[infinitesymphony]

Here is an updated version of the parts list I used for my three great-sounding Joshatdot PCB CMoys. I ordered most parts from Digi-Key, but the Alps potentiometer must be purchased elsewhere. amb stocks it and a few other essential parts, so I ordered from him wherever possible to avoid the handling fee for a small order.

Code:

[left][b]Resistors[/b] 2 - R2, RES 100K OHM 1% 50PPM 1/2W, Vishay Dale [CMF100KHFCT-ND] 2 - R3, RES 332 OHM 1% 50PPM 1/2W, Vishay Dale [CMF332HFCT-ND] 2 - R4, RES 1.5K OHM 1% 50PPM 1/2W, Vishay Dale [CMF1.50KHFCT-ND] 0 - R5, for performance, use jumpers for these positions OR 2 - R5, for ultra low-impedance headphones like IEMs if the amplifier hisses with jumpers, RES 47.5 OHM 1% 50PPM 1/4W, Vishay Dale [CMF47.5QFCT-ND][/left]

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[left][b]Power Section[/b] 1 - C1, CAP 470UF 35V ELECT FM RADIAL, Panasonic FM PSU capacitor [P12415-ND] 0 - C2, for performance, use jumpers for these positions OR 2 - C2, for safety, CAP POLYPROPYLENE .47UF 50V 1%, Panasonic ECQ input capacitors [P3888-ND] 1 - TLE2426CLP virtual ground rail splitter chip (TO-92) [296-1994-ND], or from [url=http://www.amb.org/shop/]amb[/url][/left]

Code:

[left][b]Op-amp[/b] 1 - IC SOCKET 8 PIN .300 GOLD, DIP-8 Socket [ED90032-ND] 1 or more - DIP-8 op-amp, your choice (P has better specs, PA is cheaper): Analog Devices AD823 [AD823AN-ND] Burr-Brown OPA2227[OPA2227P-ND or OPA2227PA-ND] Burr-Brown OPA2132[OPA2132P-ND or OPA2132PA-ND] Burr-Brown OPA2134[OPA2134P-ND or OPA2134PA-ND] Texas Instruments NE5532 [296-1410-5-ND or 296-7040-5-ND] Texas Instruments NE5534 [296-7042-5-ND or 296-7043-5-ND] Texas Instruments TLE2142 [296-10467-5-ND] If you elect to add decoupling capacitors on the bottom (see Extra), you can also try: National Semiconductor LM4562 [LM4562NA-ND] Burr-Brown OPA2228 [OPA2228P-ND or OPA2228PA-ND][/left]

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[left][b]Extra[/b] 1 - Alps RK0971221Z05 pot and switch, 10KΩ, from [url=http://www.amb.org/shop/]amb[/url] 2 - STRAP BATT ECON 9V I STYLE 4"LD, 9V Battery Straps [232K-ND] 2 - CONN JACK STEREO R/A 3PIN 3.5MM, In-out jacks [CP1-3533-ND], or from [url=http://www.amb.org/shop/]amb[/url] 1 - LED 3MM BLUE DIFF, Blue LED [350-1560-ND] 1 - RES 10.0K OHM 1% 50PPM 1/2W, Vishay Dale resistor for LED [CMF10.0KHFCT-ND] (go with a lower-valued resistor if you want a brighter light) 1 - knob, search for 'aluminum knob .50' and filter your choices to 6mm diameter; I chose the ML series in black matte [226-4003-ND] [u]Decoupling[/u] 2 - Vishay/BC CAP .10UF 50V CERAMIC X7R 10%, Ceramic capacitors for decoupling [BC1084CT-ND] OR 1 - (pack of two) 0.1µF 50V Hi-Q Ceramic Disc Capacitor Pk/2, ceramic capacitors for decoupling, Radio Shack [[url=http://www.radioshack.com/product/index.jsp?productId=2062365]272-135[/url]][/left]

Notes: Feel free to substitute a higher-valued Panasonic FM radial capacitor for C1, since 470uF can barely fit directly on the board anyway, or a lower-valued C1 if you plan to fit the amp into a standard Altoids tin. In general, higher capacitance = taller, higher voltage = wider. C2 input capacitors are only necessary if DC offset from your playback device is a concern; most devices have output capacitors. R5 resistors are only necessary if you have very low-impedance headphones.

The amplifier's gain is a multiple of the original signal level from the playback device. For example, a gain of 5 means that at full volume, the amplifier will be 5 times louder than plugging directly into the playback device's line output. You can change the ratio of R4 and R3 resistors if you want a gain other than ~5.54, which is the result of the combination in my list. Gain calculation uses the formula: (R4/R3) + 1. Stick with a gain of above 5 for maximum compatibility--certain op-amps are not low-gain stable.

I highly recommend adding decoupling capacitors to the bottom so that the use of the National LM4562 op-amp becomes possible--it sounds great!

 

[Filburt]

I mostly intended to use 3500 as an example parallel value when explaining how to balance bias currents. You should measure for yourself what the proper parallel value should be based on your own use. Since you are running such a low gain and one of your sources is of relatively low amplitude at its output, it may be considerably different from that value.

