rocker said:
what warhead doesn't say is that the tubes are microphoinic in the a design. <SNIP>
Rocker:
First let me say up front that I am the guy who works directly with Peter at A Designs and I am responsible for the things here in the USA. We do the same for GML, Daking, ATC, Soundelux, Brauner etc.
OK that's said so you know I am.
Here's the straight story on the A Designs. The problem is this:
1) tubes aren't microphonic in just the A Designs, tubes are microphonic in every design! That's what gives you the great guitar amp tone and ring in a guitar amp. Now the A Designs is purposefully a bare bones mechnical design and a high end audio circuit design. Real transformers input and output, real tube circuit (not some partially driven tube sidechain thingy) really nice sound-that costs money to do. Its meant to sound way better than anything else you can buy for the money. But the trade off is that you cannot have ALL the things possible, such as serious mechanical isolation of the audio boards and switches, chassis that null vibration, etc . There is this trade off but we believe it was the right one to make to offer people a choice they didn't have before.
2) Some tubes are more microphonic that others. The EF86 is one of those that is more microphonic. But in this design, its sound awesome. I can install a different tube that has less microphonics, but it sounds worse. What would you do? I say go for the sound.
3) You should not put any tube preamp in vibration prone locations: next to or under speakers or on consoles with speakers on them. Using tube pres in rooms with high SPL require some planning and forethought to decouple the vibration or [sound] pressure from mechanically impacting a tube preamp. Many other audio devices have vibration problems. CD burners are a great example. It comes down to the application: each time we dive in to the 4 or 5 direct complaints we have received, we hear about high SPL at the preamp or the A Designs was on the console bridge directly next to monitor speakers or was sitting directly in front of the speakers or even ON the speakers. In these unusual situations, we would recommend you NOT use any tube pre that is not seriously mechanically isolated from the source of the vibration.
4) We have many very high end users who have used the A Designs successfully, never a single complaint about microphonics. What are they doing different? The units are exactly the same.
5) It is possible to get low cost tube pres without mechanical sensitivity, but they don't sound anywhere near as good as an MP1. It becomes a trade off when the price is lower, to pick what you want: high end circuit design and parts or high end mechanical isolation. When the price is high, you can do it all and cover every possible user application. You can get both top end circuit design and top end mechanical isolation. This is what you get with a Fearn that costs 2.5 to 3 times what the A Designs costs. Doug does a great job with his units, I know many engineers who use them, but most people here would never be able to afford one.
6) We are working on units that have much more isolation, but it will raise the price of them all. Should the problem experienced in a rare situation or in a situation where the unit was never designed to be in the first place raise the price for everyone who has NOT had a problem? Its a problem for us to decide what's the best for all.
Hope the gives you some insight.
Brad