Goodman Dimensions 8 refurbishing

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Boris71

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Goodman Dimensions 8 refurbishing
« on: 27 Jun 2022, 04:58 pm »
Hi there,

I just started to refurbish some heavily beaten up Goodmans Dimension 8 from the 70s. A lot cheaper than several of the speakers I used to have, but they simply fit my room and sound just sweet to me. Unfortunately one tweeter seems to be damaged and a replacement for the 8 ohm Goodmans DT3 is not that easy to find. Thinking about improvement right from the beginning, any hint which "modern" tweeter might be used as a replacement? Unfortunately I have no approved specs whatsoever of the DT3. In an older auction I found the following:

Frequency range  2 - 20 KHz +/- 3 dBs
Suitable Xover frequency approx 3 kHz
Power Handling 30 Watts RMS with suitable Xover
Dome diameter  = 7/8"
Chassis diameter = 4.5"
Securing ring diameter = 4.5"
Tweeter depth = 1.25"
Tweeter weight = 600 grams/tweeter

I don't care too much about the looks, the weight etc. - it should fit technically.
Any idea?

Thanks - Boris

richidoo

Re: Goodman Dimensions 8 refurbishing
« Reply #1 on: 27 Jun 2022, 07:15 pm »
Some clues here:
https://audiokarma.org/forums/index.php?threads/goodmans-dimension-8-speakers.845710/

What's actually wrong with the tweeter?

Can you measure the voice coil resistance? Measure ohms across the tweeter terminals with the wires disconnected.
0-1 ohms bad
3-20 ohms good
infinite ohms bad

Any modern replacement tweeter would need to have similar sensitivity and physical size. It would have different specs and FR so the crossover would need adjustment. There are 4 tweeters on this speaker, so you would want to replace all four to keep the sound quality same on both sides.

It looks like the tweeter is screwed together, not just plastic glued. If the tweeter can be disassembled you might see more clues and see if it can be fixed, but that's a long shot. Look for burnt or broken wire on the voice coil. Or physical problem like hardened surround, damaged dome. When reassembling make sure VC doesn't rub on magnet = rocket surgery.

This
http://listeninn.com/Website/Used-Speakers/Goodmans-Dimension-8.htm
 says tweeter high pass filter corners at 4000Hz. Probably 2nd order electrical. That's useful if you want to adjust xo for replacement tweeters.

Boris71

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Re: Goodman Dimensions 8 refurbishing
« Reply #2 on: 27 Jun 2022, 07:27 pm »
Thanks. That‘s a starting point. Actually the tweeter sounds fine under „normal“ circumstances, but when playing a challenging track which goes really in the top heights that one tweeter starts to scratch.

I would not have a problem to replace all 4 tweeters, but if I can repair something…

I‘ll try to measure as proposed and see if I can disassemble the unit.

Thanks so far.

richidoo

Re: Goodman Dimensions 8 refurbishing
« Reply #3 on: 27 Jun 2022, 08:18 pm »
If the tweeter plays music at what seems to be the correct volume level then the VC is probably OK. So I would NOT disassemble it yet. Better to look for other causes of the distortion first.

Next step is swap amplifier channels Left to Right to make sure the problem is not electronics. Then if scratchy sound stays with that tweeter then swap the scratchy tweeter with a good tweeter from the other speaker to make sure that it is actually a tweeter problem and not a crossover or speaker connection problem.  Mark the tweeter wires and terminals so polarity doesnt get reversed by accident. I use blue painters tape bc easy to remove without marks.

Boris71

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Re: Goodman Dimensions 8 refurbishing
« Reply #4 on: 28 Jun 2022, 09:35 am »
Channel Swap makes no difference - so most probably no electronics. I have a used tweeter incoming - hopefully it's working.

Regarding the crossover, which looks pretty basic: any advise which caps might be a good replacement / improvement?
(picture is borrowed from the internet - but mine looks the same...)


richidoo

Re: Goodman Dimensions 8 refurbishing
« Reply #5 on: 28 Jun 2022, 03:18 pm »
Glad you found a tweeter.

The black caps are film caps so they dont wear out.
The blue cap is bipolar electrolytic. It requires liquid electrolyte to function correctly. Over decades they dry out and misbehave.  You can replace it with a film cap of same cap value (4.7 uF) and equal or greater voltage rating (>50V).

Normally the electrolytics are used on bass range because they typically aren't as refined on treble frequencies. But this electro is the smallest cap value so it might be your tweeter cap, in which case it could be dried out and causing the scratchy tweeter. If you can inspect xo board to verify that it is the tweeter filter cap then I would bet it's the problem.  I'm thinking it was selected for treble because it sounded better than EL CAPS.  I would replace the blue electrolytic cap with a decent film cap like Jantzen Superior-Z. You might want to also experiment with upgrading the EL-CAPs for SQ but they dont need to be changed for function. They might have been a cost cutting option since they chose something different for the more critical treble range. But I'm just guessing.

