I used to think passive preamps were superior to active preamps given right the setup, but
my recent evaluation of a modded old SS preamp has me a little befuddled. I've evaluated $10K+ active preamps in the past and was never impressed especially given their cost. In general, I've found passives to do better job. I know there's ongoing debate on this. But here's a very illuminating video on the subject by Bascom King, one of the legends of high end audio.
Interesting that
Bascom King
points out a couple times that 'intellectually' wise he really wants to like the sound of passives better, and direct to amp better. It must be difficult from an engineering mindset to let oneself relax and actually listen to music without trying to analyze components. Many engineers cannot grasp a lot of the concepts that audiophiles enjoy, as they cannot make intellectual sense to them.
As for myself, I tried 3 passive preamps about 15-20 years ago, and realized early on that a passive could not compete with a good active tube preamp to my ears. Looking back, I did not perform these trials with tube sources and tube amps, so that could have some affect on my results.
Curious that Bascom didn't mention another engineering fact of passives, that of their output impedance. The output impedance of passives varies with the setting of the volume control, often to a figure too high for the input impedance of some power amps. Also, interconnects must be kept short between passive pre and power, so mono amps behind the speakers are out. And if you want to bi-amp your speakers, that is not possible with many passives.
Sounds cynical I know, but he is selling his latest BHK Preamplifier design through P.S. Audio. Why wouldn't he say this now, and not back then when he probably heard much better as well. This clip doesn't convince me one iota.
For the ultimate transparency and source signal transfer to the amp: Direct (source to amp) is best, if you don't "bit strip" with the digital domain VC, if it does, then 10kohm passive comes in a close second, so long as the impedance are matched, which 90% of system are matched.
But if your system is not quite right and needs to be coloured in some way, then a preamp with the "right" colouration can be fix for that, but good luck finding the "right" one. As none I know of, sound like a "straight wire with gain", they all sound different to each other.
bdp24 Most of what you say is not true of transformer based passives. I had a great Sonic Euphoria passive that used autotransformers and it was great However my Shindo preamp is better Alan
Georgelofi, I agree Bascom's comments have to be taken with a grain of salt given he is on PS Audio promoting his design. However, the same argument can be applied to you since you are a manufacture of LDR passive preamps. I myself own potentiometer, stepped attenuator, LDR, and autoformer based passives believing passives are better than active preamps under the right circumstances (eg, low output impedance source, high input impedance amp, and short IC length). But my recent experience with a modest active preamp supports much of his claims. Time to reevaluate my prejudices against active preamps.
Is BK dismissing passives to promote his new active preamplifier? Or did he design his new preamplifier to be active due to his previous experiences with active/passives?
I do believe BK struggled with the passive vs active over the years and came to accept what his ears were telling him rather than what he was taught in engineering class. I don’t think this is the first time he’s telling this story just to sell a product. Seems like a honest man, despite the setting of this interview.
tbg, you're not getting an argument from me, and I've been using passive pre for years. I guess I just didn't meet the right active pre to make me change my mind.
You’ve got all the voltage gain and current you need in the sources today, as they all have the ability to overdrive all amps, any more and your just turning it down with the VC. Look at the input sensitivity of amps then look at the output of sources there is way more than you need. Cheers George
A Quote from the master Nelson Pass
Nelson Pass,
We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.
I had also tried passive preamps, but found actives to have better bass weight and punch. That is until I tried the Tortuga preamp. I was surprised that the bass equaled or bettered the active preamp I owned (an ARC-REF3) with better, tighter bass, wider and deeper soundstage (with much better channel separation), and more extended & cleaner highs. I ended up selling my REF3.
I also had a chance to compare it to another highly regarded $10k active preamp. The Tortuga's adjustable input impedance feature (2k to 200k on the balanced one) really showed how important it is to optimize the load seen by the source.
By the way, I'm using my current Tortuga LDR1B-V2 (1 balanced input, 2 balanced outputs) to drive a biamped system with a pair of Spectron monoblocks on the bass (25 kohm) and a pair of Double Kronzilla's (with a high speed differentially balanced FET input with 100 kohm impedance). The Tortuga is driving these just fine, still with bass power and punch and pristine mids and highs. The balanced ICs from the Tortuga to the amps are one set of 2 meters and one set of 2.6 meters.
