|
Post by whittie on Apr 10, 2010 6:38:13 GMT
Hi all, Just bought one of these and I have a few issues. I wrote a massive essay and my internet had a nanny so I've lost it. Short of the Long: When connected to my MP3 player, the sound is very soft. When connected to the headphone out on my stereo it is very loud. When I use the pot to control the volume anything less than full volume (no restriction) sounds REALLY terrible and very bassy. I have uploaded some pics (Hopefully they work when this is posted) over here: smg.photobucket.com/albums/v621/Tommo560/Silicon%20Chip%20Headphone%20Amp/of the build. Please be kind, this is my first ever attempt at soldering on a PCB!! I think maybe the resistors for R3 and R6 (I put 2k in) should be wire links? I will be using this amp at work with the input being the MP3 player, so whatever suits that the best I think. Also, LED#4 is not light. I don't know if this is an issue or just a dead LED, but it is not alight. Also, the DC voltage from the PSU is +-20V is that supposed to be that high, The toroidal transformer outputs the proper +-15V. Also, the 5W resistor is REALLY hot! If you could help me out that would be great, this thing sounds amazing (from my short time with it through the stereo anyways ) I have to run, I'll update when I get home. Thanks all, Tom.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 10, 2010 7:25:06 GMT
Hi Tom You will need to disconnect the PSU from the main HA PCB, and correct the voltage regulator problems first. The output voltages from the PSU should be normally between about +-14.85 to +-15.25 volts. Too high a voltage from the PSU is likely to damage the I.C. on the main PCB. I will see if I can spot anything obvious in the PSU photo that you posted. Alex P.S. Are you able to take a couple of close up photos of the PSU PCB? The resolution of the existing photo is not adequate, and many details are obscured because of the angle of the photos. For starters though, double check that you haven't swapped the LM337 and the LM317 .The LM337 should be on the RHS of your photo. What voltage are you getting at the 2 pin terminal block . Is it +5V ? BTW, the 7805 voltage regulator and associated components are not required in this application. Also, you should remove the 330 ohm PW5. See attached drawing. Doing these changes will permit easy fitting of a front panel LED, without needing to use a dropping resistor at the LED, and make the PSU run cooler,as well as perform better in this application.
|
|
|
Post by whittie on Apr 10, 2010 10:14:56 GMT
Hi Alex, Sorry about pic quality, that is Photobucket doing its thing. I have uploaded them to the FTP server heres: members.iinet.net.au/~johnwhitfield/SCHA%20Pics/They are all 12MP pics and the extra ones of the board that you asked for. The CON3 connection reads a solid 5.0V. I find it a bit weird that the CON2 reads EXACTLY 20V. I think the 15 and the 5 are adding up somewhere... Even possible? Haha, checked the 337 and 317, You were on the money, they are the wrong way round My bad, I should have picked that up when I installed them! Like I said, first electronics project. Voltage is now +-15V on each connection Booboo number two. Re-installed the power to the headphone amp the wrong way round and fried my $17 LM4562 opamp Well, back to the electronics shop for another one I installed the burr-brown chip, corrected the polarity and she fired right up. The issue with the muddy and soft sound is still there tho. I will get around the re-wiring the PSU on my next kit. I will just leave this one as "Standard" except for the amp PCB for now. I will be buying another kit and doing a full-on mod to that including the moon module for the amp For now, I would like to sort out this soft noise Issue, I will try linking across the R3 and R6 lines, but I think my POT is just terrible! **edit** Well, I wire linked R3 and R6 and it maybe about 1/10th of sweet nothing difference. That's me out of ideas. I just find it weird that the stereo is so much louder (what I would have thought would have been normal volume for the amp, and the MP3 player so soft
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 10, 2010 10:55:32 GMT
Tom Next on the agenda is to find out why one of the 4 LEDs isn't lighting. Double check that the one that isn't working is the correct way around. However, before you go any further, make sure that you still have +-15V at the power input terminals on the main PCB, just in case there is a fault on the main PCB that loads down the PSU. Alex
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 10, 2010 11:09:52 GMT
Tom In the photo of the PCB (1000986) there are 2 green capacitors either side of the link directly below the I.C. What value are they ? Are you sure that you haven't mixed them up with C1 and C2 ?
