bpribadi

I got Panasonic PCDP too I'm going to use LM2941 and LM2991. They are adjustable positive and negative regulators. This is the first time for me using them, ussually I use LM78xx and LM79xx for fix voltage, and LM317 & LM337 for the adjustable voltage. They are good if you use transformer (wall power), but they require significant drop out (Vin - Vout). Not suitable for battery powered amp. So I'm going to use Low Dropout voltage regulators. LM2941 and LM2991 need only around 0.5 to 0.6 volt higher at the input (maximum 1 volt for high current, 800 mA). So if I'm going to set the output at 7 volt, I only need 7.5 volt at the input. So I can use the normal 15 volt adapter to give me + & - 7 volts to power my amp. I think the output current of the 8620 is a bit low (30 mA) to be a CMoy, but probably when you add buffers like Pimeta, they will sound right. Well I'm building my Pimeta with AD8620, so I will let you know once it is done. But I don't have Senn, AKG, or other high impedance headphone. My RS-1, ATH-EW9, and Sony MDR-E888, are all happy with direct output from the PCDP. So my intention of building amp is just for fun, and for better sound quality than headphone output of my PCDP. You may try my Pimeta with your Senn to test it before you build it

Ok, I take 2 SMD-DIP. Just let us know when and how to pay them. Bram

Hi Heady, Yesterday I got no time to access internet, sorre for late reply Anyway I was quite surprised there is a dentist who likes electronic DIY Thanks mukegile for the information! From my point of view there are a couple of reasons why they use rail splitter: 1. Rail splitter such as TLE is the easiest approach, no need resistors divider, the TLE will splits whatever the supply voltage fed to it. But ground current will be limited to max 40 mA. Sufficient for most headphones, but more ground current is better. Here I use BUF634 which has 250 mA output current, should be more than enough for my PIMETA. 2. They want to use the maximum voltage from the supply. Let say if they use 15 volts adapter, they will get + & - 7.5 volts. If they use higher supply, they will get higher voltage to supply the Op-Amps. The higher the supply voltage, the better for the Op-Amp, as it will increase slew rate. With voltage regulator the disadvantage is the supply voltage to the op-amp will be fixed to a certain voltage, regardless the external supply voltage fed into to regulators. The advantage will be your amp will always sounds the same And you can accurately adjust the Vs+ and Vs-. But the advantage is, the voltage regulators is a very good ripple suppressor. So if the external power supply, let say adapter, is not giving a clean DC voltage, the regulators will clean it. For example, in PPA schematic, for every op-amp, there are some JFET transistors for the V+ and V- supply. Those transistors will give around 16 dB ripple rejection. Voltage regulators will give around 60-70 dB ripple rejection, so much cleaner DC supply for the op-amps for better sound. So that's why I choose to use voltage regulators Come on, DIY is fun too, don't retire so soon After you became more critical, than CMoy would not be enough for you Bram

Congratulations! What amp you use to drive it? 500 hours... that's a very long burning period Is it the can become better sounding or our ears that finaly get used to it

Here is my PIMETA like headamp. An intermezzo before building the PPA. My purpose is to make use of the AD8620 I got from AD, and also to build one decent small amp that can be powered with 2x9V battery. Here is the board layout. As ussual I'm to lazy to print proper PCB, so I'm going to use normal matrix PCB (Board layout has been modified on Aug 24) NOTE: Please don't use the previous board layout! There is a mistake on the power supply design. I have ordered the components, hopefully I can finish it by next week Any comments or correction are welcome

For those who want to save money on the PCB (like me ), and use normal matrix PCB, here is my PPA layout, complete with fuse protection for the buffers. This layout is only for one channel (measured 8x9 cm per channel), and the transformer and the bridge diode haven't been included. To understand more on the buffer protection, here is the idea: Happy DIY

You can get free samples of ICs from Analog Device. Just fill the form http://www.analog.com/Analog_Root/productP...,AD8610,00.html Just 2 would be enough for me.

