I think using Zen IV as a bridge to a tube (DHT?) is a great idea.
That would be very musical in my imagination.
> So if we use MOSFET pair (e.g. IRF610/9610) in the Zen IV or BT circuit. The transconductance could be higher too. So input impedance is lower.
Enhancement mode MOSFETs are not self biasing, and depletion mode MOSFETs has no complementary (only N channel). On top of that, MOSFETs are noisier and less linear.
Patrick
Enhancement mode MOSFETs are not self biasing, and depletion mode MOSFETs has no complementary (only N channel). On top of that, MOSFETs are noisier and less linear.
Patrick
The response to every project generates data points.
For this project, the data point is that there is fear of
violating the recommendations of the manufacturer's
data sheet, so most will not try it.
Of those who do, many will still be bothered that there
must be something wrong even if they can't hear it.
That is the same lesson taught by the D1.
For this project, the data point is that there is fear of
violating the recommendations of the manufacturer's
data sheet, so most will not try it.
Of those who do, many will still be bothered that there
must be something wrong even if they can't hear it.
That is the same lesson taught by the D1.
.....
That is the same lesson taught by the D1.
experience gained from strictly lurking at few MotoGP related forums/blogs :
even Old Geezer , crowned myriad times , must proof his value every time from scratch ..... according to majority of fans behavior
same here - spoiled kids are too spoiled
life is fun
I dare to disagree. It has little to do with what the manufacturer says.
If you dig through the digital forum, and especially that at the other place, there have been many people who have experimented with passive IVs (with or without a gain stage after) for many DACs. Many of them fearless. They have tried various values from 10 to 50 ohms. But the concense is that 10 ohm sounds best for PCM1704. There are other DACs which are more easy going. TDA1543, e.g. But then I shall go straight to passive IV for those. No need for current conveying.
Of course we can say this is all bull ****. Well, do go and try first, but please do an AB test. Because you might think that this sounds great, until you compare it with another solutions.
No, I have not tried them all. I cannot say it is wonderful at 10 ohms and horrible at 20 ohms. But I have talked to a few whose vast experience with these DACs I respect a lot. People who have done extensive measurements as well as listening. So I shall stick to their friendly advice.
There are tons of current DACs around, and every one is different. So do some research first. The Zen IV is less attractive for current DACs with a reference voltage offset (single power rail) because you then have to set the gates at 2.5V or so, thus adding extra complication.
Just my 2 cents,
Patrick
If you dig through the digital forum, and especially that at the other place, there have been many people who have experimented with passive IVs (with or without a gain stage after) for many DACs. Many of them fearless. They have tried various values from 10 to 50 ohms. But the concense is that 10 ohm sounds best for PCM1704. There are other DACs which are more easy going. TDA1543, e.g. But then I shall go straight to passive IV for those. No need for current conveying.
Of course we can say this is all bull ****. Well, do go and try first, but please do an AB test. Because you might think that this sounds great, until you compare it with another solutions.
No, I have not tried them all. I cannot say it is wonderful at 10 ohms and horrible at 20 ohms. But I have talked to a few whose vast experience with these DACs I respect a lot. People who have done extensive measurements as well as listening. So I shall stick to their friendly advice.
There are tons of current DACs around, and every one is different. So do some research first. The Zen IV is less attractive for current DACs with a reference voltage offset (single power rail) because you then have to set the gates at 2.5V or so, thus adding extra complication.
Just my 2 cents,
Patrick
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I have a question on the PCM 1794 with a Zen I/V
The PCM 1794 spec sheet in figure 31 lists the output current as -2.3 mA to -10.1 mA with an idle current of -6.2 mA. The Negative output is listed as -10.1 mA to -2.3 mA, with the same -6.2 mA idle current.Its clear to me that a 10ma idle current is not going to work on an unmodified Zen I/V.
I was wondering if an appropriate CSS would allow me to trim the Zen I/V to 1 mV and not violate the design? Perhaps even tune it for a distortion null? Or would doubling up on the jfets be a better solution?
I would be interested in everyone's thoughts.
Doug
Here is a link to download the data sheet if you need it. http://focus.ti.com/docs/prod/folders/print/pcm1794.html
The PCM 1794 spec sheet in figure 31 lists the output current as -2.3 mA to -10.1 mA with an idle current of -6.2 mA. The Negative output is listed as -10.1 mA to -2.3 mA, with the same -6.2 mA idle current.Its clear to me that a 10ma idle current is not going to work on an unmodified Zen I/V.