I'm getting a customized LDR3B-V2 with the capability to switch absolute phase on the inputs. All this without a switch or pot in the signal path. I'll be using my current LDR1B-V2 to attenuate the volume of the Spectrons to match the Krons. The Spectrons need to be attenuated by around 4 to 6 dB.
Georgelofi, I know the arguments for using passive preamps (including Nelson’s), as I am a big supporter of the passive route. Having used passives of all types for the past 9 years, I know the benefits. It’s just that this little modded active preamp has turned my views upside down. The only thing I don’t like about this active preamp is the over damped bass which doesn’t sound quite natural. Everything else is as good or better than my LDR preamp and other passives in my arsenal.
Kernelbob, I too have the Tortuga Audio preamp with variable impedance. It is the best passive I have ever tried. However, my modded active preamp, which I bought used (no longer in production) and had it modded (under $500 total for preamp and mod), is better or just as good in almost every category, except for the bass which I have indicate earlier is too damped. The Tortuga has the best bass of any other passives I’ve tried. Its bass is like that of a very good active preamp, extended and dynamic with just the right amount of natural bloom.
The first thing I would say, is how different Passive's can sound from each other. I had a chance to compare 4 Passive Pre's over a weekend, which might not have been long enough, but two were frankly poor, muddy, lacking detail, dynamics and base. I had a DIY built clone of the Music First Audio Baby reference and an actual Baby reference. Both were excellent in comparison. In fact, what one is led to expect from a Passive, quite neutral, transparent, with no hint of colouration to my ears. The actual baby reference was a little better.
On the basis of this test, I believe the MFA Baby reference is hard to beat compared with many active Pre's. Like Kernelbob, I think it clearly bettered the ARC Ref 3.
What am I using now, the Modwright 36.5? I just prefer it to a Passive, greater dynamics and a more engaging, enjoyable, musical, for want of a better word, sound. Still if you get a chance of auditioning an MFA Baby Reference in your system, give it a try. Before anyone else says it, I agree, it is quite expensive, so try and find a second hand one.
I am saying this specifically for TVC. I have said this many times and will repeat again. You need to make sure that a TVC should have a MATCHING system. You really need to look into the source voltage, amplifier sensitivity, loudspeaker sensitivity, cables, etc for your system to "come alive" with the TVC. If you have taken good care, then it is really difficult to beat a well made TVC. Years back I heard that the "core" of the TVC also made a difference. From my personal experience I have compared my $1.6K TVC to a $4K active preamp and the preamp went back to the dealer. I have plenty gain in my system and absolutely have no issues with bass or treble. At this point, my speakers go down to only 40Hz. I am looking forward to upgrade to a loudspeaker that goes down to at least 30Hz. I am sure that my TVC can easily handle that.
System matching with passive pre is critical indeed. It can make or break the sound. You really don't have to worry about that with an active pre, which I find so convenient and much less of a headache.
dracule1 System matching with passive pre is critical indeed. It can make or break the sound
You are right dracule, but lets get the "critical matching" in perspective
We (most of passive users) are after nirvana, that’s why we persist with passives and get the impedance matching right "makes the sound". Which by the way in 99% of systems is a great impedance match.
Except for some tube output sources which have ridiculous high output impedance (more than >1kohm). Or some ClassD amp that are very low input impedance (less than <10kohms). These users usually find something wrong with the sound of passives, and say active preamps are better, oblivious to the fact that they had an impedance mismatch with the passive they used.
I replaced an ARC Ref 5SE with fully balanced copper slagleformers, then eventually upgraded to fully balanced silver slagleformers. I have tube sources (Ref 2SE phono and Ayon CD-07 player) plus OPPO 95. Gain is never a problem. For HT, I use additional 3 copper slagleformers (single-ended center and rear channels from OPPO 95) in slave mode in another box, hence no need for HT processor and HT bypass. For HT L+R main channels, OPPO XLR outs are used.
With autoformer passive, no background noise, high resolution, and controlled bass. And in multi-channel HT, I am getting high fidelity sound. I may consider going active but will still use autoformers as volume control.
