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Post by PinkFloyd on Nov 30, 2013 20:41:46 GMT
[/quote]I'm a little unsure about the transformer. I have the one pictured here but it definitely isn't a torroid. You don't know of a source for torroids for those of us across the water in the US, do you? I'd be happy to buy some bits from you but I figure the shipping to the US would be atrocious. Otherwise I'm just looking for more information on the mods you did to stabilize(?) the input power, and anything else people have found to improve the amplifier. I have made a first pass through most of the Panda threads, but I haven't collated all the modifications into a digestible format yet. I know I need to source some ~120 ohm capacitors for the output impedance for my K701s. Ceramic, Poly, carbon? I'm not really sure how to go about selecting the type of output cap.[/quote] You don't need output capacitors.... you need output "resistors". 120ohm Metal film types will be fine, you can also try different values of resistors between 10 - 120 ohms.... I preferred 75 ohm in my Panda. That transformer you got from hifidiy looks like a good one so just use it  No need to stabilize the input power as the regulation takes place onboard the Panda PCB.... just feed it 18V AC and it will do the rest. Mike. |
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Post by imstimpy on Dec 1, 2013 13:43:31 GMT
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Post by imstimpy on Dec 2, 2013 18:37:58 GMT
The hardest part of the Panda so far has been deciphering why the different pieces go in different areas, finding them on the circuit diagram and the PCB, and understanding the few erroneous labels in the BOM/PCB. I've got a neat list of items that have been previously documented in various places: Errors -> Correction (location on PCB): Dale resistor 1/2W3 x4 (populated at 2.2)) Gold 25V100UF x1 -> 16V100UF x1 (populated at cap location 100UF) voltage regulator tube 3.9V x1 -> diode 3.9V x2 (populated at diode location 3.9V) voltage regulator tube 18V x4 -> diode 18V IN4746 x4 (populated at diode location 18v) Warnings: There are both Dale 1K and KOA 1/4W1K resistors on the BOM and are both labeled 1K on the PCB There are Dale 1.47K and Dale 1/2W1.5K resistors and are both labeled 1.5K on the PCB. The striped KOA resistors are all located near the power supply side. The larger Dale resistors go in the wider spaces nearest to the output side. I have a bit of confusion about a mismatched part vs the BOM. The BOM calls for a Gold 25V100uF cap located near the relay, 4.7uF cap, and 47uF cap. I received a tiny 16V100uF cap instead. All pictures I've seen show the 25V cap. Can I use this 16V cap or should I order a 25V cap as the BOM calls for? |
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Post by imstimpy on Dec 2, 2013 23:02:41 GMT
I followed this procedure for testing Idss, and this procedure for testing Vgs. Knowing very little about the process, I can only assume I read the descriptions and diagrams correctly. Matching results for 2SK246 JFETs: Idss - Vgs (off) 5.16mA - 2.64V 5.17mA - 2.65V 5.25mA - 2.68V 5.29mA - 2.67V 5.70mA - 2.83V 5.73mA - 2.83V 5.98mA - 2.92V 6.06mA - 2.94V 6.09mA - 2.95V 6.16mA - 2.97V Regardless of which data I use, the order and deviation is roughly the same. Unless somebody tells me otherwise, I'm going to select the highest 4 to pair at Q6/Q8 and Q15/Q16 and the next 2 for the other 2SK246 position (unlabeled on the circuit diagram). |
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Post by imstimpy on Dec 8, 2013 22:46:59 GMT
It lives! Connecting the diyhifi transformer was a bit of a debacle but I've got it powering. I'll draw up the connections in MS Paint sooner or later. The transformer is rated at 18V but the measured output is 21V. I'm not sure if that is related to my DC voltage at the 1k5 resistors going no lower than 1.54V. When it originally powered on the DC voltage was 1.90V o.0. Now, I'm only measuring the voltage across a single 1k5 resistor at a time, but I have matched the voltages for each channel. I need to touch up the DC offset still as it sits at 15-18mV right now.
I decided to power it up with the 16V100uF cap at C26. I have yet to actually measure a voltage there but my suspicion is it should be 16-21V DC (depending upon the transformer). I have a 25V100uF cap on order but I couldn't wait for the shipment.
My output resistors are currently NTE 1W-82ohm 2% metal film resistors. I have some Kiwame parts on order but, again, I couldn't wait.
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Post by blackeyeliner on May 14, 2015 18:17:56 GMT
Need help. Built my kit, works perfectly well, apart from hum. I tried literally everything: DC adjusted (to near zero), PCB grounded to chassis, potentiometer shaft grounded, AC wires braided, signal cables shielded, tried juggling around PCB, on-off button, jack terminal, that's not it. All connections reflowed. Voltages on D669/B649 checked. PCB is clean. Potentiometer is definitely out of question (changed for a new one, definitely original).
