Re: signal
The transistors. We need to know what the voltage measures with the negitive meter lead to ground. The positive lead should then be connected to the emitter of each transistor, then the base of each and the collector of each. With these voltage measurments it can be determined if the circuit is working correctly.
The 12 volt DC range for starters then lower ranges if the reading is very near the bottom of the meter scale.
From your discription I could just be a headphone amp. To use it with the CD player you have, it will need a volume control before the preamp.
Later BZ
bonsai171 said:
The transistors. We need to know what the voltage measures with the negitive meter lead to ground. The positive lead should then be connected to the emitter of each transistor, then the base of each and the collector of each. With these voltage measurments it can be determined if the circuit is working correctly.
The 12 volt DC range for starters then lower ranges if the reading is very near the bottom of the meter scale.
bonsai171 said:
From your discription I could just be a headphone amp. To use it with the CD player you have, it will need a volume control before the preamp.
Later BZ
voltages
Here are the voltages of the various capacitors:
c1: 1/2 volt
c2: 1/2 volt
c3: 5.5 volts
c4: a voltage drop
c5: 5 volts
c6: 5.5 volts
c7: 1 volt
c8: 5.5 volts
What do you make of the voltage drop at c4? That seems kind of strange. It seems like the voltage of c2 and c4 should be the same (are they both part of the first gain stage??)
Dave
Here are the voltages of the various capacitors:
c1: 1/2 volt
c2: 1/2 volt
c3: 5.5 volts
c4: a voltage drop
c5: 5 volts
c6: 5.5 volts
c7: 1 volt
c8: 5.5 volts
What do you make of the voltage drop at c4? That seems kind of strange. It seems like the voltage of c2 and c4 should be the same (are they both part of the first gain stage??)
Dave
(just a thought)
Is the problem occuring on both channels or just one? You might try disconnecting the power from one channel at a time to see if the problem exists in both channels or just one. That might help isolate the problem.
A scope would be nice but I'm guessing that one is not available.
Is the problem occuring on both channels or just one? You might try disconnecting the power from one channel at a time to see if the problem exists in both channels or just one. That might help isolate the problem.
A scope would be nice but I'm guessing that one is not available.
transistor voltages
Hdtv man, here are the voltages for each part of the transistors:
Q1:
Emitter: 1/2 volt
Collector: 3.75 volts
Base: 1.5 volts
Q2:
Emitter: 2 volts
Collector: 25 volts
Base: 3.5 volts
Q3:
Emitter: 1/2 volt
Collector: 3.75 volts
Base: 1.5 volts
Q4:
Emitter: 2 volts
Collector: 25 volts
Base: 3.5 volts
Rwbrown:
Both channels are equally distorted.
Hope this helps! Thanks again guys
Dave
Hdtv man, here are the voltages for each part of the transistors:
Q1:
Emitter: 1/2 volt
Collector: 3.75 volts
Base: 1.5 volts
Q2:
Emitter: 2 volts
Collector: 25 volts
Base: 3.5 volts
Q3:
Emitter: 1/2 volt
Collector: 3.75 volts
Base: 1.5 volts
Q4:
Emitter: 2 volts
Collector: 25 volts
Base: 3.5 volts
Rwbrown:
Both channels are equally distorted.
Hope this helps! Thanks again guys
Dave
Strange... Your schematic shows C2 and C4 with different polarities and I believe that C2 shows the correct connection. I really don't know if this is a problem but it does not look correct to me. Most circuits that I have seen have the + side of the electrolytic on the amp side and the - connection going to the input connector. There may be more knowlegable people out there who can comment on this. (I am not an EE or even close)
Could this have caused the strange reading on C4?
(ps. I suggested trying one channel at a time since I have seen cases where the bad side caused both channels to distort. Hooking up one side at a time isolated the bad one.)
Don't give up yet!
Could this have caused the strange reading on C4?
(ps. I suggested trying one channel at a time since I have seen cases where the bad side caused both channels to distort. Hooking up one side at a time isolated the bad one.)