Thanks H! Jan Meier's included to many feature that I'm not interested with. And capacitor in the audio line which is what I'm trying to avoid. I like amp with less components and as simple as possible. I believe less components with good design will give the best sound. Don't worry, I'm not going to give up on the LM6171 so easily, until I found good way to deal with the DC offset Anyway I have planed to build the PIMETA like (sorry, not MINT as what I wrote above) when I got the AD8620 from AD, so it is just an intermezzo

SO-8 to PDIP-8 For the free AD8610 and AD8620 Thanks!

Aarrgghhh... those approaches don't work either Anyway, look at the bright side , I learn a few things from my experiments which I can share it with you: 1. Buffer cannot be use stand alone in audio circuit if you expecting 0 volt at the input and output without the input signal. Means, to avoid input and output offset, buffer must be put in the feedback loop. BUF634 has more balance input circuit than the HA3-5002, it produces about 1/20 DC offset than HA3-5002. But still has to be put in the loop. 2. Adjusting the Vs+ and Vs- does reduce the buffer DC offset. But the adjusment is extreme, so it became not applicable. I can get 0 volt DC offset when I adjust the Vs to +4 and -15 (which is ridiculous). About the same value for both BUF634 and HA3-5002. So, my board will keep becoming a test board I have another good thing to share, I didn't hear any audible hum eventhough the transformer is close to the audio circuit. I thing this is due to the shielded input cable. I keep the shield to the last 5mm from the input pin of the IC. Again the S-VHS cable prove it's ability to suppress hum Try this cable for interconnect, they are good for normal purposes. Probably the high end fans would go for silver cables So what's next... I plan to build MINT with my AD8620 and BUF634, while testing the Low Dropout voltage regulator LM2991 and LM2941 (they seems good, but they are expensive )

I made one long time ago, if I found it, I will post it. Basically there are two methods, constant current (easy to build) and trickle charge which often need micro processor. For constant current, the rule of thumb is 1/10 of the battery capacity. Means if for 170 mAH, you can just feed it with 17-20 mA with voltage about 3-5 volts higher than the battery.

Are you going to share it with us I don't mind to pay if the price is right

Hi aaa, why not buy the OPA637? It is faster than OPA627. I know that we have to set the gain at 5 or more, but that shouldn't be a problem right? Buy from Farnell, for 10 pieces it cost around SGD 35.- per IC. I will take 4 ICs if we want to start group buy Bram

Ooohh... Yeeeaaaa.... You are very right !!! If possible don't use any cap on the audio line Headphone can take a few mV DC without any problem, so don't worry about it.

I think you forgot something... How does it sound ? We would like to hear your comments

I hate to say that the amp schematic above is not working as expected The problem is not with the LM6171, but with the HA3-5002 buffer. I just realized that the 5002 input is not precisely balanced with the supply voltage, but slightly higher, and from the input there is a very small current flow out, about 1.5 uA. So what's the big deal with this 1.5 uA? I put 1 Mohm resistor (which is to high after I relook at the datasheet) at the buffer input, with 1.5 uA flowing out, it produce 1.5 volt at the input . Same voltage at the buffer output, amplified by the LM6171, producing almost 10 volt DC at the headphone output Lucky I checked before I blow my can Now I'm listing a few ways to solve this problem: 1. Adjust the Vs for the buffer until I can get 0 volt at the input (and output). This means buffer and LM6171 must have seperate voltage regulator. 2. Try BUF634 (modify my board). Any more suggestion? Thanks! Bram

Wow... Wow... Wow... Very impressive! Nicely done And another 'wow' for all the 'expensive' components The soldering work for the Oscon near the Op-Amp is fantastic Where did you buy the Neutrik combi-jack ?

Hi Heady, Try the small pot from Bourns. Farnell has them. I forgot the order code. I will give you the order code later.