It's a very low volume hum, barely listenable but you can notice it between tracks. It's right ear only. Does not get louder with volume increase. Sounds like a 50 Hz hum + some higher frequency tone. How to troubleshoot? It doesn't let me call it a finished amp!
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Post by PinkFloyd on May 14, 2015 19:28:08 GMT
Have you got the amp on top of other equipment? If so, maybe try moving it a bit further away....... It could also be a ground loop.
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Post by blackeyeliner on May 14, 2015 20:47:05 GMT
Have you got the amp on top of other equipment? If so, maybe try moving it a bit further away....... It could also be a ground loop. Nope, standing alone. Also the hum is there when no equipment is around, connected or even turned on... Ground loop is also not in question, as, again, it's there when the amp is not connected to anything, and on top of that, there's no ground connection in the AC network where I live, hence ground terminal on the IEC jack is not connected anywhere. |
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Post by PinkFloyd on May 14, 2015 21:28:48 GMT
Have you got the amp on top of other equipment? If so, maybe try moving it a bit further away....... It could also be a ground loop. Nope, standing alone. Also the hum is there when no equipment is around, connected or even turned on... Ground loop is also not in question, as, again, it's there when the amp is not connected to anything, and on top of that, there's no ground connection in the AC network where I live, hence ground terminal on the IEC jack is not connected anywhere. Tricky one mate, especially as you have no earth connection in your country..... where are you? The Sahara Desert? have you tried fitting a class X2 suppression cap across L/N? 470nF class X2 will be a good starting point. What concerns me is the fact it is only happening on one channel..... erm, leave it with me and I'll have a look through my notes...... you can bet your bottom dollar that it will be something trivial and not something that is immediately suspect. Mike. |
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Post by blackeyeliner on May 14, 2015 21:46:01 GMT
Nope, standing alone. Also the hum is there when no equipment is around, connected or even turned on... Ground loop is also not in question, as, again, it's there when the amp is not connected to anything, and on top of that, there's no ground connection in the AC network where I live, hence ground terminal on the IEC jack is not connected anywhere. Tricky one mate, especially as you have no earth connection in your country..... where are you? The Sahara Desert? have you tried fitting a class X2 suppression cap across L/N? 470nF class X2 will be a good starting point. What concerns me is the fact it is only happening on one channel..... erm, leave it with me and I'll have a look through my notes...... you can bet your bottom dollar that it will be something trivial and not something that is immediately suspect. Mike. Thanks so much for your help! I am not afraid of learning new things, but still very new to electronics. I live in Russia, we really don't have any kind of ground on our AC network, it's just two wires. Actually, it does not influence anything really that much, apart from some special cases. I haven't tried suppression cap. What kind of cap do I look for and where to fit it? I am eager to try if it helps. The hum is really in one channel and it's the right channel only. And it's something on the board, i.e. moving the board, grounding anything does not even remotely change the hum. |
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Post by blackeyeliner on May 31, 2015 10:00:17 GMT
Tricky one mate, especially as you have no earth connection in your country..... where are you? The Sahara Desert? have you tried fitting a class X2 suppression cap across L/N? 470nF class X2 will be a good starting point. What concerns me is the fact it is only happening on one channel..... erm, leave it with me and I'll have a look through my notes...... you can bet your bottom dollar that it will be something trivial and not something that is immediately suspect. Mike. So, no ideas? |
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Post by Deleted on May 31, 2015 10:19:12 GMT
Try comparing the Capacitance multiplier voltages. i.e. Base, emitter and collector of Q3 and Q12 in both channels.
There is a circuit on page 1 of the thread.
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Post by blackeyeliner on Jun 5, 2015 14:41:59 GMT
Try comparing the Capacitance multiplier voltages. i.e. Base, emitter and collector of Q3 and Q12 in both channels. There is a circuit on page 1 of the thread. Hi! Just measured them: Right channel (where the hum is): B649: -17.15V, -24.03V, -17.73V D669: +17.15V, +23.85V, +17.75V Left channel (dead silent): B649: -16.98V, -24.01V, -17.55V D669: +17.11V, +23.63V, +17.68V Seems normal. Hum still there. |
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Post by Deleted on Jun 5, 2015 22:14:44 GMT
The voltage readings are O.K as evidenced by just under 600mV across each base - emitter junction.
You could check the capacitors (C3 and C4) on the base of the multiplier transistors to see that there are no dry joints and that the capacitors are O.K.
If the voltage drops across the 1K5 resistors of the input FETs in both channels are also similar, with only a few mV difference between each pair of 1K5 resistors, and the voltage drop across the 10 ohm output emitter resistors are close in each channel too, then it appears likely that you have some kind of earthing problem. Possibly in the input and volume control area.
Alex
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Post by PinkFloyd on Jun 5, 2015 22:43:41 GMT
Re-flow every solder join, it's a dry joint...... 97.3% sure.
