AudioCircle
Other Stuff => Archived Manufacturer Circles => Promitheus Audio => Topic started by: roymail on 16 Dec 2009, 03:25 am
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After lots of reading, I am considering trying the TVC standard version. Do transformer type passives remove the concerns over impedance matching and cable length?
My present amp has an input impedance of 47K and seems to be a good match for my 20K stepped attenuator. However, I'm lead to believe that some amps may be a more difficult match for these type passives. Is such the case with the Promitheus TVC? Thanks. :)
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I would not say it removes but it does minimize the issues of impedance matching and cable length
if a stepped attenuator can work well a TVC would work better in this situation.
The only issue with the TVC is the gain factor. Have not found an amp that does not suite the TVC unless because gain is in suffice.
the TVC can drive amp impedance from 5K and above.
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Thanks for the helpful information. If I understand correctly, the Promitheus is a good match for any amp with an input impedance of above 5K (20K to 100K are most common) provided the source can provide enough gain. In my case 1.8V is enough gain for most recordings and 2V is even better. Of course that issue can also be addressed by increased speaker efficiency.
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Here is another important piece of info for matching the TVC to an amp. It was posted by AC member Brown in another thread.
The lower the better [referring to input sensitivity]. Below 1 mv is desirable. TVCs are at their best when connected to an amp with very low input sensitivity. Further use cables under two meters.
Anyone else want to comment on this?
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Below 1 mv is desirable.
Read that as 1V and not 1mV
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duh! 1V :duh:
Thanks, milpai.
Is the TVC very cable sensitive as to quality, not length?
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i'm really now curious to hear after this explanation from promitheus that impedance hardly matters with a TVC how can i run my 2.8k output impedance DAC into 10k power amp via promitheus DAC without any issues?
pls explain, many thanks
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Hi people, this is my first post in this forum, no personal experiences yet to share on the TVC, because I do not have one at the moment... just ordered the balanced version. I am trusting all the positive opinions, and the fact thas this design is just technically "sweet". You know, all preamps deal with "low level" signals: low voltage, low amperage, and the musical information flows thru variations in the amplitude of this electrical current. The nemesis of voltage is impedance. If you control the voltage/amplitude of this delicate signal flow with resistive elements, as in traditional potentiometers, it seems clear that you are truncating the signal itself. The "brakes" that you apply this way afect the whole electrical current, energy is lost in the process so it seems obvious that the signal before the potentiometer is not the same after it. It is like having a flow of water from a 10 cm pipe and tying to routing it to a series of pipes from 10 to 1 cm. It is not possible without throwing away more and more water with each smaller pipe. The impedance of the smaller pipes is too high, so what you do is reduce the flow to fit. You have to throw away water. Yes, you still reveive water, but a lot less compared to the original flow, and a low volume means a small pipe, you know. In this analogy, what the TVC does is the opposite: it "changes" the diameter of the smaller pipes by lowering the impedance and increasing the current as the volume goes lower. In other words, you receive more or less the same amount of "water" in any setting, since the decreasing voltage is compensated proportionally by higher current and lower impedance. Well, at least theoretically sounds good, and signal integity should be superior with a TVC. It would be nice to see some graphs of signal loss before/after resistive elements, versus the TVC.
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How would the tvc then compare to the resistor based lightspeed which has the advantage of using no volume pot in the signal path?
Thanks!
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How would the tvc then compare to the resistor based lightspeed which has the advantage of using no volume pot in the signal path?
Thanks!
The advantage of that design is NO contact points as in a conventional attenuator. Same can be said for the selector switch. That is why my TVC has one input. Since the LEDs drive the LDRs it is the speed of light not contacts. Very interesting concept.
Until recently the reliability of the LDRs was questionable. Not any more. I have to do some more research.
BTW guys if you have a Promitheus DAC and do not use the BNC connection remove the switch and connect the pulse transformer directly to the RCA. Your gonna be a happy camper. The switch has a purpose if needed but IMO it afects the signal. Without it you be the judge.
charles
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Thanks Rollo!
Will the LDR sound better than the TVC or vice versa?
Am not a techie guy but i have the SE TVC version. Can i do the tweak as you suggested...thanks again!
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Thanks Rollo!
Will the LDR sound better than the TVC or vice versa?
Am not a techie guy but i have the SE TVC version. Can i do the tweak as you suggested...thanks again!
If you own the Promitheus DAC by all means. IMO a big difference in clarity and top end focus.
charles