Preamp to Main amp impedance matching...what's your ratio?

I've found impedance matching doesn't seem to matter that much do long as it's an active pre. A bigger deal with passives.

If really concerned get the Burson Cable+ which takes care of impedance mismatches.

As for the definition of preamp, I don't believe it even means any kind of pre power amp gain though just indicates volume control of some description. Doesn't even mean input selection or EQ.

I've had great results with both passive and tube preamps though passive is fussier needing a strong signal. Not all sources or power amps get along with passive.
 
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Robust line drive from source components allow passive controllers to do their best. Feeble sources that have low drive capability do better with an active gain stage. A simple unity gain active buffer can handle most sources with adequate rms voltage level, regardless of drive energy.
 
Pio1980 said:
No, not really. Low is good, it helps negate cable and other loading issues. Many CJ preamp line stages are simple cathode follower or similar line drive, and may invert acoustic polarity. See instruction manual for the specific model for particulars.
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As
david1111 said:
@wyn palmer
Is there a possibility that the 200 ohm output of my Conrad Johnson is too low? Llike they may have made it to mate with a CJ mosfet amp?
Thanks for the info.

Dave
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The issue of "desirable output impedance range for a preamp" is a complex one, so let's look at a few issues.
1. Output bandwidth/load considerations.
In general, having an output bandwidth greater than say, 500kHz is hard to justify, and it's perhaps better if it's significantly less- say 200kHz. Less than that and some attenuation at 20kHz starts to appear, more and unwanted signals can pass through potentially exposing the power amp to intermodulation of out of band signals down into the audio band.
3kohms and 250pF or 300ohms and 2500pF give you c.200kHz. Low capacitance video or phono cables are c. 20pF/ft and if you have multiple runs to various devices several hundred pFs is not unlikely. Also the input stages of some power amps can be quite capacitive- the Rogue M180 looks like about 4000pF! All this put together suggests that the stage should be designed to drive a capacitance in the order of 5000pF max while keeping a bandwidth of c.200kHz. That suggests an output impedance in the 150 ohms region.
2. Output stage stability.
Open loop stages are generally not subject to stability issues. This is not entirely true, but it might as well be.
Stages with negative feedback often do require an additional resistor in series with the output in order to maintain stability due to the phase shift introduced by the capacitive load. Counter intuitively perhaps, this resistor gets smaller as the capacitive load gets bigger and it gets bigger as the closed loop bandwidth of the driving stage gets smaller. However, this resistor generally falls in a range between c. 1 ohm and several hundred ohms.
There is also no downside, from a stability point of view, in having too large a resistance.
So, all in all 200 ohms seems like a pretty fair value to have.
 
wyn palmer said:
Why? What possible reason would there be for this to be true?
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Just my experience. Try limiting the variables in your "system" to only changes in input impedance of the power amp and test/listen. You can use a Rowland, Threshold, or a few other amps that have such a capacity.

For example, the Rowland Model 1 has input impedances of 100k, 20k, and 600. Given the large difference in values, I could hear a difference. Same thing with the Threshold SA series amps that have input impedances of 50k and 600.

Personally, I prefer a preamp with low (<100 ohms) output impedances as it allows a lot easier mating/flexibility with power amps, all other things being equal.

Is impedance matching the be all end all? No but it is something to consider.
 
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mjw21a said:
I've found impedance matching doesn't seem to matter that much do long as it's an active pre. A bigger deal with passives.
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My experience is different with an active pre.

Case in point, a long time ago I had access to an ARC LS2 and LS2B preamp which I tried to use with my Threshold SA4e. At 50K Ohms input impedance on the power amp, it sounded fine. But at 600 Ohms, it sounded tinny and lacked a lot of bass. Almost like the bass drivers in my speakers were not working. YMMV
 
FWIW, the LS2 has an output impedance of 200 Ohms and the LS2B has an ouput impedance of 400 Ohms. So while they may be in the "optimal range" for preamps, it wasn't in this case.
 
edwyun said:
FWIW, the LS2 has an output impedance of 200 Ohms and the LS2B has an ouput impedance of 400 Ohms. So while they may be in the "optimal range" for preamps, it wasn't in this case.
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The obvious question is. Was the preamp AC coupled, and if so what was the capacitance?
Generally components tend not to specify input/output impedances vs. frequency- although they absolutely should.
For example, if the output impedance consists of a 1uF cap in series with 200 ohms real then there will be about a 2dB attenuation in signal level into 600 ohms real and an additional -3dB LF cutoff at c. 230Hz.
 
wyn palmer said:
The obvious question is. Was the preamp AC coupled, and if so what was the capacitance?
Generally components tend not to specify input/output impedances vs. frequency- although they absolutely should.
For example, if the output impedance consists of a 1uF cap in series with 200 ohms real then there will be about a 2dB attenuation in signal level into 600 ohms real and an additional -3dB LF cutoff at c. 230Hz.
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The other thing is that not every preamp is actually capable of driving a usable voltage into 600 ohms even if the output impedance is 200 ohms.
I discussed this type of issue, with an example, earlier.
 
