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Projects => Headphone amplifiers => Topic started by: CapRock on February 01, 2011, 03:52:46 AM

Title: QRV-08 hum
Post by: CapRock on February 01, 2011, 03:52:46 AM
Hi Per,
     I just completed the QRV-08 and got it mounted in its case and all wired up.  I wanted to test it in the most basic way so I hooked up the AC power inlet to the terminal (X3) and hooked up my trs jack for the headphones to X2 and powered it up.  As soon as it powers on I get a really loud hum.  I am in the U.S. and I am using the transformers from you BOM (Hahn 230/40) even though we are on 115.  LED's H4 and H2 illuminate at power up but H1 and H3 stay dark.  The parts in your BOM that said do not use I left those spots blank, the parts that said short with tin jumper I jumped with a leftover lead from through hole resistors.  What do you think I need to do to get it working?
Title: Re: QRV-08 hum
Post by: peranders on February 01, 2011, 06:56:45 AM
All LED's must be on. Do you have +- 12 volts in both channels? How much is your AC voltage really? 230/24 is better since I used 230/12 with 230 VAC in.
Title: Re: QRV-08 hum
Post by: CapRock on February 01, 2011, 06:14:08 PM
My Mains voltage I measured at 120.5 VAC.  I will check for 12 volts on the board later.  Where is a good place to check for 12 volts?  The transformers I am using are 230V 50-60hz, will these be ok for me?
Title: Re: QRV-08 hum
Post by: peranders on February 01, 2011, 06:27:44 PM
It could be anywhere where you have 12 volts, please consult the schematics where you see 15V_R, 15_L, -15V_R, -15V_L.
Title: Re: QRV-08 hum
Post by: CapRock on February 02, 2011, 06:48:29 AM
I just checked the voltages around the board.  My input voltage was 121.6VAC and everywhere that was labeled 15V on the schematic I was getting between 4.16 and 4.39v which is obviously bad.  I also attempted to adjust the trimpots P1/P2 to read 0V across R1 and turning them either direction had no effect on the voltage reading across R1/E1.  Any Ideas?  Will these transformers work with the voltage I am getting here?  could I have damaged any parts by powering it up with these transformers? 
Title: Re: QRV-08 hum
Post by: peranders on February 02, 2011, 08:19:22 AM
You must first make sure that your power supply is working. What is your raw DC voltage? Should be 20-25 V.
Title: Re: QRV-08 hum
Post by: CapRock on February 02, 2011, 06:26:31 PM
I checked for 25V at the positive leg of the bridge rectifiers.  Here are my results

BR3: 10.16
BR4: 0
BR1: 6.78
BR2: 0
Title: Re: QRV-08 hum
Post by: peranders on February 02, 2011, 06:30:40 PM
You should measure at the NEG pin for the negative voltages.

+ pin is GND for the negative voltages, please check the schematics so you see where you should measure.

Can you measure the AC voltage on all four windings?
Title: Re: QRV-08 hum
Post by: CapRock on February 05, 2011, 06:17:52 PM
ok so today my mains input voltage is 119.1 VAC.  BR1: +14.2, BR2: -8.47, BR3: +21.5, BR4: -6.61.  Ac voltage at tr1/tr2 prim 1 is .2 V.  Ac voltage at prim 2 for both is 119.1
secondary voltages are as follows:

