Doc modding Marantz imperial 7

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

This site has been way too quiet on the diy front of late so here is a quick dose for all those who are interested (anyone ?)

My thoughts have been all over the place of late as regards speakers. Multiple drivers, infinite baffle, quasi omni, speakers in the floor etc. Never say never to any of it and some of the ideas i will try in time. In order to progress i had to do something and something simple to make it easy and quick to do.

In order to use what i have available and to try and not buy any more drivers at the moment i decided to revisit upward firing tweeters. I tried it with my little cabs laying on their back on the floor in front of the big bass cubes but could not get a result with that thrown together, sub optimal experiment. There needs to be a forward firing tweeter in my opinion so thoughts went back to when i added my MS902S speakers in to the mix a year or two back with them firing up and sat on the big bass cubes next to my little semi omni cuboids.

That set up was sub optimal also - another independent cab just plonked next to the other with a tweeter firing up, wired in parallel to the other front firing visaton. Diffraction, lobing, wrong heights blah blah - there were many things wrong with it but it did give a little clue to what to expect if done right (if there is a right way). As i wired it in parallel then i gained 3dB for the tweeter section that i didn't really want - tweeter is already more efficient than the other drivers.

So i decided to use the tweeters out of my B&W P4 transmission lines. 1" metal dome with phase rings and neo magnet. As i wanted them up firing i made a template out of cardboard which fits on top of my little cuboid cabs with a lip at the back where a hole could be made to push the tweeters in to. Much better than using another cab at the side and the tweeter is right next to the 5" up firing driver and much nearer acoustically to the front firing tweeter. I would have put the lip at the front to get the up firing tweeter as close to the front firing one as possible but i did not want anything interfering with the front tweeter so at the back it went.

Image

Image

I was trying to not have an increase in dB by paralleling it with the other tweeter so decided to run it in series with the front firing tweeter and so effectively there should be no difference - spl should stay the same. In effect the volume of the front tweeter should reduce as the voltage is shared by both tweeters (they are similar specs) and the load represented to the amplifier is doubled. Yes there are two tweeters now but they are not closely coupled on the same baffle so i don't think there is any dB increase due to that.

I have been listening to a few recordings especially hot ones with a lot of treble energy in order to try and highlight any differences. Yes there are differences. The music is not as in your face as before. Not that it was a problem as my set up is semi omni and we all know the effect of that. But the volume of the front firing tweeter is reduced. I can still tell it is doing it's thing and helping give some imaging and sound staging. From my recent experiments i have come to the conclusion that i can't live without a forward firing tweeter. It is essential to hear the very top end and to help with imaging etc. So i have still got that but at a reduced level.

The up firing tweeter is also doing it's thing and giving more air to the whole performance. I noticed that last time i tried a tweeter up and front firing but the set up was much more sub optimal than this one. I am really enjoying the presentation with this set up, i think i may be on to something here. Recordings with too much treble are much more bearable now. But i think it may be a bit too polite now. I am going to remove the padding resistors and see what happens.

It struck me that the treble is of much better quality than before then i realised that because i have shared the work between two tweeters that each has less to do. That can only be good for distortion and power handling. First order high pass filters on tweeters do get criticised for their shallow rolloff which means it having to produce a lot of low frequencies that it wouldn't with a higher order filter.I realise that putting two tweeters in series will have changed the high pass filter's knee frequency a little but that can be dealt with at a later stage (if at all :grin: ).

More to come folks :dance: By the way, no measurements were taken during this exercise. If that displeases you then please remember that i am doing this for my own ears (and my family) and i care not what others think. I don't go to bake off's to get patted on the back by peers (or torn to bits), it does not interest me. This is a pleasurable journey from which i am learning many things and that i owe to Richard, i just wish i had done it earlier so he could got a bit of amusement out of it. If others are inspired to have a go at what i have done then good. If it works out for you then excellent. If not then at least you had a go and can learn from it.

Adios amigos :grin:

PS I hope Tomasz enjoys the pictures :grin:
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Right, well the tweeter padding resistors are out. One less component in the chain. Oh wait a minute ......i replaced a component that costs pennies with one that costs a lot more :shhh: :shhh: :shhh:

I need to listen to more music but i may have struck lucky with the levels here :dance: There is not vastly too much treble like i thought might happen. There definitely doesn't need to be any more and if i do need to pad it down in the end it wont be much. Or shove another tweeter in there and hope to get rid of some more spl via room reflection and added distance for the wave to travel to reach my cloth ears. It would be more in the omni directional spirit as well.

