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Chinese DIY EAR 834P Phono Preamp Build - What has gone wrong?


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After Pass ACA Amp Kit Build, I thought that I can handle this but I was mistaken. This is a different league of its own. There is so certain manual came with it and had to look closely finished build photo and do some google research.

 

After spending many hours, finally finish building it but there is no sound.?     

 

Here are things that I checked so far.

 

+ 3 x 12AX7 Tubes. Checked with 2 different sets (each set 3 tubes) and result is same so no tube issues.
+ Signal In and Out cables (RCA sockets to PCB Joints) are checked with Multimeter for conductivity and they are fine.
+ All solder joints were triple checked and made sure no cold solder
+ Original 2K 3W resistors were out of value so got replacement one from RS Online and replaced.

+ DC voltage from Power Supply Board measuring 6.49v and Main Board DC IN is 6.34v with tubes installed so it seem fine.

 

My guess is that tube stage cathode voltage is lacking because tube is just barely glowing and hard to see glow.

 

Can anyone help me how to measure the cathode voltage out of 3 tube stages? And if you have built one before and had same issue, please do share.

 

Hope other forum members who are thinking of building one learn from mistakes made here. 

 

* I understand that tube amp involves high voltage so will be cautious.

 

Thank you for sharing suggestion and ideas.

 

Schematics Diagram

Hb16c03a8313c43f1949ca8de58850632Y.jpg

Completed PCB Board

 

Y5F621q.png

 

Cathode Resistors Highlighted

 

8wiAc3J.jpg

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It finally works. Yeah...   I believe that the issue was the connection between power supply board and main board. There are a few connection joints between the board but the connection seem

In general, yes, less is better.  However, do you know if the circuit board has plated-through holes?  Most good boards do.  If not, however, you need to solder both sides so that the component lead m

You have a fault condition where possibly huge Current is causing the resistor to burn out.  I’d be using the same wattage  rating resistor or lower as it acts like a “fuse” until you work out what  h

A quick google will bring answers:

 

To measure voltage drop across the cathode resistor set your multimeter for DC Volt measurement, clip the black probe to chassis ground (so you can use just one hand to do the measurement) and put the red probe on the tube socket cathode pin . You can also put one probe on each leg of the cathode resistor.

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2 minutes ago, Gryffles said:

A quick google will bring answers:

 

To measure voltage drop across the cathode resistor set your multimeter for DC Volt measurement, clip the black probe to chassis ground (so you can use just one hand to do the measurement) and put the red probe on the tube socket cathode pin . You can also put one probe on each leg of the cathode resistor.

 

My My... Why I could not find this when I do research..  

 

Dumb question.. Does it have to be tubes installed? I am a bit worry about tubes getting damaged during measurement. 

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Its all good mate 

 

Yes with tubes installed. It wont damage tubes but if you are worried connect the probes with power off and then turn on. Without tubes you wont get accurate readings as no load

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First thing, always ,measure the power supply voltage.   What is the voltage on the output of the regulator (on top of first 22uF filter cap, junction with emitter of the transistor).

 

1 minute ago, Spider27 said:

Dumb question.. Does it have to be tubes installed?

 

Yes

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8 minutes ago, aussievintage said:

First thing, always ,measure the power supply voltage.   What is the voltage on the output of the regulator (on top of first 22uF filter cap, junction with emitter of the transistor).

 

 

Yes

 

Thank you for the suggestion measuring power supply voltage.       Ah... Another super dumb question..

Are you referring MJE13009 transistor? if so, how do I measure supply voltage?  

 

IMG_8426.jpg

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Just measured cathode Vol resistor reading and here are the findings.

 

Stage 1

Cathode resistor R4 (2.2K) : Left Channel 9.8mv, Right Channel 10.6mv

 

Stage 2

Cathode resistor R5 (2.2K) : Left Channel 0.8mv, Right Channel 0.7mv

 

Stage 3

Cathode resistor R6 (68K) : Left Channel 32mv, Right Channel 31.6mv

 

Not sure how far they are from target value....

