmp supply (actually +13.7V) called "+C".
Those errors make me lose trust in that schematic.
It may be close enough as a general idea but each part should be checked/matched with what's actually on the PCB.
Of course, the amp works or they wouldn't have sold so many but the schematic is iffy.
To: J M Fahey....wow I think you are nailing this. Funny you said this,...
"I guess either the jack is damaged, has bent leads, whatever, or re-soldering shorted nearby contacts or leaf switches are worn or bent or PCB is contaminated , and now those 13.7V cxan contact the *audio* pins. They travel backwards to your guitar and make a scratchy mess."
Because when I cleaned the amp pots with Deoxit Gold G5, I sprayed all pots on the PCB in their place. I had quite a mess and continued to spray other components like input jacks and tube sockets. Even tried to tighten up the tension on the two input jacks so the cord would fit more snug. Then I proceeded to blow all the excess spray off with an air compressor. Reassembled the amp and that's when the problem started. So...then I thought the spray might be contaminating the PCB. So I sprayed a product 70% Isopropyl Rubbing Alcohol mostly on the underside of the board and lightly brushed with a tooth brush. Also sprayed it on the pots and input jacks. I wasn't to sure about spraying the alcohol on the component side of the PCB so I didn't. Then lightly blew off and dried the whole thing with air compressor. Could I have damaged something? Or do I just clean it better?
You probably either bent a jack contact, or in spraying cleaner, some dirt wound up lodged in the contacts. No, your alcohol didn't hurt anything.
I have other input jacks I can try out on the input board by just soldering the replacement jack to the input board in a way that it bypasses original jack and still uses the resistors ( which I have checked out and are fine ) but like Fahey says the schematic seems to be wrong? Here's what I have, 3 wires,... Red (I) Black (G) Purple (CA). 1st what does Purple (CA) represent?
Hurray!!! I removed the channel 1 input jack from the input PCB. Installed a two wire input jack on the input PCB to the Tip/Red (I) and Sleeve/Black (G). All voltage is gone at instrument cord and PROBLEM SOLVED!!! So.....what did I just eliminate? I can't for the life of me see anything wrong with the 5 point input jack that I just removed. Here is the Amplifiers input jack features posted in the users manual:
INPUTS — Input 1: 0 dB. - Most sensitive input. Input 2: -8 dB. - Less sensitive input for Steel guitars and ex- tra-high output pickups. NOTE: Inputs have true active summing, therefore two guitars of any impedance may be summed together by using both inputs. It is also possible to use a "Y" cord to give even more gain. (Single guitar Y-ed into the two inputs).
Anybody? Will this setup that I just did work from here on out? Safely? Effectively? What features did I just lose? (if any).
Well, those powered 22k resistors were sent to the input for *something* .
I guess they might trigger some kind of electronic mute although that's not clear from the not_too_accurate schematic.
Suspect same as Enzo: when tightening jacks you bent some contact.
You may use the amp as is, with the simpler jacks, and if it works for you, fine, but the proper repair is to hunt down exact same model jacks and replace them.
Thank you all very, very, much! At least I know the problem was at the input jacks PCB.
One last question,... do you know what the (CA) Purple wire on the input PCB which goes to the main PCB is for? Basically 3 wires. Red(I) Black(G) and Purple(CA)
In the schematic:
I = input
G = ground
CA = who knows.
I think the schematic is drawn wrong. I do not believe the CA point from the jacks is connected right to C+. That would do nothing useful. Look at the drawing on the right, where CA is now. Transistor Y. Why not trace where CA goes and see if maybe it goes to the base of Y instead of the collector.
Just looking, I'd predict the CA is some sort of mute, and plugging into either jack defeats it.
:-\ Well......it's not the jack. Basically if I eliminate the Purple wire (CA) which I confirmed touches the Tip of the cord when cord is inserted and touches nothing when not,....the amp will work fine on a simpler two wire jack AND the original jack less the (CA) circuit. So the problem lies within that (CA) circuit? Correct? I tried to physically follow that circuit but got lost in the process to many times. (Seeing cross eyed now) :loco What next?... to keep the full features of the input jacks.
I'm going to try and describe what I see as the schematic of the input jacks:
When cord is inserted,
•Red(I) contacts Tip.