I was wondering if an appropriate CSS would allow me to trim the Zen I/V to 1 mV and not violate the design? Perhaps even tune it for a distortion null? Or would doubling up on the jfets be a better solution?
I would be interested in everyone's thoughts.
Doug
Here is a link to download the data sheet if you need it. http://focus.ti.com/docs/prod/folders/print/pcm1794.html
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I think the best solution is to add a ccs to compensate for the current offset and let the output stage deal with the AC current variations.
However +/- 3.9mA is probably to much to handle with a low distorsion for a stage limited by the idss of the fets to around 10mA idle current (BL grade).
You can go a bit higher by paralleling and using higher grade (V, hard to find).
However +/- 3.9mA is probably to much to handle with a low distorsion for a stage limited by the idss of the fets to around 10mA idle current (BL grade).
You can go a bit higher by paralleling and using higher grade (V, hard to find).
You are quite right. My position is that if you find a
deficiency in the circuit as presented, then consider the
variations available. It's easy to parallel more Fets,
choose different Fets, raise the current, add more supply,
adjust the Gate DC, and resistively load the input to
accommodate the needs of a given DAC chip.
As you would expect from me, I have been playing with exactly that for the last 2 years; not necessarily along the same lines, but nevertheless.
The reason for pointing out the "deficiencies" is by no means to discredit the design, but rather to stimulate ideas for improvements.
Patrick
Yes. NP's and your inputs are really helpful. I think no matter how,
I will try to use parallel JFETs + Cascoding BT MOSFET. Build the working prototype first then trying to increase the bias of JFET (increase the transconductance) to approach 10R. (I think after parallel, it will be ~ 15R, and increasing Input JFET (GR grade) and parallel near to its Vdss. Hope could be around 10R)
Thanks,
You are quite right. My position is that if you find a
deficiency in the circuit as presented, then consider the
variations available. It's easy to parallel more Fets,
choose different Fets, raise the current, add more supply,
adjust the Gate DC, and resistively load the input to
accommodate the needs of a given DAC chip.
yes all true, but in the case of the sabre, you may just end up back at the D1
although I am interested in trying out the lovoltech jfets in a D1 type circuit too in place of the mosfets. I think its (the ZEN) a great and elegant circuit with lots of tweakability, but any way I look at it for the sabre there are too many compromises or solutions are too complex and the beauty of the circuit is lost
because low impedance is not an option for best sabre performance, it really has to be almost no impedance
indeed I do thanks to you among others, I wasnt hinting for hints, I have already ordered some to play around with and have also suggested them to acko for his IV design. when they arrive i'll probably have a go on breadboard. until they get here and I have a changce to put them into real world designs for the first time, i'm not making any plans
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Hi,
Last weekend i matched some Jfets again and i had two sets of j74's matched at 11.4 ma, a k170 at 11.5 and one at 1.6. I figured this would be close enough but to my surprise it is not. The j74's give a drain voltage of 16.2V with a 2k2 load where the sk170's give about 11.9V. The drain resistors are close enough not to be able to cause this difference. Input offset is at about 25 mv dc.
I don't quite understand how this could be unless the offset is related to the dac chip itself. Test setup for the matching is two 9v batteries in series, source and gate connected together and using 10 as the drain resistor. Just swapping polarity for the j74 versus k170. The unit sounds very good nonetheless.
I tried to measure signal at the input of the i/v stage. I could not detect any signal there.
anybody got a suggestion?
regards
joris
Last weekend i matched some Jfets again and i had two sets of j74's matched at 11.4 ma, a k170 at 11.5 and one at 1.6. I figured this would be close enough but to my surprise it is not. The j74's give a drain voltage of 16.2V with a 2k2 load where the sk170's give about 11.9V. The drain resistors are close enough not to be able to cause this difference. Input offset is at about 25 mv dc.
I don't quite understand how this could be unless the offset is related to the dac chip itself. Test setup for the matching is two 9v batteries in series, source and gate connected together and using 10 as the drain resistor. Just swapping polarity for the j74 versus k170. The unit sounds very good nonetheless.
I tried to measure signal at the input of the i/v stage. I could not detect any signal there.
anybody got a suggestion?
regards
joris