Paul79, I really didn’t think anyone would be interested because it’s no longer made and is considered mid fi to most. It’s the Acurus RL11 that was modified. Acurus was considered the little cousin to Aragon. The stock preamp is nothing to write home about, but once it’s modified to be direct coupled and run in Class A with better output mosFETs and power supply upgrade, etc, it beat every passive I have in almost all categories of music reproduction important to me.
"Except for some tube output sources which have ridiculous high output impedance (more than >1kohm). Or some ClassD amp that are very low input impedance (less than <10kohms). These users usually find something wrong with the sound of passives, and say active preamps are better, oblivious to the fact that they had an impedance mismatch with the passive they used."
Yes, I completely agree. Most of my sources have output impedance less than 100 ohm and my amps have input impedances 50k to 100kohm. Although my tube DAC has output impedance ~1.6kohm, it still sounds great in my setup using passive pre.
1.6Kohm could also sound fine so long as the amp is still over 33kohm, because the 1.6kohm has to drive the combined load of passive + the amp.
If you have say 33kohm amp and 10kohm passive that's a combined impedance the source sees of just under 8kohm, a 1.6Kohm source will drive this no problem as the ratio is still 1:5, but a ratio of 1:10 is the really the minimmum one should aim for, and then it could sound even better instead of fine.
George, sometimes it's just too much of a hassle to match your system to a passive preamp, although you can get some great results when all the stars align. Sometimes an active can be as or more rewarding without the hassle. As it stands now, I like both in my system, but the active pre just does more for me overall.
Not really, like I said over 90% of systems are a perfect match for a 10kohm passive, it's the few oddball high impedance tube output sources that are the trouble.
eg: like the well know "cottage industry" dac with a 12AX7 output tubes at 3kohms!!!, the 12AX7 was never meant to be an output tube buffer. High gain input tube for phono/preamp/poweramp stages yes but an output tube?? Really??
It is not just about gain but I believe also about control of the interconnects, impedance matching and frequency variations with impedance. The passives I have used include several resistor types (including Endler direct to amp - i.e., no interconnect) and Bent-type TVC, but not LDR. All had excellent clarity but all missed out in the areas of bass drive and tonal depth compared to my reference, which is a no-gain, buffered preamp with a Shallco attenuator using great-sounding AN tantalum resistors, Lundhal coupling transformers and an outboard choke-filtered power supply. My conclusion was that even with a 4V source, amps with 100K ohm input impedance, and short, balanced interconnects, the passives were not able to match the tonal saturation of the buffered preamp.
We'll soon have an optional solid state buffer output stage for our Tortuga preamps. We've been trying various designs for quite a while now and have settled on a JFET output stage with a servo DC offset correction and direct DC input (no coupling cap). I've been listening with and without a buffer for a while now and am challenged to discern whether having the buffer improves dynamics, bass or just gives it more "authority". Above all trying to do no harm. It may well depend on the combination of other gear - sources/amps - that you have. Still, for those who simply will not consider a passive preamp under any circumstances, offering a buffered LDR preamp (i.e. an active version) seems to make sense.
There are two parameters interconnects have that could influence the sound with a passive, resistance and capacitance. And they would have to be very high to have any effect.
Resistance is nothing to worry about as it would be so low it’s not even worth considering,, even in 5mts of interconnect.
Capacitance: A 10kohm passive has at worst output impedance of 2.7kohm, with a bad case cheap interconnect of 100pf per ft, if you had 2mts that equates to 600pf cable capacitance. This would have a HF roll of effectively at -3db at 98khz!!!
There is no having to controll the interconnects full stop with a 10kohm passive!!
That’s why you should always use a 10kohm passive, as a 20kohm passive with the above interconnects would be -3db at 49khz. A 50kohm passive would be -3db at 20khz as you can see that does cause a HF cut in the audio band.
Let me remind you what Nelson Pass said.
Nelson Pass,
We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.
In my last all SS system I ran a heavily modded passive McCormack TLC-1 preamp (always on Agon for a grand or less) along with a stock McCormack DNA-500 and it was dead quiet, incredible sound. I like my tubes but that McCormack SS setup sounded damn good.
On the argument that passive is better/worse than an active preamp, just keep in mind that the preamp is just another piece in the audio signal line that his helping shape the sound. Even a DC blocking signal capacitor in a passive preamp can shape the sound somewhat when the capacitor charges/discharges the audio waveform as it passes through.
