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In Reply to: RE: Direct Coupled 2A3 Alternatives: Morrison SRPP or Micro posted by David Lawrence on June 15, 2015 at 19:17:52
The micro was my first experience with SE and is a fine sounding easy to build little amp. I say go for it.
dave
Follow Ups:
I built one and used it as my main amp for quite a while. Great litle amp, and as Dave said pretty easy to build.
.
Hi Dave,
Thanks a lot for the advice. I've heard other good things about the Micro. This is the one I'll try. I see there is some past discussion about risks of fast B+ in this design. Did you do anything to slow that down or add a switch on the secondary for the B+ on the power transformer?
Cheers,
David
David,The Morrison Micro WILL pass a signal, input to output, but other than that, it needs to be a far more sophisticated approach to become anyone's "keeper" amp.
There are several problems with the design, no one has mentioned, I will name two :
( 1 ) You can NEVER ever parallel two high mu 6SL7 triodes, and get the ultimate in clarity and diction on words. The two triode sections are different, and it produces SKEWS into the grid of the Finals tube. Audible. NG.
( 2 ) The need to optimally bypass the Rks is NOT addressed at all by J.C., and this is critical to the overall sound of the music from such a circuit. So, the Morrison Micro is a "no - go", sophomoric, incomplete. A waste of time and money as a build in my opinion.
A FAR better circuit, and a better thought-out approach, is to copy the 1994 Sound Practices article, by Ciro Marzio and Cristiano Jelasi, using 1/2 of a 12AX7 as the driver triode. They more thoroughly address Rk bypassing in a manner that is imperative to include in your build, and they do not parallel driver tube sections.
But, Marzio and Jelasi make other errors, and if you wanna discuss corrections with me, feel free to do so.
A turn-on delay ( manual ), taken from the Marzio-Jelasi article, is enclosed for you - and all others to see. I use it now in my Type 45 DC amp.
Jeff Medwin
Edits: 06/20/15 06/20/15 06/20/15
Here we are !!
Jeff Medwin
I set the timer to 90 sec, and the voltage ramp up nice and easy, barely overshoot over the preset b+.
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