Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Unluckily for my tweeters I am starting to prefer the little full range driver :whistle: Or should I call it a mid tweeter as it doesn't go right down and if it did then the distortion would spoil it. I played with the positioning of the sphere it is in quite a bit today. With them severely toed in you get a better sound when off axis. I also like them angled up by about 40 degrees at the same time.

If I made it so the small sphere was not fixed down but just rests on three supports equidistant around the edge of the up firing driver then I can tweak the position according to how many people are listening and where they are sat. If I am on my own then I can optimise it for just one seat :dance: If I rigidly connected it to the mid bass sphere underneath then I would lose that flexibility. Just need to make sure the three supports are soft on thd ends for a bit of vibration decoupling and so moving things doesn't mark the bottom of the sphere. Also the signal wires from the lower sphere will have to flexible enough to allow free movement.

Doing a mini four to eight line array with thd little mid tweets would lose this flexibility although it is very appealing in lots of other ways like increasing sensitivity and steering the beam. It limits directivity in the vertical plane so get little ceiling or floor interaction. The beam width gets wider though (I think) which is good if you have listeners sat around the listening area. Stand up and you lose output though, but we are always sat on sofa's unless we are dancing (we do that a bit in 70's disco nights :dance: )

One problem with line array is all those drivers in a line which are all a slightly different distance from your lug oles. That is why people curve them to equalise the distance. That is a construction nightmare if you ask me :hand:

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Re: Doc modding Marantz imperial 7

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karatestu wrote: Thu Oct 21, 2021 6:51 am
Floyd Toole apparently said comb filtering looks bad on a graph but the brain is expecting it. Anybody have a view on that statement ?
Comb filtering can be interpreted in the brain as height information, depending on where it's centered. Further up in frequency, it's best avoided if you can. Smooth baffle edges promote diffraction instead of re-radiation so will minimise comb filtering...
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karatestu (Thu Oct 21, 2021 8:18 pm)

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Re: Doc modding Marantz imperial 7

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karatestu wrote: Thu Oct 21, 2021 7:10 pm
Latteman wrote: Thu Oct 21, 2021 2:12 pm I have / had a similar imbalance between speakers and used mono volume controls to assist- with the Richard Allan CB4 tweeters this has not become a problem for me as the sound seems to be balanced better
I have considered dual volume controls but not sure the family will like them. Anyway, first things first - I haven't even got a volume control at the moment :lol: For whatever set up I keep at work I don't think I will use one and just keep using a potential divider made of two resistors soldered together per channel. As a treat for myself I might get some bulk foil resistors for it :guiness; . I won't be needing a source selector either :dance:

Home is a different story though as there will be two or three sources and I want it to be family friendly. Nobody will be allowed to touch the turntable however :grin:
My "preamp" went through a few iterations (tried and hated a switched attenutator) before looking like this.
preamp.jpg
preamp.jpg (144.81 KiB) Viewed 1029 times
The main volume knob is compliantly mounted, so i can just lift it slightly and move L or R individually. The pots are 50k bourns 10 turn wirewound pots, completely non-magnetic and sound better (to me) than those damn switches.
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karatestu (Thu Oct 21, 2021 8:23 pm)

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Re: Doc modding Marantz imperial 7

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Oh and the "TLA" logo is me poking fun at all those companies...

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Re: Doc modding Marantz imperial 7

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Some clever engineering there Rex. Some toothed cogs ?
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Re: Doc modding Marantz imperial 7

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The cogs are from an HP laser printer.
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karatestu (Fri Oct 22, 2021 5:19 am)

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Re: Doc modding Marantz imperial 7

Unread post by Latteman »

How much do the domed dust caps of a mid bass affect sound? The doping covers them- I’ve considered adding a false dome on to the dope??? Thoughts Stu?
Analogue Source -
Denon DP47f- Ortofon mc20 supreme
Ifi Zen Phono
Doug Self balanced Pre amp
Akai 4000DS mk2 R2R
Digital Sources- IfI stream, Ifi Neo idsd Dac; Tidal / Radio Paradise
Amplification Nva 30vdc mono blocks
Speakers Lii Audio F-15 in Open Baffle; Ls6
Weiduka AC8.8- for digital sources
Mini BMU for analog sources

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Re: Doc modding Marantz imperial 7

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Latteman wrote: Fri Oct 22, 2021 12:09 pm How much do the domed dust caps of a mid bass affect sound? The doping covers them- I’ve considered adding a false dome on to the dope??? Thoughts Stu?
I wouldn't bother Peter. If I am not mistaken the dust cap produces mostly the higher frequencies that we want to attenuate the most and probably where most of the nasty break up resonances are.

Pointless imo.
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I bit more playing about with these 2" cone full rangers and doped 6.5" kevlar.

I didn't want to go straight to 300Hz xover so decided to use another inductor which has -3db at 1.5kHz. Two caps in parallel for 28.8uf for the high pass on the 2" FR.

I didn't know what to expect ofc. All I can say is the presentation has livened up no end. There is something not right with the xover but what I can conclude so far is that doping really does take some life out of a driver

Reduced the cap value a bit and that's better :guiness;
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Re: Doc modding Marantz imperial 7

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Still far from happy. I may try padding down the full range just to see if it is a sensitivity mismatch between thd two drivers. If that is not the problem then God knows. This metal driver is now shouting at me. Maybe needs running in. When only doing tweeter duties I really liked it. If things don't change then that's all it will be doing - treble.

A single dome tweeter with first order high pass even as high as 6kHz really can't cope and that really is crystal clear now I have tried a 2" cone. It isn't as sensitive on paper as a dome but you wouldn't know it. Maybe there is something else at work here. Adding extra tweeters also showed how much detail hiding distortion is produced by a single one with 6dB/ octave high pass filter.

If you think about it with a 6kHz xover, the tweeter is only 6dB down at 3kHz, 12dB down at 1.5kHz and 18dB down at 750Hz. A tweeter's resonance is usually around 1200Hz or higher and you really don't want it producing any meaningful output at resonance. A fourth order linkwitz Riley (24dB/octave) would be down 48dB by 1.5 kHz.

Three tweeters sounded so much better than one but having them at 90 degrees to each other and situated near walls was bringing a slight confusion to proceedings. The 2" cone has proven that without a doubt. It sounds as clear, detailed and effortless as three tweeters but without the confusion as it is a single driver and is pointed away from thd front and side walls. It's a shame it is only 84dB but what do you expect from a 2" cone :grin: It doesn't sound so insensitive when you listen to it.

I can see myself using this 2" cone as a tweeter, it sounds lovely in that role even before being run in. Playing any lower might not be an option unless it sorts itself out or I get a handle on something I have done wrong. I do know I won't be using passive speaker level filters. I hate the bloody things as they interact with the drivers and I can't design a xover to save my life. Passive line level is so much easier to do for a numpty like me as it only involves capacitors and resistors. It sounds better also imo.

I am starting to get thoroughly disheartened with this speaker designing lark. As I try different things it points out to me how wrong I was doing it previously in certain areas. Can't quite believe how shit some aspects have been, and I raved about the sound at times. What a fecking know nothing idiot J am. The more I learn the more I realise what little I know, I am wasting my time with this. Four years down the drain. I might as well put my B&W P4's back together and be done.

This thread is now ended. Sorry, anybody who was actually interested will have to get their entertainment and laughs somewhere else :(
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