Doc Mod Drivers

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Dr Bunsen Honeydew
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Re: Doc Mod Drivers

Unread post by Dr Bunsen Honeydew » Mon Mar 20, 2017 8:49 pm

Even if you have negative comments PLEASE give feedback as it is part of the experience file for EVERYONES help.

Also with Doc Modded existing drivers.

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Quarknosis
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Re: Doc Mod Drivers

Unread post by Quarknosis » Mon Mar 20, 2017 9:20 pm

Dr Bunsen Honeydew wrote:Push the bass driver in and see if you hear a hiss from anywhere around the cabinets. I forget did you get Doc Mod tweeters or others. How long did you run them for, they need a couple of weeks of continuous use to run in. Un run in sounds like you heard, also a slight muddyness that disappears when they run in.
I'll certainly give the drivers a push and see /hear if there is any leakage . I only had the 8 inch drivers, no tweeters at this time.

It was about 10-11 weeks between finishing the Doc Mods and finding the first pair of vintage speakers so they should have been well run in.
NVA BMU - NVA Phono 1 - Systemdek IIX/Rega RB250/Denon DL160 & Philips CD 104 with NOS mod - TIS & SSP mkii - NVA AP70sa - Epos ES11.

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Dr Bunsen Honeydew
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Re: Doc Mod Drivers

Unread post by Dr Bunsen Honeydew » Mon Mar 20, 2017 9:58 pm

Did you hear changes in that time. If it is existing tweeter I think DQ went to 15 or 16 ohms. Another 6 inches from the wall sounds as if it will help.

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Quarknosis
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Re: Doc Mod Drivers

Unread post by Quarknosis » Tue Mar 21, 2017 4:52 pm

I tried pushing the drivers in this morning, I couldn't hear any hissing.

The sound of the speakers did seem to become more relaxed with time as I remember, but as it has been a few months since I last used them I don't have a direct memory of what they sounded like exactly. As always it will be interesting to listen to them again. I might put them on the end of the AP20 for the time being but positioning is going to be less than ideal as they will need to be about 2 inches out from a stud wall.
NVA BMU - NVA Phono 1 - Systemdek IIX/Rega RB250/Denon DL160 & Philips CD 104 with NOS mod - TIS & SSP mkii - NVA AP70sa - Epos ES11.

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spacejay
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Re: Doc Mod Drivers

Unread post by spacejay » Mon May 01, 2017 4:11 pm

Doc,

you have probably forgotten the story about me buying Allison One speakers quite a few years ago, but the upshot of the story was that the crossovers were smashed to buggery. Anyhow it occurred to me today, can these be doc modded or are they not suitable?

Lurcher300b
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Re: Doc Mod Drivers

Unread post by Lurcher300b » Tue May 30, 2017 2:35 pm

I had a weekend of getting less done than I originally planned, mainly due to stuff not arriving when hoped. But I did have a play with the modified speakers that DrB sent me some time ago.

When I first tried them, they needed huge amounts of power to get any volume from them, and at the same time most of what I could hear was the tweeter distortion. I heard much the same when I took them to Colins place. Putting them against a wall helped by bringing the bass up, but I could still hear the tweeter having a hard life.

So DrB suggested I tweak the resistor in series with the tweeter. Took them apart, and it had a 12R and 3u3 cap in series. Having a quick measure with some pink noise and a phone app like Steve uses showed a interesting peak at 4k. I would guess about where I heard the nastiness. But the HF and LF were about the same level, so I didn't want to alter the resistor as the overall levels seemed about right. The 4k peak made me wonder if the tweeter and woofer were overlapping more than they should, so I tried a 2u3 cap in place of the 3u3 cap (well actually two 4u7 in series as that's what I had on hand), the measurement now showed the peak at 4k had gone away, and listening to them it was much better. TBH, very much better, I have had a couple of evening listening to them now, and they do do a lot of things right, lowest bass is missing, but given the size of the box its rather impressive. The tweeters are held in with bluetac at the moment, and keep falling out.

I have some caps on order, and will try 2u2 and 2u to see what's better, and then glue the tweeter back and take them to Owston.

Still needs shedloads of power to get any volume, and I don't think they can do the loudness I would need for a 100% of the time speaker, they wont replace the OB's as they stand, but its rather annoying that they have made me aware of some things that fostek could be doing better.

I have to now believe there is merit to treating the cone. I will have to get those Graham 5/9's and try them just to make sure I am not being impressed by the difference instead of some absolute value in them.

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Dr Bunsen Honeydew
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Re: Doc Mod Drivers

Unread post by Dr Bunsen Honeydew » Tue May 30, 2017 3:19 pm

I think I know why this happened. As standard with that doped bass driver I use a Visaton G20 SC 8ohm (or my doped cheap Chinese special). For some reason, I forget why as it was a while ago, those B&W mods were fitted with Visaton G25 FFL 8ohm. G20 is for 3khz up and the G25 for 2khz up, so the G25 was giving too much output at the wrong points. Down to me I should have noticed, but lots of things being done at the time and these went very quickly to Dave (DSJR) who had them on loan and seemed happy with them, so I didn't investigate them. They were never a feature here in my system. Thanks Nick for finding it and sorting them out.

_D_S_J_R_
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Re: Doc Mod Drivers

Unread post by _D_S_J_R_ » Tue May 30, 2017 6:39 pm

I found the B&W speakers a bit hard going in a direct sounding 'monitor' sense as I reported at the time, but I really genuinely appreciated the clarity they offered over the whole range over other speakers I had at home and I missed it greatly when they returned to NVA Towers and were replaced by the geriatric but still endearing old IMF Compacts (not the Super Compact) which are amazingly good for a 1971 design. Not having any means of measuring them, I wasn't sure if this 'presence-forwardness' was normal or if this could be tamed al bit. The lack of efficiency never seemed a problem although I accept the volume control needed to be advanced a little further (none of my amps here are wimps).

Glad the cap tweak has sorted it. Whether I'll get the chance to try them again I don't know, but I confirm that the heavy totally sealed box and tautly damped main driver, coupled with an excellent and basically 'sweet' tweeter does work incredibly well, even as they were and used with NVA amps, which have no hardness or grain to them.

P.S. One of them had a tiny air leak and believe me, in THIS speaker, it was clearly audible on powerful bass notes. The bass cone really does need to be almost impossible to push in and it should spring straight back out with no gentle motion.
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Quarknosis
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Re: Doc Mod Drivers

Unread post by Quarknosis » Thu Jul 20, 2017 2:44 pm

Doc,

I've been looking in the archive to try and find faceplate size info for the tweeters but without success, can you let me know what the measurement is? It seems that the cut out required is either 70mm or 72mm from what I've been able to find.

Does anyone who has fitted the tweeters have pictures of them that they can post or link to?
NVA BMU - NVA Phono 1 - Systemdek IIX/Rega RB250/Denon DL160 & Philips CD 104 with NOS mod - TIS & SSP mkii - NVA AP70sa - Epos ES11.

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Dr Bunsen Honeydew
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Re: Doc Mod Drivers

Unread post by Dr Bunsen Honeydew » Thu Jul 20, 2017 3:13 pm

Which tweeter my modded Chinese one or the Visaton ones If Visaton google G20se

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