O2 amp CRC, diode, cap, and heatsink mods

jschristian44 - I had to fly out of town on biz for a few days. :) Yes, that looks great! So if you haven't already compare the bass on that modified channel with the other unmodified in your headphone. I'm really liking the 3db boost. Enough that I'm leaving it on most of the time now. Not a failing of the O2 in any way, of course, more a failing of my headphones and my ears on the low end. :p

pasang - variable boost is definitely possible. I've seen that added to a few amps, but probably with additional circuitry. I pondered it briefly when coming up with this one and it seemed to require an additional op-amp at the minimum. Wouldn't be the easy resistor replacement like this one with the fixed boost, plus it would require another pot mounted somewhere and there isn't any room left with the B2-080 box. Somebody out there probably has a slick and easy circuit for variable boost that would work with the O2 though, probably in the taller B3-080 box. If so, please post!
 
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just make the R in the RC youve got there a pot

ahh edit: you can tell i still havent actually built the pcbs i have here, i presume the resistor in the RC you have there is the standard FB resistor? yep just checked. ok so you can do this without an extra opamp, let me have a think about it. oh and btw youre using an X7R ceramic for bass boost signal filter? seriously? come on! just use a small panasonic pps or polypropylene film. the pps are available in small SMD parts; you could just solder it and a SMD thin film resistor in series accross the standard R16/22 positions
 
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Hey qusp! Good idea on using a SMD capacitor. Yeah that really should be a film cap in the signal path but the ceramic was small enough to fit, given the large amount of capacitance needed, plus we are messing with the sound anyway in the boost circuit. Please do post a surface mount alternative! :)

For jschristian44 and anybody else following along, the issue is that ceramics are not terribly linear and generally not used in the signal path. See here: The "Sound" of Capacitors and here http://greygum.net/sbench/sbench102/caps2.html
 
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sure you could bling it up with a mundorf SIO (i'd love to see RS's face) film cap and duelund carbon resistor (zfoil preferred but their advantage has basis in fact) but really it doesnt have to be a huge expensive film, just a panasonic pps, which i love, they are designed for exactly this purpose ie. analogue filters. here is the part i would use for $1.09 each, as its a 0.1uf +/-2% part, you can save 5c by getting the +/-5% or if it has to be a ceramic use an np0/c0g grade MLCC.

the part linked above is a 1210 size, which is pretty manageable, but you could go with a 1913 or even larger at the risk of losing the advantage and it may not be possible to fit the RC across the bottom of the resistor on top, but they turn out to be >30c more. i would go the 2% as this is direct signal path and at that price difference its hard to think of a reason why not.

if you want a bit fatter bass but not more volume of bass, just a wider bandwidth boost ie. you want the boost to include some of the lower mid-bass as well, you can choose a 0.22uf part, or lower cutoff you could use 0.047uf. they are available in through-hole as well, but they are a bit large and i would choose another part like a vishay polypropylene film and foil box cap.

the resistor i would go with is my favorite tight-ish tolerance thin film that doesnt break the bank, the susumu, now 3k0 isnt the most common value but they have one for $0.11 in 0.5% but its only available in 0805 size, which may or may not put some of you off. theres a panasonic 1210 size thin film in 3.3k but thats an odd size and they are 0.1% tolerance so are $1.10. stackpole 1% thin film 1206 size for $0.09 but if you can justify it and 0805 is too small, i would recommend the vishay 3k01 0.1% 25ppm 0.4W for $1.05 which are usually a pretty colour too =)

heres the pps film
its 1210 (3225 Metric) which means 0.126" L x 0.098" W (3.20mm x 2.50mm)

[IMGDEAD]https://media.digikey.com/photos/Panasonic%20Photos/ECH-UB-UX%20SERIES%201210_sml.jpg[/IMGDEAD]
 
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BlueRob

Member
2008-12-05 11:37 pm
By request, here is a step by step guide to building the bass boost modification.

This build is for the 3dB of boost as described above, using: two 3.0K 1% 1/8W resistors; 1 0.1uF 50V X7R MLCC ceramic axial capacitor; and 1 miniature DPDT switch. These parts are shown in the first photo for ID.

