A New Take on the Classic Pass Labs D1 with an ESS Dac - Page 6 - diyAudio
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Old 6th March 2010, 09:16 PM   #51
DaveM is offline DaveM  United States
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Personally, I have no problem being patient, and I will do that. In my opinion, if one is impatient, they can work on the problems at hand and volunteer to help with the development. I've done a GB myself and I was amazed at how much work it ended up being. Mine was a simple machined part, never mind a complicated electronics development project. This one will without a doubt take some time.
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Old 7th March 2010, 03:18 PM   #52
qusp is offline qusp  Australia
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I have been patient (this has been happening for 4 months now and thats just since this thread was started, all i'm saying is that due to the lack of communication and seeming slowed/stalled development, I have to go another way. I understand owen has a life and that he iust doing this probably for himself but sharing with the community, but I suggest he updates the thread with some real and accurate information on what is going on; if that info is that he simply does not have the time at the moment because of other commitments, thats perfectly fine, but periodically popping up and saying he hasnt forgotten about it and that the project is moving forward; and then promptly disappearing again is frustrating me. I repeat my well wishes and hope you get through whatever is taking your time well owen. if you get this finished i'll reassess the sutuation then, but I think the build I have undertaken to replace this in the ackodac output stage is going to be pretty amazing and my second option is a PTFE borbely active I/V

Last edited by qusp; 7th March 2010 at 03:25 PM.
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Old 8th March 2010, 04:15 AM   #53
opc is offline opc  Canada
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Hi Guys,

Looks like a few people are getting restless here, so I figured I had better pop in. Sorry for the long time away, I've shelved this project as I await the arrival of the Buffalo II DAC I purchased. It won't be in until March 15th, and I'm hoping to have boards done shortly thereafter.

As for development status, I've attached what I consider to be the final product in its best possible form. It's what I'm using now, and It's good enough that I'm done playing with it.

You can feel free to build it with almost any mosfet you choose, and it will work very well, but I suggest larger, higher current fets as that was the only trend which consistently measured better. IRF540's work perfectly, so do FQA46N15's. My personal favorite, and the best measuring device is the lateral ACD101NDD if you can get your hands on it. I rolled ten different matched sets of fets in and out of this stage, and most measured so closely that the difference wasn't worth worrying about.

I've foregone the entire B1 buffer section, so you now have only one gain stage/device. The output impedance is about 185 ohms which is better than the B1 anyhow. Fewer parts, better performance, better sound, lower cost. This circuit is really only for balanced use, if you want SE, use an op-amp as a diff to SE converter, or a transformer.

You can toss this together on a piece of veroboard in an hour, and give it a listen. No need to wait for a PCB, although one is coming.

I really enjoy it, it's one of my favorite little circuits. Please excuse the hand drawn schematic...

qusp,

I'm sorry that you feel I let you down, but you really need to have a little more appreciation for the amount of work that goes into this stuff, and the fact that your attitude in the last two posts makes an already thankless effort all the more daunting. I posted this circuit here so that people would give it a try, enjoy it, and hopefully give me feedback on what they thought of it. If you want a polished finished product, delivered in a timely manner, then there's a hi-fi dealer in your area that would love to take a few grand off your hands and give you just that.

I do this for fun, and I share what I do in the hopes that someone, somewhere will be able to take it and run with it. I've always got half a dozen projects on the go, some of them many years old, and a life that will always take priority. For the past month this has taken a back seat, plain and simple.

I suggest you try the new circuit, I think you'll like it. It's easy to put together on a prototype board, it costs next to nothing, and you can have the enjoyment of a funny looking prototype while you wait for PCB's. If you chose to use another I/V stage, then that's fine with me.

Cheers,
Owen
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Old 8th March 2010, 07:41 AM   #54
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Hi Owen, great work and thanks for posting your finding and esp. your circuit.

Sorry if I had some questions, I had thought that the drain resistor (185R) determines the I/V gain and source resistor (400R) set the bias current (guess I am wrong). So how to calculate the output voltage to be 2Vrms for this?
I have a dac with only 1.2ma current and just follow original D1 circuit but use 2K for drain resistor to have reasonable output.
Thanks.
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Old 8th March 2010, 08:12 AM   #55
Yunick is offline Yunick  Sweden
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Thanks alot for sharing Owen,
I tried the circuit you posted on the first page with my buffalo DAC with great result.

I also have a question,

Without the dac attached, I adjusted the trimpots to read 0V, measured between the input and ground. Is this correct or should I adjust to 1.65V between input and ground?