TR1:
sec1: 7.7
sec2: 7.5
sec3: 0
sec4: 0

TR2:
sec1: 12.8
sec2: 12.7
sec3: .3
sec4: .5
Title: Re: QRV-08 hum
Post by: peranders on February 05, 2011, 09:40:55 PM
Do you have two primary windings?
Title: Re: QRV-08 hum
Post by: CapRock on February 05, 2011, 10:54:13 PM
I believe so.  I used the exact ones from your bill of materials.  both transformers primary 1 was .2V, and both primary 2 were 119.1V.  Am I measuring something wrong? I cant find a data sheet for these transformers.  Hahn BV EI 382 1194 are what I am using.
Title: Re: QRV-08 hum
Post by: peranders on February 05, 2011, 10:58:00 PM
My transformer has only one primary winding and there are also only two holes in the pcb.
Title: Re: QRV-08 hum
Post by: CapRock on February 06, 2011, 12:45:07 AM
ok, mine is mounted on the PCB so it is only one primary then.  The pole that is pre varistor is 119.1 on both transformers, the pole that is post varistor is .2 on both transformers.
Title: Re: QRV-08 hum
Post by: peranders on February 07, 2011, 06:37:51 PM
You should have 115 VAC across the varistor and also at each transformer. Personally I'll doubt that you can use 230/40 transformer. You should have 24 V.
Title: Re: QRV-08 hum
Post by: CapRock on February 08, 2011, 04:42:38 AM
Ok do you know of a suitable replacement if I can desolder them from the board?  Something that would fit in the same holes would be great but mounting it to the case is ok too. thanks
Title: Re: QRV-08 hum
Post by: peranders on February 08, 2011, 06:10:45 AM
You could check your supplier where you have go the transformer you use but Farnell has a type 1689063 which will work.
Title: Re: QRV-08 hum
Post by: CapRock on February 09, 2011, 02:04:52 AM
OK ill check my US supplier. here are the specs I will search for let me know if any of these are incorrect.
input voltage: 230VAC single primary
single secondary with 12 volt output
2.3 volt power rating

is that right? even though I'm on 115 the 230 input voltage will be ok. Im assuming that when I hit this transformer with 115 volts it will put out 24 volts instead of 12 right?
Title: Re: QRV-08 hum
Post by: CapRock on February 09, 2011, 03:02:06 AM
is it a problem if the power rating is higher than 2.3V if all the other specs are correct?
Title: Re: QRV-08 hum
Post by: peranders on February 09, 2011, 06:21:42 AM
If you put in 115 V into a 230 V transformer you will get half the output voltage. No problem to use use higher VA rating more than size.
Title: Re: QRV-08 hum
Post by: CapRock on February 10, 2011, 02:10:15 AM
OK I just want to be sure I order the right thing this time.  The one you sent me a link to is 230V input and 12volt output on a single secondary.  So for me that will be 115V input and 6 volt output on a single secondary.  Is that what I want? the schematic calls for a 230/2X15, so wouldnt I need a 230/2X30 transformer?  If you could just post the specs I should look for on input voltage, how many secondaries I need and what output voltage they should be I would have a better understanding of what to buy, thanks
Title: Re: QRV-08 hum
Post by: peranders on February 10, 2011, 10:15:58 AM
Wrong of me.

Correct type for 230 VAC mains
1214583 230/2 x 12 V

1214591
This type will fit for you, 230/2x24V
http://se.farnell.com/myrra/44168/transformer-2-3va-230v-2-x-24v/dp/1214591
Title: Re: QRV-08 hum
Post by: CapRock on February 24, 2011, 08:25:10 PM
Hey Per,  My replacement transformers came in and I just installed them.  The voltages are still not right.  Even testing the secondaries of the transformers, I am getting wrong voltages.  It also just occurred to me that the power hits the varistor before going to the transformers.  Since I used the one you suggested in your bill of materials for 230VAC and I am on 115VAC will I need a different value varistor?  could that be the problem, if not what else can I do?  I am still getting LED's H2 and H3 to illuminate but the other 2 stay dark.   
Title: Re: QRV-08 hum
Post by: peranders on February 25, 2011, 10:59:46 AM
The varistor is in parallel and now with perhaps a bit high value but it will not interfere for voltages under 250 VAC in. The varistor should be 150 Vor so.

How are your voltages right now? Can you give me some values? Anything hot?
Title: Re: QRV-08 hum
Post by: CapRock on February 26, 2011, 01:12:17 AM
ok here are a list of voltages for the transformers.  I have no idea why they would be outputting such different voltages.  All solder joints are solid.  let me know what I should do next.
input: 119
TR1 pin 1: .3v
TR1 PIN 5: 119
TR1 PIN 6: 5.6
TR1 PIN 7: 5.5
TR1 PIN 9: 0
TR1 PIN 10: 0

TR2 PIN 1: .3
TR2 PIN 5: 119
TR2 PIN 6: 21.3
TR2 PIN 7: 21.2
TR2 PIN 9: .3
TR2 PIN 10: .4
Title: Re: QRV-08 hum
Post by: peranders on February 27, 2011, 09:27:18 PM
Can you measure across each secondary wings please?

