The reason
Well, basically because I don't like passive preamps.
Or you use very good (expen$ive) and short interconnects, or the sound degrades.
Anyway, the Gaincards have volume pots (actualy rotary switches with resistors), but from there goes a very short piece of wire to the chip.
Elkaid said:
Well, basically because I don't like passive preamps.
Or you use very good (expen$ive) and short interconnects, or the sound degrades.
Anyway, the Gaincards have volume pots (actualy rotary switches with resistors), but from there goes a very short piece of wire to the chip.
Re: The reason
Koinichiwa,
A competently engineered passive Linestage has no problems with either output impedance/load OR with undue loading of the source. It is really easy.
Sayonara
Koinichiwa,
carlosfm said:
Well, basically because I don't like passive preamps.
Or you use very good (expen$ive) and short interconnects, or the sound degrades.
A competently engineered passive Linestage has no problems with either output impedance/load OR with undue loading of the source. It is really easy.
Sayonara
Re: Re: Re: The reason
Koinichiwa Steve,
Most active preamplifiers will not tollerate such an extreme load, methinks you'll have to buffer the input, maybe with a 4:1 stepdown transformer, in which case the input Z is a more managable 3200 Ohm.... Or you could just use a BUF634... ;-)
Sayonara
Koinichiwa Steve,
Steve Eddy said:
As it happens, I'm working on a power amp which has a 200 ohm input impedance. I'd like to see a passive which could drive it without severe loading losses (no more than -3dB).
se
Most active preamplifiers will not tollerate such an extreme load, methinks you'll have to buffer the input, maybe with a 4:1 stepdown transformer, in which case the input Z is a more managable 3200 Ohm.... Or you could just use a BUF634... ;-)
Sayonara
low i/p Z
Would that be a gainclone inverting i/p power amp with 200 ohms i/p Z or a different variety ?
I reduced my + input resistance from 10k to zero ohms and liked the results very much. Now I am interested to discover how lowering the feedback Z will affect the sound.
has anyone tried this ?
mike
Steve Eddy said:
As it happens, I'm working on a power amp which has a 200 ohm input impedance. I'd like to see a passive which could drive it without severe loading losses (no more than -3dB).
se
Would that be a gainclone inverting i/p power amp with 200 ohms i/p Z or a different variety ?
I reduced my + input resistance from 10k to zero ohms and liked the results very much. Now I am interested to discover how lowering the feedback Z will affect the sound.
has anyone tried this ?
mike
Re: Re: Re: Re: The reason
But if you use a 4:1, then most all of the voltage gain of the amp (which is using a 1:5) will be lost. At that point, you just might as well just use a high current buffer and slap it on the preamp and drive the speakers from there.
Actually I've already got a preamp for it. Just that your original post made it sound as if you had some way to drive such a load passively without loading loss.
se
Kuei Yang Wang said:
But if you use a 4:1, then most all of the voltage gain of the amp (which is using a 1:5) will be lost. At that point, you just might as well just use a high current buffer and slap it on the preamp and drive the speakers from there.
Actually I've already got a preamp for it. Just that your original post made it sound as if you had some way to drive such a load passively without loading loss.
se
Re: Re: Re: Re: Re: The reason
Koinichiwa Steve,
I figured you where using a stepup input transformer, but why on earth one with 200 ohm input impedance? How about a 5k:80k (1:4) which gives gain and much saner impedances. A 200 Ohm input impedance will not even sit well in Pro Audio systems.
Sure do. Just use a 600 Ohm version of a TVC driven from a source that can tolerate 200 Ohm worst case load.... ;-)
BTW, I have driven a nominally 600 Ohm input of a transformer (S&B TX-905 1:4 10k secondary) from a nominally 10k TVC with no ill effects, but the secondary was unloaded... It simply had too much gain for my taste and I switched to a 877 as 10k:10k or 10K:40K selectable.
Sayonara
Koinichiwa Steve,
Steve Eddy said:
I figured you where using a stepup input transformer, but why on earth one with 200 ohm input impedance? How about a 5k:80k (1:4) which gives gain and much saner impedances. A 200 Ohm input impedance will not even sit well in Pro Audio systems.
Steve Eddy said:
Sure do. Just use a 600 Ohm version of a TVC driven from a source that can tolerate 200 Ohm worst case load.... ;-)
BTW, I have driven a nominally 600 Ohm input of a transformer (S&B TX-905 1:4 10k secondary) from a nominally 10k TVC with no ill effects, but the secondary was unloaded... It simply had too much gain for my taste and I switched to a 877 as 10k:10k or 10K:40K selectable.
