1. No ad-hominem
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Once i get the bit in my teeth things can move quickly with these projects. Not always good to go too quickly and do too many changes / modifications as you can't work out what did what in isolation and then it is harder to back track if need be. When working on prototypes it is quicker as there is not so much focus on appearance.
The isobaric semi omni's really are breathtaking, i dont know how else to describe it. The amount of times my hair has stood up on the back of my neck, hell, i was nearly moved to tears the other day when i installed aTIS between cdp and preamp. That is what it is all about - emotion and the way the music moves you. The more nva stuff i get (and the more nva design principles i have incorporated into my speakers) the more i realise this. Feck the naim pace rythm and timing this is the real deal. They are all prat's to go along with it.
All from bits I have in stock. Avondale power amp boards the same as my other four monoblocs with MBR2000CT schottky rectifier diodes and a cap bank of six times 6,800uf with very low value inductors in series between the caps. Transformers will be a bit of a compromise with what I have available. Either some 100VA EI transformers or a couple of old Naim NAP140 transformers which say 200VA on them but by the size of them I think that must be bending the truth a little
This experiment involves having to add two more sockets to my preamp so may take a while. Two more interconnects and speaker wires also needed from what I have available here. Then I can play with having the tweeters cap and resistor at the speaker end or right on the output of the amp boards.
Watch this space.............
They are a bit Heath Robinson at the moment - much like the rest of my system Using just the inner sleds of some old Naim power amps for heat sinking, the rest of the amps are cobbled together in a rather untidy fashion but with AC parts kept away from DC, amplifier boards and any signal wiring.
Had a bit of an incident yesterday when I hooked up one of the amp boards incorrectly and did not notice before switch on Basically I wired up the negative volts from the cap bank to the zero volts connection on the amp board and the zero volt connection from the cap bank to the negative volts input on the amp board. I could not work out why I had just over a volt DC offset at the output and the bias could not be adjusted from zero. Thought I had blown feedback cap or bias cap or long tailed pair or all three.
Turns out that when I had spotted and corrected my wiring mistake the dc offset and bias went back to normal. Phew. Hooked them up to a stunt speaker and they work fine. Don't know how I got away with that one ???????????
Currently playing Weather Report Domino Theory and all sounds well. I will give my verdict about triamping later when I have done some more listening. Shame I have had to put the naca 5 back in and the transformers and interconnects are different to the other four monoblocs. I thought putting the smaller transformers on the tweeters would be the best bet as they are less demanding on the power supply,
Thread sub title - The Never Ending Bodge. Could be the title for a book
Yes, each driver in my speakers has it's own independent amplifier board, power supply, transformer, speaker cables, interconnect back to the preamp. Hang on, that is not strictly true as the two 12" bass drivers in isobaric configuration in each speaker share an amplifier. Hope I have made myself clear. Right speaker bass drivers (2 of) = one monobloc, right mid driver = one monobloc, right tweeter = one monobloc, left speaker bass drivers(2 of) = one monobloc, left mid driver = one monobloc, left tweeter = one monobloc. Six in total.
Some might say that it is overkill and I am not sure what I think of it yet. As I had the parts in stock (as it were) it was easy to try.
With my old transmission line 2 way speakers I moved the crossover to directly behind the power amps instead of having them in the speaker. I could not believe the increase in clarity. Still not sure why it happened. I am going to try doing the same with the tweeter's high pass filter (3.3uf cap) and padding resistor and see what happens. It may or may not be better, don't know until I try. One thing that I don't have to worry about this time is having a bass inductor too near a transformer - hum is the result.
Frankenstein sheep ???? The never ending bodge - that is about right at the moment. Thing is I am having so much fun (and learning lots) messing about with the whole of my system and I cant leave it alone. To that end, bodging is easier and much quicker when you have no cases and flying leads all over the place. I just have to be careful where I put my hands
I should may be take a picture of it but I don't want to get in trouble with the internet diy hifi safety police. No one has access to the room it is in except me. Once it is all finished I may box it up neatly (wooden cases) but I am not sure I ever want it to be finished..........................