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MJL21193 17th September 2007 07:13 PM

Comments, opinions on this equalizer.
2 Attachment(s)
I got this for nothing. It's a Realistic model #31-2000 made in Korea for Tandy.
It's in fine shape, no scratches or damage. It works fine, seems to have good functional control over the frequency bands.
Is it a good unit? I know, most "audiophiles" would say these are nothing more than distortion mills, no place for even the best of them in a superior system.
I like the ability to contour the sound to my preference and at least try to overcome some of the room problems. I also like the way this unit looks - it matches the equipment that I have.

OK, main question: If this is truly a pile of garbage circuit wise, is it worth building a circuit of filters for it with low noise op-amps?
The current circuit is all discrete, using (mostly) transistors 2SC1222 and 2SA953.
A pic of the insides is coming but here's the front:

MJL21193 17th September 2007 07:19 PM

2 Attachment(s)
Here is the inside.

MJL21193 18th September 2007 01:02 AM

Hey! Is it really that bad? :)
Someone must have an opinion.

OzMikeH 18th September 2007 02:42 AM

Looks like a sensible layout but does look like a cheap board and components. (the single turn trimmer resistors in the middle of the left hand board)
Plenty of potential improvements, power supply filtering, any electrolytic series capacitors, replacing ribbon cable with screened cable.

Give the pots a clean and see if you like it. It may be a distortion mill but so is a SET tube amp!
Who cares what anyone else thinks?

MJL21193 18th September 2007 03:31 AM

Hey Mike,
It seems to work well as is, but I'm up for improving it. Good points with the caps, filtering and ribbon cable.
It's my intention to integrate it into my active 3-way system (whenever that gets done:rolleyes: ). My HTR does have pre-outs but no power-ins (or a tape loop), so I really haven't been able to give it a try with good speakers.
I though someone on here would be familiar with this unit and lend some guidance as to it merits.

planet10 18th September 2007 05:16 AM

I've had one of those thru here... sounds pretty much as bad as most of them (actually i've not even heard big buck ones that didn't subtract more than any gain)


MJL21193 19th September 2007 12:12 AM

Certainly if anyone has seen one, it would be you.:)
Like I said, I haven't had the opportunity to give it a serious listen. I expect it will reveal it's deficiencies on my new speakers.

If the unit were only used for "cut" and not "boost" do you think this could make a difference. If I rebuilt the circuit, I would have it so it would only cut the selected frequency, with no option for boost.
It also has overall gain, controllable with a pair of front panel knobs. It also has a bypass button for quick A/B comparison.

Limhes 22nd September 2007 06:37 PM

I don't expect that to be a real improvement. The problem with equalizers is that they introduce lots of phase shifts throughout the whole frequency band.

MJL21193 23rd September 2007 12:39 AM


Originally posted by Limhes
lots of phase shifts throughout the whole frequency band.

This unit uses inductors so phase shift is certain. If I were to re-build, I would use phase coherent filters, without using inductors.

I'm still waiting on the opportunity to give it a good listen. My ears ain't what they used to be, so it might fool me. ;)

MJL21193 3rd January 2008 09:18 PM

2 Attachment(s)
I dig up this older thread because I have made some tests on this equalizer.
First was a listening test. I found that if I used it to cut only, it worked very well. The sliders cover quite a sweep, too much in my opinion - they go from -12db to +12db. Cutting (or boosting!!)any part of the audio spectrum by any more than 2-3db means there are other, more serious problems to address.

I had the unit attached between my pre-out on my Yamaha HT receiver and the input to my (new) active amp . It was fine, I could effectively reduce some of the frequencies that I find too harsh on most speakers (low mid to mid - 300hz to 1000hz).

I then ran some tests on Right Mark Audio Analyzer. Connected through my lab computers sound card, I ran three tests: 1/ with the unit on but all of the sliders flat. 2/ All of the sliders on both channels with a 2db cut. 3/ All of the sliders on both channels with a 2db boost.
Here's a screen shot of the results window. First test of the group is the sound card test (provides the baseline performance).

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