Sayonara
Re: Re: Re: Re: Re: Re: The reason
Well, seeing as this particular version of the amp isn't intended to be used with other equipment, the 200 ohm input impedance wasn't an issue.
The reason it is 200 ohms is due to something of a compromise in keeping the number of components down to just seven.
The transformer is "normally" intended to have a 39.2k load on it which gives a 1.5k ohm input impedance. But in this case, it's driving a bipolar emitter follower so base current is something of an issue.
I actually prefer a little bit of current through the secondary of the transformer but when I opted to go with a resistive load rather than a constant current source for the follower, the bias current required tripled and of course so does the base current.
Going with the 4k load relieves the transformer secondary of some of the bias current. But of course leaves you with a 200 ohm input impedance.
Of course I could just keep the 39.2k load and use a resistor from the base to the positive rail and determine how much base current goes to the secondary, but then that would be 8 parts, not 7.
Yeah? Since when did you start recommending TVCs?
Yeah. Just depends on what you're looking to get in the end.
se
Kuei Yang Wang said:
Well, seeing as this particular version of the amp isn't intended to be used with other equipment, the 200 ohm input impedance wasn't an issue.
The reason it is 200 ohms is due to something of a compromise in keeping the number of components down to just seven.
The transformer is "normally" intended to have a 39.2k load on it which gives a 1.5k ohm input impedance. But in this case, it's driving a bipolar emitter follower so base current is something of an issue.
I actually prefer a little bit of current through the secondary of the transformer but when I opted to go with a resistive load rather than a constant current source for the follower, the bias current required tripled and of course so does the base current.
Going with the 4k load relieves the transformer secondary of some of the bias current. But of course leaves you with a 200 ohm input impedance.
Of course I could just keep the 39.2k load and use a resistor from the base to the positive rail and determine how much base current goes to the secondary, but then that would be 8 parts, not 7.
Yeah? Since when did you start recommending TVCs?
Yeah. Just depends on what you're looking to get in the end.
se
Re: Re: Re: Re: The reason
Kuei (T) ,
I was talking Passive.
I meant a pot.
If you put a buffer it's not passive anymore.
Just because it has a gain of 1, it's not passive.
If a preamp needs a PSU it's not passive (at least for me, that is).
The suggestion you make is what some people call a "buffered passive preamp".
True passive preamps almost always suffer from lack of dynamics, among other things...
Kuei Yang Wang said:
Kuei (T)
,I was talking Passive.
I meant a pot.
If you put a buffer it's not passive anymore.
Just because it has a gain of 1, it's not passive.
If a preamp needs a PSU it's not passive (at least for me, that is).
The suggestion you make is what some people call a "buffered passive preamp".
True passive preamps almost always suffer from lack of dynamics, among other things...
Re: Re: Re: Re: Re: The reason
Koinichiwa,
You deliberatly choose to misunderstand me. I recommended adding a buffer to the Amplifier, to make it's input more compatible with normal equipment.
As for your comments on "passive preamp's" above and previously, you are simply refering to incompetently designed passive line controllers. A competently designed passive line controller does not have any of these problems.
Of course, if you want to design a passive line controller in a fashion that can be consdiered competent than you cannot use a variable resistor. That simply does not work well and cannot work well.
Sayonara
Koinichiwa,
carlosfm said:
Kuei (T)
I was talking Passive.
I meant a pot.
If you put a buffer it's not passive anymore.
Just because it has a gain of 1, it's not passive.
If a preamp needs a PSU it's not passive (at least for me, that is).
The suggestion you make is what some people call a "buffered passive preamp".
True passive preamps almost always suffer from lack of dynamics, among other things...
You deliberatly choose to misunderstand me. I recommended adding a buffer to the Amplifier, to make it's input more compatible with normal equipment.
As for your comments on "passive preamp's" above and previously, you are simply refering to incompetently designed passive line controllers. A competently designed passive line controller does not have any of these problems.
Of course, if you want to design a passive line controller in a fashion that can be consdiered competent than you cannot use a variable resistor. That simply does not work well and cannot work well.
Sayonara
Re: Re: Re: Re: Re: Re: The reason
Sorry Kuei, you're right, I should have read your note again.
It was not deliberated.
Please, give us more details.
Could you have a passive preamp far away from the amps (say 3 to 5 meters) with good results?
Without ultra expen$ive interconnects?