The inductors are all air-core so no benefit to change those.

There are no resistors, which is a sign of a very talented and/or lucky speaker designer.

Get the tweeter and everything else fixed before consider SQ upgrades to avoid rabbit hole.  :lol:

planet10

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Re: Goodman Dimensions 8 refurbishing
« Reply #6 on: 28 Jun 2022, 04:32 pm »
I had a pair of these with a toasted tweeter, took it into the dealer and they got me a new one. Never very impressed with the speakers.

dave

Boris71

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Re: Goodman Dimensions 8 refurbishing
« Reply #7 on: 28 Jun 2022, 06:30 pm »
Quote
Normally the electrolytics are used on bass range because they typically aren't as refined on treble frequencies. But this electro is the smallest cap value so it might be your tweeter cap, in which case it could be dried out and causing the scratchy tweeter. If you can inspect xo board to verify that it is the tweeter filter cap then I would bet it's the problem.  I'm thinking it was selected for treble because it sounded better than EL CAPS.  I would replace the blue electrolytic cap with a decent film cap like Jantzen Superior-Z. You might want to also experiment with upgrading the EL-CAPs for SQ but they dont need to be changed for function. They might have been a cost cutting option since they chose something different for the more critical treble range. But I'm just guessing.
Fantastic - I only know the Mundorfs as an „audiophile“ cap - guess that‘s too much for a non highend speaker?
I‘ll start step by step for sure - guess repairing the cabinet and put some walnut veneer on it will be the longest part… ;)

Quote
I had a pair of these with a toasted tweeter, took it into the dealer and they got me a new one. Never very impressed with the speakers.
I bought mine private for $100 and had no big expectations. However, in my room and to my taste they sound surprisingly good and I dumped much more expensive speakers for them. But it‘s as always the question what you‘re looking for in a speaker, how is your room situation, what are your preferences…

planet10

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Re: Goodman Dimensions 8 refurbishing
« Reply #8 on: 28 Jun 2022, 06:55 pm »
Very good price.

dave

JCarney

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Re: Goodman Dimensions 8 refurbishing
« Reply #9 on: 28 Jun 2022, 08:25 pm »
Hi Boris,
I do not know if they would have the same tweeter or not, but vinyl david has a pair of Goodmans Maximus 1 vintage minispeakers for $650 in the regional audiophiles GAS (Gateway Audio Society) circle. Look in the GAS Flea Market thread on page 33. Just thought I'd mention it. Might provide back up drivers or a new to you pair of small two ways from a company you know you like the house sound of.

Good luck,
JCarney

Boris71

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Re: Goodman Dimensions 8 refurbishing
« Reply #10 on: 29 Jun 2022, 12:17 pm »
Quote
I do not know if they would have the same tweeter or not, but vinyl david has a pair of Goodmans Maximus 1 vintage minispeakers for $650 in the regional audiophiles GAS (Gateway Audio Society) circle.
Thanks for the hint, but different tweeter definitely - and I'm not going to start collecting new speakers, I still have more than enough - besides the fact that shipping to Switzerland might get a bit expensive... :)

JCarney

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Re: Goodman Dimensions 8 refurbishing
« Reply #11 on: 29 Jun 2022, 03:06 pm »
 :lol: Yeah, shipping would be a bit much.

JCarney

Boris71

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Re: Goodman Dimensions 8 refurbishing
« Reply #12 on: 2 Jul 2022, 01:41 pm »
Let the games begin…







richidoo

Re: Goodman Dimensions 8 refurbishing
« Reply #13 on: 2 Jul 2022, 02:09 pm »
Please post a picture of the reverse side of the crossover board so we can see what that blue cap does. Thanks!

Boris71

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Re: Goodman Dimensions 8 refurbishing
« Reply #14 on: 2 Jul 2022, 02:18 pm »
You were guessing right - it goes to the tweeter…


richidoo

Re: Goodman Dimensions 8 refurbishing
« Reply #15 on: 2 Jul 2022, 02:27 pm »
 :thumb:

What film cap are you thinking about to replace  it?

Boris71

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Re: Goodman Dimensions 8 refurbishing
« Reply #16 on: 2 Jul 2022, 02:33 pm »
Quote
What film cap are you thinking about to replace  it?
Thought the Mundorf M-evo-470… - or your Jantzen proposal. I have to look what‘s available…

Boris71

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Re: Goodman Dimensions 8 refurbishing
« Reply #17 on: 3 Jul 2022, 12:39 pm »
Let the cabinet work begin…


Boris71

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Re: Goodman Dimensions 8 refurbishing
« Reply #18 on: 12 Jul 2022, 07:13 pm »
Made some good progress on the cabinets and the caps arrived today…







Boris71

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Re: Goodman Dimensions 8 refurbishing
« Reply #19 on: 5 Aug 2022, 05:54 pm »
Finished the first, the 2nd will be ready tomorrow. Improvised a bit with the connectors. So far I‘m pretty happy with the result.