solderdude
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Post by solderdude on Apr 27, 2013 23:17:37 GMT
This Thread will be used to ask questions or advice on everything regarding the filter board. The instruction manual (pdf file) can be downloaded here on: DIY Audio Heaven All boards are sold out. New boards won't be available. This board will be replaced by a 'Kameleon' type of filterboard which has replaceable 'modules'. Expect this to become available around the summer of 2016. |
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dicky
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Post by dicky on Apr 28, 2013 6:50:37 GMT
You have PM.  |
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solderdude
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Post by solderdude on May 2, 2013 9:11:09 GMT
Dicky spotted an omission (another one, the first one was already corrected) in the Fostex T40/T50 BOM lists (also true for the Paradox). The filter manual has been updated. When the manual was used for modified Fostex T40RP-mkII/T50RP?Paradox it is recommended to download the manual again. For all the other headphone BOM lists noting has changed. Also the manuals for modifications on the T40RP-mkII/T50RP with DT770 pads and SRH-940 pads have been updated. These manuals can be found here: diyaudioheaven.wordpress.com/schematics/headphone/ |
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Post by tommyb on May 3, 2013 18:10:20 GMT
Hi,
Psyched to have found this forum (and the website)!
I would definitely be interested in two or three assembled filters if that will be an option, one for Fostex T50RP, one for AKG K501 and possibly one for Hifiman He-500 (which I don't own at the moment, but would love to in the future).
Unfortunately my Fostex cans are in the States while I'm in Sweden, probably won't see them until X-mas... Oh well, I guess patience is a virtue.
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dicky
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Post by dicky on May 3, 2013 18:19:58 GMT
Hi Frans, I built a T50RP filter this afternoon and it's up and running.  It was a piece of cake to put together in just over 2 hours - great instructions, Frans!  I haven't tried adjusting it yet though - I just set the trimmers to their mid-point to check it was all working fine. I assume Px02 adjusts the 3kHz boost/cut?  I do have a problem with it - there is some noise when at max volume (the noise is not there without the circuit so it's not the head amp). However, I'm not too concerned because this noise was present in the previous filter (v1 PCB plus add-on 3kHz lift filter built on veroboard) so I assume I have a noisy PSU, mains or other external interference. I'll check again when I get it in a case. Thanks again, Frans. |
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solderdude
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Post by solderdude on May 3, 2013 19:41:06 GMT
The circuit does add some noise.
It's inherent to the circuit and the needed amount of boost (in case of the T50's)
With less gain or boost the noise will drop.
There is one cure but it limits the filter in some ways and that would be to replace the opamp notch section with a real inductor.
This introduces other things.
The noise is only heard with amplifiers set at high listening levels.
When music would be playing at the same potmeter setting you would probably end up being deaf in no-time.
Px02 sets the 3kHz and should be in 'mid' position most likely.
Px01 sets the 20kHz boost and must be at max position (fully CW)
a screened enclosure may help also.
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solderdude
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Post by solderdude on May 3, 2013 19:44:53 GMT
Hi, Psyched to have found this forum (and the website)! I would definitely be interested in two or three assembled filters if that will be an option, one for Fostex T50RP, one for AKG K501 and possibly one for Hifiman He-500 (which I don't own at the moment, but would love to in the future). Unfortunately my Fostex cans are in the States while I'm in Sweden, probably won't see them until X-mas... Oh well, I guess patience is a virtue. Welcome to the forum Tommy B, Javier will be making the assembled filters for the European continent. Jeremy (Garage 1217) for the USA/Canada region. The HE-500 filter and T50RP have been 'confirmed' to do what they are supposed to do. Fortunately Javier owns (and loves) the K501 so can test and 'tune' it personally. |
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dicky
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Post by dicky on May 3, 2013 20:07:07 GMT
The circuit does add some noise. It's inherent to the circuit and the needed amount of boost (in case of the T50's) With less gain or boost the noise will drop. There is one cure but it limits the filter in some ways and that would be to replace the opamp notch section with a real inductor. This introduces other things. The noise is only heard with amplifiers set at high listening levels. When music would be playing at the same potmeter setting you would probably end up being deaf in no-time. Px02 sets the 3kHz and should be in 'mid' position most likely. Px01 sets the 20kHz boost and must be at max position (fully CW) a screened enclosure may help also. Frans, the noise is not constant - it changes as I move my hand around the PCB. I have a feeling there is EMI. I'll let you know once I have it in a case (hopefully in the next 2 weeeks). If the 20kHz section is at max position, why not replace it with resistors? |
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solderdude
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Post by solderdude on May 3, 2013 20:13:37 GMT
It can be replaced with resistors but when you feel it is too much you can dial the boost down.
