If after that you still prefer an active preamp, then it's the colouration/distortion of it you like, which is a bandaid fix for something else that's wrong. Its not a bandaid- an active line section can control an interconnect cable and reduce its artifact. A passive cannot. |
This could be caused by a ground loop. A ground loop can exist if your equipment is built without a proper grounding scheme.
If you float the ground pin of the amplifier power cord from the wall (using a hardware store ground cheater) and the buzz is solved then it is the amp. If this works best on the preamp than the preamp could be at fault. In either case it is not recommended to operate the system without the equipment being properly grounded- there is the risk of shock or fire hazard if a component develops a fault.
If you are able to sort out which component is the culprit, you will have to come up with a solution. The best solution is to have a proper grounding scheme installed in the defective equipment. If the manufacturer gives you pushback on this have them give me a call (seriously- setting things up right is not that hard).
Otherwise an isolation transformer for the problematic unit could sort things out. |
Passive volume controls and digital controls offer their own colorations. You are certainly not throwing the money away if the active preamp delivers on its promise. They can be plenty quiet on high efficiency speakers if the system is set up correctly. |
The problem with a passive is that it can act to functionally reduce the value of the coupling cap that might be in the source, such as a DAC. In doing so this is how bass impact can be lost. The other problem is that the system will be a lot more sensitive to cable artifact. This is likely the why of Nelson Pass' comment.
In a high efficiency system, it is more elegant to simply not have the gain. Power amps typically have about 30 db because speakers might only have 87db efficiency. But what if the speaker is a good 15-20db more efficient? Then it makes sense to have less gain in the amp, so the preamp or source can have the volume control in a reasonable (higher) position.
If you think about it, amplifier and preamp manufacturers have a difficult dance; to have enough gain to work with lower efficiency speakers but be quiet enough to work with higher efficiency speakers too.
We solve the problem by offering a jumper plug for our amplifiers that replaces one of the voltage amplifier tubes, thus reducing the gain (and the noise floor) of our amplifier.
With regards to grounding: If your equipment is built correctly there should be no need to resort to exotic grounding solutions like a copper stake in the yard. 'Built properly' means that the chassis and the circuit ground are two different things. This has been challenging for a lot of high end audio designers; but if you are going to meet the directives for the CE mark or similar, this is a problem that will have to be dealt with. |
George, you can't count on a preamp having a 47K input impedance- that is for phono, not a line section, which might often be more like 100k.
Amplifiers frequently have 100K input impedances too. When you run impedances that high and then introduce a high impedance (passive volume control) between the source and the amplifier, the result will be that the system is going to be extremely sensitive to cable colorations. There will also be a loss of bandwidth as capacitance in the cables take their toll. In addition, if there is any input capacitance in the amplifier it will not matter if the source is direct coupled- you will loose bass impact.
There is no 'blasphemy'. As much as I respect him (I think of him as one of the top ten designers worldwide) Neslon Pass is simply wrong about this although I agree that it makes no sense to have a lot of gain and then burn it off. There are more elegant ways to do it than passive controls though.
A simple solution is a buffered volume control. This offers proper volume control performance with it acting as a mild tone control or hindering dynamic impact. |
Yingtonggao, what you report is a buzz. But you did not report hiss, which says to me that the gain is not the culprit. There is some hookup (like a ground loop of a poorly shielded cable) which is allowing the buzz to manifest. |
Yingtonggao, what this suggests to me is what I mentioned in my first post on this thread. It may be that the preamps you have tried so far have troubles with ground loops, but it could also be a problem in the amplifiers. Have you tried any of the suggestions I offered? |
Actually if a ground loop is present it will more likely manifest as a buzz. It is rare to see a ground loop only produce 60Hz! |
Yingtonggao, did you try using a ground cheater on the power cord of the preamp? If it works it is not a solution, but an indicator. |
My comments on voodoo are just that some believe that an active preamp can actually add real musical information that the source isn't providing, this shatters me that some can believe this. You won't get any argument out of me on this! I am of the opinion though that passives *loose* detail, not that actives *add* it... I also agree that if you can get by will less gain, so much the better. So we do offer or preamps with no gain in the line stage, just our direct coupled tube output, which has no gain driven by the volume control. However: We have had pretty good luck with getting low noise without removing the gain stage in the preamp, even on speakers of that efficiency (we have customers using speakers that are 107db), which is why it is obvious that preamp gain is *not* the problem! **If it were, hiss would be the complaint, not buzz!** I feel like I did not put enough emphasis on that last sentence but I don't want to yell :) |
After all it will be the most transparent/dynamic way of being true to the sound of the source there is going direct, as it is also a prefect match as well. This is only true in certain situations can cannot be regarded as universal. In this case we are seeing testimony that the active unit is sounding better than direct. |
Dentdog, do you have hum when nothing is connected to the phono section input? |
George's Lightspeed is IMO one of the best PVCs made, but- If then you don't like this, by all means colour it to your liking with a active preamp of your choice, this is why ALL active preamps sound different as they are not a strait wire with gain, as Nelson Pass alludes to in his statement. And if other can't see this they cannot see the forest through the trees and believe in voodoo. this quote is rendered entirely fictitious by the last sentence. IME PVCs usually have more coloration, not less, than a competent line section (although as I have pointed out in the past it is because the math of the situation goes against you when trying to use an outboard PVC, Nelson Pass or no; I am sure if he ran the math he would come to a similar conclusion). Try running 30 feet of cable between the PVC and the amps and you will see what I mean. I find that the better a line stage is, the more they sound like real music. Now if you really want to make a PVC work, the thing to do is install it in the amplifier so you don't have the math issues associated with the cable. Don_s, you were correct- I meant 'without'. |
