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The cathode has a flat on the side of the LED - this is the polarity indication. Lead length convention can vary and is _not_ 100% reliable guide to polarity. But the flat is always the cathode and can be checked even after the leads have been cropped.
Determining LED Polarity - Tech Tips - Engineering and Component Solution Forum- TechForum │ DigiKey
Finally soldered the new leds on the top of the board, lets hope there is a connection. Also went ahead of myself again and made another mistake I soldered the pot to the board, so now I'll never get it in a box, since I have no clue as to where to put the hole in the front plate. The hammond chassis so many use is to small for my preferred inletmodule. Maybe I'll just mount it on a board an se if it works just for the hell of it before I put it on the shelf...
I soldered the pot to the board, so now I'll never get it in a box, since I have no clue as to where to put the hole in the front plate. The hammond chassis so many use is to small for my preferred inletmodule. Maybe I'll just mount it on a board an se if it works just for the hell of it before I put it on the shelf...A few questions...
Saw this build and was intrigued, (Actually saw the T2, another easy-looking build, first but prefer P-P and MOSFETs to SE and BJTs.)
Main questions:
1) The 'pitch' at the beginning of the article implies that the amp works well with everything from IEMs to planars, quite an achievement given the absence of switchable gain. Anyone have experience using it with sensitive IEMs like the Etymotics?
2) Builders, what was your approx. total build cost? diyStore Kit price ~$190; would sourcing the parts directly produce a savings?
I've built kits from Dyna, Hafler, and Van Alstine so I think I can handle stuffing the board, but I wish there was a 'turn-key' chassis solution. I've seen pics of the amp on a 'picture frame' type stand and it looked nice (probably good for cooling too).
Currently using an O2 with the AGDR Audio 'booster board' which is a pretty extensive mod. Works fine but my soldering iron finger is getting the 'itch' and this looks like maybe a fun fall or winter project. It just has to work with both IEMs and my 250Ω Beyers.
Thanks in advance for any guidance or suggestions.
Saw this build and was intrigued, (Actually saw the T2, another easy-looking build, first but prefer P-P and MOSFETs to SE and BJTs.)
Main questions:
1) The 'pitch' at the beginning of the article implies that the amp works well with everything from IEMs to planars, quite an achievement given the absence of switchable gain. Anyone have experience using it with sensitive IEMs like the Etymotics?
2) Builders, what was your approx. total build cost? diyStore Kit price ~$190; would sourcing the parts directly produce a savings?
I've built kits from Dyna, Hafler, and Van Alstine so I think I can handle stuffing the board, but I wish there was a 'turn-key' chassis solution. I've seen pics of the amp on a 'picture frame' type stand and it looked nice (probably good for cooling too).
Currently using an O2 with the AGDR Audio 'booster board' which is a pretty extensive mod. Works fine but my soldering iron finger is getting the 'itch' and this looks like maybe a fun fall or winter project. It just has to work with both IEMs and my 250Ω Beyers.
Thanks in advance for any guidance or suggestions.
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dB Cooper,
I found this link to a WHAMMY BOM:
Mouser Electronics
The total is $102 +/-
I didnt see a case in the list, thats going to add some cost...
Fyi.
Alex
I found this link to a WHAMMY BOM:
Mouser Electronics
The total is $102 +/-
I didnt see a case in the list, thats going to add some cost...
Fyi.
Alex
Post #1 of this thread says
which makes me think that the Mouser Shared Shopping Cart may not include the AC power inlet module, or the power transformer, or the chassis. It might be worth further investigation.
edit- I also don't see any connector(s) for the left and right input signals. RCA jacks and/or 3mm TRS jack seem not to be on the list.
_
which makes me think that the Mouser Shared Shopping Cart may not include the AC power inlet module, or the power transformer, or the chassis. It might be worth further investigation.
edit- I also don't see any connector(s) for the left and right input signals. RCA jacks and/or 3mm TRS jack seem not to be on the list.
_
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Personally (not being a 'cable guy') I could live without an IEC power cord, and it seems like just using a regular cord with a strain relief and soldering to the board would alleviate crowding in that corner with that particular case...
What does the optocoupler do in this circuit?
I don't recall seeing a power line fuse in the schematic but I might have missed it... Shouldn't there be one?
What does the optocoupler do in this circuit?
I don't recall seeing a power line fuse in the schematic but I might have missed it... Shouldn't there be one?
The 4N35 optocoupler does a few things -
The optocoupler has two sides when looking at the schematic, the diode and the transistor. They are linked optically, not electrically, so the two sides of the optocoupler can share different voltages that don't effect the other side. as the current change in the LED side of the opto it will glow brighter or dimmer, which controls how much the transistor side conducts - in this circuit the current through the LED is directly equal to the mosfet current, and as it gets brighter it controls the BJT, whereby the BJT "burns up" the excess dc bias voltage.