As far people who like their passive preamps, it really depends on the sonics coming from your source. So many DACS/sources can still have that digital type square waveform sound that lacks bass and can be thin. In this case, a great tube or Class A preamp can really help things. If the source is tube based or has multiple Class A circuits that are filtering/shaping the sound from the DAC chip, a passive preamp may sound better than an active (depending on equipment choice / synergy). I describe some of this effect in this post here:
A tube or Class A preamp can help further shape this waveform. It can actually translate more bass from the original DAC waveform and may even give you more midrange body and overall better volume. Things may sound louder. On the other hand, a very "solid-state" non Class A preamp may just attempt to reproduce the sound waveforms exactly as they entered the preamp with little or no shaping.
I do not normally get in on these type of conversations but the facts are everyone is correct. Passive is the best interface sonically, least parts to hurt the sound. BUT If the device cannot drive the load (input impedance) of the next device (usually amplifier) properly then a preamp or a product with current gain is necessary to drive the input load and get the best sound (performance) of the device being driven. To overly simplify one product drives the next if you do not have enough voltage or current than passive will not sound as good.
I have a 1996 version of his Pass Labs Aleph P preamp that has separate controls for gain and volume. His advice was to set the gain as low as you can and the volume as high as you can for your basic listening and use the remote to adjust the volume.
I've gotten the up-grade itch several times, but have yet to find anything I like better. Amps and speakers have changed but the Alpeph P has been a constant.
To be totally successful in using a passive-pre the rest of the system must be built/chosen with the accomodation in mind. This doesn't really require compromises IMO since the things that work best also make for a better system. In such a case gain can only be detrimental to the sound since any active device with gain will also surely add colorations to the sound. I've been using the passive approach most of the last 30 years. For the last 15 it's been TVC/AVC based devices. I've occasionally tried promising low gain active designs up to $5K but have always come back to the TVC's purity and quietness.
All the above 5 post have valid statements, the best preamp is no preamp, this is closest to a straight piece of wire sound.
Source direct or through a simple direct coupled passive is the most transparent/dynamic way of hearing the source.
You may not like the sound this way because your hearing the source for what it is, does this mean you add an active preamp to colour that sound hopefully in the right areas or get a source that doesn't need to be coloured?
The best preamp is no preamp?... Possibly... but only if the recording was perfect and recorded in an ideal space with phenomenal room acoustics. Otherwise? I still prefer Technicolor movies over the plain variety. I know.. Not real... But, so much more pleasing and stimulating to your soul. After all, that is why we seek to listen to music! Recording engineers know this. That is why they will often times add effects and enhancements to what was recorded.
I learned my big lesson when I began op-amp swapping with my high quality pre-amp/phone amp. No piece of equipment is neutral. Even the passive ones. For there are various kinds of passive preamps that produce different sound! So? Create your own "neutrality" of sound. One that produces a believable sound that YOU THOROUGHLY ENJOY. Not one we are to be told is enjoyable but does not quite move you. It always has to be quality - low noise - design. That never varies. C'est la vie.
"Create your own "neutrality" of sound. One that produces a believable sound that YOU THOROUGHLY ENJOY. Not one we are to be told is enjoyable but does not quite move you. It always has to be quality - low noise - design. That never varies. C'est la vie."
Sage advice. You're a true philosopher. But there are many in high end who will try to convince you what the "truth" should be and what should be "enjoyable". And they will charge an arm and a leg for it.
"The best preamp is no preamp?... Possibly... but only if the recording was perfect and recorded in an ideal space with phenomenal room acoustics. Otherwise? I still prefer Technicolor movies over the plain variety. I know.. Not real... But, so much more pleasing and stimulating to your soul. After all, that is why we seek to listen to music! Recording engineers know this. That is why they will often times add effects and enhancements to what was recorded.
I learned my big lesson when I began op-amp swapping with my high quality pre-amp/phone amp. No piece of equipment is neutral. Even the passive ones. For there are various kinds of passive preamps that produce different sound! So? Create your own "neutrality" of sound. One that produces a believable sound that YOU THOROUGHLY ENJOY. Not one we are to be told is enjoyable but does not quite move you. It always has to be quality - low noise - design. That never varies. C'est la vie."