 

 

Cathod Vol Reading.jpeg

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3 minutes ago, Ihearmusic said:

does not sound right.

Have you checked your supply voltage yet?

Thank you for confirming and I doubted that the figure would not be right since there is no sound and tubes are not glowing bright enough.

 

Re; supply voltage, it is embarrassing to admit and I do not know how to measure it..  ?

 

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2 hours ago, Spider27 said:

how do I measure supply voltage

 

Black lead connected to ground/common,  red lead on the junction of the 22uF cap, the 2k resistor, and the emitter of the regulator transistor.

 

oh,  and be careful

 

 

16 minutes ago, Spider27 said:

Stage 1

Cathode resistor R4 (2.2K) : Left Channel 9.8mv, Right Channel 10.6mv

 

Stage 2

Cathode resistor R5 (2.2K) : Left Channel 0.8mv, Right Channel 0.7mv

 

Stage 3

Cathode resistor R6 (68K) : Left Channel 32mv, Right Channel 31.6mv

 

Not sure how far they are from target value....

 

 

Way too low.   

 

Edited by aussievintage
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1 minute ago, Spider27 said:

Thank you for confirming and I doubted that the figure would not be right since there is no sound and tubes are not glowing bright enough.

 

Re; supply voltage, it is embarrassing to admit and I do not know how to measure it..  ?

 

Next to the R6 resistor in the 3rd stage is a fat blue 100 ohm resistor. Measure on either site the voltage reverenced to ground. That will give us some indication

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There's a white triangle on that board that reads 285V.    Obviously a test point.  Measure it (ref. to ground)

 

edit:  two of them actually

Edited by aussievintage
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19 minutes ago, Ihearmusic said:

Next to the R6 resistor in the 3rd stage is a fat blue 100 ohm resistor. Measure on either site the voltage reverenced to ground. That will give us some indication

 

Voltage through 100 ohm resistor on left channel is 0mv and right channel is 2.5mv which is almost nothing..

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15 minutes ago, aussievintage said:

There's a white triangle on that board that reads 285V.    Obviously a test point.  Measure it (ref. to ground)

 

edit:  two of them actually

Just measured those two points after running about 10 mins and both test point voltage measured that Left channel 0mv and right channel 2.5mv.

 

If I understood correctly, the test point should provide 285v so supply voltage definitely went wrong...

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Just now, Spider27 said:

 

Voltage through 100 ohm resistor on left channel is 0mv and right channel is 2.5mv which is almost nothing..

 

I don't think you have any high voltage supply.  Maybe that regulator isn't working - check the 285V test point.  If nothing there, go back to before the regulator to the raw DC on the 100uF caps

 

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1 minute ago, Spider27 said:

Just measured those two points after running about 10 mins and both test point voltage measured that Left channel 0mv and right channel 2.5mv.

 

 

Doesn't need to run for 10 mins.  The supply is solid state, voltage should be there as soon as you turn it on.

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Yep, sounds your regulator could be the problem. you need do measure the voltage coming of the transformer and then after the rectifier before the regulator.

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3 minutes ago, aussievintage said:

 

I don't think you have any high voltage supply.  Maybe that regulator isn't working - check the 285V test point.  If nothing there, go back to before the regulator to the raw DC on the 100uF caps

 

 

Thank you. Yes, I fully agree that there is something wrong with Primary Voltage. My toroidal transformer primary AC Vol out is 240v and Secondary 6.3v.  Secondary Out AC 6.3v seem working through Power Supply Board to Main Board because the DC Vol measurement shows 6.29v.

 

However, primary AC voltage 240v does not seem to transferring correctly.

 

First of all, I may need to check AC 240v out from Toroidal transformer is working. 

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Toroidal Transformer seem working fine. Primary AC out 253v and Secondary AC Out 6.5v so it looks like voltage regulator might be the issue. 

 

May I ask how to check if regulator is working? If regulator is the issue, do I just change the MJE13009 NPN Power transistor?

 

Thank you very much for the guidance. 