Actually only one wire link from the wiper to the 'max' side would suffice.
I have my Px01 set at about 90% so not entirely fully CW.
For some headphones where the BOM lists are merely suggestions based on graphs out there it could be very handy to dial in the exact amount of lift/decrease.
a shielded enclosure (connected to GND) is almost obligatory.
Noises that increase with holding hands above it are most likely gone when properly shielded.
Make a cardboard box around it and line it on the outside with alu-foil.
Connect that alu-foil to the GND of the circuit (screen of the RCA's) and you can check if screening helps.
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dicky
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Post by dicky on May 3, 2013 20:34:17 GMT
Fair enough, Frans. I already have an EMI shielded Hammond case on order.
I noticed that the ICs (particularly 102 and 202) seem to run warmer than in v1 of the PCB?
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solderdude
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Post by solderdude on May 3, 2013 21:17:24 GMT
hmmm that's strange and seems to point towards oscillation ?
Are they noticeably warmer than the other 2 ?
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dicky
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Post by dicky on May 4, 2013 9:41:30 GMT
Frans, I measured the IC temperatures (degrees C):
New PCB: IC102-29, IC202-28, IC101-27 and IC201-27
Old PCB: all 3 ICs-22
So the ICs are running warmer on the new board, but are within a couple of degrees of each other. There's more going on at the IC1/2 end of the new board; whereas on the old board there is a fairly even distribution of components over the whole PCB. Maybe that has an effect?
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solderdude
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Post by solderdude on May 4, 2013 9:55:49 GMT
Are the PS voltages the same ?
Did you use the same opamps ?
Are both PCB's 'on' for the same amount of time ?
Are the circumstances around the PCB the same (free air around it, vertical or horizontal on the same surface) ?
on +/- 12V each opamp dissipates 0.25W
a DIP package has a thermal resistance of 102°C/W so with 0.25W an increase (opposite the surrounding temperature) of 25°C can be expected so when the air is 20°C a junction temperature of 45°C is possible (so lower temperature on the outside)
150°C is allowed.
In a fully closed enclosure the temperature will rise even further as the total PCB emits 1W (not counting regulators or DCDC converters dissipation) which will heat up the internal air even more.
In any case the 150°C junction temperatures will not be reached even in a fully closed enclosure.
judging from the temperatures there are no oscillations.
I also didn't have them on my test-board as well (also a T50RP filter circuit).
Swap out opamps from the boards (when the PS voltages are the same) and see if it changes.
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dicky
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Post by dicky on May 4, 2013 12:20:31 GMT
PSU voltage is the same (+/-12V via 24v DC and TLE2426).
New PCB uses 4 off LM4562.
Old PCB uses 3 off TL072.
The new PCB had been on for about 3 hours and the old one for 1 hour and are next to each other (no cases - so free air) when I measured. The new PCB ICs are all now at 28. Ambient is around 18.
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Post by tommyb on May 5, 2013 17:38:18 GMT
Hi, Psyched to have found this forum (and the website)! I would definitely be interested in two or three assembled filters if that will be an option, one for Fostex T50RP, one for AKG K501 and possibly one for Hifiman He-500 (which I don't own at the moment, but would love to in the future). Unfortunately my Fostex cans are in the States while I'm in Sweden, probably won't see them until X-mas... Oh well, I guess patience is a virtue. Welcome to the forum Tommy B, Javier will be making the assembled filters for the European continent. Jeremy (Garage 1217) for the USA/Canada region. The HE-500 filter and T50RP have been 'confirmed' to do what they are supposed to do. Fortunately Javier owns (and loves) the K501 so can test and 'tune' it personally. Thanks for the welcome and the info, Frans! I'll get in touch with Javier about the filters. Is there anything preventing one from putting two filters (plus power supply) in the same box with a switch to toggle between them, so one can use the same box for two headphones? |
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