not so sure about r109 myself..... it's the collector load for q5, and the collector voltage on q5 is correct. i'm leaning more towards r105/103 which are the feedback divider to the inverting input of the diff amp, or c56 which provides local negative feedback to the + input of the diff amp
R103 reading 11.4k, R105 reding 122k all within range.
Again I played around wtih R105 and R106, I can't get the voltmeter to get high, it start off at 20k and then it is stuck at around 33k and slowly moving up 0.1 k at a time. But when I desoldered the resistor from the PCB it reads a perfect 122k on the voltmeter.
I also decided to give the amp another try tonight, had it hooked up to the system. It seems that I have to turn the volume a little louder than before until start to distort, about 60%. A little better than before... Or maybe it was my imagination.
Again, at lower volume and mono the amp sounds totally awesome! The very second I turn it up to 60% it sounded like my left speaker had blown up.
Thanks for everyone's help so far. Hopefull we will get to the bottom of this soon.
Again I played around wtih R105 and R106, I can't get the voltmeter to get high, it start off at 20k and then it is stuck at around 33k and slowly moving up 0.1 k at a time. But when I desoldered the resistor from the PCB it reads a perfect 122k on the voltmeter.
I also decided to give the amp another try tonight, had it hooked up to the system. It seems that I have to turn the volume a little louder than before until start to distort, about 60%. A little better than before... Or maybe it was my imagination.
Again, at lower volume and mono the amp sounds totally awesome! The very second I turn it up to 60% it sounded like my left speaker had blown up.
Thanks for everyone's help so far. Hopefull we will get to the bottom of this soon.
Mr. p-car said:
You are sitting in front of a piece of equipment, that can be used as a simple signal generator: Your computer.
Just found this link:
Signal generator
Maybe it's of some use.
Happy new year, and happy huntin'
Ebbe
Ok guys, after a 2 hours learning curve I finally sort of figured out how to get a wave on the scope!!
"My temporary work bench.... family dinning table"
In any case, I was able to use the idea posted by es44 and was able to find a signal generating software that utillizes the PC's sound card to generate a range of frequencies.
http://www.e-dsp.com/software-functionsignal-generator/
So I connected my notebook's headphone output to the RCA input of the AMP and made sure that the AMP switch is set on stereo mode and the gain is turned all the way up. And started to trace the signal line according to the schematic's dark line.
Basically the dark highlighted line follows the path of the transistors all the way to the output.
Here is a picture of the first transistor Q1 and Q2 right before the signal enters transistor, top wave is left channel, bottom wave is the right channel
This is what the signal looks like after the Q1 and Q2
This is what the signal looks like after the Q5 and Q6
So I guess the problem is the Q5 transistor?
Q5 calls for a Si PNP transistor, the only one I was able to get was a NTE187 T-PNP Si, General purpose output, which is flat unlike the original half circle transistor and also has a little metal tab heat sink things on there. Can I use this transistor instead?
Almost there!!!
While I was going at it with the digital camera, here is my temporary equipment setup...
My MIT terminator bi-wire
My Counterpoint tube preamp
Thank you guys very much for sticking around with me on this
"My temporary work bench.... family dinning table"
In any case, I was able to use the idea posted by es44 and was able to find a signal generating software that utillizes the PC's sound card to generate a range of frequencies.
http://www.e-dsp.com/software-functionsignal-generator/
So I connected my notebook's headphone output to the RCA input of the AMP and made sure that the AMP switch is set on stereo mode and the gain is turned all the way up. And started to trace the signal line according to the schematic's dark line.
Basically the dark highlighted line follows the path of the transistors all the way to the output.
Here is a picture of the first transistor Q1 and Q2 right before the signal enters transistor, top wave is left channel, bottom wave is the right channel
This is what the signal looks like after the Q1 and Q2
This is what the signal looks like after the Q5 and Q6
So I guess the problem is the Q5 transistor?
Q5 calls for a Si PNP transistor, the only one I was able to get was a NTE187 T-PNP Si, General purpose output, which is flat unlike the original half circle transistor and also has a little metal tab heat sink things on there. Can I use this transistor instead?
Almost there!!!
While I was going at it with the digital camera, here is my temporary equipment setup...
My MIT terminator bi-wire
My Counterpoint tube preamp
Thank you guys very much for sticking around with me on this
I troubleshot an amp with similar problems. A big suspect is ANY coupling caps above 1 uf, so C53, C54 which are 10 uf caps are suspect. At some point in time, I would replace them with Blackgate 60099 from our advertiser www.partsconnexion.com. Thay are 10 uf 50 V non-polar caps. An ohmeter MIGHT show something. Might not. Even if they were replaced, I'd still suspect them.
The mono thing is a clue, which makes me believe it's pre-amp related.
Ypu can lift a lead on these caps and cross the channels with a piece of wire and see if the problem flips channels. If it does it's in the input section. If it doesn't it's later.
The mono thing is a clue, which makes me believe it's pre-amp related.
Ypu can lift a lead on these caps and cross the channels with a piece of wire and see if the problem flips channels. If it does it's in the input section. If it doesn't it's later.
Anatech,
Now, I am confused. If you look at my picture of the incoming signal rigth after the RCA inputs, it looks like the scope is displaying a pretty consistent clean signal. Maybe not???
Here is another picture of the measurement after Q5 transistor (Top is the left problem channel, bottom is the working right channel)
OK, so this point I figured what the heck I will just replace the Q5 and see if that does the trick, nothing to loose.