Have you turned the rectifier bridges right?

What are your raw DC voltages?
Title: Re: QRV-08 hum
Post by: CapRock on March 01, 2011, 01:57:44 AM
hey per here are the results.  I resoldered the bridge rectifiers and now my voltages are even but no led's are illuminated

TR2:
across pins 6 and 7: 3.6v
across pins 9 and 10: 4.4v

TR1:
across pins 6 and 7: 3.6v
across pins 9 and 10: 4.4v

BR3: 2.1v
BR4: 2.8v
BR1: 2.1v
BR2: 2.9v
Title: Re: QRV-08 hum
Post by: peranders on March 01, 2011, 06:14:07 AM
Did you switch over the voltmeter to DC when you measured the voltage across the rectifiers?

Voltage across R32, R33, E32, E33?
Title: Re: QRV-08 hum
Post by: CapRock on March 01, 2011, 03:43:32 PM
Yes I switched it to DC. and I measured across the positive and negative legs of each rectifier.  All of my rectifiers are mounted with the dc output legs (+/-) facing the large electrolytic caps, is this correct?  I will measure resistor voltages when I get back in town tomorrow evening. 
Title: Re: QRV-08 hum
Post by: CapRock on March 06, 2011, 10:07:37 PM
Yes I switched it to DC. and I measured across the positive and negative legs of each rectifier.  All of my rectifiers are mounted with the dc output legs (+/-) facing the large electrolytic caps, is this correct?  I will measure resistor voltages when I get back in town tomorrow evening.

voltages posted below:
r32:  2.9v
r33:  2.1v
E32:  2.9v
E33:  2.1v
Title: Re: QRV-08 hum
Post by: peranders on March 06, 2011, 10:25:38 PM
You have exactly the same problem in both channels. Are the electrolytic caps turned right? Anything hot?
Title: Re: QRV-08 hum
Post by: CapRock on March 07, 2011, 01:58:53 PM
Electrolytic caps are turned the right way.  They look exactly the same as the ones in the picture on the QRV-08 page.  I Have not noticed anything hot.  Like I said before I mounted the snap in electrolytic caps on the top of the pcb and the though hole electrolytic caps on the bottom.  What is your email maybe I can send you a few pictures and see if anything stands out to you as a problem.  What could be causing the lack of voltage at the secondary of the transformer?  Is it even possible that parts that come after it in the chain effect its voltage?
Title: Re: QRV-08 hum
Post by: peranders on March 07, 2011, 08:06:26 PM
What is your voltage after the regulators? Is it zero volts?
Title: Re: QRV-08 hum
Post by: CapRock on March 07, 2011, 11:58:59 PM
The voltage after the regulators is as follows: (I measured at the output tab of each regulator)

ic10: -2.94
ic7: .63
ic18: -2.92
ic14: .63

whats next?
Title: Re: QRV-08 hum
Post by: CapRock on March 11, 2011, 02:26:09 PM
So what do you think I should check next regulator voltages posted in last post
Title: Re: QRV-08 hum
Post by: peranders on March 11, 2011, 05:32:07 PM
I'm not sure you have damaged something or not with your high supply voltage but you must remove the short circuit.

