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Monday, February 28, 2011

'Voicing' of an Amplifier


Often people ask me: 'How do you voice your amplifiers?'. The answer might be surprising to most of you, to some even shocking: I don't. At least not in the common sense of amplifier voicing that I exchange components and tubes after it is built until I like the sound. In fact I do very little comparisons of capacitors, resistors etc. And I find tube rolling really boring.

For me the voicing happens in the conceptual stage of the amp. Usually I start a development with some basic requirements: Budget, expected output power, expected gain, etc. Also constraints like size and number of chassis. Based on these I make my choice of circuit topology and components. During this planning stage I already have the sound of the finished amp or preamp in my head. When it is assembled and I like the sound I have no urge to fiddle with it. If I don't like the sound I look for the cause. I rather try new concepts rather than swapping parts in an existing amp.

Don't get me wrong. I do think that components have an impact in sound. I classified component types in sound categories for myself and depending on the project constraints I select from the appropriate category. When I plan a project, I select the components which will deliver the best quality within the given budget constraints. Based on the budget I select the most suitable components. There I rather distinguish between component types, not brands. For example best quality NOS paper in oil caps, thoriated tungsten filament DHTs for the cost no object amps. Current manufacture MP in oil or foil caps and a mix of DHTs and indirectly heated tubes if budget is constrained. Indirectly heated tubes for lower budget designs. I try to avoid electrolytic caps whenever possible.

There is a lot of focus on irrelevant details in many discussions on tube forums IMHO. For example people ask about which hook up wire to use or which capacior, without any reference to the circuit. There are also heated discussions about DCR of chokes and transformers and about the sound of rectifiers going on. But the rectifier topology is hardly being looked at. Going from the commonly used full wave rectifier with center tap secondary to the more elaborate Graetz bridge with 4 diodes brings a magnitude of an order of improvement compared to fiddeling with different rectifiers or chokes, in my experience.

In my opinion and experience components or wire don't make or break the sound of an amp. A good and stable design will sound good with generic parts and wire. A bad concept will sound bad even with the best parts and silver wire.

Yes I do use silver wire (teflon insulated solid core) in my more expensive designs and it does improve the sound of a very good amp by yet another little bit. But the increase in sound quality in a low budget design will not be worth the cost of silver wire. That money would be better spent on moving one level up in circuit topology. For example by going to transformer coupled from a cap coupled design.

In my view everything in an amp should be balanced. It is pointless to spend 90% of the cost and effort on a small detail and ignore the rest.

I don't want to discourage people of tube rolling. By all means if you have fun with it. Do it! Just keep in mind that the difference in sound you hear between different brands of the same tube, might not be related to the tubes, but rather the amp. If there is a big difference in sound between tubes of various brands or age, this might indicate a design weakness. Limited head room for example (see my related post about tis topic). In a well thought through and stable design tube rolling will only show miniscule differences.

Best regards


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