•Black(G) contacts 3 surfaces: 1-Sleeve 2-Ring 3-Becomes disengaged from Red(I) when cord is inserted.
•Purple(CA) contacts Tip also. (yes it's dedicated right to the tip)
Resistors:
68k inline with Red(I) Tip
22k inline with Purple(CA) Tip
Can anybody draw it? Is it different from what the schematic shows?
Also Enzo, I think I get what your saying about transistor Y. Isn't that the voltage amount that was showing up at the tip of my cord? Bad transistor?
If the schematic even suggests the real circuit, the I and CA do not connect directly to the jack, they connect through resistors. I is what should connect to the two tip contacts, but through 68k resistors. Those two rsistors cross connected through the two jacks is the same as the classic Fender input. You can verify this by plugging into each jack. Jack number two should be noticeably less loud, just like a zillion Fender amps.
I have no idea about wire color, for all we know it wasn't the same amp to amp. So follow the wire from I over to the main board. Does it go to a cap, and only to that cap? Schematic says 0.047uf.
And I suspect it is correct, but verify that G goes to the ground trace.
As to CA, are the two 22k resistors there on the jack board? Clearly using either jack activates the CA line. I remain convinced it is a mute. A mute keeps the amp quiet until something is plugged in. That would be the only feature of it. If you do not find it noisy with no instrument connected, then you already have the "feature".
But if you cannot visually trace the circuit, trace it as far as you can with certainty, and note a landmark on the board at the farthest point. Then try to trace it further. If you are not sure, use your ohm meter to verify if the next point really is connected to the previous progress. Zero ohms between two points, means they are connected. If we can find a connection from CA point to transistor Y, at least we can start from there.
AH, you just posted as I typed.
When you say connects to tip, are you finding the resistance of the 68k or 22k? Or are you seeing a direct connection.
Don't know what kind of jack it is, but are you saying that both live contacts in it BOTH touch the tip and not one for ring?
Is the jack soldered to a circuit board, or are the loose wires soldered to the jack direct? If wired, verify the contacts and cutouts have not been reversed.
The (CA) has the 22k resistors on each jack which contacts each jack Tip. The (I) has two 68k for both jack Tips. Checking ohms while the resistors are on the board, the 22k's read 22k. The 68k's read 34k. But the 68k's off the board read 68k each.
Correct. Both (CA) and (I) touch the Tip.
I've attached pics of the jack. Disregard the large Red & Black wire used for a simple 2 wire jack.
more pics
more..
Those jack switches look to be bent in a way that prevents the switching function to work properly.
Great...if it's that simple. Can you recommend a website where I can order replacements? And what type I should order? I can solder new ones on. It's worth I try
I wouldn't be considering the jacks at all but since I did fiddle with both of them in an effort to snug up the fit.
I think I might have found the culprit. Thanks to g1's remarks. Out here on my phone, pouring over the pictures of the disassembled jack, I can see that the (CA) contact is bent back which allows it to touch the Tip! I don't think it's supposed to! It should be in the (G) position until disengaged by the Sleeve of the cord!!!!
(I feel like Gene Wilder in Willy Wonka!!!)
I shall bend it back this evening to confirm.
The (CA) should never touch the Tip in the first place!!! Wahoooooo!!!!!!
So...you guys think I'm crazy? Or got it solved?
Crazy? ... no.
You have been told this countless times for the last couple days ::)
Note to self...DON'T "JACK" WITH AN ALREADY WORKING JACK!!! Especially a fairly complicated one!
Sorry guys. Thank you so much for your patience and help!
I feel the need to explain my stupidity. Cleaning the pots I can do and have done before. But when I decided to fiddle with the input jacks I had no idea that they were the type of muting jacks or whatever. Nor was I even familiar with that type of input jack. Little did I know the headaches and frustration I would create for myself by trying to adjust the tension by pushing on the tip and the sleeve tongs. Since the Jack is basically enclosed in plastic and soldered to the board the damage is not visible to the eye. Still, even when I removed the Jack from the board and looked inside I didn't understand why two tongs were touching the tip of the cord! Because of my lack of knowledge on what to look for in this type of input jack I just looked at it for hours on end. But when I finally posted a picture of what I was looking at, that's when "g1" said, "Those jack switches look to be bent in a way that prevents the switching function to work properly". What?...jack switches? Good lord! It was staring at me right in the face! Of course!...I pushed on that tong which bent that piece over which now touches the tip! BINGO! How stupid can I be!