The second photo shows the leads of one of the 3.0K resistors bent at right angles, with a small 1mm or so space between the bend and the resistor body on each end. The other 3.0K resistor and the 0.1uF capacitor are hooked together by first bending one lead of each into a "U" shape with pliers. Then the two U's are coupled together and soldered at a right angle, as shown, to form a "V" shape. Two sections of wire are then cut, stripped, and one end of each soldered to half of the DPDT switch.

The 3rd photo shows the V shaped resistor and capacitor soldered onto the ends of the 3.0K resistor. The free ends of the "V" assembly are bent in a "U" shape with pliers, hooked around the ends of the 3.0K resistor between the right angle bends and the body, then soldered.

The 4th photo shows a closeup of the switch connections.

The 5th and 6th photos show the two free ends of the wires coming from the switch soldered to each end of the capacitor on the "V" shaped assembly, then the whole thing inserted into the O2 PCB holes for R22 and soldered. Twisting the wires at a rate of 3 turns per inch or so would be a good idea before final mounting of the switch.

The other channel would be done the same way with two more 3.0K resistors and another 0.1uF capacitor soldered into a V with wires coming off the capacitor. The two switch contacts just below the two that were used here (same side of the switch) would go to the wires on the other channel. That assembly goes into the hole for R16.

And the final result is... IT ROCKS! :D I have to say I really like the 3dB bass boost results. Not too much and not too little. Just enough to correct for the natural bass drop-off of the headphones (and probably of my ears). For someone who really is into bass 6dB would be worth trying.

On one hand a person could say that a mod like this goes completely counter to the design philosophy RocketScientist has for the O2, of passing the signal through with no alteration. But on the other hand a case can certainly be made that at some point along the signal chain - source, amp, or separate EQ box - some EQ may be preferable as per personal taste and/or correction of component issues like bass dropoff in a certain model of headphone.

Enjoy! :)

Awesome Awesome work/mods!

I´m about to receive the PCB for my O2 in hopefully a couple of days (fingers crossed) and in the mean time I was test driving a new pair of Etymotic Er4p IEMS which I think will match nicely with the O2 but I was seriously thinking to add a bass boost of some sort since these IEMs are "bass shy".

This mod is just what I was looking for!

Did you thought at some point to have a 3 way switch (off/bass+/bas++) kind of thing? in order to have a lets say...3db or a 6db gain with a flip of the switch?

I dont know if this approach will add up noise or affect the overall gain thou.

Anyhow great work and keep those mods flowing!

Cheers!
 
qusp: thanks for that info! Lol - I know you like those zfoils! :D I agree about the Susumu 0.1% and 0.5% stuff. I didn't know those even existed before the Wire. I'm all about 0.1% these days. Just something stuck in my head about getting the resistance value that I have actually specified. Plus for balanced circuits, like keeping that input offset balanced to CMR null out on the Wire, 0.1% makes all the difference. I know that is part of why the Wire numbers are so good.

Those larger SMD part sizes do look manageable. I'll have to get some in and give it a try.

BlueRob: Hey thanks! I have to give RocketScientist a big thumbs up for making such a great amp to start with. I've had a lot of fun messing with it. :D

There is one hiccup that has shown up on that bass boost modification. jschristian44 requested that mod. When he went to actually build it we couldn't find any DPDT switches small enough to fit on the O2 front panel and clear the inside of the box with the standard B2-080 enclosure. Seems the smallest I can find at Mouser or Digikey is 0.5" high while the space available above the gain switch in the box is about 0.4". So jschristian44 is winding up not using the switch and just leaving the boost on all the time.

If a taller B3-080 box were used the switch should fit. There also may be enough room on the back panel, above the R1 and R2 resistors, for the switch, just make sure to tightly twist the wire pairs since it goes over the power supply stuff and those are high impedance signal-path lines.

Good thoughts about switchable 3dB/6dB! I'll have to think about that. Also just variable boost, but that requires yet another pot that would pretty much demand using the B3-080 case.
 
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BlueRob

Member
2008-12-05 11:37 pm
Fortunately for me I haven't decided or bought the suggested B2-080 box so I will have extra room for accommodating the bass boost switch ;)

On the other hand, may be a third DPDT Pushbutton Switch like the one listed in the BOM for the gain boost might fit the B2-080 box, and help to solve the clearance issue for the chaps like jschristian44 who are dealing with this mod...it seems to be under 0.4" and it could be placed over the original gain switch.... what I can see from the pics of the front plate there is enough room ¿?
 
