Doc modding Marantz imperial 7

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Alfi
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Re: Doc modding Marantz imperial 7

Unread post by Alfi » Thu Nov 30, 2017 4:42 pm

Oh yes, it sure will Stu..

You mentioned clean windows as Docs favorite metaphor regarding NVA products - how about open windows on a bright spring day?


Alfi.
Last edited by Alfi on Thu Nov 30, 2017 4:53 pm, edited 1 time in total.
Heavily modified LP12, Sole VIII sub-chassis with "In Sole" suspension, Ai bearing, PU7, Norton Airpower clone, etc, etc. PL71 & AT OC7, NVA Phono 2 (MC), NVA P50, NVA A20 power amp, home made birch ply Allison 6/Cube 1 clones, NVA SSC's, LS6.

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Dr Bunsen Honeydew
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Re: Doc modding Marantz imperial 7

Unread post by Dr Bunsen Honeydew » Thu Nov 30, 2017 4:49 pm

That is listening to the music itself, live, without a PA, as then you have a window again.

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Thu Nov 30, 2017 5:14 pm

How are you getting on with your diy semi Omni's Alfi ? Wipes the floor with point & squirt.
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Alfi
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Re: Doc modding Marantz imperial 7

Unread post by Alfi » Thu Nov 30, 2017 5:26 pm

I love them Stu.

They are not fully finished yet - needing vanishing but the sound they project is suiting me very well. Even so I assume they are not a good as the Docs Cube1's but they are far more even-handed and altogether more natural than the JPW P1's /AP2's I have. People mention LS3/5A's as being great with voices, well I love listening to FM radio too and with the good signal I have here voices are so natural and clear, who needs any BBC monitors?

I just wonder if it's of value in steel lining them. What do you think?

I must admit I'd like to try your isobaric design one day.

Alfi.
Heavily modified LP12, Sole VIII sub-chassis with "In Sole" suspension, Ai bearing, PU7, Norton Airpower clone, etc, etc. PL71 & AT OC7, NVA Phono 2 (MC), NVA P50, NVA A20 power amp, home made birch ply Allison 6/Cube 1 clones, NVA SSC's, LS6.

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Thu Nov 30, 2017 5:50 pm

I don't think the steel lining is as important with birch ply but I should think adding some is bound to bring an improvement (if you can live with the reduced cabinet volume). How thick is your ply ? Have you any bracing in there (if there is indeed any room to do it) ?

I am yet to add any steel to the isobaric bass cubes or the small cabs. My Marantz cabs have been steel lined to within an inch of their lives with angle steel in the corners and thick plate covering every available surface. That reminds me, I was going to stick some steel on the outside of these prototypes but forgot with all the experimenting and isobaric adventures. I wont be putting any on the inside that's for sure as it would be a lot of work to open them up, pull out the back baffle, steel line and then put them back together. I guess adding steel to the outside of these prototypes will have the same effect and be a lot easier for me. Can you imagine what they are going to look like when all the rusty off cuts are glued on the outside :lol: I will do it as my next speaker dabbling. I can just imagine the next bison kit induced headache :roll: I will report back.

My doc mod MS902S have been forgotten about with all this isobaric 3 way semi Omni business. They have 8mm angle inside and 7mm plate and you will not believe how much they weigh and how hard they are to move. I must get them finished some time. Last time I listened to them they were very, very, very tight sounding - oh yes. Unfortunately I went over the top with the doping and had to soak it in white spirits until the bison kit came off. I think that was only possible because they are an aluminium continuous cone with no dust cap. Came off very cleanly and when I get around to playing with them again I must remember to go slowly with the layers of dope :epopc:

What drivers have you got in them ? The doc's are excellent. Also the acrylic cabs of the cube's will probably give them the edge.
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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Thu Nov 30, 2017 6:21 pm

Trials with parallel and series isobaric wiring are finished.

I have come to the conclusion that parallel is better. :grin: It is juicier and a fuller sound - if you know what that means ? :grin:
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Re: Doc modding Marantz imperial 7

Unread post by Alfi » Thu Nov 30, 2017 9:34 pm

karatestu wrote:
Thu Nov 30, 2017 5:50 pm
I don't think the steel lining is as important with birch ply but I should think adding some is bound to bring an improvement (if you can live with the reduced cabinet volume). How thick is your ply ? Have you any bracing in there (if there is indeed any room to do it) ?

I am yet to add any steel to the isobaric bass cubes or the small cabs. My Marantz cabs have been steel lined to within an inch of their lives with angle steel in the corners and thick plate covering every available surface. That reminds me, I was going to stick some steel on the outside of these prototypes but forgot with all the experimenting and isobaric adventures. I wont be putting any on the inside that's for sure as it would be a lot of work to open them up, pull out the back baffle, steel line and then put them back together. I guess adding steel to the outside of these prototypes will have the same effect and be a lot easier for me. Can you imagine what they are going to look like when all the rusty off cuts are glued on the outside :lol: I will do it as my next speaker dabbling. I can just imagine the next bison kit induced headache :roll: I will report back.

My doc mod MS902S have been forgotten about with all this isobaric 3 way semi Omni business. They have 8mm angle inside and 7mm plate and you will not believe how much they weigh and how hard they are to move. I must get them finished some time. Last time I listened to them they were very, very, very tight sounding - oh yes. Unfortunately I went over the top with the doping and had to soak it in white spirits until the bison kit came off. I think that was only possible because they are an aluminium continuous cone with no dust cap. Came off very cleanly and when I get around to playing with them again I must remember to go slowly with the layers of dope :epopc:

What drivers have you got in them ? The doc's are excellent. Also the acrylic cabs of the cube's will probably give them the edge.
Yes, I think Doc has mentioned in the past that Birch ply is OK without steel lining so I wheel leave all alone. I used 18mm Baltic birch for my cubes with no additional bracing as they appear solid enough.