Remove R3/E3 by this the amp will be disabled. What happens? More supply voltage? Still short circuit?
Title: Re: QRV-08 hum
Post by: CapRock on March 15, 2011, 03:28:17 AM
I removed E3/R3 and it did not change the voltages at all.  I also tried removing the electrolytic caps that I had mounted to the bottom of the circuit board and that also did not change the voltages.  Do you want me to take a closeup picture of the power section of the circuit and see if you notice anything visibly wrong?
Title: Re: QRV-08 hum
Post by: peranders on March 15, 2011, 06:17:55 AM
It might be a good idea before you cut any traces. I think we can agree on that you have the same error in both channels. You can send big pictures to peranders at sjostromaudio dot com
Title: Re: QRV-08 hum
Post by: CapRock on March 16, 2011, 12:45:52 AM
Yes I agree.  Clearly I have the same problem with both channels.  I will send pictures to your email right now.  It may take 2 emails because of the size of the photos, thanks.
Title: Re: QRV-08 hum
Post by: peranders on March 16, 2011, 06:24:39 AM
I can't see much and certainly nothing wrong. Could please a take pictures in daylight and more towards the parts? Can you take so I can see the text in the semiconductors?
Title: Re: QRV-08 hum
Post by: CapRock on March 16, 2011, 01:47:26 PM
Yes is there a certain section of the board you want me to focus on or do you need detailed pics of the whole thing
Title: Re: QRV-08 hum
Post by: peranders on March 16, 2011, 05:54:11 PM
Details of the whole board with special attention to the semiconductors.
Title: Re: QRV-08 hum
Post by: CapRock on March 28, 2011, 07:57:21 PM
I am having trouble getting pictures with enough detail of the semiconductors to read the values/markings.  At this point I will do whatever it takes to get this thing working.  Is there any chance of me shipping it back to you to look over and paying you through paypal for your time.
Title: Re: QRV-08 hum
Post by: peranders on March 28, 2011, 09:07:36 PM
I'm afraid I have no possibility to repair this board but you must take a guess and assume that the regulators might be defect therefor you must cut the traces with +- 12V to the amps. If you still have more or less zero volts raw voltage, then you have to concentrate on the regulators.
Title: Re: QRV-08 hum
Post by: CapRock on March 28, 2011, 10:26:41 PM
ok, can I separate the amp from the regulators by simply removing the tin jumpers on the bottom of the board, it looks as if on the schematic these connect the regulators to the amp?  Or do I actually need to cut traces,  How many traces will I need to cut if so?  which regulators do you think may be causing the problem? thanks per
Title: Re: QRV-08 hum
Post by: peranders on April 01, 2011, 09:38:34 AM
Do you have tin on all tin jumpers? In case if this is true you will have a massive short circuit.
Title: Re: QRV-08 hum
Post by: CapRock on April 01, 2011, 02:57:32 PM
here are the jumper positions that I used bare wire jumpers (is that the same as a tin jumper?) are these causing the problem?

J1
J2
J4
J5
Title: Re: QRV-08 hum
Post by: peranders on April 01, 2011, 03:26:43 PM
I see that I have forgotten to mention these jumper. You should have one jumper at the time. This is for the input bias current adjustment.

http://sjostromaudio.com/pages/hifi-projects/36-hifi-projects/92-qrv06-headphone-amp?start=4 Here I have mentioned this.
Title: Re: QRV-08 hum
Post by: CapRock on April 02, 2011, 06:11:59 AM
I checked the link and that was for the qrv 06. And I did not see anything about jumpers on the page. Can you list all the jumpers I should be using so I can take off the ones that I don't need.
Title: Re: QRV-08 hum
Post by: peranders on April 02, 2011, 02:45:46 PM
The described a patch which I designed in. Remove J1, J2, J4, J5. You could remove the J3 and J5 but it's necessary. J3, J5 is for selecting desired output impedance.
Title: Re: QRV-08 hum
Post by: CapRock on April 04, 2011, 05:42:23 AM
ok I removed the jumpers and here are a list of my voltages.  LEDS are still dark



input voltage: 119.8 VAC
TR2 pins 6 and 7: 11.57 VAC
TR2 pins 9 and 10: 12.35 VAC
TR1 pins 6 and 7: 11.86 VAC
tr1 pins 9 and 10: 12.69 VAC

BR3: 11.17 VDC
BR4: -12.03 VDC
BR1: 11.23 VDC
BR2: -12.30 VDC
Title: Re: QRV-08 hum
Post by: peranders on April 04, 2011, 09:25:24 AM
Better but 12 VAC should generate 15-16 VDC

What about the voltages out from the regulators? You can measure this at J1, J2, J4, J5. The pads  in mind are those closest to the designators. You measure with respect to ground.
Title: Re: QRV-08 hum
Post by: CapRock on April 05, 2011, 04:35:01 AM
ok here they are in VDC