Don't give up yet!
strange capacitor thing
rwbrown,
yes that does look really strange! If c1 and c2 are the first gain stage, it would make sense that each of the capacitors would have an equal amount of gain. If you look at the very last stage of the preamp, there is also a slight difference in voltage between those capacitors too (c3 and c5), which seems to show that there is a slight loss in dB on the right side. The instructions in the kit show that the c4 cap is supposed to be hooked up this way, but it doesn't seem right at all
Also, i tried hooking up just one channel of the input and the same of the output, first for the left channel, and then for the right channel. In both cases, there is still massive distortion..
Dave
p.s. The idea of switching that cap around is very tempting!!
rwbrown,
yes that does look really strange! If c1 and c2 are the first gain stage, it would make sense that each of the capacitors would have an equal amount of gain. If you look at the very last stage of the preamp, there is also a slight difference in voltage between those capacitors too (c3 and c5), which seems to show that there is a slight loss in dB on the right side. The instructions in the kit show that the c4 cap is supposed to be hooked up this way, but it doesn't seem right at all
Also, i tried hooking up just one channel of the input and the same of the output, first for the left channel, and then for the right channel. In both cases, there is still massive distortion..
Dave
p.s. The idea of switching that cap around is very tempting!!
The plot thickens.... Take a look at c11 - c12 and r4
now take a look at c13 - c14 and r7 ...
You'll notice that capacitors in the same position are not the same value(?!). c11 does not = c13 and likewise c12 does not = c14 ! The values of those puppies are reversed in the diagram between the right and left channels. The question thus becomes -> "Why?"
We need someone much better than I at these sorts of things to say which one is correct. Those channels should be identical(I'm pretty sure of this but don't really know which side is correct.)
now take a look at c13 - c14 and r7 ...
You'll notice that capacitors in the same position are not the same value(?!). c11 does not = c13 and likewise c12 does not = c14 ! The values of those puppies are reversed in the diagram between the right and left channels. The question thus becomes -> "Why?"
We need someone much better than I at these sorts of things to say which one is correct. Those channels should be identical(I'm pretty sure of this but don't really know which side is correct.)
volume control
Hello,
Thanks for pointing that out. At the moment there is a volume control on the preamp, but it is after the output circuit. Is it normal to place the volume control directly after the rca inputs?? That seems similar to the way a passive preamp works- by attenuating the input signal, and then sending it to the amp.. In any case i'll try it!
Dave
Hello,
Thanks for pointing that out. At the moment there is a volume control on the preamp, but it is after the output circuit. Is it normal to place the volume control directly after the rca inputs?? That seems similar to the way a passive preamp works- by attenuating the input signal, and then sending it to the amp.. In any case i'll try it!
Dave
volume before preamp
hello,
The volume control before the preamp definitely didn't work. I almost blew my 8" woofers out doing this. Everything is definitely wired up right, but a huge amount of hum and distorted signal came out of the preamp when the amp turned on. I have a loaner tube preamp from a local audio shop at the moment, and it is playing some music for me now. Luckily everything is ok with the speakers and equipment.. i think it's time to throw in the towel on this project.. building components isn't for me. Fortunately the kit was very inexpensive..
Dave
hello,
The volume control before the preamp definitely didn't work. I almost blew my 8" woofers out doing this. Everything is definitely wired up right, but a huge amount of hum and distorted signal came out of the preamp when the amp turned on. I have a loaner tube preamp from a local audio shop at the moment, and it is playing some music for me now. Luckily everything is ok with the speakers and equipment.. i think it's time to throw in the towel on this project.. building components isn't for me. Fortunately the kit was very inexpensive..
Dave
Don't give up just yet!
The capacitors C2 C4 must have the positive side pointing at the base of the transistor.
The thing that bothers me is the 25v at the Q2 and Q4 collector. This i think indicates one of two things.
The PSU delivers too much voltage or you have some oscillations in the circuit.
The capacitors C2 C4 must have the positive side pointing at the base of the transistor.
The thing that bothers me is the 25v at the Q2 and Q4 collector. This i think indicates one of two things.
The PSU delivers too much voltage or you have some oscillations in the circuit.
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