Alex P.S. I will just make new posts each time I have a question.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 10, 2010 11:38:47 GMT
Tom Perhaps it is just the angle the photo was taken, but could you also double check that there are no solder bridges between the 4 lots of power transistor terminations under the PCB ? i.e. each of the 3 terminations (base,collector and emitter) are clearly separated. Alex
|
|
|
Post by whittie on Apr 10, 2010 14:00:01 GMT
Tom Next on the agenda is to find out why one of the 4 LEDs isn't lighting. Double check that the one that isn't working is the correct way around. However, before you go any further, make sure that you still have +-15V at the power input terminals on the main PCB, just in case there is a fault on the main PCB that loads down the PSU. Alex Hi Alex, Thanks for the help mate! The LED's are all good for orientatin and they all are seeing 1.84V. I did have an issue where I incorrectly installed 2 the wrong way around so I had to man handle them out so I may have damaged one. The voltage is good though and I'll never see the LED and I don't have another so I shouldn't need it right? The voltage to the main PCB is +15.11v, -14.74V when the amp is running.
|
|
|
Post by whittie on Apr 10, 2010 14:01:58 GMT
Tom In the photo of the PCB (1000986) there are 2 green capacitors either side of the link directly below the I.C. What value are they ? Are you sure that you haven't mixed them up with C1 and C2 ? Alex P.S. I will just make new posts each time I have a question. The two caps say "2A473J" and to be honest I don't know if they belong there, but they came in the bag and are the same shape as drawn on the PCB... C1 and C2 are blank cause I don't know what goes there either. There is a photo of all the left over bits I had, for this reason. The two yellow, square, caps (?) left over read "1n2 J", again, no Idea what this means. I also have 3 caps (?), little round brown things, two read 101, one read 47. Also not sure where these go. As you can tell, My knowledge of electronics is probably more than most, but still SERIOUSLY lacking! It's been a while since I studied it at uni or did it in any sort of hobby capacity.
|
|
|
Post by whittie on Apr 10, 2010 14:10:22 GMT
Tom Perhaps it is just the angle the photo was taken, but could you also double check that there are no solder bridges between the 4 lots of power transistor terminations under the PCB ? i.e. each of the 3 terminations (base,collector and emitter) are clearly separated. Alex I don't know what it is you are referring to, but the only solder bridges are in places where links are by the PCB anyways so I didn't bother re-soldering them. I also tried linking across R3 and R6, to no effect. Thanks! Tom.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 10, 2010 23:45:53 GMT
Hi Tom Remove those 2 green capacitors, and fit the 2 x 47pF capacitors that you should have been supplied with. The present values will cause severe HF rolloff. Also, you should check that there is very close to 0mV at both of the 47 ohm series output resistors. Does the Altronics instructions give the Altronics catalogue numbers of the components supplied ? If so I would recommend that you replace the unlit LED, which would appear to be damaged, despite having the correct voltage drop (at present) Alex P.S. The Altronics catalogue number for the red LED is Z0700. I don't know why they supplied 2 x 101 marked ceramic capacitors. If you only have 1 x 47pf ceramic capacitor, then you could use those 2 x 100pF capacitors instead.