Pinkie.
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Post by PinkFloyd on Jun 5, 2015 22:48:04 GMT
Pics of the underside would help.
Mike.
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Post by blackeyeliner on Jun 5, 2015 23:58:03 GMT
The voltage readings are O.K as evidenced by just under 600mV across each base - emitter junction. You could check the capacitors (C3 and C4) on the base of the multiplier transistors to see that there are no dry joints and that the capacitors are O.K. If the voltage drops across the 1K5 resistors of the input FETs in both channels are also similar, with only a few mV difference between each pair of 1K5 resistors, and the voltage drop across the 10 ohm output emitter resistors are close in each channel too, then it appears likely that you have some kind of earthing problem. Possibly in the input and volume control area. Alex Will check what you listed. As for the earthing problem - hum is there when no input is connected (I mean, physically to the board - no wiring), and it's also there when no potentiometer is installed. Also I triple-checked the connection between Alps ground and board ground, all channels etc. |
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Post by blackeyeliner on Jun 5, 2015 23:59:00 GMT
Re-flow every solder join, it's a dry joint...... 97.3% sure. Pinkie. That might be true, I'm still new (not a newbie, but new) to electronics. I will re-solder everything tomorrow + pictures. |
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Post by blackeyeliner on Jun 7, 2015 18:09:31 GMT
Well, I checked everything I could.
Voltage across 1.5K resistors is 1.500V / 1515V
Across 10 Ohm resistors - 0.600 / 0624
I reflowed each and every solder joint in the channel, hum still there. It's really really silent, but well noticeable, especially when the amp turns on or off. It's definitely a 50 Hz hum. I think I have to order a new Panda board to really be debug it. What a joke that will be, if new one will hum as well. Or, I might go and get an oscillograph and trace the source of this hum.
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Post by blackeyeliner on Jun 7, 2015 18:18:44 GMT
Here's photo of the underside of the board i.imgur.com/Xb1SkIN.jpgI know the Alps connection points are damaged - I damaged them while trying to remove the alps from there (the first idea back when I assembled it was that the alps was faulty, so I bought a new one and installed it on the amplifier itselr, rather than on the board. However, I checked connection between alps and the board - it's fine. Plus, the hum was there before that as well. |
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Post by Deleted on Jun 7, 2015 23:06:26 GMT
blackeyeliner
I can't see anything obvious with the underneath of the PCB.
Perhaps a clear photo of the amplifier itself, complete with wiring, may suggest a way to help overcome the problem.
It may still be a poor PCB design too.
Alex
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Post by blackeyeliner on Jun 13, 2015 17:13:18 GMT
So I got oscillograph and here's what the infamous hum looks like. This is the healthy left channel. Some background noise is there, but I can't say I hear it: i.imgur.com/zRNG9LO.jpgThis is the humming right channel: i.imgur.com/fQQpnLR.jpgClearly there is an additional wave that I hear quite clearly. I think I could trace it back the signal chain but I don't really understand where I can measure safely on the board. |
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Post by PinkFloyd on Jun 13, 2015 19:27:16 GMT
Thinking back, I had a similar hum on one of the Pandas I built and it turned out to be a broken ground track under the potentiometer..... I had removed the pot (for some reason) and obviously managed to cock the track up into the bargain. Do a continuity check on all the pot connections and you may just find the culprit.... IIRC I soldered a piece of wire from the pot connection to the next pad in the chain and it solved the problem.
Mike.
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Post by blackeyeliner on Jun 14, 2015 11:42:22 GMT
Thinking back, I had a similar hum on one of the Pandas I built and it turned out to be a broken ground track under the potentiometer..... I had removed the pot (for some reason) and obviously managed to cock the track up into the bargain. Do a continuity check on all the pot connections and you may just find the culprit.... IIRC I soldered a piece of wire from the pot connection to the next pad in the chain and it solved the problem. Mike. Hi Mike! Thanks for this. I ran a full test of what is connected where - I have 100% ground connection everywhere, so I mean, the chassis, the ground terminal of the IEC jack, ground of the headphone jack, grounds of all power capacitors, everything is the same ground. Tracing the schematic back using the oscilloscope, I see that the source of the hum lies somewhere outside of the main amplification area, that is, the hum is there on bases of all four transistors in the right channel (and is absent on all four of the left channel's). |
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Post by blackeyeliner on Jun 14, 2015 17:05:11 GMT
Here's what I found tracing the signal path down the board. I was using the tone generator to identify the signal path and then silenced it down to see where the hum starts. It _seems_ like I found the place, where it starts: i.imgur.com/IGkkF1i.jpgIndicated with a yellow arrow is a 22 uF capacitor. I think, it's the C8 on the board. On one side of it, the signal is clean, on the other - it looks like a saw. Is it possible that this capacitor creates this? |
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