BlueRob: Good thoughts, but that slider switch is PC board mount style. The switch for the boost would have to be panel mount with a threaded collar and nut.

One thing to watch out for with the B3-080 case - the B2-080 front panels won't fit (not tall enough). There were some B3 panels made during a group buy a few months ago, but I'm not sure if anyone is selling B3 front panels now. The case comes with blank panels though, so you could always drill it yourself if you have a drill press! :) The measurements RocketScientist gives on his blog for the panel should work as long as you measure from bottom-up.
 

coolhead

Member
2010-03-28 5:30 pm
sure you could bling it up with a mundorf SIO (i'd love to see RS's face) film cap and duelund carbon resistor (zfoil preferred but their advantage has basis in fact) but really it doesnt have to be a huge expensive film, just a panasonic pps, which i love, they are designed for exactly this purpose ie. analogue filters. here is the part i would use for $1.09 each, as its a 0.1uf +/-2% part, you can save 5c by getting the +/-5% or if it has to be a ceramic use an np0/c0g grade MLCC.

the part linked above is a 1210 size, which is pretty manageable, but you could go with a 1913 or even larger at the risk of losing the advantage and it may not be possible to fit the RC across the bottom of the resistor on top, but they turn out to be >30c more. i would go the 2% as this is direct signal path and at that price difference its hard to think of a reason why not.

if you want a bit fatter bass but not more volume of bass, just a wider bandwidth boost ie. you want the boost to include some of the lower mid-bass as well, you can choose a 0.22uf part, or lower cutoff you could use 0.047uf. they are available in through-hole as well, but they are a bit large and i would choose another part like a vishay polypropylene film and foil box cap.

the resistor i would go with is my favorite tight-ish tolerance thin film that doesnt break the bank, the susumu, now 3k0 isnt the most common value but they have one for $0.11 in 0.5% but its only available in 0805 size, which may or may not put some of you off. theres a panasonic 1210 size thin film in 3.3k but thats an odd size and they are 0.1% tolerance so are $1.10. stackpole 1% thin film 1206 size for $0.09 but if you can justify it and 0805 is too small, i would recommend the vishay 3k01 0.1% 25ppm 0.4W for $1.05 which are usually a pretty colour too =)

heres the pps film
its 1210 (3225 Metric) which means 0.126" L x 0.098" W (3.20mm x 2.50mm)

ECH-UB-UX%20SERIES%201210_sml.jpg
How about Polyethylene Naphthalate capacitor like this LDEDC3100KA5N00 - KEMET - CAPACITOR PEN FILM 0.1UF, 63V | element14 Malaysia in that position? I use to have 2 still seal in a plastic bag.

-coolhead
 
Could you tell me if your amp has better battery life on you 9.6v batteries? If not, did they change performance in any other way?

I unfortunately haven't run the O2s on batteries enough to have any useful measured runtimes. Runtime would be related to the battery capacity though. The blue Tenergy 8.4Vdc "9V" cells are rated at 250mAhr vs. 230mAhr for the white MaHa 9.6Vdc "9V" cells, so in theory the two should give almost exactly the same runtimes for a given load. Battery mAhr ratings are well known to be inflated on many imported cells (NiMH and Lithium) so either or both battery mAhr ratings could be off in the night though.

The 9.6V cell just gives 9.6V - 8.4V = 1.2V, another single NiMH cell's worth, of voltage swing on each rail, raising the voltage level at which clipping would occur in the two O2 amp stages. For low impedance headphones (32R, 80R), requiring only small voltage swings, either battery voltage is probably fine. But with high impedance (600R, 250R) and low sensitivity cans that need large voltage swings, the extra 1.2V may make all the difference. Even at full charge of around 10.5Vdc that 9.6V(nominal) cell is still 1.5V below the AC rails of +/-12Vdc, which themselves are marginal for some 600R low efficiency cans.

But... that is all just theory. :) It would be interesting to hear from anyone using the blue "8.4V" Tenergy cells who have actually experienced clipping with the O2 using high impedance headphones. Also anyone who has done some real-world battery run time tests on the O2.
 
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