|
|
|
Post by whittie on Apr 11, 2010 2:22:27 GMT
Hi Tom Remove those 2 green capacitors, and fit the 2 x 47pF capacitors that you should have been supplied with. The present values will cause severe HF rolloff. Also, you should check that there is very close to 0mV at both of the 47 ohm series output resistors. Does the Altronics instructions give the Altronics catalogue numbers of the components supplied ? If so I would recommend that you replace the unlit LED, which would appear to be damaged, despite having the correct voltage drop (at present) Alex P.S. The Altronics catalogue number for the red LED is Z0700. I don't know why they supplied 2 x 101 marked ceramic capacitors. If you only have 1 x 47pf ceramic capacitor, then you could use those 2 x 100pF capacitors instead. I owe you big time Alex! I went back through everything I have and found another 47pf capacitor, which makes two, so I will install them now. The two 47ohm series resistors reads 0.0mV on he left and 4.5V on the right..... The right channel also doesn't have any sound any more. **EDIT** OK, well it does, but only for a half second or less when I first turn the power on and off. Once everything starts up, the sound in the right channel cuts out! The sound is still very soft too. I've had another good look over the board and can't see anything sus any more, and apart from those few caps and a couple of resistors (2x7.4k and 2x1.2k) that I can't place, everything is there. Is there supposed to be anything in place for C1 and C2? I still have two square, yellow, things with 1n2J written on them.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 11, 2010 2:54:55 GMT
Tom Is the side with 4.5V at the 47 ohm resistor, the same side as the LED that doesn't glow ? The highs will improve with the 47pf capacitors fitted, and you can leave C1 and C2 vacant in this version. Let's concentrate on getting the right side working, and worry about it being soft until later ? It could be that your source is at a fairly low level, and if you plugged a normal CD player into it, it should be fine, assuming no other problems. You will need to try something like that later on, and if it is O.K. from a CD/DVD player we can then increase the gain to suit your source. Alex
|
|
|
Post by whittie on Apr 11, 2010 8:32:31 GMT
Tom Is the side with 4.5V at the 47 ohm resistor, the same side as the LED that doesn't glow ? The highs will improve with the 47pf capacitors fitted, and you can leave C1 and C2 vacant in this version. Let's concentrate on getting the right side working, and worry about it being soft until later ? It could be that your source is at a fairly low level, and if you plugged a normal CD player into it, it should be fine, assuming no other problems. You will need to try something like that later on, and if it is O.K. from a CD/DVD player we can then increase the gain to suit your source. Alex Alex, Correct. The LED#4 is on the right hand side, the same side as the headphone output and that is the side with the 4.5V on the 47ohm resistor. Ok, no problem, I am just trying to list all the issues to try and help with diagnosing the problems. Tom.
|
|
|
Post by whittie on Apr 13, 2010 9:40:28 GMT
Well big thanks to Alex, sandyk, for his help in solving this.
Turns out when I installed the led I had a bad solder so that was causing the right channel to cut out.
It now works and sounds amazing!
I would also just like to point out to anyone considering it that with the help of this board a complete noob, me, was able to build this including purchasing everything required for less than $200au and about 15 hours fun. What a bargain amp!
|
|
|
Post by whittie on Apr 17, 2010 11:13:22 GMT
Amp finished and cased: Can't say enough for the help this board provided in terms of initial research and SandyK for his help troubleshooting. Without this reference I would have spent double and bought something not as good!! Tom.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 17, 2010 11:20:13 GMT
Amp finished and cased: Can't say enough for the help this board provided in terms of initial research and SandyK for his help troubleshooting. Without this reference I would have spent double and bought something not as good!! Tom. Nice work Tom. ;D All you need now is a JLH to further improve that low end response. Alex
|
|
|
Post by whittie on Apr 17, 2010 11:33:36 GMT
I'll be the first to admit this wasn't the best Casing job, but when the JLH arrives and I can get all the parts I'll be building a second version in a nice Ally case to get the looks to match the performance of this thing!
I really am overly impressed by it's performance and it has been an enlightening experience. Next time I need a new piece of HIFI kit I'll sure be checking out DIY!
|
|
|
Post by whittie on Apr 20, 2010 16:08:00 GMT
Wow I hate you SandyK!!! I have been using the SCHA for about 3 days now and I've taken it to work where I listen to the most music and I'm listening with headphones through my $1200 integrated amp now at home.... IT'S TERRIBLE!!!! Wow, I NEED to get another SCHA for home! On another note, I am getting a lot of humming at medium volume on the amp. Low volumes are good and so is full volume (literally, flat out) but anything in between has a lot of hum
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 20, 2010 21:49:29 GMT
Hi Tom Do you have a wire between the "Earth"pin on the PCB and the IEC socket's mains earth on the aluminium that the transformer is mounted on ? I didn't need it with this one, but the "Earth " pin is close to the earth tag on the aluminium. Also, you will need an earth lug connected from the shaft at the front of the volume control (or soldered to the metal body of the potentiometer ) to the same main earth point. ( The photo was from during testing, before fitting a USA type Toroidal transformer) Alex
|
|
|
Post by whittie on Apr 22, 2010 0:49:55 GMT
Indeed I do not have the board earthed... I have grounded the IEC mains to the POT but from my understanding when reading the instructions it said the amp board should be grounded to chassis earth but not the same earth as the psu PCB.
I got confused here and thought "plastic case, therefore, no earth, I won't solder it, so I just connected the mains earth to the volume pot.
