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hbc hbc is offline

diyAudio Member

About Me

  • About hbc
    Biography
    electronic engineer
    Location
    Cambridge uk
    Interests
    nature of reality, babies
    Occupation
    analog designer in printer company
    Country
    United Kingdom

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General Information
  • Last Activity: 24th December 2014 09:12 AM
  • Join Date: 19th October 2010

Blog

View hbc's BlogRecent Entries
Latest Blog Entry

Posted 14th March 2014 at 11:40 PM by hbc Comments 0
Posted in Uncategorized
I bought a pair of these in about '95 and modified them a bit. I blocked up the ports, stuffed them with fluff, replaced the inductor with an air cored type, and rewired with CAT5. I also removed the top cages and grills which subsequently got lost, and also removed the rubber from the woofer voice coil, and put in a phase plug fashioned from some dowel.

I lived happily with these for about 10 years, ending up with an 18" subwoofer which used an equalised bass guitar speaker. The advantage of this equalisation was a degree of cancellation between the sub and the little woofers, resulting in a very smooth lump free transition in the listening position.

I found them to be an excellent tool in the development of audio stuff, it was quite easy to discern the difference between different types of cables, for me and friends, etc etc.

I bought another pair but I was wondering if the tweeters were fried as they sounded a bit dull compared to my modded...

Posted 5th March 2014 at 04:17 PM by hbc Comments 0
Posted in Uncategorized
I have a pair of tired Goodmans Magnum SLs. They are in reasonable condition, but one mid is blown, and they have no front covers. I tried grafting a new mid on to the broken one, expecting I would need to do some crossover work, but it really did not sound good. A very unpleasant sound that I found quite fatiguing and unpleasant to listen to coming from the upper bass lower mid area, quite a relief to turn it off actually. I put bigger and bigger choke on the woofer to try and filter it away, but that didn't work. I took of the dust cap in case that was causing it but no.


I am thinking of re-purposing the boxes now, but first did just check the woofer to make sure it has a problem. Below are some distortion plots, for a good one, the bad one and also for a Wharfedale Dovedale 3 woofer, with fixed rubber (Note the different scale). These plots were done at quite low level, like normal neighbour friendly listening levels.

Posted 9th December 2013 at 01:00 AM by hbc Comments 0
Posted in Uncategorized
The EAR 834p, is a marvellous and clever circuit, in its various optimisations and design features that are often not really understood... I acquired my second one a while ago, my first one was tweaked quite successfully to make very acceptable sound by adjusting the 10pf to 5pf and changing output CF to ECC81, and removing some surplus output potential dividers, and careful valve selection. Lowest noise first, and highest gain second.

However, it went away...

The problem I have seen with these is that they sometimes suffer muddy woolly sound in the bass which tends to spoil the over all effect. The new phono box I recently got suffers this way. Now I am suspicious of feedback loops, and how they work. I suspected that the 834p was maybe running a little short of gain in the lower registers. As I enjoy heresy, and after much consideration, I decided that bootstrapping the second stage ought to give me some more gain for the feedback loop to work. See circuit...

Posted 11th October 2013 at 12:28 AM by hbc Comments 0
Posted in Uncategorized
After the Magisters went I started missing them. Much irrational thought later I decided that I needed some Dovedales. It may be some left over residual memory of some super 8s I had when I was young, they were very nice despite the lack of tweeter (retrospective young thought). The big Dovedale woofers look similar with the green felt, bit nervous of those strange pink domes though... Anyway, eventually "won" some with mint drivers slightly tatty boxes. Long story short the rubber had got stiff, but not yet brittle.

Sulk, got the Magnums... (must have bass now). After much research and thought, the Dovedales don't seem to be a standard size for foam, and I had got to the point of contemplating cutting away some of the cone to fit a flat foam. I was tidying up the garden when I found a 700 inner tube I had changed recently.
At this point I thought what have I got to loose, so gave it a good wash, (lots of washing up liquid applied neat), chopped out the valve...

Posted 1st October 2013 at 12:07 AM by hbc Comments 0
Posted in Uncategorized
To try to recreate the Magister experience I hooked up the Magnums to the little ECL86 amp mentioned previously. I was greeted again with enormous deep bass, but not as happy over all, a rather lumpy frequency response, and a big question, what's going on... So I hooked up my Hybrid amp and the Magnums sounded a bit more normal, but the bass was considerably reigned in, disappointingly.

I think the Magnums like being back against the wall, they seem happy there and the in room response is now quite civilised with a nice boom free sound and bass is only there when it should be.

Still confused, had the ECL86 on the bench to measure to try and find out what's up. The frequency response looks a bit rolled off to the bottom, so no help there, but the treble peak is looking quite promising, explaining the "prominent" treble. After some wriggling the little amp surrendered its output impedance, all be it with significant 50Hz artefacts.

The output...
Recent Comments
Thanks for sharing ...
Posted 5th December 2012 at 01:20 PM by simonov simonov is offline
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