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Don't you ,mean secondary out in both instances, the primary side is the input to the transformer.

 

Sorry but was bugging me ;)

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1 minute ago, muon* said:

Don't you ,mean secondary out in both instances, the primary side is the input to the transformer.

 

Sorry but was bugging me ;)

You are right. Thank you for correcting me. :) 

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10 hours ago, Spider27 said:

Toroidal Transformer seem working fine. Primary AC out 253v and Secondary AC Out 6.5v so it looks like voltage regulator might be the issue. 

 

May I ask how to check if regulator is working? If regulator is the issue, do I just change the MJE13009 NPN Power transistor?

 

Thank you very much for the guidance. 

 

OK, you have ac out of the transformer.  Next, check that you have raw DC after the main rectifier.  There should be a high voltage (330 volts or so) on the positive terminal of the first 100 uF capacitor.  The 1K3 resistor may be a convenient point to measure it.

 

If there is raw DC, check the voltage reference at the base of the transistor (top of the string of zener diodes).  If there is voltage there, check the output of the regulator right at the emitter of the transistor (the 2K resistor should be a convenient point to do this)

 

Also, generally check for bad solder joints.  Follow the high voltage, measuring it at various points between where it is present, and where it was not (the 285V test points).  Try to establish exactly where it stops.

 

 

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2 hours ago, aussievintage said:

 

OK, you have ac out of the transformer.  Next, check that you have raw DC after the main rectifier.  There should be a high voltage (330 volts or so) on the positive terminal of the first 100 uF capacitor.  The 1K3 resistor may be a convenient point to measure it.

 

If there is raw DC, check the voltage reference at the base of the transistor (top of the string of zener diodes).  If there is voltage there, check the output of the regulator right at the emitter of the transistor (the 2K resistor should be a convenient point to do this)

 

Also, generally check for bad solder joints.  Follow the high voltage, measuring it at various points between where it is present, and where it was not (the 285V test points).  Try to establish exactly where it stops.

 

 

 

Thank you very much. I will check them out soon.

 

Just one quick question. Is 2K resistor correct one? Because I can see 1K3 resistor but could not see 2K resistor. I see 3K resistors just beside 1K3 resistor.

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38 minutes ago, Spider27 said:

 

Thank you very much. I will check them out soon.

 

Just one quick question. Is 2K resistor correct one? Because I can see 1K3 resistor but could not see 2K resistor. I see 3K resistors just beside 1K3 resistor.

 

 

Look at the schematic.  The 2K is after the regulator, the 1K3 is before it.

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23 hours ago, aussievintage said:

 

 

Look at the schematic.  The 2K is after the regulator, the 1K3 is before it.

Gee. I must been blind. Thank you very much.

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Posted (edited)

Before checking voltage, I checked the components one more time and found a few issues.

 

1) 1K3 Resistor gone bad. When I measure it with multimeter, it shows O.L and it looks slightly burnt so need replacement.

2) Left channel 2K3 resistor is incorrect value. It should be 2K but show 0.7K as value. 

 

Good thing is that NPN Power Transistor was fine when I tested it after removing it from circuit.

 

For replacement of those two resistors, is it okay to use wire wound resistor like below linked ones? I have only used either Carbon or Metal Oxide film resistor so far and not sure if Wire Wound Resistor would be ok to use.

 

https://www.jaycar.com.au/2-2k-ohm-5-watt-wire-wound-resistor/p/RR3306

https://www.jaycar.com.au/1k-ohm-5-watt-wire-wound-resistor/p/RR3298

 

The reason for asking is that resistors in those value are sold in Wire Wounded Resistors from local store and it will be expensive to order from Mouser or RS Online for couple of resistors after adding postage and takes quite a bit of time to receive them by mail.

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Looks like the 1k3 has acted like a fuse and been blown by excess current.  So you need to find out why before you replace it or it will just happen again.  And if you replace it with a higher wattage type then something else will probably take over the role of a fuse and blow.

Are you SURE the power transistor is OK?  In my experience as a tube DIYer these silly semiconductor things destroy themselves at the slightest chance.  Not like tubes which are much more robust.