Thanks Digi and Heady! I almost blow my BUF634 Somehow I thought BUF634 and HA3-5002 share the same pin configuration, and I use the HA3-5002 pin config to build my test board. I don't have HA3-5002 at hand, only a couple of BUF634. I almost plug in the BUF634 and power them on... lucky I did a final check and I just realize BUF634 has different pin configuration. The board are ready, all cable has been connected, but no casing at the moment. Just note for the audio cable, I found S-VHS cable at SLT (SGD 2.5 / meter), and I like them. They come in a pair of coaxial cables, covered, so looks like a single coaxial. The material is Pure OFC, and have direction on the cable outer insulator. The size is just nice, not too small and not to big. The shield has been proven to be effectively suppres hum. Previously I use normal audio cable (about the same price) for interconnect, and my CMoy suffer from hum, not at home, but in office. After using the S-VHS cable, the hum gone. I'm going to get HA3-5002 tomorrow from Farnell. Since it is much cheaper to buy 10 pcs, I'm going to buy 10, the rest are for my PPA project in the near future. But if any of you need HA3-5002, you can share the purchase with me, since it will be cheaper to buy 10 pcs or more. Just PM me. The power supply is working fine, adjusted to +/- 16.000 Vdc So waiting to get the buffers Bram

Thanks! Well, it will in theory, but I hope it won't be audible, at least. Well this is test board for prove of concept, so I don't know what will be the result I just hope it will sound good, if not, then it will be modified. I haven't look at Jan's design, thanks for the link, it will sure give some additional knowledge Anyway, what is T version? Different packaging of the buffer is it? I will look at the datasheet.

Then who will volunteer to eat the sweets to get the tins

My main purpose building this test board is to test the LM6171 Op-Amp. Some people said it sounds very good, probably the best op-amp in the world. This Op-Amp has a few great features: 1. Very high slew rate : 3600 V/uS 2. High output current : 100 mA It is known that slew rate is one of the most important factor of a good amplifier. The higher the slew rate, the better the amp. Just for comparison of slew rate: OPA2134 : 20 V/uS OPA637 : 135 V/uS AD8610 : 60 V/uS And for the price of SGD 5.6 per IC (single op-amp), LM6171 is really a temptation for DIYers. But the problem here is, LM6171 is non JFET input op-amp. Means we have to deal with output DC voltage offset. Ussually the approach is to put capacitor at the output to block the DC offset, but we know it will degrade the sound quality. To match the positive and negative input impedance is the better approach, but practically no source (line out) will be able to drive it. Because it means the source has to be powerfull enough to drive a few hundreds ohm or less than a hundred ohm load. Normally line out can only drive 22 kohm or higher. Another problem with highspeed op-amp is oscillation. We have to keep the wiring short to avoid paracitic capacitance and inductance. And to avoid oscillation, we have to use a low value (1 kohm or less) for the feedback resistor. 510 ohm is the recommended value from the LM6171 datasheet. For gain 6.6 as what I have set, I have to use the combination of 510 and 91 ohm. The Thevenin value of those resistors is 77.2 ohm. It means that we have to put 77.2 ohm impedance at the + input. There is no line out would be able to drive 77.2 ohm impedance. So I put a buffer at the input to drive it. The volume pot is put before the buffer. With this configuration, the + and - inputs of LM6171 will 'see' constant impedance all the time. Simple approach, but so far I've never seen anybody took this approach with LM6171. I know that the buffer slew rate (2000 V/uS) is less than the LM6171 slew rate, but to me it is already high enough compare to other design with different op-amp. I think even source the line out will not have such a high slew rate, correct me if I'm wrong P1 is to fine tune the + input impedance. Ri1 is for buffer output protection, to avoid short circuit if P1 accidently turned to 0 ohm. I use wall power to get high supply voltage, as we know the higher the supply voltage, the higher the op-amp slew rate. So I will set it to +/- 16 volts. The power supply is the standard LM317 and LM337 combination. So here it is, my test board for the LM6171. Not 100% done, I will still need to connect all the cables, and put it in a nice metal casing (3x6x2 inches). Hopefully I would be able to power it up next week. I will post my impression of how it sounds, or does my approach work to deal with the LM6171 DC output offset. Additional note, I also put 2 jumpers, J1 and J2. They are to test the class A biasing using JFET cascode method. If J1 and J2 jumpered, the LM6171 will be biased to class A operation (like in the PPA). So I'm curios to hear what's the different it will make with LM6171. I just can't wait to test it Board layout:

Ok, next week is national day (sg's) already, any progress of the Amp ? I never tried A47, wonder how it sounds

Thanks Huangyong!

Thanks Charismatic! I will contact them