There were a variety of Si PNP transistors at Fry's, so I picked up 3 of them.
T-PNP, Si Low noise, High gain AF Preamp
T-PNP, Si Audio Amp, driver
T-PNP, Si Darlington Amp, Preamp
Which one would you guys recommend that I use as the replacement?
Now, I am confused. If you look at my picture of the incoming signal rigth after the RCA inputs, it looks like the scope is displaying a pretty consistent clean signal. Maybe not???
Here is another picture of the measurement after Q5 transistor (Top is the left problem channel, bottom is the working right channel)
OK, so this point I figured what the heck I will just replace the Q5 and see if that does the trick, nothing to loose.
There were a variety of Si PNP transistors at Fry's, so I picked up 3 of them.
T-PNP, Si Low noise, High gain AF Preamp
T-PNP, Si Audio Amp, driver
T-PNP, Si Darlington Amp, Preamp
Which one would you guys recommend that I use as the replacement?
Sine waves look like this:
http://en.wikipedia.org/wiki/Sine_wave
What's the p-p value of the output from the sound card which is the same as "Right after the RCA's", right? This is what your showing. right?
Lower the volume of the sound card until you get a sine wave on the scope.
Use no more than 1 V p-p for starters as an input to the AMP. Trace this signal through the amp to the speaker on the good channel. Then and only then can you start turning up the gain on the AMP and/or sound card.
What you are seeing is "Clipping" which isn't good for a lot of things: ears, AMPS or speakers. That top signal that your showing is exibiting "Ringing". That's not good either.
Reminder that measured DC values are usually with NO SIGNAL APPLIED! unless otherwise noted.
http://en.wikipedia.org/wiki/Sine_wave
What's the p-p value of the output from the sound card which is the same as "Right after the RCA's", right? This is what your showing. right?
Lower the volume of the sound card until you get a sine wave on the scope.
Use no more than 1 V p-p for starters as an input to the AMP. Trace this signal through the amp to the speaker on the good channel. Then and only then can you start turning up the gain on the AMP and/or sound card.
What you are seeing is "Clipping" which isn't good for a lot of things: ears, AMPS or speakers. That top signal that your showing is exibiting "Ringing". That's not good either.
Reminder that measured DC values are usually with NO SIGNAL APPLIED! unless otherwise noted.
"Lower the volume of the sound card until you get a sine wave on the scope."
Turn down the level on the generator until it doesn't clip. This amp can be driven into clipping with 0.5V RMS.
"Reminder that measured DC values are usually with NO SIGNAL APPLIED! unless otherwise noted."
I would think that since the preamp board is class A that the DC voltages wouldn't change.
Turn down the level on the generator until it doesn't clip. This amp can be driven into clipping with 0.5V RMS.
"Reminder that measured DC values are usually with NO SIGNAL APPLIED! unless otherwise noted."
I would think that since the preamp board is class A that the DC voltages wouldn't change.
Please do not use NTE or ECG brand transistors. a suitable transistor can be found and will perform better.
As mentioned I would also check the tube preamps output. Switch channels on the amplifier and see if the problem follows. Its not uncommon to have a DC problem on the output of a tube preamp.
NTE. ECG, and SK transistors are all "replacement" transistors, and intended for general purpose repair use. they are suitable for troubleshooting, or a "must have it fixed now" repair. but for high quality audio, i wouldn't use them unless it were an emergency (such as a band needing their crown amp fixed for a gig that night).
Hi unclejed613,
I normally stocked the proper semi's for band gigs. I always had enough to do matched sets on a channel. Same for popular signal transistors drivers and TO-126 types.
Now I don't have to do this (having sold the shop), but it's still nice to have them. You only need to stock the larger ones in TO-3 and TO-3P these days along with MJL1302 and it's compliment.
I don't see any reason to use those NTE / ECG / SK mystery parts. If the band is that desperate (they don't have any backup amps ???!), they can rent an amp.
-Chris
I normally stocked the proper semi's for band gigs. I always had enough to do matched sets on a channel. Same for popular signal transistors drivers and TO-126 types.
Now I don't have to do this (having sold the shop), but it's still nice to have them. You only need to stock the larger ones in TO-3 and TO-3P these days along with MJL1302 and it's compliment.
I don't see any reason to use those NTE / ECG / SK mystery parts. If the band is that desperate (they don't have any backup amps ???!), they can rent an amp.
-Chris
You cannot count on these transistors to be an exact replacement or sometimes even close. I have seen too much gear and repaired the same that has been touched by an unskilled technician using this junk.
To give a specific example here.. In the last 5 years I have repaired in excess of 75 GAS Ampzilla's, SAE 2200's, 2300's,2400's and 2500's that some morons have tried to use NTE and ECG parts in.
General purpose use....hmmmm I can't think of any off hand. I can however give hundreds of mistaken substitutions that were offered by NTE and ECG. No, you cannot count on them for an emergency repair either. They are best left on the shelf to collect dust.
Hey Joe,
How many real parts can you buy for the price of one "replacement brand"? For signal transistors you can easily buy 10 real ones for every NTE / ECG / SK mystery part you purchase.
When I see these in a unit, they are on the required parts list. That is not negotiable with me.
-Chris
How many real parts can you buy for the price of one "replacement brand"? For signal transistors you can easily buy 10 real ones for every NTE / ECG / SK mystery part you purchase.
When I see these in a unit, they are on the required parts list. That is not negotiable with me.
-Chris
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