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Post by Deleted on Aug 8, 2011 20:35:28 GMT
Hi Dicky,
Great ... Yep, the 120 Ohm must go, otherwise a large part of the configurability is gone. Also have a play with the gain settings.
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Post by dicky on Aug 8, 2011 20:44:03 GMT
I set the output resistance to 1R using the jumpers and set the gain to maximum. It's still relatively quiet but working well enough.
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Post by Deleted on Aug 8, 2011 20:59:49 GMT
It is quite possible it isn't playing very loud as it 'effectively' has a 220 Ohm output resistance at this point (even when set to 1 Ohm). max output power in 32 Ohm is (in this case where extra 120 Ohm is added) about 50mW max in 32 Ohm as opposed to 200mW (6dB) It should be playing considerably louder (and better) when a headphone plug without any resistors is mounted.
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Post by dicky on Aug 8, 2011 21:07:53 GMT
OK Frans, I'll remove the resistors tomorrow. My eyes are shot now and I've sniffed enough flux fumes for today. I'll report back tomorrow.
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Post by Deleted on Aug 8, 2011 21:15:08 GMT
Congrats Dicky!! We getting a full review when finished?
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Post by dicky on Aug 9, 2011 5:24:38 GMT
Thanks Javier, I will but I'm sure it's not working correctly. I just removed the resistors from the HP socket but the output level is unchanged and still quite low. It's listenable - probably at a level you might use late at night - but doesn't go anywhere near loud enough.
I'll check the pot connections tonight to see if I've got something wrong and have a play with the gain settings.
I'll let you know how I get on.
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Post by dicky on Aug 10, 2011 5:56:38 GMT
I checked all the measurements in the manual and the additional ones in the thread above and all was in spec. PSU=+/- 16.34V, Offset voltage -0.3 (L) to +1.7mV (R) with 0V when JP18 and JP28 are set. The DC protection circuit was working as advertised. OK, so I checked the pot connections and they were fine. I even connected the inputs directly to the board to rule out a dodgy pot. The amp is working but the volume is still low. I re-checked all the resistor and electrolytic values and all are correct. There are no obvious problems on the board or with my soldering. So that's me stumped.
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Post by Deleted on Aug 10, 2011 5:58:42 GMT
Dicky What are you using for a source ? Alex
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Post by dicky on Aug 10, 2011 7:15:55 GMT
Hi Alex,
I've tried my CD player and mini APE via a DACmagic and I've also tried an iPod.
Regards,
Dicky
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Post by dicky on Aug 10, 2011 7:30:47 GMT
Oh, and just to note that using the same sources into my Panda and X-CAN V2 I get the full range of volume.
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Post by Deleted on Aug 10, 2011 8:00:09 GMT
Can you adjust the gain by using the jumpers and does this help ?
Can you connect the headphone out from the ipod directly to the input of the amp (adjust volume with the ipod) ? so without vol potmeter in place. use the AC coupled mode (jumpers next to the input caps removed).
The DC test (1.5V) in low gain setting gave about the proper values on the output ? In this case the amp is amplifying correctly.
the maximum gain should be MUCH higher than the Panda's. I can even make it to distortion levels with the headphone out from a very soft playing MP3 player ?
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Post by Deleted on Aug 10, 2011 8:13:47 GMT
Just a silly question Dick, what setting are you using for gain?
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Post by dicky on Aug 10, 2011 11:15:38 GMT
Hi Frans, I set different gain values using the jumpers and the gain changed up or down accordingly - so more gain is available but it is still too quiet. Nowhere near Panda volume I already tried the iPod method to eliminate the volpot and had the same results. I'll try the AC coupled mode when I get home. I did the DC test with JP10, 13, 20 and 23 set as instructed and there was 0V on the output (CON6)
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Post by dicky on Aug 10, 2011 11:17:31 GMT
Javier, I have tried higher gain settings but mostly used the default setup for the testing. Bizarrely, it passess all the tests so I'm guessing there's something really stupid that I've done.
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Post by Deleted on Aug 10, 2011 11:34:00 GMT
Try the method with the 1.5V battery and the 390k resistor (no headphones connected please !) The jumpers next to the input caps MUST be placed and the DC servo jumpers must be removed.