I used these for bass I drivers because I had two new for £32.00 each. https://www.monacor.com/products/compon ... /sph-225c/ I can't say they are better than the drivers Doc uses but at the price I paid for the Monacor's it seemed too good to pass up. Suitably doped they perform very well to my ears.

For tweeters I used Visaton G 20 SC's that the Doc advised I use for my JPW's so they were swopped out and I used those huge 3.3mF Russian PIO's in series with the tweeter.

I can imagine the sheer mass of your MS902S' as my JPW P1's weighed in at over 20kg's each.

Regards.

Alfi.
Heavily modified LP12, Sole VIII sub-chassis with "In Sole" suspension, Ai bearing, PU7, Norton Airpower clone, etc, etc. PL71 & AT OC7, NVA Phono 2 (MC), NVA P50, NVA A20 power amp, home made birch ply Allison 6/Cube 1 clones, NVA SSC's, LS6.

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Dr Bunsen Honeydew
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Re: Doc modding Marantz imperial 7

Unread post by Dr Bunsen Honeydew » Thu Nov 30, 2017 9:44 pm

karatestu wrote:
Thu Nov 30, 2017 6:21 pm
Trials with parallel and series isobaric wiring are finished.

I have come to the conclusion that parallel is better. :grin: It is juicier and a fuller sound - if you know what that means ? :grin:
Never make presumptions though. You have high current transistor amps, someone with lower current capability as with valve amps may prefer the other way.

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karatestu
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Re: Doc modding Marantz imperial 7

Unread post by karatestu » Thu Nov 30, 2017 10:48 pm

Alfi wrote:
Thu Nov 30, 2017 9:34 pm
karatestu wrote:
Thu Nov 30, 2017 5:50 pm
I don't think the steel lining is as important with birch ply but I should think adding some is bound to bring an improvement (if you can live with the reduced cabinet volume). How thick is your ply ? Have you any bracing in there (if there is indeed any room to do it) ?

I am yet to add any steel to the isobaric bass cubes or the small cabs. My Marantz cabs have been steel lined to within an inch of their lives with angle steel in the corners and thick plate covering every available surface. That reminds me, I was going to stick some steel on the outside of these prototypes but forgot with all the experimenting and isobaric adventures. I wont be putting any on the inside that's for sure as it would be a lot of work to open them up, pull out the back baffle, steel line and then put them back together. I guess adding steel to the outside of these prototypes will have the same effect and be a lot easier for me. Can you imagine what they are going to look like when all the rusty off cuts are glued on the outside :lol: I will do it as my next speaker dabbling. I can just imagine the next bison kit induced headache :roll: I will report back.

My doc mod MS902S have been forgotten about with all this isobaric 3 way semi Omni business. They have 8mm angle inside and 7mm plate and you will not believe how much they weigh and how hard they are to move. I must get them finished some time. Last time I listened to them they were very, very, very tight sounding - oh yes. Unfortunately I went over the top with the doping and had to soak it in white spirits until the bison kit came off. I think that was only possible because they are an aluminium continuous cone with no dust cap. Came off very cleanly and when I get around to playing with them again I must remember to go slowly with the layers of dope :epopc:

What drivers have you got in them ? The doc's are excellent. Also the acrylic cabs of the cube's will probably give them the edge.
Yes, I think Doc has mentioned in the past that Birch ply is OK without steel lining so I wheel leave all alone. I used 18mm Baltic birch for my cubes with no additional bracing as they appear solid enough.

I used these for bass I drivers because I had two new for £32.00 each. https://www.monacor.com/products/compon ... /sph-225c/ I can't say they are better than the drivers Doc uses but at the price I paid for the Monacor's it seemed too good to pass up. Suitably doped they perform very well to my ears.

For tweeters I used Visaton G 20 SC's that the Doc advised I use for my JPW's so they were swopped out and I used those huge 3.3mF Russian PIO's in series with the tweeter.

I can imagine the sheer mass of your MS902S' as my JPW P1's weighed in at over 20kg's each.

Regards.

Alfi.
Wow, you did well to get those drivers for 32 squids, they are on the link you posted for over 200 eouro's :o

The visaton are very sweet tweeters, it makes me wonder why i bother keeping the ms902s metal domes they are completely different league. I think i might develop a hernia moving all these speakers about.
Dr Bunsen Honeydew wrote:
Thu Nov 30, 2017 9:44 pm
karatestu wrote:
Thu Nov 30, 2017 6:21 pm
Trials with parallel and series isobaric wiring are finished.

I have come to the conclusion that parallel is better. :grin: It is juicier and a fuller sound - if you know what that means ? :grin:
Never make presumptions though. You have high current transistor amps, someone with lower current capability as with valve amps may prefer the other way.
With my current amps (excuse the pun) parallel is better. I have never owned a valve amp and don't think i will ever venture to the dark side :twisted: There wasn't a huge difference between the two and if i were to try running the whole shebang from one amp i would put them in series. 16 ohms (bass) in parallel with 8 ohms (mid) in parallel with 20 ohms (tweeter plus padding resistor) equals 4.2 ohm load on the amp. Perfectly doable, unless i got my sums wrong. :roll:
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Alfi
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Re: Doc modding Marantz imperial 7

Unread post by Alfi » 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.
Heavily modified LP12, Sole VIII sub-chassis with "In Sole" suspension, Ai bearing, PU7, Norton Airpower clone, etc, etc. PL71 & AT OC7, NVA Phono 2 (MC), NVA P50, NVA A20 power amp, home made birch ply Allison 6/Cube 1 clones, NVA SSC's, LS6.

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