The optocoupler appears to be a variable resistor in parallel with the inside 10k resistors - it changes the gate bias with the collector-emitter junction as the opto coupler looks at the current through the mosfet sources. The LED part of the opto has a 1.2v constant drop, this is used in conjunction with R18 to set bias current across the source resistors. If the current is too high it will make the LED brighter, that modulates the base of the transistor, and the collector-emitter junction will decrease its apparent resistance in parallel with the inside 10k resistors, changing the ratio of rail voltage to ground, decreasing the amount of voltage on the gates, and keeping the bias stable as the load swings.
Is a simple solution - its a single part and it automatically adjusts. If there is any drift the optocoupler will compensate immediately No resistors to measure across and potentiometers to adjust
Check this guide out for more circuit details:
"WHAMMY" Pass DIY headphone amp guide
Alex
The optocoupler has two sides when looking at the schematic, the diode and the transistor. They are linked optically, not electrically, so the two sides of the optocoupler can share different voltages that don't effect the other side. as the current change in the LED side of the opto it will glow brighter or dimmer, which controls how much the transistor side conducts - in this circuit the current through the LED is directly equal to the mosfet current, and as it gets brighter it controls the BJT, whereby the BJT "burns up" the excess dc bias voltage.
The optocoupler appears to be a variable resistor in parallel with the inside 10k resistors - it changes the gate bias with the collector-emitter junction as the opto coupler looks at the current through the mosfet sources. The LED part of the opto has a 1.2v constant drop, this is used in conjunction with R18 to set bias current across the source resistors. If the current is too high it will make the LED brighter, that modulates the base of the transistor, and the collector-emitter junction will decrease its apparent resistance in parallel with the inside 10k resistors, changing the ratio of rail voltage to ground, decreasing the amount of voltage on the gates, and keeping the bias stable as the load swings.
Is a simple solution - its a single part and it automatically adjusts. If there is any drift the optocoupler will compensate immediately No resistors to measure across and potentiometers to adjust
Check this guide out for more circuit details:
"WHAMMY" Pass DIY headphone amp guide
Alex
Interesting...
Seems like this may not be ideal for IEM use with the 'stock' gain. I suppose the gain could be set appropriately but I'd still like to be able to change that easily.... which means a switch. I know enough to follow Dynaco etc style instructions but don't trust myself to follow a schematic or do the gain resistor calculations correctly. This is one of the things I like about my agar-modded O2, I have the two gain settings 'dialed in' for 22Ω IEMs and 250Ω fullsizers respectively.
Seems like this may not be ideal for IEM use with the 'stock' gain. I suppose the gain could be set appropriately but I'd still like to be able to change that easily.... which means a switch. I know enough to follow Dynaco etc style instructions but don't trust myself to follow a schematic or do the gain resistor calculations correctly. This is one of the things I like about my agar-modded O2, I have the two gain settings 'dialed in' for 22Ω IEMs and 250Ω fullsizers respectively.
Gain is set by R1 and R4 for right and R12 and R8 for left channel by relationship:
G_right = (R1+R4)/R1
G_left = (R12 + R8)/R12
Currently R1&R12=1k and R4&RR8=4.75k so Gain is 5.75x or 15.2dB. This is a perfectly fine value for most moderate sensitivity headphones.
If you have 115dB/mW bal armature IEMs, a gain closer to 6dB may be better. Change R1 and R12 to 4.7k and you should have about 6.1dB gain.
Note that this approach unbalances the opamp inputs a bit but preserves the feedback value. Then the input 1k on the other side (R2 and R7) can also be changed to 4.7k to keep things balanced. Or you could change R4 and R8 to 1k and that also gets 6dB gain, but changes the feedback value and might affect stability. it will probably be fine and nothing is going to explode so don't worry too much.
Alternatively, an attenuator (resistor divider) can be placed on the input after the input jack.
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Alternative observation:
R4, R8 are driven by the power output - so driving a low impedance is not a problem, and therefore and alternative to get down to 6dB gain as XRK's good suggestion above, you could just reduce R4, R8 to 1K, and all will be well in terms of fairly-well balanced input impedances at the opamp.
C2,C7 increased to 470pF would exactly compensate.
NB - XRK's previous suggestion or this, are both 'quieter' than just attenuating the input, to amplify it again; and that just might matter if you want to drive IEMs.
HTH.
R4, R8 are driven by the power output - so driving a low impedance is not a problem, and therefore and alternative to get down to 6dB gain as XRK's good suggestion above, you could just reduce R4, R8 to 1K, and all will be well in terms of fairly-well balanced input impedances at the opamp.
C2,C7 increased to 470pF would exactly compensate.
NB - XRK's previous suggestion or this, are both 'quieter' than just attenuating the input, to amplify it again; and that just might matter if you want to drive IEMs.
HTH.
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