JPV said:
Is this a stupid question?
I find it interesting to know the experience of people on this
JPV
john curl said:
This is the schematic of the I/V:
http://www.twistedpearaudio.com/docs/linestages/ivy_schematic.pdf
To answer the question with what I know:
I have made preamp line level 600 ohm drivers with 100KHz open loop bandwidth, and high global negative feedback, with 2 pole eq. Settling time was not a big problem, nor was stability with difficult loads. My 6V rms distortion was less than .001% at 100KHz. It was for a piece of test equipment, more than 25 years ago.
I would not design this way for audio quality. Different set of specs for best performance
I have made preamp line level 600 ohm drivers with 100KHz open loop bandwidth, and high global negative feedback, with 2 pole eq. Settling time was not a big problem, nor was stability with difficult loads. My 6V rms distortion was less than .001% at 100KHz. It was for a piece of test equipment, more than 25 years ago.
I would not design this way for audio quality. Different set of specs for best performance
Dual Pole Compensated (DPC)
Hi Jean-Pierre,
It's certainly not a stupid question. DPC (also called TPC) widens the (NFB loop) bandwidth, resulting is less distortion. BUT.. in the same time the phase response is affected, resulting in overshoot of the step response. Therefore, I don't like this technique and I will never use it. If it sounds better or worse, I don't know, sorry.
BTW, there exists a cousin of DPC: Transition Miller Compensation (TMC). This trick does not affect the phase response. However, it only reduces the distortion of the output stage (thus not the other stages).
Regards,
Edmond.
JPV said:
Hi Jean-Pierre,
It's certainly not a stupid question. DPC (also called TPC) widens the (NFB loop) bandwidth, resulting is less distortion. BUT.. in the same time the phase response is affected, resulting in overshoot of the step response. Therefore, I don't like this technique and I will never use it. If it sounds better or worse, I don't know, sorry.
BTW, there exists a cousin of DPC: Transition Miller Compensation (TMC). This trick does not affect the phase response. However, it only reduces the distortion of the output stage (thus not the other stages).
Regards,
Edmond.
Joshua_G said:
Joshua,
Are you sure this is an I/V converter? Doesn't look like it. Does this DAC have current or voltage output, is there somewhere a DAC data sheet?
Jan Didden
Yes I read that. But the schematic Joshua linked to isn't an I/V but a differential receiver with some 2nd order filtering. You could probably turn it into an I/V (if you would switch to a current-out DAC of course) if you shorted out the input series resistors and make some other component value changes.
I see this is described in the manual.
Jan Didden
I see this is described in the manual.
Jan Didden
By the way Edmond, how are your efforts with the Mosfets going? Sorry forgot to ask before, I always become excited when it comes to my amp 😀
Also thanks a lot for the equation, Ovidiu, analytic understanding is always the best.
Have fun, Hannes
Also thanks a lot for the equation, Ovidiu, analytic understanding is always the best.
Have fun, Hannes
Hi Hannes,
Progress is very slow, partly because the renovation of my apartment, partly due to technical difficulties, i.e. overload protection as well as clean recovery from overdrive. In the mean time I'm analyzing several (slightly) different topologies and will post the results soon.
Regards,
Edmond.
Progress is very slow, partly because the renovation of my apartment, partly due to technical difficulties, i.e. overload protection as well as clean recovery from overdrive. In the mean time I'm analyzing several (slightly) different topologies and will post the results soon.
Regards,
Edmond.
janneman said:
The DAC analog output is in current mode, the IVY input resistors are shorted, this it operates as I/V.
I've done this to my small headphone amps. It's easy to do "live". I can't say I hear any major difference, if any at all. I've also tried it on AD829 wich have a comp pin. Choosing good sounding transistors is far more important.scott wurcer said:
Getting back to the topic of this thread, did/does anyone have any more information available on the "blowtorch" pre-amp ?
Aside from the photo of what I presume is a rats nest prototype in post #11 on page 1 (the layout reminds me of the preamp I built whilst at school many years back, except that I used plain matrix board instead of PCB's and I wired it using the component leads. IIRC the circuits came from practical wireless) there doesn't seem to be much else.
The case looks OK although I can't see why the rear panel was made separate. The CNC/milling machine could have left the metal in place and then the rear panel holes could have been drilled straight into the case. For the lid/base, it is a shame they didn't machine a deep slot all round and have the lid drop into it, as a "waveguide beyond cut-off". That would have taken care of many potential EMC susceptibility and radiation issues. Perhaps they did this for the final design.
If they were really worried about EMC then alternate connectors such as those from Lemo would be better as they offer 360 degree shield connection and have caps to cover and shield unused connections. If the price mentioned in this thread is correct (>$10,000 !!!) then something better than RCA's would not go amiss, and the necessary external cables could be offered.
For conducted EMC problems then ferrites on the cables at the connectors are extremely good and we use them, along with the other techniques above on all out military equipment.
For a high end unit there appear to be a lot of cheap capacitors, and I am puzzled by the use if IC's on the boards given the contempt John Curl seems to have for them.
I guess only JC can tell us if it is real picture of a real "Blowtorch" preamp and what the production version look like.
If anyone out thre has one can you post more pics with board close ups ?
Aside from the photo of what I presume is a rats nest prototype in post #11 on page 1 (the layout reminds me of the preamp I built whilst at school many years back, except that I used plain matrix board instead of PCB's and I wired it using the component leads. IIRC the circuits came from practical wireless) there doesn't seem to be much else.
The case looks OK although I can't see why the rear panel was made separate. The CNC/milling machine could have left the metal in place and then the rear panel holes could have been drilled straight into the case. For the lid/base, it is a shame they didn't machine a deep slot all round and have the lid drop into it, as a "waveguide beyond cut-off". That would have taken care of many potential EMC susceptibility and radiation issues. Perhaps they did this for the final design.
If they were really worried about EMC then alternate connectors such as those from Lemo would be better as they offer 360 degree shield connection and have caps to cover and shield unused connections. If the price mentioned in this thread is correct (>$10,000 !!!) then something better than RCA's would not go amiss, and the necessary external cables could be offered.
For conducted EMC problems then ferrites on the cables at the connectors are extremely good and we use them, along with the other techniques above on all out military equipment.
For a high end unit there appear to be a lot of cheap capacitors, and I am puzzled by the use if IC's on the boards given the contempt John Curl seems to have for them.
I guess only JC can tell us if it is real picture of a real "Blowtorch" preamp and what the production version look like.
If anyone out thre has one can you post more pics with board close ups ?
I used the new Neutik XLR's with built-in EMI and was very pleased at a noticable reduction in some stubborn "pin 1" problems in my digital field recorder.
They put multiple RFI caps in a little circle arrangement around the outside edge of the shield, surprising for a commercial product.
They put multiple RFI caps in a little circle arrangement around the outside edge of the shield, surprising for a commercial product.
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