Are you SURE there isn't a short from the power supply rail to ground somewhere? Check and re-check all the wiring.  Re-check all the transformer wiring.

Is the board known to be fault-free? QC on some Chinese products can be lacking.

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36 minutes ago, RoHo said:

Looks like the 1k3 has acted like a fuse and been blown by excess current.  So you need to find out why before you replace it or it will just happen again.  And if you replace it with a higher wattage type then something else will probably take over the role of a fuse and blow.

Are you SURE the power transistor is OK?  In my experience as a tube DIYer these silly semiconductor things destroy themselves at the slightest chance.  Not like tubes which are much more robust.

Are you SURE there isn't a short from the power supply rail to ground somewhere? Check and re-check all the wiring.  Re-check all the transformer wiring.

Is the board known to be fault-free? QC on some Chinese products can be lacking.

 

Thank you very much for your feedback.

 

I will recheck all the wiring and power supply rail.

 

Re: power NPN transistor, I followed this video and checked and seem fine.

 

 

Re: quality of the PCB board, it looks high quality & well made but not sure if it is fault free because this is the first DIY Kit from China that I am trying and probably the last given the troubles I am having comparing with other well known DIY Kit such as ACA and Elekit. ?

 

 

 

 

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On lenco heven there is a thread where many are using this board, and in some cases modifying it.

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47 minutes ago, Spider27 said:

 

Thank you very much for your feedback.

 

I will recheck all the wiring and power supply rail.

 

Re: power NPN transistor, I followed this video and checked and seem fine.

 

 

Re: quality of the PCB board, it looks high quality & well made but not sure if it is fault free because this is the first DIY Kit from China that I am trying and probably the last given the troubles I am having comparing with other well known DIY Kit such as ACA and Elekit. ?

 

 

 

 

Do you have a dim bulb tester for protection when turning on? You will be aware of these if your familiar with the ACA kit and related forum on DIY Audio. Might save you a lot of hassle

 

https://www.diyaudio.com/forums/power-supplies/167579-light-bulb-tester.html go to the post by member 6L6

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When you say no sound, can I ask if there was any kind of hum or hiss detectable from either channel? Any sound from plugging or unplugging inputs? Did you actually test with the signal from a cartridge?
 

FWIW I notice only some of your solder joints on top of the board show solder that has flowed through from the bottom. That’s not necessarily wrong or bad, but I’d probably reflow all joints with a little extra solder to help eliminate the risk of a cold joint. 

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1 minute ago, RCAJack said:

When you say no sound, can I ask if there was any kind of hum or hiss detectable from either channel? Any sound from plugging or unplugging inputs? Did you actually test with the signal from a cartridge?
 

FWIW I notice only some of your solder joints on top of the board show solder that has flowed through from the bottom. That’s not necessarily wrong or bad, but I’d probably reflow all joints with a little extra solder to help eliminate the risk of a cold joint. 

 

Thank you for asking... No hum or hiss at all. No sound coming from speaker at all......

Actually Right channel was working temporarily and after soldering a few joints again, right channel also not working (no sound output at all).

 

Re: solder, I just solder from bottom of PCB and was not sure if I need to pour solder more into the hole all the way to the top of the board. I thought that just enough solder is better than too much solder ?

 

When I replace those two resistors, I will put more solder to help eliminiate the chance of cold solder. 

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It’s interesting that you got some sound originally on one channel. Apparently something broke after resoldering some joints. I can’t imagine you fried anything with excess heat (although maybe?) so I’m still wondering if there’s a cold joint especially since you’re not even getting hiss at the output. ?

 

I’d be inclined to put in a signal and connect via an amp to a test speaker, then if voltages are ok, use a chopstick to gently tap all components including sockets and see if you hear noise or crackles.

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16 hours ago, Spider27 said:

Before checking voltage, I checked the components one more time and found a few issues.

 

1) 1K3 Resistor gone bad. When I measure it with multimeter, it shows O.L and it looks slightly burnt so need replacement.