I'll take the amp home over the weekend and see how I go with soldering the amp PCB to a common earth with the IEC mains and the POT case.
At least I'm learning something everytime I go near this thing, it's great ;D
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Apr 22, 2010 1:53:47 GMT
Tom In the photo that I attached above, you will also see that the transformer is mounted on a piece of aluminium that is spaced a little above the bottom of the plastic case. This helps to keep the plastic case from getting too heated by the transformer, as well as providing a direct path to IEC earth if the primary of the transformer gets damaged by some kind of mains surge. Alex
|
|
|
Post by whittie on Oct 15, 2010 0:09:00 GMT
Hey guys, me again. Well, i was so impressed with the first scha I built that I bought another of these last weekend. This time I followed ALL the mods, including psu and transistors I skipped last time and its amazing! The bass extension is insane! I also picked up everything for a jlh and now just waiting on the board from the UK to put the parts on and then a fancy case this thing deserves. This second amp is so good I went back and did the psu mods to my first amp, along with a blue velvet pot I was trying to Chase away some static noise issues. However, I have a persistent humming noise in this amp. It's soft and gets louder as the volume goes up, but dissapears at full volume... I don't have this issue with my second amp, just this first one still. I thought it might have been due to the non modded psu, thats why i went back to it, but apparently not. Does anyone have any ideas? I compared the two amps side by side and they look identical! Also, this amp is for home, but I just realised due to the sensitivity of it, it amplifies the bageebas out of the noise from my usb dac, so any suggestions on a decent usb dac that doesn't produce silly amounts of static and sounds really nice with these head amps? Thanks a million, Tom.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Oct 15, 2010 2:19:06 GMT
Hi Tom Is the earthing identical ? Are you using the Earth pin on the HA PCB connected back to mains earth ? Sorry, but I can't really help with the USB DAC issue. Some PCs are much better than others in this respect . That is why I use SPDIF Out from my Asus Xonar D2X soundcard. I presume that the USB DAC has it's own dedicated mains PSU ? Have you tried bonding the case of the DAC to a rear screw on the PC itself? Perhaps even trying that with the main earth of the SC HA. I fitted a banana socket to the rear of an earlier SC HA for that purpose. Alex
|
|
|
Post by petef on Oct 16, 2010 1:24:00 GMT
Tom, it sounds as if you have an earthing issue in your amp. Good practice calls for star earthing, which as it's name implies means all of the earths go back to a central star point. It really doesn't matter where it is, but the earths should all be as short as possible and from reasonably heavy gauge wire. Typically you'd bring in your earth from the IEC connector to e reasonably central location and run all your earths to there. The idea is to have all the earths at precisely the same potential. Be careful of any loops in the wires, particularly need transformers, as they will act as additional windings. Clearly you shouldn't have any loops if the earth paths are as short as possible anyway.
If you still have a hum after taking care of that, and I'd think the above is most likely, make sure your inputs leads, wires to the pot etc are routed well clear of the power supply section, in particular the transformer. Let us know how you go, but I'm sure that will fix the problem.
Pete
|
|
|
Post by whittie on Oct 17, 2010 6:00:18 GMT
Thanks for the thoughts guys.
I opened the SCHA back up and rewired the Earth's to make them as short as possible and that didn't do anything at all. I have noticed that the humming noise is only an issue in the right channel. The only thing that is different between this amp and the second amp I built is that I am connected to the secondary headphone output, with the first not connected to anything. Could this be causing the issue?
I followed with the ground loop theme and noticed that the USB DAC only made noise when the usb cable was connected, and then it made no noise when the laptop was running on batteries instead of on power. So, the issue is with the power supply for the laptop. I have the same issue with huge interference when charging the laptop and using the VGA output, in fact that is why I use the HMDI output instead of VGA to connect to anything.
To cure this problem I snipped the 5V, ground and shielding wires in the USB cable I am using. The USB signal is only sent through 2 wires, although USB cables have 5 wires. Given the USB DAC has it's own power source, the three extra cables are redundant. This disconnects the earth and shielding between the USB DAC and the laptop and made a big difference. It's not totally gone, but it's very quite only when the SCHA is turned to full volume, which I wouldn't be able to notice the hum at those volume levels anyways!!!
Tom.
|
|