J5: -9.59
J4: 8.64
J2: -9.37
J1: 8.48
Title: Re: QRV-08 hum
Post by: CapRock on April 09, 2011, 08:05:03 PM
I posted the DC voltages you had asked for.  Is there anything else I need to test?
Title: Re: QRV-08 hum
Post by: peranders on April 10, 2011, 03:56:52 PM
Values of the smoothing caps, C27, C28? 2200 uF? Do you have any oscillscope? It would be interesting to se how much ripple you have on the raw voltage. With 12 VAC, you should have approx. 15-16 VDC at least. Do the red LED's shine?
Title: Re: QRV-08 hum
Post by: CapRock on April 15, 2011, 03:35:11 AM
Hi,
   LED's do not shine and yes I am using 2200uf for the c27, c28, G27, G28 snap in caps on top of the board.  And then on the bottom side of the board I have 2200UF caps for C29, C30, G29, G30.  I do not have a scope, is this something I will need for further testing?
Title: Re: QRV-08 hum
Post by: peranders on April 15, 2011, 09:02:47 AM
You don't need smoothing caps on the solder side but it won't hurt electrically. The regulators may work but the input voltage is too low. I'm also really suspicious about your high ripple voltage voltage. It should be rather flat since you have 4700 uF as smoothing. With nearly 13 VAC, you should have 17 VDC. Are the amps working? Much hum?

You must get in touch with an oscilloscope owner.
Title: Re: QRV-08 hum
Post by: CapRock on April 18, 2011, 05:47:40 PM
Hey per can you give me a list of everything you need me to test with the oscilloscope?  I know an owner but he is not very close to me so I would like to try and do this in one trip if possible.
Title: Re: QRV-08 hum
Post by: peranders on April 18, 2011, 06:52:49 PM
Since you have around 12 VAC, you should have 12*1.4 as top voltage after rectification and the min voltage should be maybe 1-2 volt under. The frequency must be 100 Hz for 50 Hz or 120 Hz for 60 Hz. If you have 50 or 60 Hz the rectifier bridge may be broken.
Title: Re: QRV-08 hum
Post by: CapRock on April 21, 2011, 04:49:33 PM
Hmmm. Is it really possible that all of my rectifier bridges broke in the same exact way?  So if I get ahold of a scope where is a good spot to test the frequency of power?  Or am I not understanding and I need to test something else. I will hook everything back up today and see what it sounds like
Title: Re: QRV-08 hum
Post by: peranders on April 21, 2011, 07:11:53 PM
The rectifier bridges might be Ok but your raw input voltage needs some investigation.
Title: Re: QRV-08 hum
Post by: CapRock on April 21, 2011, 11:28:13 PM
So I wired it up today and tested it and it works.  there is no buzz/hum until the last 2 steps of my attenuator and it is almost not audible, so it is very low.  LED's are still dark though.  I tried to adjust the bias trimpots and they have no effect on the voltage across R1/E1.  E1 was reading .006VDC and R1 was reading .022VDC.  The sound is good and it stays tight and clean even when very loud.  I have to leave the jumpers on though because when I remove them the sound was crackling and distorting.  Any Idea why the trimpots wont work?  Also, as I said before I am not very familiar with oscilloscope's, so what is it exactly that you would like me to measure and how do I measure it?  I'm  sure my friend that owns the scope will be able to help me though this, thanks.
Title: Re: QRV-08 hum
Post by: peranders on April 25, 2011, 07:53:29 PM
The reason why the LED's not are on is that the input voltage is too low, assuming that the regulators are correct.
Title: Re: QRV-08 hum
Post by: CapRock on April 27, 2011, 07:46:56 PM
since my voltage is not high enough do you think I am still not hearing the full potential of the amp?  If it is worth it I will continue to search for the problem.
Title: Re: QRV-08 hum
Post by: peranders on April 27, 2011, 08:23:05 PM
The amp will most likely work properly but the power supply rejection isn't so high so clean supply is essential but as you have noticed a small of hum will slip through. It would be interesting to see how your raw voltage look like. Depending how it look you can disable the LM317/337 preregulators. By this you will "earn" 2-3 volts but it could be tricky if you don't have the right tools.