 

[MisterX]

You plannin on using a pot in this amp?

 

[Logistics]

^^^ The Alps pot is listed in the parts.

Is this for the PCB 1.03, because C1 uses a Radial cap, not an Axial. Use a Panasonic FM for very low impedance and high ripple.

 

[MisterX]

Quote:

^^^ The Alps pot is listed in the parts.

He must have changed it after the fact.

I would strongly suggest replacing the input cap "jumpers" with 1k resistors.

Or you could cheat and steal the mini3 values.

 

[infinitesymphony]

Quote:

Originally Posted by Logistics /img/forum/go_quote.gif Is this for the PCB 1.03, because C1 uses a Radial cap, not an Axial. Use a Panasonic FM for very low impedance and high ripple.

Yes, and thanks for catching my mistake.

I've replaced:
1 - C1, CAP 25V 470UF ELECT AXIAL, Vishay Dale PSU capacitor [4217PHCT-ND]

With:
1 - C1, CAP 470UF 25V ELECT FM RADIAL, Panasonic FM PSU capacitor [P12389-ND]

I've also moved the Alps pot to the top of the "Extras" section, since it didn't really belong in the power section.

 

[infinitesymphony]

Instead of jumpering the input capacitor section, I'll use 1 KOhm resistors for safety. I've added them as C2 in the power supply section. (Thanks Filbert and MisterX).

 

[infinitesymphony]

Correct me if I'm wrong... Since I won't be using input capacitors, DC offset will be a concern, so I need to properly bias the amplifier. Are the resistor values I've chosen adequate for my setup, and if not, what will I need to do to figure them out?

Also, an excerpt from the AD8397 data sheet:

Quote:

POWER SUPPLY AND DECOUPLING The AD8397 can be powered with a good quality, well-regulated, low noise supply from ±1.5 V to ±12 V. Careful attention should be paid to decoupling the power supply. High quality capacitors with low equivalent series resistance (ESR), such as multilayer ceramic capacitors (MLCCs), should be used to minimize the supply voltage ripple and power dissipation. A 0.1 μF MLCC decoupling capacitor(s) should be located no more than 1/8 inch away from the power supply pin(s). A large tantalum 10 μF to 47 μF capacitor is recommended to provide good decoupling for lower frequency signals and to supply current for fast, large signal changes at the AD8397 outputs.

Will using two 9V batteries overpower the op-amp? Also, should I use a 10 uF to 47 uF instead of a 0.1 uF capacitor for decoupling, or is that section referring to a separate capacitor?

 

[Logistics]

Using ceramics is a cheap and convenient way to accomplish this, but I would use a polypropylene film (non-metallized), the same one suggested for use as the input cap on the generic cMoy build is acceptable. The size of the capacitor affects which frequencies it removes or the noise it filters off so you want to keep the 0.1uF.

As far as the output caps, I thought the cMoy didn't call for output caps. Bottom line is, if you do use output caps, you want them to be bipolar or rather non-polarized, and ideally they should be films. It is easy to get 10uF or 47uF in an axial film, but they are bulky and expensive. You could use a Panasonic SU from Digi-Key, but electrolytics are not ideal in a signal path... tantalums are not much better. With the good quality power cap, I don't think this would be necessary, anyway. Manufacturers usually suggest some tiny power cap like a 10uF when it should be 100uF or a 100uF when it should be 1000uF; it's crazy the way they do that, but it saves money and space, both much more important to most manufacturers.

I thought it was worse to have a resistor in the signal path then a capacitor. Thoughts? Does he want a non-inductive resistor, if he does use one?

 

[NelsonVandal]

Quote:

Originally Posted by infinitesymphony /img/forum/go_quote.gif Correct me if I'm wrong... Since I won't be using input capacitors, DC offset will be a concern, so I need to properly bias the amplifier. Are the resistor values I've chosen adequate for my setup, and if not, what will I need to do to figure them out? Also, an excerpt from the AD8397 data sheet: Will using two 9V batteries overpower the op-amp? Also, should I use a 10 uF to 47 uF instead of a 0.1 uF capacitor for decoupling, or is that section referring to a separate capacitor?

I've had no problems with AD8397 running at 9 V, but at 18 or 24 V there sometimes seem to be stability problems because it gets burning hot. Many PINT (18 V supply) users have reported stability problems as well. If your amp is designed for two 9 V's, why not fill it up with seven AAA's instead and get a good battery life.

Just use the same resistor values as in PINT or Mini3.

With 18 V supply and a 3 k LED-resistor, you're going to have a very bright light.

 

[infinitesymphony]

Quote:

Originally Posted by Logistics Using ceramics is a cheap and convenient way to accomplish this, but I would use a polypropylene film (non-metallized), the same one suggested for use as the input cap on the generic cMoy build is acceptable. The size of the capacitor affects which frequencies it removes or the noise it filters off so you want to keep the 0.1uF.

I think I might stick with the ceramic, if only for size considerations. This capacitor is going on the extremely small SOIC-to-DIP adapter board.

