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I have a few questions, very very basic in nature:What does a buffer do?Is the tube buffer an additional signal-path component, or is there an equivalent solid-state part that does "buffering" when the tube is bypassed/not installed?Regarding the Sonicap bypass upgrade for the M901, what are the Sonicaps replacing and/or bypassing?
By adding the "bypass" cap (over both other caps), you're changing the sonics of the caps. That's as much as I know. It's a cap in parallel with the others. This is covered well in the GR Research forum apparently.
Why use a 'by-pass cap'?Think of a capacitor as an energy storage device. Capacitors will store and release energy and are often used for that very reason. In the loudspeaker application though we are wanting to use them for the capacitive effects and not their energy storage capabilities.The larger the cap the more energy it can store. Also larger caps take longer to charge and to discharge this stored energy. Different types of caps store and release energy at different rates too. For instance electrolytic caps are more known as being fairly slow to charge and discharge compared to other types of caps. However they are much less expensive and are often used in loudspeakers especially if large values are needed. Polypropylene caps like those used in many speakers are a faster cap. Not all poly caps are the same though. The really good ones are considerably more expensive than the more commonly used types.When an audio signal is sent through a cap there is a small amount of lag time from charge to discharge. Often with larger caps, even after they are discharged there is still a small charge that is left as it did not completely discharge. The smaller values typically used in speakers like AV123's x-ls are not too bad. But there is still always some signature to the caps in the signal path. The audible effect is a smearing of the music. Notes will have a little trailing edge to them that blend into the next note. Again the larger the cap value the greater this effect.By-passing the caps on the board with a fast discharging cap like 0.1uF (really small value) Sonicap Gen II will effectively short the larger cap out. The capacitance is hardly changed but shorting the larger cap with the small one will discharge it very quickly.What it does to the sound is reduce smearing. Music is cleaner with more dead space between notes. Many audiophiles refer to this as Blacker Blacks. Upper level detail and resolution is notably better as well.
Sorry I can't be more helpful.
Any difference in the 12ax7 and the 5814?
Hi - I'm not sure what the question is asking exactly but these are very different tube types... What is the type of tube recommended by Gary? (I thought the Dodd buffer used the 6DJ8 type.)
You're too humble Seth; you definitely answered my questions!And Don, thanks for pasting that info on bypass caps. It's been very helpful for me in understanding this mod. Now I want it!
What does a buffer do?
Let me start by saying that I am not an electronics engineer, but I have been into DIY hi-fi for many years, and have been lucky enough to have been reviewing hi-fi for over five years. So I'll have a go at answering the question.What is a buffer and what is its role in a hi-fi system? It is (usually) an active circuit that isolates one part of your hi-fi circuit (that's every thing in your hi-fi system) from another part. By isolating, I don't mean cutting them off from one another, we could do that more easily (and cheaply) by cutting the wires that join them together, but then we wouldn't have any sound! What the buffer does is stop one part of the circuit having a detrimental effect on another.The main job that a hi-fi buffer does is 'sorting out' impedance mis-matches. Various parts of the hi-fi system have input and output impedances. Impedance is a bit like resistance but for AC signals (instead of DC). As a rule of thumb, the output impedance of a circuit should be about ten times lower than the input impedance of the circuit that comes after it. Something as simple as a pot has an input and output impedance but they are usually the same. So if we take the Sensation amplifier for example, if its input impedance is 100K (I don't know what it actually is) then the ideal impedance of the pot would be 10K. And if a DAC comes immediately before the pot, then the output impedance should be no higher than 1K (in theory). If the impedance matching is not optimal, the ability of the whole system to transfer power efficiently from the source to the speakers, will be compromised, and the sound quality will suffer.Improving impedance matching using a buffer will produce large benefits, and in my experience the improvements always outweigh any loss of transparency caused by adding extra circuitry to the system. The improvements that you will hear are down to the buffer improving the impedance matching more than the added circuit having any other effect on the sound. However, the components used in the buffer may also change the sound of the whole system. Valves, transistors, Jfets, and opamps can all be used for buffering, and which will sound best, will depend on personal tastes, and the rest of the equipment in the hi-fi system. I guess what I am saying is that there is no magic in using valves, it's the impedance matching buffer that gives the most improvement although the valves may give something that is beneficial too.I've tried both valve buffers and solid state buffers with the Sensation. They sound slightly different but I can't honestly say one is better than the other. What I do know is that in my system, the sound is significantly better with the buffer in place than without it.
The addition of a good buffer stage typically improves image fullness and the density of images (less "thin" or fragile sounding), larger soundstage size, increased slam and macro-dynamics (the loud part of the dynamic range).
Yep, that's what it does.