wyn palmer said:
The other thing is that not every preamp is actually capable of driving a usable voltage into 600 ohms even if the output impedance is 200 ohms.
I discussed this type of issue, with an example, earlier.
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Agreed. ___ KOhms, not 600 Ohms, is the typical power amp input impedance that you would typically want.
 
edwyun said:
FWIW, the LS2 has an output impedance of 200 Ohms and the LS2B has an ouput impedance of 400 Ohms. So while they may be in the "optimal range" for preamps, it wasn't in this case.
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wyn palmer said:
The obvious question is. Was the preamp AC coupled, and if so what was the capacitance?
Generally components tend not to specify input/output impedances vs. frequency- although they absolutely should.
For example, if the output impedance consists of a 1uF cap in series with 200 ohms real then there will be about a 2dB attenuation in signal level into 600 ohms real and an additional -3dB LF cutoff at c. 230Hz.
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The specs for the LS2 output impedance state:

200 ohms main output. 400 ohms Balanced 1, Balanced 2 (10K ohms minimum load and 2000pF maximum capacitance)

I'm not surprised it didn't sound good at 600 ohms, most likely due to too small a coupling cap as Wyn Palmer said.
https://www.arcdb.ws/LS2/LS2.html
 
rothwellaudio said:
I'm not surprised it didn't sound good at 600 ohms, most likely due to too small a coupling cap as Wyn Palmer said.
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Or, choice “B”, Audio Research expects you pay attention to their recommendation of a minimum 10k load.

Their power amps of that day were 100k single ended and 200k balanced.
 
Lots of useful info in this thread, but I think there's been only a few people that read my first post. Now were talking about ARC gear and it's specs?

The whole point was for people to list their preamp output Z and their main amp input Z. This is the information I wanted to know. I'd like to get a consensus on what ratio a majority of people get away with using, with their main systems that they really enjoy listening to. A few people have listed theirs, and I thank you. You don't even need to know the impedances, just list your model numbers and I'll look them up.

I didn't realize it would go down this path. It's similar to asking what cables people use with their gear, then all of the replies are about if cables actually make a difference, instead of just listing your your cables and gear used. I'm not interested in what people's opinions are about the subject of impedance matching...I just want to know what your actual impedances are. Many read farther into my original post than intended.
 
Sonance'84 said:
. . . The whole point was for people to list their preamp output Z and their main amp input Z. This is the information I wanted to know. I'd like to get a consensus on what ratio a majority of people get away with using, with their main systems that they really enjoy listening to. A few people have listed theirs, and I thank you. You don't even need to know the impedances, just list your model numbers and I'll look them up. . .
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The three preamp/power amp combos I've owned and enjoyed:

conrad-johnson PV3 - don't know the output impedance
McIntosh MC240 - 250,000 ohms

Linn LK1 - 71.5 ohms
Linn LK280 - 3830 ohms (both as measured by Stereophile in their review)

Audio by Van Alstine OmegaStar - 100 ohms
Audio by Van Astine Insight 240 - 24,000 ohms (both from forum discussions by Frank Van Alstine; no specs in the manuals)
 
Interesting thread. It would be even more interesting if I understood more of this stuff. I'm learning as I go.

I have a Schiit Vidar amp being delivered on Friday and now I'm concerned about it matching my preamps.

Right now, for example I have three preamps that all have an input impedance of 47K ohms. The amp I'm using them with has an imput impedance of 100K ohms. They all work great together. I can't hear any kind of 'mismatch'.

The Schiit Vidar has an input impedance of 22K. Will this work with my 47K preamps?

From what I've read so far, this doesn't seem right.

Thanks for any help.
 
SWL3600 said:
Interesting thread. It would be even more interesting if I understood more of this stuff. I'm learning as I go.

I have a Schiit Vidar amp being delivered on Friday and now I'm concerned about it matching my preamps.

Right now, for example I have three preamps that all have an input impedance of 47K ohms. The amp I'm using them with has an imput impedance of 100K ohms. They all work great together. I can't hear any kind of 'mismatch'.

The Schiit Vidar has an input impedance of 22K. Will this work with my 47K preamps?

From what I've read so far, this doesn't seem right.

Thanks for any help.
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It's the output impedance of the pre that matters. What's the output?
Basic rule is that the input impedance of the amp should be a minimum of ten times the output impedance of the preamp.
 
I'm running 6 amps that each have 25k ohms input impedance and a preamp that has 47 ohms output impedance (!). Even if all 6 amps were simply wired in parallel off one pair of preamp outputs, that would still be an impedance ratio of over 88x.

But they aren't wired in parallel. My Yamaha C-80 preamp has two sets of preamp outputs (one inverted, one normal), and 4 of my amps are bridged (two pairs). So the way I have things wired, it would be more like 2 "amps" per set of preamp outputs. I'm not sure exactly what effect bridging has on the input impedance of the amps, and I don't really know how having two sets of preamp outputs enters into the equation either. But if 88x is the worst case scenario, and it's highly likely that i'm above that, I'd say that I'm good to go. With 47-ohms output impedance, the Yamaha C-80 could power just about anything.
 
I used a volume control driving a unity gain buffer to make cable capacitance a non-issue. I don't really need to amplify the line level sources at all.
 
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