Re: Doc modding Marantz imperial 7
Posted: 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.
Audiophile discussion, articles, bake-offs, Doc-Mods, music. NVA reviews, loan scheme, orders & support. Phono stages, amplifiers, semi-omni speakers, cables, headphone amps, digital, vinyl.
https://www.hifisubjectivist.org/
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.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 I will do it as my next speaker dabbling. I can just imagine the next bison kit induced headache 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
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.
Never make presumptions though. You have high current transistor amps, someone with lower current capability as with valve amps may prefer the other way.
Wow, you did well to get those drivers for 32 squids, they are on the link you posted for over 200 eouro'sAlfi wrote: ↑Thu Nov 30, 2017 9:34 pmYes, 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.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 I will do it as my next speaker dabbling. I can just imagine the next bison kit induced headache 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
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.
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.
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 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.Dr Bunsen Honeydew wrote: ↑Thu Nov 30, 2017 9:44 pmNever make presumptions though. You have high current transistor amps, someone with lower current capability as with valve amps may prefer the other way.
Even so Alfi, that is a substantial saving