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In the Forum: Melquiades Amplifier
In the Thread: Valve Preamplifier for Macondo/DSET
Post Subject: Still only a thought bubblePosted by anthony on: 4/27/2019
 Romy the Cat wrote:
Still, I feel that methodologically it is not right way to build a playback.   

No disagreement from me on this point.  This is all just a thought bubble for now.  Even if I wanted to press go on this project based on past experience it would be about a year before the parts were wound and least a year.  There are DSET's and horns to finish, a room to treat, other fish to fry.  

I like to try and think several steps ahead and incorporate those ideas into current actions.  Instead of getting Macondo tuned and then going "time to build a valve preamp to improve xxx or yyy", I will have researched the subject and will be able to say time to build a 10Y or 2P29L preamp starting with this particular circuit that I like.  And because this is potentially on the horizon I will leave enough room on the equipment rack to fit the boxes.  Anyhow, I should make it clear that a valve pre is not an imminent project until I start to build my LCR phonostage, which is not going to happen until I get Macondo up and running in full. 

So please think of this thread as trying to investigate which direction I could go regarding valve preamplification.  To date I have identified 6x gain, low output impedance, broad bandwidth, some current capability, manageable microphonics.  Let's see what can be found. 

 Romy the Cat wrote:

Again, I do not know what frond end you use.

My preferred source is a Phasure NOS1a G3 dac.  The thing has no discernible sound of it's own.  It outputs 1.25VRMS SE and I run it at -6dB because it needs a little attenuation to sound its best which means 0.625VRMS.  I don't know if it is the IV stage of the dac or if it is the software that affects SQ...I suspect the software.  It can push a lot of current.  The Placette dims the NOS1a a bit....whitens some of its colours...cramps a little dynamics.  I can live with this because the Placette also brings remote source switching and volume control.  

 Romy the Cat wrote:
 Some of the frond-ends have output stages that might be easily tweaked to get extra dozen dBs. I you do insist to have a separate gain stage then you need to decide if you will be driving it into Placette or you will substitute the Placette. If you will be driving the gain stage into Placette then you do not have any concern with output impedance and the array of the available topologies is wide open, this is the direction that I would go. If you are willing to make a preamp that will replace Placette then I feel it will be VERY hard to.

I was thinking about replacing the Placette, but to be honest had not considered a separate gain stage just for the dac...perhaps that is doable.  

 Romy the Cat wrote:
 I love the 10Y but I have no idea how it doe as preamp and with the transformer that you will be using (wish in my view will be the definitive element of you preamp).

Ale Bartolas Hybrid Mu Follower eliminates the output transformer.  The output impedances I quoted earlier in this thread were using that topology, so a 10Y without output transformer has 8x gain and circa 30R output impedance. 

The first SS pre with 3x or 4x gain (that I started two or three years ago for another project) will be in operation soon.  I will play with tweaking it a bit and compare it to the Placette to see what I have got.  It should be enough gain for all of my sources apart from my dac.  Yes I am loyal to that dac.  I did the hard yards comparing it to several other contenders and it came up trumps so I would need convincing to seriously consider moving it along.

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