Well, A picture is worth a thousand words. I know I would have never discovered this on my own.
Thanks a million to all of you! I definitely learned something.
Jeff O
Something else to learn. Looking at the second photo, and any other interior shots of the jack, the two contacts do not both touch the tip, unless they are bent. That is clearly a TRS jack, and the 22k resistors go to the ring terminals.
Thank you Enzo,... just completed the straighten of all bent tongs and used ohm meter to confirm proper positioning (and visual too) with and without cord plugged in. The amp is clean as a whistle (and down & dirty). Hummmm....TRS jack? Tip-Ring-Sleeve jack I'll remember that for sure!!! :)
Reading back......your post all makes sense now! I guess "I is just too slooooow :duh" Thanks for the "edumacation" J M Fahey.
And I did find those exact jacks online if ever needed. :dbtu:
Quote from: J M Fahey on August 17, 2015, 07:33:42 PM
1) thanks drgonz for the schematic :dbtu:
2) 13.7V DC??? OUCH !!!!!!!!!!
3) I see you are sleeping with the enemy :o
Don't get the full picture yet, but the schematic shows what looks like an "input in use" sensor circuit, not sure if it's some kind of mute or it enables some function, but there you have 2 x 22k resistors connected straight to jack ring pin leaf contacts and on the other end to "CA" .
Said ring pins are grounded if nothing is plugged in, you'll have current passing through the 22k resistors.
If you plug into any of both inputs, one 22k resistor gets open and you halve passing current; if you plug in both, you fully stop current there.
That can be detected for some function I mentioned.
The only "CA" I find (you might find others) is on the emitter of "Y" 2N5401 , to the right bottom of the tubes area, which is also connected to the power supply node "C+" , which happens to be .... +13.7V :trouble
Now those +13.7V shouldn't be a problem because if:
a) nothing is plugged in, 22k resistors get shorted to jack ring legs , so 0V there.
To boot, jack tip legs are also grounded, as an extra security layer.
b) you plug into 1 or 2 inputs:
the jack tip contact gets ungrounded, and signal gets into the preamp.
c) the jack ring contact also opens, current through 22k resistors stops, some function is triggered.
You have +13.7V 2 mm away from signal contacts, but it "SHOULD" be no problem, meager 13.7V can (should) not be able to jump 2mm of air or PCB material .
I guess either the jack is damaged, has bent leads, whatever, or resoldering shorted nearby contacts or leaf switches are worn or bent or PCB is contaminated , and now those 13.7V cxan contact the *audio* pins.
They travel backwards to your guitar and make a scratchy mess.
So I would replace those jacks, while out clean the PCB area very well, I'd use Isopropyl alcohol because it dissolves both grease and salts (Big Brother does not let you USA kids to buy 94% ethyl alcohol ;) ) and recheck that DC voltage dissapears.
This is what tip and ring means, applies both to plugs and to matching contacts in jacks:
(http://i258.photobucket.com/albums/hh245/amp_surgeon/trs-explanation.jpg)
By the way the amp schematic has tip and ring jack contacts drawn the wrong way, tip (wherev 68k resistor go) should be drawn the furthest away from the sleeve/ground contact, and ring between them ... as it physically appears in a plug.
And the input sensing circuit is also wrong: as drawn, whether 22k resistors are grounded or not , voltage at 2N5401 transistor does not change, since it comes straight from the nominal "+15V" OpAmp supply (actually +13.7V) called "+C".
Those errors make me lose trust in that schematic.
It may be close enough as a general idea but each part should be checked/matched with what's actually on the PCB.
Of course, the amp works or they wouldn't have sold so many but the schematic is iffy.
Inexperience does not always equal stupidity. Not only is this a TRS jack, but has 2 internal switches (normally closed), one on the tip, one on the ring. Thus the 5 pins.
The schematic representation for that jack would be diagram XII on the attached page.
And they get much more complicated than that. Switchcraft has a whole other page of more complicated type jacks, this is the "simple" page. ;)
Thank you g1, I feel a little bit better after looking at the Jack schematic page :-\
In case anyone is interested, attached is pg.2, with the more "complex" jack schematics.