Thanks again for your work!
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Old 8th March 2010, 12:13 PM   #56
qusp is offline qusp  Australia
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Owen, no I totally understand how much work goes into it, i'm undertaking my own design for a portable output stage for the buffalo II (just for myself and first time i've ever taken anything like this on; yes i'm a bad headphone geek), I have the buffalo32 I and i'm sure version 2 will be great. all the same I chose it for the portable only because of the simplified requirements for different regulated voltages which makes it much more workable for a battery supply, I am going ahead with the ackodac for home, because I feel it is a better option personally and I like to have some input and feeling of DIY, the TP gear is great dont get me wrong, but its not very DIY IMO

no I dont feel let down mate, you misunderstand me, I simply couldnt hang on waiting when it was clear that it wasnt going ahead as planned. and thats totally cool with me mate, as others have mentioned this is out of your own time and the repayment you would get for the boards would be unlikely to even make a dent in the time put in to design and support it. just when you made such a large decision, it would have been nice if you let those waiting in on it, it happened before for personal reasons and then it looked like you had disappeared again. as you know from my earlier posts in the thread I had other plans as well and I simply decided to go ahead with them because they were a known quantity.

so thanks mate, i'll keep an eye on it, but its not quite so appealing anymore

good luck with it, i'm sure it will sound as good as it looks. likely you'll get more on the pre-order as well this way

Last edited by qusp; 8th March 2010 at 12:31 PM.
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Old 8th March 2010, 12:20 PM   #57
qusp is offline qusp  Australia
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oh hell, you know now that schematic is there and the fact I have most of the parts means that I will likely knock it up but to make it any kind ofpermanant solution I w0ould have to get your permission to get my own PCBs made, the fact its now going to be for tghe B32V2 means pin headers are nolonger a possibility and my build 'm tring to keep everything well integrated and short as short interconnections. so perhaps it is best if I knock it up on proto, will let you know if I do.

please dont take this as me not being thankful for your time, that was never my intention

Last edited by qusp; 8th March 2010 at 12:25 PM.
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Old 8th March 2010, 02:55 PM   #58
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Hi Owen,

great job. I am curious, you originally had a different FET shown. Did you make your final selection based on the sound quality or just electrical performance? Was it just coincidence that the best measuring was also the best sounding?

I am building a very similar I/V, but was planning to use the original IRF610. Now I may try a few of the other devices.

Do you think the sonic differences between FETs is worth experimenting with? or in your experience do they all sound about the same?
Thanks!
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Old 8th March 2010, 05:18 PM   #59
opc is offline opc  Canada
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Hi Guys,

ChuckT: This circuit won't give you the gain you'll need with such low current output from the DAC. I can run a simulation later tonight and let you know what the best values would be. If i were you, I'd settle on less gain to get maybe 1 VRMS since you probably have more gain than you need later on. I'll get back to you.

Yunick: I did mine by adjusting to 1.65V with no dac, then attaching the DAC and re-adjusting to make sure. This reference depends on the DAC of course, so consult the datasheet for the correct value. Some of the TI DACs want to see 2.5V there.

qusp: That's the spirit... it's so simple that you might as well give it a shot. If you want to simplify it further, you can omit the 0.01 and 0.0027 caps for initial testing. I would suggest using them in the final version however.

Jmertz: I ditched the original fets mostly because nobody seemed to like using the odd pinout/footprint. They also ran very hot because they were so small. As for sound quality, we're treading into dangerous waters. The measured differences are somewhere in the range of -102dB and -107dB THD+N. I personally don't believe that anyone could reliably identify one fet from another, but I'm sure others would argue that. I think the perceived difference had to do with the better temp stability of the larger parts, and I was probably biased by whet I knew was the best measuring devices.
It would be fun and easy to do a blind shootout, but I'm not the one to do it.

Cheers,
Owen
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Old 8th March 2010, 05:37 PM   #60
Yunick is offline Yunick  Sweden
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Quote:
Originally Posted by opc View Post
Hi Guys!
Yunick: I did mine by adjusting to 1.65V with no dac, then attaching the DAC and re-adjusting to make sure. This reference depends on the DAC of course, so consult the datasheet for the correct value. Some of the TI DACs want to see 2.5V there.
Cheers,
Owen
Thanks for your reply Owen,

I will rebuild my I/V to your new schematic and adjust for 1.65V at the input.

Thanks again,

Best Regards
David
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