, so tomorrow I'll get to work again in the boards.Hi
I have changed some ZTX450. I managed to improve voltages, but I'm having problems in Q4. 🙁
I removed a SK389 and.... I've seen in Q4 area I have 14 volts !!!!, so I'll replace SK389 by a pair of 2SK170 if this component is the source of the problem.
Any tips for mounting the 2SK170? 😎😎
Regards
I have changed some ZTX450. I managed to improve voltages, but I'm having problems in Q4. 🙁
I removed a SK389 and.... I've seen in Q4 area I have 14 volts !!!!, so I'll replace SK389 by a pair of 2SK170 if this component is the source of the problem.
Any tips for mounting the 2SK170? 😎😎
Regards
Hey guys
I changed the SK389 by a pair of 2SK170 and now I have better results in one of the boards.
In the left channel, I have a voltage of ,07 Volt before the R25. In Q5 area I'm still somewhat high voltages . In the area of the Q8-11 I have voltages of .06 to .09 volt. Is this correct or do I have to change the 2sk170 in this area?
On the right channel (yes it´s blue ) still have problems in the area of Q4, I check 29 volt whith a new pair of 2SK170. I changed the Q4 (ZTX450) but the result is the same.
Anybody can give me some idea?
Regards
I changed the SK389 by a pair of 2SK170 and now I have better results in one of the boards.
In the left channel, I have a voltage of ,07 Volt before the R25. In Q5 area I'm still somewhat high voltages . In the area of the Q8-11 I have voltages of .06 to .09 volt. Is this correct or do I have to change the 2sk170 in this area?
An externally hosted image should be here but it was not working when we last tested it.
On the right channel (yes it´s blue ) still have problems in the area of Q4, I check 29 volt whith a new pair of 2SK170. I changed the Q4 (ZTX450) but the result is the same.
An externally hosted image should be here but it was not working when we last tested it.
Anybody can give me some idea?
Regards
Looks like you don't have a proper PS ground connection on that board, or a break in the ground trace somewhere so only the area around Q3 has a proper ground....
Roscoe
Roscoe
Thanks for your response Roscoe. I dedicate a few hours to see if the problem is the ground at that point.
If I get around this point would have already finished the left channel in the absence of seeing what the problem is on the right channel.
Regards
If I get around this point would have already finished the left channel in the absence of seeing what the problem is on the right channel.
Regards
1st channel seems to be working about fine, even if some voltages differ
On the second one, some voltage readings are illogical, like after Q3, about Ok, but after, reading down shcematic the readings go up, which is impossible 😱 so, might need to change Q5 and the 4 jfets too; on the 2nd stage Q4 and the 389 seem blown ...
nAr
Hi Guys!
Thanks for the replies.
I've been working on the blue channel and I changing:
Q4, Q3, Q5, 1N4739 and C15
Inexplicably, I had a short and this produced these values so strange in that channel. 🙁
Now these are the new values:
The voltage on Q8-Q11 is very similar between both channels.
Right now I'm thinking of changing again Q4, since the values are still quite different from the scheme.
Can I use my second stereo?
Regards
Thanks for the replies.
I've been working on the blue channel and I changing:
Q4, Q3, Q5, 1N4739 and C15
Inexplicably, I had a short and this produced these values so strange in that channel. 🙁
Now these are the new values:
The voltage on Q8-Q11 is very similar between both channels.
Right now I'm thinking of changing again Q4, since the values are still quite different from the scheme.
Can I use my second stereo?
Regards
17V seems too high on the drains of 1st stage jfets.
Seems there is still problem in the Q5 / Q4 area. The K389 seems alive but passes the double of the current it's designed for.
Try the other channel with the LP turntable ... can you hear music ?
Best,
nAr
Hey guys!
Thanks again for the replies!
Right now I'm listening to an album of Chet Baker (... in NY) on my new Pearl! 🙂🙂🙂🙂
With voltages as they are, the two channels sound great . In a few days, I will change the channel Q4 law to lower the voltage of 20 volts and leave it exactly the other channel (13 volt) for safety, because I haven´t any ZXT450 on good condition (again).