A typical explanation for why passives sometimes don’t perform as well as actives is that the source doesn’t have enough voltage/current to push the signal through a passive to the amp. I think this was even mentioned by someone in this thread. While that can be true, I submit that this is all too often misunderstood and not the limiting issue.
Regardless of the line source type (CD, DAC, phono stage etc.), that source doesn’t know whether it’s connected to a passive or active preamp. All it "sees" is the impedance it’s driving into. If that impedance gets too low the source’s output stage won’t be strong enough (current capacity) to deliver the voltage signal properly because the current demand is too high (resulting in poor dynamics, flabby bass etc. ).
With active preamps, the source sees only the input impedance of the active preamp - typically 10k or higher. With passive preamps (resistive types like pots, stepped attenuators and LDRs), the source sees the combined impedance of the passive preamp in parallel with the amp.
If the passive has a stand alone input impedance of say 20k and is connected to an amp that also has a 20k input impedance, the combined effective impedance seen by the connected source is 10k. No different that the active in the above example.
If a given passive with a decent inherent input impedance disappoints relative to an active alternative, I would submit it’s not simply because the source can’t deliver the goods.
The related question of impedance matching (sufficient impedance bridging) is the number one topic with passive preamps. What we’ve found in actual practice with our LDR preamps in combination with countless different customer sources and amps is that impedance matching is rarely a limiting factor.
For what it's worth, Emmanual Go, producer of the superb lineup of First Sound tube preamps initially marketed a passive preamp. Eventually he began to engineer, manufacture, and sell dual mono actives with separate power supplies. I recently paid Mr. Go to install the two "S" upgrades in my FSPD III and an incredibly quiet, dynamic, and musical preamp jumped yet another notch in performance. It is the only component I've owned during 45 engaged in this hobby that I've never considered selling.
Mitch2 6-17-2016 4:59 am EDT It is not just about gain but I believe also about ... frequency variations with impedance.
This is a good point that warrants additional emphasis, IMO. If the component that is driving a resistive-based passive preamp has an output impedance that is essentially constant over the frequency range, and if the component that is being driven by the passive preamp has an input impedance that is also essentially constant over the frequency range, then what might otherwise be an impedance incompatibility will simply result in a slight reduction in gain (putting cable effects aside, which are a separate issue, and assuming that the mismatch is not so extreme that the source cannot comfortably supply the necessary current).
But if for example the source component has a coupling capacitor at its output, resulting in a substantial rise in output impedance at deep bass frequencies, or if the output impedance varies significantly in other parts of the spectrum for whatever reason, using that same passive preamp may result (depending on the specific numbers that are involved) in objectionable irregularities in frequency response and/or phase response.
Perhaps that factor, differences in how source component output impedances vary as a function of frequency, is one contributor to the divergence of opinion about passives.
What we’ve found in actual practice with our LDR preamps in combination with countless different customer sources and amps is that impedance matching is rarely a limiting factor.
And yet, you are planning on introducing a buffered version of your preamp. I am sure your LDR attenuator preamps sound very clear and natural, and I know how attractive that can be from the Goldpoint/Endler/JaySho (i.e., Bent) preamps I have had here, but I will not be the least bit surprised if you find that your LDR attenuator with a good buffer stage sounds even better. At a minimum, it should broaden the range of components that mate well with your preamps.
Myself being in audio gof over 40 years now have bought from the A groups In recommended componends and have had some great equipment I have found having an active Linestage preamplifier dynamics and imaging Especially complex orchestra dound more real especially Vacuum tube. Recently I did something totally different .since I have owned single ended amplifiers and wanted to see what was all the fuss .I can say by keeping things Very simple in one gain stage the sonic purity is second to none.after yhst experience I had a very gifted Electronics designer build me a DHT preamplifier Single ended -Direct Heated Triode Preamplifier completely transformer based Including the Audio output section.the only capacitors are 2 Big poly oil caps and Copper bypass caps . Using 6 Lundahl transformers and chokes. Using the WE 274 rectifier tube, WE 101D aufio tube ,as well as a choice to use the 26 tube.these are far more linear then a 12ax7,or 6sn7 indirect heated tube. These tubes run very cool and the magic is incredible . The transformers Make a huge step up in sonics accuracy and dynamics and Bass using a 300b Or 2-3 does also work but it is a power tube first and a waste of heat to achieve the same goal. If this were commercials sold it would be at least $1 3k I have yet to find a another passive or active preamp that is built this well with all premium parts including all Neotech Single Crystal wire used throughout Including their best Silver Gold Alloy signal wire. The famous Coincidence DHT 101D preamplifier uses solid state rectification and capacitor coupled. Which is very good but a solid step below rectifier, Transformer coupled unit. Once you experience a top DHT model done correctly ,9 out of 10 would want one if they can justify the price.
