Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Fri Dec 01, 2017 1:55 pm

Alfi wrote:
Fri Dec 01, 2017 11:36 am
Stu I lied about the cost, they were £35 each BNIB. I couldn't believe my luck - they were the last 2 available so I grabbed them.

One day I may try the Visaton KE 25 tweeter but they are costly at over £100 each.


Alfi.
Even so Alfi, that is a substantial saving :clap:

With tweeters I guess you need to know that they sound good with a first order high pass filter. £100 .....gulp.

These Russian 3.3uf paper in oil caps really are the dog's danglies aren't they :dance:

And yes, isobaric is really worth the effort. Give it a go - but you would need two more identical mid / bass drivers and I wonder if you can find anymore at £35 ?

Stu
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Simon Hickie
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Re: Doc modding Marantz imperial 7

Unread post by Simon Hickie » Sat Dec 02, 2017 6:08 pm

I don't know, I move house and lose the internet for 10 days and all hell lets loose!
“The reasonable man adapts himself to the world: the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.” George Bernard Shaw.

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Sat Dec 02, 2017 8:43 pm

I was wondering where you had got to Simon. :grin: Hope the house move is going smoothly. You will be able to start your speaker build now. :epopc:

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.
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Tue Dec 05, 2017 6:21 pm

I am in the process of putting together two more monoblocs so that I can triamp these beauties. :dance:

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 :naughty:

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.............
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Fri Dec 08, 2017 11:46 am

Well, the two extra monobloc amps are up and running on tweeter duties only.

They are a bit Heath Robinson at the moment - much like the rest of my system :lol: 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 :shock: 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,
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antonio66
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Re: Doc modding Marantz imperial 7

Unread post by antonio66 » Fri Dec 08, 2017 12:11 pm

Excuse my ignorance Stu, does this mean you are using six mono block boards?
My set-up: PT Too,Rega 250 AO mods, Lyra Helikon, NVA Phono 2 + Extra PS, Project CD Transport/Project LPSU, Calyx 192 dac, NVA P50, NVA A60, Cube 3's. Headphones Senn HD700s and NVA AP10H. SSP/SC interconnect and NVA LS5 speaker cable.

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Re: Doc modding Marantz imperial 7

Unread post by Dr Bunsen Honeydew » Fri Dec 08, 2017 12:21 pm

I am waiting for it all to be struck by lightening and a Frankenstein sheep to emerge from the speakers. :shock:

Thread sub title - The Never Ending Bodge. Could be the title for a book :lol:

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Fri Dec 08, 2017 12:35 pm

antonio66 wrote:
Fri Dec 08, 2017 12:11 pm
Excuse my ignorance Stu, does this mean you are using six mono block boards?
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.
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Fri Dec 08, 2017 12:44 pm

Dr Bunsen Honeydew wrote:
Fri Dec 08, 2017 12:21 pm
I am waiting for it all to be struck by lightening and a Frankenstein sheep to emerge from the speakers. :shock:

Thread sub title - The Never Ending Bodge. Could be the title for a book :lol:
:lol: :lol: :lol: 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 :grin:

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..........................
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Fri Dec 08, 2017 12:47 pm

Oh and I realise now how I got away with the wiring mistake - the zobel network saved me :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: I knew it was there for something :lol: :lol: :lol:
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