Quote:

Originally Posted by NelsonVandal /img/forum/go_quote.gif I've had no problems with AD8397 running at 9 V, but at 18 or 24 V there sometimes seem to be stability problems because it gets burning hot. Many PINT (18 V supply) users have reported stability problems as well. If your amp is designed for two 9 V's, why not fill it up with seven AAA's instead and get a good battery life.

Ah, in that case, I won't run dual 9Vs. Thanks for the information!

Quote:

Originally Posted by NelsonVandal Just use the same resistor values as in PINT or Mini3.

So, R3 = 120 KOhms, R4 = 620 KOhms. I see that this works out to around 100 KOhms with a gain of ~5.

I'd heard that using such high-valued resistors would significantly increase the noise floor, so I'd hoped to avoid them. Plus, aren't these high values only necessary if input capacitors are used?

Quote:

Originally Posted by NelsonVandal With 18 V supply and a 3 k LED-resistor, you're going to have a very bright light.

The usual specification is for a 2 KOhm LED resistor, so I thought that 3 KOhm would be enough... I guess I forgot about the effect of adding another 9V battery. Would 3 KOhm be enough for one 9V? The person I'm building this for will almost certainly prefer a dim light to a blinding one.

Edit: Nevermind! I'm not sure what prompted me to put "3 KOhm" when 10 KOhm is the bare minimum on Tangent's site. I've updated the parts list with a 10 KOhm LED resistor.

 

[NelsonVandal]

Quote:

Originally Posted by infinitesymphony /img/forum/go_quote.gif So, R3 = 120 KOhms, R4 = 620 KOhms. I see that this works out to around 100 KOhms with a gain of ~5. I'd heard that using such high-valued resistors would significantly increase the noise floor, so I'd hoped to avoid them. Plus, aren't these high values only necessary if input capacitors are used?

Yes this is going to be very noisy. Sorry, but I meant the "low-noise version" (page 2 in the PINT-shematic) with 1.2 k and 6.2 k resistors and 1 k input transistors and no coupling cap. The DC-offset is acceptable with these values. You could also use the Mini3 values 330/330 and 1.5k.

 

[infinitesymphony]

Quote:

Originally Posted by NelsonVandal /img/forum/go_quote.gif Yes this is going to be very noisy. Sorry, but I meant the "low-noise version" (page 2 in the PINT-shematic) with 1.2 k and 6.2 k resistors and 1 k input transistors and no coupling cap. The DC-offset is acceptable with these values. You could also use the Mini3 values 330/330 and 1.5k.

Oh, okay, thanks for the clarification. Is there any reason to choose the PINT values over the Mini3 values, or vice-versa? Both have a gain of ~6, but the results in the formula (R4*R3)/(R4+R3) are 1005 and 275 respectively... What does that formula measure again, and would the difference matter?

Filburt said he had used 3 KOhm and 15 KOhm resistors in R3 and R4, which lead to a gain of 6 and 2.5 KOhms. Is this another alternative?

 

[holland]

Quote:

Originally Posted by infinitesymphony /img/forum/go_quote.gif Will using two 9V batteries overpower the op-amp? Also, should I use a 10 uF to 47 uF instead of a 0.1 uF capacitor for decoupling, or is that section referring to a separate capacitor?

18V is fine. It's split to be +-9V.

MLCC 0.1uF is fine for decoupling. Keep the pins as tight as possible. Long leads from "boutique" caps for decoupling can add inductance, which may not work properly for decoupling. The AD8397 spec is very specific about length and lead length adds to the distance from the pin to the cap. If the designers were so specific, I find it good to follow their advice...they made the chip afterall. Add a 10 to 47uF at the battery entry point, before the big power caps. The spec references 2 caps.

What I have done on my cmoy is a 10uF tant at entry, a single 1000uF cap (better PSRR, etc.) rail to rail before the TLE2426 and much smaller caps after, from each rail to ground. I think I used 100uF there, but basically whatever I had on hand. It seemed better to me, but could be psycho-acoustics.

Also, there's a chance that you may need an output resistor. I've hit a few opamps which hate certain headphone loads (most likely be the cable capacitance) and triggered the chips into oscillation. The headphone in question was the K81DJ. The AD8397 was one of them, the AD8066 was the other. You may need to break out the exacto knife for that. I had to use a 20-ohm resistor, as 10 didn't seem to work. AMB had a small resistor inside the feedback loop (to handle headphone insertion and the temp short) and a ferrite bead outside for cable capacitance. That would be more ideal, IMO, but trickier.

 

[holland]

Quote:

Originally Posted by infinitesymphony /img/forum/go_quote.gif Filburt said he had used 3 KOhm and 15 KOhm resistors in R3 and R4, which lead to a gain of 6 and 2.5 KOhms. Is this another alternative?

Those values are fine, but I would use a small a value as possible (and would tend to go for the Mini3 values). Resistors add noise. The larger the value, the more the noise. I actually used different values on my cmoy, because I started with a more traditional setup. I used 825, 4.7K and 1K. Since you're going to order, go for the lowest values that you can. The Mini3 values are proven, so I would say it's fine to go that low.