But if for example the source component has a coupling capacitor at its
output, resulting in a substantial rise in output impedance at deep bass
frequencies, or if the output impedance varies significantly in other
parts of the spectrum for whatever reason, using that same passive
preamp may result (depending on the specific numbers that are involved)
in objectionable irregularities in frequency response and/or phase
response.
This comment by Al gets to the issue that I often hear about- when a passive is used, bass impact suffers (I hear about this far more often than a high frequency rolloff, for which George supplied pretty good numbers earlier in this thread).
This is because many sources, analog and digital, use an output coupling capacitor. The series resistance added when a passive is inserted into the signal chain can exacerbate the increased output impedance at low frequencies caused by the coupling capacitor. This explains why the bass often has less impact at any setting below full volume.
This is not to say that this happens in all cases! But it happens often enough that the passive/active 'conversation' is not likely to go away anytime soon.
The bass problems cited don’t just exist with passive preamps.
Yes there are some sources that have output coupling caps, and if they lose bass into a 10kohm passive, they will also lose the same bass into many class D amps some linear amps some of Pass Labs Amps and also may active speakers, as these are also 10kohm input impedance.
Ralph is right about this, but the problem is the output coupling cap of the source is too small.
EG: with a source output coupling cap of 2uf into any of the 10kohm loads above, you will have a -3db at 7hz point. If it were 1uf it would be -3db at 15hz. If .5uf -3db at 30hz.
As you can see a sources output coupling cap of at least 1uf or bigger is needed not to hear any bass roll off with any of the above 10kohm loads.
Saying that I hate caps in the signal path, give me direct coupling any day over it, as all caps have their own sound as well.
Hi Audioman58, The Coincident Statement Line Stage is as you note utilizes SS rectification. To the best of my knowledge there are no capacitors in the signal pathway, it uses instead an interstage transformer. The Line Stage you're describing sounds like it's a very special product, Congratulations on your ownership and may it provide you many years of happy listening. Charles,
Now think about adding a variable resistance out the output of a capacitor (which already has reactance). The resistance of the divider network that comprises the passive volume control is in two parts- the part in series with the capacitor and the part that goes to ground. You can see that the series portion is being added to whatever reactance the capacitor already has. As you can see from the tutorial, reactance values are higher at lower frequencies (several examples are provided). What this means is that the capacitor has to be a **lot** larger in order to not experience a significant increase in effective output impedance if a passive control is used!
The tutorial does describe the effect of an added resistance- immediately it begins to talk about filters, which is what this thread is about as well.
Designers of audio electronics like to keep the coupling caps used to values that are as small as possible for several reasons. One reason is that the cap will introduce more coloration if it is made larger. Another reason is that the coupling cap should not express a timing constant that is lower than that of the power supply that is running the circuit. If this rule is broken, the circuit can exhibit low frequency instability, which can result in increased IM distortion and in severe cases, 'pumping' and 'motorboating' effects. So it is important to avoid arbitrarily larger coupling cap values- they **have** to adhere to proper design rules.
As a result, I think it incorrect to characterize a source as having an insufficient coupling cap value when what we are really talking about here is standard accepted engineering principle. This is why even a solid state source (like our Oppo CD player in our shop) can have an audible loss of bass impact when a passive volume control is used at anything other than full volume.
I regard this as a coloration effect- and is why I prefer a **properly designed** line section, as it can avoid this problem without adding coloration of its own. I do stress emphasis however on the **properly designed** caveat.
You must have a verified phone number and physical address in order to post in the Audiogon Forums. Please return to Audiogon.com and complete this step. If you have any questions please contact Support.