2) Left channel 2K3 resistor is incorrect value. It should be 2K but show 0.7K as value. 

 

Good thing is that NPN Power Transistor was fine when I tested it after removing it from circuit.

 

For replacement of those two resistors, is it okay to use wire wound resistor like below linked ones? I have only used either Carbon or Metal Oxide film resistor so far and not sure if Wire Wound Resistor would be ok to use.

 

https://www.jaycar.com.au/2-2k-ohm-5-watt-wire-wound-resistor/p/RR3306

https://www.jaycar.com.au/1k-ohm-5-watt-wire-wound-resistor/p/RR3298

 

The reason for asking is that resistors in those value are sold in Wire Wounded Resistors from local store and it will be expensive to order from Mouser or RS Online for couple of resistors after adding postage and takes quite a bit of time to receive them by mail.

You have a fault condition where possibly huge Current is causing the resistor to burn out.  I’d be using the same wattage  rating resistor or lower as it acts like a “fuse” until you work out what  has drawn such current, using a higher wattage  rating resistor will only mask the issue and will not help.   So get cheap 1-2 watt resistors.   Surprise to see no fuses on the PSU on either the secondary or primary of the transformer.   If I were chasing this I would check that  I have the correct voltage >285VDC b4 it gets to the transistor MJE 13009.   This may involve removing MJE 13009 and leaving it out of the circuit and power up.  If you get  greater than 285VDC  after the 1.3k resistor than it’s obvious it’s the MJE 13009, be aware by doing this the the circuit is live and working and that the high voltage   greater than 285VDC will remain after you have switched off!  You need it to be discharged b4 you do any work.   Removing MJE 13009 will isolate the rest of the circuit from the fault condition.   If there is higher than 285V after resistor 1,3k when MJE 13009 is disconnected, which I’m assuming there is because the 1.3k resistor has gone opened, I would be checking the pins on the transistor and tracing the base/collector/emitter to ensure that the circuit pcb corresponds to the circuit diagram, this will ensure that the white print on the pcb isn’t incorrectly indicated to allow you to incorrectly place the orientation of MJE 13009.
A note on MJE13009; On semi has two styles of connection and Vishay and all others have  one,  if you have a Onsemi equivalent you need to check the data sheet to see which style you have as the pin configuration is different between style one and two;  however,  this could also be a printed error on the data sheet as I have no idea why you would have different pin configuration compared to standard.



 

 

 

Edited by Addicted to music
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9 hours ago, Spider27 said:

 

Thank you for asking... No hum or hiss at all. No sound coming from speaker at all......

Actually Right channel was working temporarily and after soldering a few joints again, right channel also not working (no sound output at all).

 

 

Sounds like there is a short somewhere in the left channel that caused excess current that eventually blew the 1k3 resistor.   Meanwhile, the Right channel worked fine until that resistor blew and disconnected the PS. 

Check for solder bridges between PCB tracks.

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9 hours ago, Spider27 said:

Re: solder, I just solder from bottom of PCB and was not sure if I need to pour solder more into the hole all the way to the top of the board. I thought that just enough solder is better than too much solder ?

 

In general, yes, less is better.  However, do you know if the circuit board has plated-through holes?  Most good boards do.  If not, however, you need to solder both sides so that the component lead makes the connection between sides of the board.

 

 

6 minutes ago, RoHo said:

Check for solder bridges between PCB tracks.

 

Definitely

 

also check the transistor pinout and orientation (and the orientation of all the diodes and capacitors)

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aussievintage is onto it !

I've played with similar looking Chinese phono boards that definitely look like through holes and are not.

A simple continuity test proved they weren't.  I soldered the top of the holes around the pins and it was all go  !

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13 minutes ago, miyouzaic said:

aussievintage is onto it !

I've played with similar looking Chinese phono boards that definitely look like through holes and are not.

A simple continuity test proved they weren't.  I soldered the top of the holes around the pins and it was all go  !

Thank you. I will do continuity test to see if they are through holes. It looks like they do but better check it to make sure.

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