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Old 9th May 2003, 09:06 AM   #11
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Join Date: Mar 2003
Location: Lisbon, Portugal
Default Re: Re: Re: Re: The reason

Quote:
Originally posted by Kuei Yang Wang
Koinichiwa Steve,
Or you could just use a BUF634... ;-)

Sayonara

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...
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Old 9th May 2003, 10:24 AM   #12
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Re: Re: Re: Re: The reason

Koinichiwa,

Quote:
Originally posted by carlosfm



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
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Old 9th May 2003, 11:03 AM   #13
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Default Re: Re: Re: Re: Re: Re: The reason

Quote:
Originally posted by Kuei Yang Wang
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.
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?
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Old 9th May 2003, 11:32 AM   #14
moamps is offline moamps  Croatia
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Hi,

Balanced passive preamp with good transformer attenuator (Sowther like) will work very satisfactory at length about 5m or more using ordinary Mogami wire and Neutrik XLR-s. IMHO

Regards
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Old 9th May 2003, 11:40 AM   #15
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Quote:
Originally posted by moamps
Hi,

Balanced passive preamp with good transformer attenuator (Sowther like) will work very satisfactory at length about 5m or more using ordinary Mogami wire and Neutrik XLR-s. IMHO

Regards

Maby, but the price of that good transformer...
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.
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Old 9th May 2003, 11:58 AM   #16
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: Re: Re: Re: Re: Re: Re: The reason

Koinichiwa,

Quote:
Originally posted by carlosfm


Sorry Kuei, you're right, I should have read your note again.
It was not deliberated.

That's cool then.

Quote:
Originally posted by carlosfm

Please, give us more details.

http://www.mfaudio.co.uk/passive_pre.htm

Click the image to open in full size.

Quote:
Originally posted by carlosfm

Could you have a passive preamp far away from the amps (say 3 to 5 meters) with good results?
Without ultra expen$ive interconnects?
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.
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Old 9th May 2003, 12:07 PM   #17
mikelm is offline mikelm  England
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Default transformers V opamps

I agree that good transformers are not cheap but the general reaction I have heard from those that have tried them ( including myself ) is that they are more transparent than most ( if not all ) other options.

mike
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Old 9th May 2003, 12:10 PM   #18
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Koinichiwa,

Quote:
Originally posted by carlosfm


Maby, but the price of that good transformer...
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....

Quote:
Originally posted by carlosfm


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
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Old 9th May 2003, 12:26 PM   #19
moamps is offline moamps  Croatia
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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 &quot;larger sonic footprint&quot; than transformers and active circuits, no matter how good have an even larger one"

You are very fast. That is my point to.

Regards
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Old 9th May 2003, 12:56 PM   #20
greg7 is offline greg7  United States
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Default 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.
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