I really am astonished at the increase in quality of the treble and high mid range. I am hearing very low level detail that was masked before like little percussion parts, backing vocals, phrasing of vocals. It must be down to the lower distortion from doubling up the number of tweeters. Now i know what the line array guys go on about.

Ways forward. Double up on the 5" mid bass driver as well so that can also benefit from lower distortion through not having as much work to do. I will keep them as closely coupled as i can to minimise any lobing. Can't really double up on the bass drivers without taking them out of isobaric mode and putting them in the floor to run push push in a true infinite baffle (volume of back space over 10X the drivers combined VAS).
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Re: Doc modding Marantz imperial 7

Unread post by Latteman »

Instead of doubling up on the 5” what about introducing a full range unit- I’ve heard Ant’s full range and mimicked it on a smaller scale- I used cheap drivers but was impressed- even extended the twizzers/ I plan to look at this further as a project next year
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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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Hi Peter.

Yes of course i have thought about them. I willl probably try some out at some point. I looked in to BMR drivers but they need a high pass filter and cone woofer for the bottom end .

It's all swings and roundabouts in the end , a huge revolving trade off. I think i have chosen where my current priorities are;

Filter less if possible
Semi omni
Capable of the lower frequencies
Tight bass (sealed box or IB)

Doubling up on drivers has really opened my eyes to lower distortion through the drivers not having as much excursion. I don't even play particularly loud and the benefits are still plain to hear. Another trade off i guess. Multiple drivers is getting away from the idea of a single point source but i can use it to further the omni directional properties of the design. It's all getting more complicated but then Richard did think his cubix (pro) were the pinnacle of his speaker design efforts.

Tweeters firing to the front, up, side and even the back
12" firing forwards, sideways , upwards
5" firing upwards, sideways.

Plenty of possibilities there to add more drivers. Different sizes of driver, box size and different levels of doping would lead to drivers coming in and out of operation at different frequencies. This may help with blending everything together. I don't think they all have to be identical drivers either.

Depending on how everything is wired up then several of the same type of driver (e.g 12", 10", 8", 6.5", 5.25", 4", 1" dome) don't all have to be outputting the same level. I could have three tweeters and wire them up with two in series and one in parallel. The one in parallel would obviously have a higher output than one of the series wired tweeters. I think the front firing tweeter is one that could have lower output .

By adding drivers and being clever (if that is actually possible for me) with wiring and direction of fire i can get rid of tweeter padding resistors. The only way to get rid of the high pass filter cap is to;

Use full range driver
Make a floor to ceiling line array
Put the high pass filter (an extra capacitor) in the input stage of the tweeter power amps. That is in effect one of the filters that Richard purposefully left out of his design although they are usually high pass very close to DC so as not to roll off bass. If i did insert one it would be working at a very different frequency (the same as that created by the 3.3uf cap and the tweeter).

So is it worth all the hassle of removing all components between amplifier output and tweeter ? Removal of the padding resistor can be done by adding various drivers and losing spl by firing direction, added distance from room reflections and clever wiring. The capacitor is a different matter. Would moving it to before the power amplifier bring any benefit ? Richard could not do it for general sale because it is too bespoke and would only work in individual circumstances. Ahh the beauty of diy :grin: When i asked him about doing it at line level he said not to bother but then Richard's answers were not always what they seemed.

Bloody hell, another essay that could be complete :Bllocks:
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

I am currently removing the tweeters from my MS902S that i doped on the inside of the dome with plastidip. These measure 4 Ohms when i continuity test them so this spices things up a little. They will play louder than the other two tweeters (8 ohms) i think. Spl is unknown but these things don't matter so much at the moment.

I am going to put these side mounted on the little cuboid cabs facing inwards i think. Will try outward facing as well in due course. These are going to be wired in series with the other two so 8R + 8R + 4R = 20R. That's the same as the visaton plus padding resistor (8R + 12R). Don't think that has much significance though apart from the load on the amp.

Back shortly when i have lashed it up :grin:
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Tweeters are attached and wired in series after the B&W tweeter. :dance: A further display of aesthetically pleasing precision engineering :lol:

Image

I couldn't use the tweeter without the surround as the voice coil is attached to it. So it is screwed on the side with as much overlapping the side of the box as the wires would allow. Now this must be diffraction city but it will be good enough to show any merit i should think.

Turned it on and nothing blew up but not listened yet :epopc:
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Fook me :shock: :shock: :shock:
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

Too busy listening to type owt yet :grin: :grin: :grin:
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Re: Doc modding Marantz imperial 7

Unread post by karatestu »

:animals-cow: I've got loads of work to do but i can't drag myself away :animals-cow:
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