How?
Kuei Yang Wang said:
Sorry Kuei, you're right, I should have read your note again.
It was not deliberated.
Please, give us more details.
Could you have a passive preamp far away from the amps (say 3 to 5 meters) with good results?
Without ultra expen$ive interconnects?
How?
Re: Re: Re: Re: Re: Re: Re: The reason
Koinichiwa,
That's cool then.
http://www.mfaudio.co.uk/passive_pre.htm
It is exactly that what I have/had. I recently re-arranged my system and put the Digital EQ that used to be on it's own little rack to be placed at the listening position and put this into my rack. While the EQ was in it's own rack on wheels it was connected by 6m balanced cable, driven by the passive preamp that you could say became the prototype for the unit illustrated above.
In the end, usually if the source can drive the cable you are using, a competently designed passive will drive it too. That is unless of course you take all that signal (current) and low output impedance of your source and throw it away, as incompetently designed passives usually do.
At the moment, if I put the EQ into bypass my passive preamp drives 3m Balanced cable using each a pair of 50 Ohm coax Cables, plus the input capacitance of a WE 437A (around 175pF) quadrupeled due to the input transformer with 1:2 stepup at the amplifier input. I'd estimate the differential capacitive load of the cables as 150pF and the effective input capacitance of the Amplifier as around 700pF. In total 850pF load capacitance. Still sounds fine, with no observable rolloff.
In measurement terms, I measured the passive line controller into 10k//1nF from a 1K Source. The behaviour in terms of HF rolloff equalled closely that I would have expected without the passive controller in circuit, excepting the added around 600 Ohm copper losses.
Sayonara
PS, I was peripherally involved with the development of the MFA unit as advisor, but other than that I have no connections, I do not earn commision on units sold, get paid for design input or anything of the like.
Koinichiwa,
carlosfm said:
Sorry Kuei, you're right, I should have read your note again.
It was not deliberated.
That's cool then.
carlosfm said:
http://www.mfaudio.co.uk/passive_pre.htm
An externally hosted image should be here but it was not working when we last tested it.
carlosfm said:
It is exactly that what I have/had. I recently re-arranged my system and put the Digital EQ that used to be on it's own little rack to be placed at the listening position and put this into my rack. While the EQ was in it's own rack on wheels it was connected by 6m balanced cable, driven by the passive preamp that you could say became the prototype for the unit illustrated above.
In the end, usually if the source can drive the cable you are using, a competently designed passive will drive it too. That is unless of course you take all that signal (current) and low output impedance of your source and throw it away, as incompetently designed passives usually do.
At the moment, if I put the EQ into bypass my passive preamp drives 3m Balanced cable using each a pair of 50 Ohm coax Cables, plus the input capacitance of a WE 437A (around 175pF) quadrupeled due to the input transformer with 1:2 stepup at the amplifier input. I'd estimate the differential capacitive load of the cables as 150pF and the effective input capacitance of the Amplifier as around 700pF. In total 850pF load capacitance. Still sounds fine, with no observable rolloff.
In measurement terms, I measured the passive line controller into 10k//1nF from a 1K Source. The behaviour in terms of HF rolloff equalled closely that I would have expected without the passive controller in circuit, excepting the added around 600 Ohm copper losses.
Sayonara
PS, I was peripherally involved with the development of the MFA unit as advisor, but other than that I have no connections, I do not earn commision on units sold, get paid for design input or anything of the like.
Koinichiwa,
Hey. Stop shifting goal posts. You never said anything about price. The best is rarely cheap. That's life. Though the very best in life is usually free....
I think you would want to FIRST try this out and secondly comment, rather than to prejudge. In my experience resistive volume controls have a "larger sonic footprint" than transformers and active circuits, no matter how good have an even larger one.
When I compared my transformer passive against a rather special "buffered passive" (here the INPUT is buffered and the passive section is very low impedance and used in a shunt control type arrangement with a Z-Out < 300R worst case) the improvements with the transfromer where so drastic, that friend of mine who had build the buffered passive "to save money" felt it had been a complete waste of money and went out and put the long green down for transformers. Try it.
Sayonara
carlosfm said:
Hey. Stop shifting goal posts. You never said anything about price. The best is rarely cheap. That's life. Though the very best in life is usually free....
carlosfm said:
And it may have more sonic "signature" than the best op-amps/buffers... (I think).
You loose that only advantage of a passive preamp: it should have (almost) no sonic effects, but that's theory.