What voltages do you get on R51/52 in this case. ?
This way we can determine if the amp operates correctly.
Panda gain (standard) is only 6x (15dB) This amp should be around 20x in the highest gain setting and about the same (5x) in low gain setting.
Are you sure the 270 Ohm resistors actuall are 270 Ohm, and the 33 and 1 Ohm resistor are also correct values ?
Gain is determined by the SMD resistors and it is not very likely but in case I soldered in the wrong values you might want to check them.
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Post by dicky on Aug 10, 2011 11:40:52 GMT
OK - I'll do that test. Just to confirm, I set JP10 and JP20 and remove JP18 and JP28 and measure voltage at R51 and R52 near the centre of the relay. I should get ~0.9V.
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Post by Deleted on Aug 10, 2011 11:43:48 GMT
yes that should be about it. When you set the gain jumpers this voltage should rise accordingly. The relay should be off so you should not be able to measure DC at the output connector.
If this voltage is correct the gain is correct too.
don't forget the 390k resistor in series with the battery. At the input connector of the amp 0.19V should be present. With 5 times gain it should be around 0.95V on R51/52. with 20 times gain it should be around 3,7V on R51/52.
If this is the case the amp is doing what it should do. Only the value of the output resistors could be wrong in that case (if the sound starts distorting at lower levels already)
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Post by dicky on Aug 10, 2011 11:53:00 GMT
Arooga! I don't recall any 1 ohm resistors. There are 4 off 1Meg ohm resistors in the BOM - 2 SMD and 2 SFR25. I definitely soldered 1M resistors in - I'll check the values of the SMDs too. The others are definitely 270R and 33R.
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Post by Deleted on Aug 10, 2011 12:06:35 GMT
R10 and R35 should be 1 Ohm
You can also bypass them (put in a short) or fit any value between 0 Ohm and 4.7 Ohm. The sound would have to be really, really, really soft with 1M on that position and start to distort at very low levels already. ?
The 4 1M resistors are in the DC servo path.
The maximum output power should be marginally smaller than the Panda (with a 120 Ohm)
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Post by dicky on Aug 10, 2011 12:13:59 GMT
Hi Frans - I think you have found the problem. R10 and R35 are listed as 100k in the BOM - so that's what I fitted. I'll fit shorts tonight (I don't have any other values I can use) and see what happens.
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Post by Deleted on Aug 10, 2011 12:37:19 GMT
Yes you are correct. Part says 100k and description says 1 Ohm. I'll go kill myself now... where is a bridge.. or a railway crossing. Sorry for that... must inform other builders *slaps on head* that explains the soft sound.
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Post by dicky on Aug 10, 2011 12:49:10 GMT
No problem Frans, if I had any experience I'd have noted the discrepancy. Hopefully all will be well now. Can I leave the shorts in or should I replace them with 1R resistors in the near future?
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Post by Deleted on Aug 10, 2011 12:53:25 GMT
I use the amp with the shorts but you can also solder 1 Ohm in parallel (the 100k doesn't do anything) on top or the bottom of the board. In that case you do not have to desolder the 100k.
When testing with low Ohmic output , high Ohmic load and very high (unrealistic high) capacitive loads it performed better (more stable, less ringing) with a 1 Ohm resistor.
If there is a 100k in there it will be playing loud once the correct value is in there !
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Post by dicky on Aug 10, 2011 18:44:29 GMT
Hi Frans, I've soldered a short across the 100k resistors in R10 and R35. Now I've got another problem ......... it's just blown my socks off! ;D She lives and sounds sweet. More subtle than the Panda and smoother too. I'll give her a good listening to for a week or so on 19x gain, BW-0 and 100R output resistance before I start to play with the configurations. (Listening on HD250 linear.) Thanks for all your help today - it's very much appreciated.
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Post by Deleted on Aug 10, 2011 18:51:13 GMT
Glad it works !
have a play with the jumpers and see if you can find a sweet spot for all your headphones.
Did your socks survive the blowing off your feet ?
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