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In the Forum: Melquiades Amplifier
In the Thread: Planning my DSET
Post Subject: Answers....Posted by Romy the Cat on: 5/26/2015

 anthony wrote:
I plan to build a fullrange Melquiades for a friend and then if that works out the DSET 6 or 7 channel version for myself.

That is very good approach in my view. The problem is in this approach that you have to have high sensitively speakers that you would be able to use with that test full-range Milq. The behavior of the Full range Milq win this other speaker might be not the same as it would be with Milq.  So, generally I would suggest to have a Milq (or any other amp the you might like) to drive your particular acoustic system with all passive filtration and spend at least 6 month to feel comfortable in this configuration and to figure out your crossover strategy. (Or to develop new listening objectives and consequential frustrations). Then you can slowly to do DSET and line filtration.
 anthony wrote:
If you are willing I would like to work through this in stages.  This is a project that will evolve with time as I build the speakers and move them into the new room.  Initially there will be 5 Channels:
Raal Lazy Ribbon - Direct Tube Drive 
S2 into 400Hz tractrix
S2 into 250Hz tractrix
Fane 8M into 115Hz tractrix
Scanspeak 25W/8565-00 towers – 8 drivers each

Naturally I “endorse” this configuration and I think it might do very well. My only concern is that I feel that Raal Lazy Ribbon are a bit too wide and too midrangy for use above 12K. The standard Raal Lazy Ribbon drop 10dB at 6K that is not bad but if you made Alex to make the ribbon twice more narrow then it will have steeper drop and you have a bit more “punchier” HF with the lower filter order.  The standard Raal Lazy Ribbon as I understand are meant to be used in two-3 way acoustic system where tweeter is crossed at 2.5-3.5K, so you would need to run 3-rd or 4th order to get the result you want. BTW, I very much might be wrong about it but I do think that the narrower ribbon would be beneficial. Does it worth to pay to Alex extra for a custom job and to be able to get “some” improvement? I do not have the answer to this question.
 anthony wrote:
Bias adjustment in the first stages.  Looking at the final 6 Channel circuit diagram the bias for Channels A, B and C are all fixed and non-adjustable.  How do you manage the varying gain of the 6E5P tubes?

Yeas, there is no bias adjustment in this driver stage nether I see a need to do it. You need to adjust bias if it going away and in some other occasions but in this amp it is not necessary.  The amp is set to get 200V on the driver stage and it would mean approximately 4.3V in grid. Yes, some of the tubes have a few DB leas or more gain but you do not change “gain” by setting bias. If you have on place 190V or 210V it truly goes not make any difference. Keep neat 200V on place and near 15K load and it would be fine. Saying it I would like to note that nothing shall prevent you to add your own bias adjustment if you feel so. Just be informed that any dealing with bias line is supper affective to sound, in fact ever more then dealing with grid in my mind.  You might gain some questionable benefit by having bias fine-dialed but you would need to put a trimmer in the bias line. Well, I find it is to be at least debatable…
 anthony wrote:
Gain structure.  What is the output from your pre-amp?  Mine is 1.5V RMS and 33 Ohm.  I am trying to get an idea about my required size for the 30K input resistor.

My pream has no gain. My frontend have high output and can swing I believe 3.5V. I think Bidat at 0dB digital can push 5V but this would send the Milq grid to plate currents and you do not want to be there with indirect heating. You can calculate the gain of the amp. The driver has average of 33dB, +- a few DB. The output stage has I believe 3-4times. Then you need to subtract whatever you OPT consumes. You will not have a high gain with this amp as it is two stager. If you have a Macondo-like configuration and very large room (let sat over 800-1000 sq foot) and low output frond end and no active preamp then you will feel that you have not enough volume sometime.  The whole beauty of Milg that you have let say 4V in the input and to have the am on A1 you might run a wide range of the frond end, including high output.  The 30K input resistor is kind of less relevant in Milq DSET as the input impedance of other channels will screw all input impedance picture.
 anthony wrote:
ULF through the Scanspeak line array.  My calcs are that at 15W, the SPL at the listening chair would be about 98dB at 20Hz, and much higher at 100Hz.  This is loud enough for sure, but in your experience is the 6C33C/Scanspeak combination good near the amplifiers maximum power?  

You will be able to drive Scanspeak line array from Milq ONLY in case you have VERY small room, you are very lucky (as I was a few years back where the arrays were at active location of the room) and if it were not a full range but 18-22W LF only amp. Otherwise I would go for a different amp. It need o be said that it is very hard to prognosticate anything,

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