I think you would want to FIRST try this out and secondly comment, rather than to prejudge. In my experience resistive volume controls have a "larger sonic footprint" than transformers and active circuits, no matter how good have an even larger one.
When I compared my transformer passive against a rather special "buffered passive" (here the INPUT is buffered and the passive section is very low impedance and used in a shunt control type arrangement with a Z-Out < 300R worst case) the improvements with the transfromer where so drastic, that friend of mine who had build the buffered passive "to save money" felt it had been a complete waste of money and went out and put the long green down for transformers. Try it.
Sayonara
Hi,
Carlosfm
Price of good transformer preamp can be about 500 € (two Sowthers, good switcher, connectors, etc.). Any preamp (passive or active) have unique sonic signature. I agree that long wire running isn't specialty of passives, but some another advantage are obviously (no power supply needed, no ground problems, simplicity, smaller overall noises,...).
Kuei Yang Wang
"In my experience resistive volume controls have a "larger sonic footprint" than transformers and active circuits, no matter how good have an even larger one"
You are very fast. That is my point to.
Regards
Carlosfm
Price of good transformer preamp can be about 500 € (two Sowthers, good switcher, connectors, etc.). Any preamp (passive or active) have unique sonic signature. I agree that long wire running isn't specialty of passives, but some another advantage are obviously (no power supply needed, no ground problems, simplicity, smaller overall noises,...).
Kuei Yang Wang
"In my experience resistive volume controls have a "larger sonic footprint" than transformers and active circuits, no matter how good have an even larger one"
You are very fast. That is my point to.
Regards
Passive pre- impressions
Passive (unbuffered) preamps certainly aren't perfect -- they have upsides and downsides like everything else.
I mentioned in my first post that I'm trying out the Channel Island passive preamp, which is simply a 10K pot with input selection capability. I have a perfect system for a passive: short, low capacitance interconnects, good DAC (i.e., strong 2V output stage) and amp with high input impedance and low (750 mV) sensitivity. I've been listening to it and here's some impressions.
Even in my 'optimized' environment there is indeed diminished dynamics and bass -- everything seems to have slowed down slightly, taken a deep breath and begun pacing itself for a longer race rather than a sprint. This is with a very fast, highly detailed (IMO) and fairly powerful SS amplifier, no less. Imaging has been pushed back slightly as well. The upside, however, is crystal clarity, greatly enhanced detail and soundstage placement and SMOOTHNESS (above all else). A whole layer of 'electronic' sound is gone, and the top end is much smoother in particular. Thankfully the passive hasn't "leaned" out the sound, either. Instruments and vocals are still thick and palpable even if there more reticent. It's like my SS preamp was over-energizing the sound, making it nervous, fatiguing, too fast-paced. The sound is much more liquid now. But, I can see where not everyone would like the sound with a passive. Makes my system more cerebral than emotional. Depends on sonic preferences and priorities. Mine include detail retrieval, imaging and smoothness, especially in the treble. So I like it and just may keep it and sell or trade off my active preamp. But I can see where others wouldn't like it, for sure.
Passive (unbuffered) preamps certainly aren't perfect -- they have upsides and downsides like everything else.
I mentioned in my first post that I'm trying out the Channel Island passive preamp, which is simply a 10K pot with input selection capability. I have a perfect system for a passive: short, low capacitance interconnects, good DAC (i.e., strong 2V output stage) and amp with high input impedance and low (750 mV) sensitivity. I've been listening to it and here's some impressions.
Even in my 'optimized' environment there is indeed diminished dynamics and bass -- everything seems to have slowed down slightly, taken a deep breath and begun pacing itself for a longer race rather than a sprint. This is with a very fast, highly detailed (IMO) and fairly powerful SS amplifier, no less. Imaging has been pushed back slightly as well. The upside, however, is crystal clarity, greatly enhanced detail and soundstage placement and SMOOTHNESS (above all else). A whole layer of 'electronic' sound is gone, and the top end is much smoother in particular. Thankfully the passive hasn't "leaned" out the sound, either. Instruments and vocals are still thick and palpable even if there more reticent. It's like my SS preamp was over-energizing the sound, making it nervous, fatiguing, too fast-paced. The sound is much more liquid now. But, I can see where not everyone would like the sound with a passive. Makes my system more cerebral than emotional. Depends on sonic preferences and priorities. Mine include detail retrieval, imaging and smoothness, especially in the treble. So I like it and just may keep it and sell or trade off my active preamp. But I can see where others wouldn't like it, for sure.
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