I selected the input impedance of the switch that I mounted on the back you can get a good fit.
The only noise "suspect" is a constant HUMMMMMMMMM. I guess it must be due to a mass.
Any recommendations?
Best Regards
Thanks again for the replies!
Right now I'm listening to an album of Chet Baker (... in NY) on my new Pearl! 🙂🙂🙂🙂
With voltages as they are, the two channels sound great . In a few days, I will change the channel Q4 law to lower the voltage of 20 volts and leave it exactly the other channel (13 volt) for safety, because I haven´t any ZXT450 on good condition (again).
I selected the input impedance of the switch that I mounted on the back you can get a good fit.
The only noise "suspect" is a constant HUMMMMMMMMM. I guess it must be due to a mass.
Any recommendations?
Best Regards
I forgot to mention that the HUMMMMM is relatively low. If you raise the volume of the preamp, lot may hear but is obscured by the music.
Regards
Regards
The turntable GND must be connected to Audio GND at phono preamp.
For internal wiring, do a star ground from PSU GND node. Each place you need a GND reference, use a single wire from PSU GND to make it. Only inputs can be connected "as is", eg the normal way. A shielded cable in that position may help.
Best,
nAr
Nar: Thanks for your help!
So, only the inputs must be connected "as is" OK. I will follow your advice and I use a cable from the PSU GND for reference. 😎
I have here a shielded Mogami and I think I will be very useful for this.
Regards
So, only the inputs must be connected "as is" OK. I will follow your advice and I use a cable from the PSU GND for reference. 😎
I have here a shielded Mogami and I think I will be very useful for this.
Regards
Hey guys!
Nar, I followed your advice and the noise of mass has disappeared.
I can only regulate the right channel Q4.
In my input impedance selector I used the following range:
10 Ohm
40 Ohm
100 Ohm
250 Ohm
500 Ohm
1K Ohm
47K Ohm (This is the resistance R27)
Regards
Nar, I followed your advice and the noise of mass has disappeared.
I can only regulate the right channel Q4.
In my input impedance selector I used the following range:
10 Ohm
40 Ohm
100 Ohm
250 Ohm
500 Ohm
1K Ohm
47K Ohm (This is the resistance R27)
Regards
Good, but you may want to investigate more to see why one channel reg. works, and the other doesn't.
If you post again some new voltages, maybe we could help more
Best,
nAr
Hey guys
I measured the voltage (outputs GND carrying to PSU) and I have had virtually no changes. Voltage on Q5, 17 volt
Right now I have connected the GND output to the Rcore-ground and although the voltages are equal, but the HUM has completely disappeared.
On this picture you can see the output GND connect to PSU GND.
There is still detail that is escaping me. Still, the pre sounds pretty good.
Does the 9 volt battery will have something to do?
Regards
I measured the voltage (outputs GND carrying to PSU) and I have had virtually no changes. Voltage on Q5, 17 volt
Right now I have connected the GND output to the Rcore-ground and although the voltages are equal, but the HUM has completely disappeared.
An externally hosted image should be here but it was not working when we last tested it.
On this picture you can see the output GND connect to PSU GND.
There is still detail that is escaping me. Still, the pre sounds pretty good.
Does the 9 volt battery will have something to do?
Regards
An externally hosted image should be here but it was not working when we last tested it.
The Duo:
An externally hosted image should be here but it was not working when we last tested it.
The 9volt battery can be used in place of D1
It is not normally used, and not needed in the 'normal' build.
What is the voltage at the base of Q5. It should be 1/2 voltage of that at the emitter of Q3 (~24v), so close to 12v. If it's not then it could be that your resistors are not both 10k ohm, or there is a solder joint that is not solid, or maybe damage to the transistor Q5.
Those are the things I would check for. You can measure the resistance of R18 and R21 to ensure they are both 10k. The circuit shouldn't affect the measured value much at all, with the circuit turned off, of course.
Those are the things I would check for. You can measure the resistance of R18 and R21 to ensure they are both 10k. The circuit shouldn't affect the measured value much at all, with the circuit turned off, of course.
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