AIWA A30 Amp - UK Vintage Radio Repair and Restoration Discussion Forum

its ur aerial · 23rd Mar 2023, 9:23 pm

Are any Forum members familiar with the 1980 Aiwa Amplifier model SA 30K.
The one I am trying to repair and restore has a O/C vol pot on one gang .
It is a 100k, two gang pot but has 4 pin connections not 3 as normal.
I have disassembled the pot in the vain hope of repairing it, and the 4th pins on each gang measure as a fixed resistance of approx 4 ohms connecting to the middle slider pin.
I have tried finding a circuit diagram on the net, to clarify the reason for 4 connections, but have had no success.
Needless to say I can not obtain an identical part just the normal 100k two gang type with 3 connections on each section.
Has any members any idea what the 4th connection is for

Ken, G6HZG.

Nickthedentist · 23rd Mar 2023, 9:39 pm

Ken, it's almost certainly for "loudness compensation", i.e. to make the sound "richer" at low volume levels by boosting the bass, to compensate for the human ear's lack of sensitivity to quiet, low-frequency sounds (I think!).

Most people would replace it with a normal 3-terminal pot and be done with it. That feature was frowned on by HiFi purists anyway.

its ur aerial · 24th Mar 2023, 7:10 am

Nick, many thanks for the reply, that all makes sense,

because tracing back the print on the main PCB it would appear it goes back to the Loudness switch.
New pot on order, so we should soon have a result

I honestly don't remember seeing this arrangement before, but the memory is not what it was.
Many thanks again Nick.

Ken, G6HZG.

Edward Huggins · 24th Mar 2023, 10:17 am

This "Loudness" feature appears on many amplifiers of the period. Phiilps used them as well as a "Presence" control to boost the mid-range and was said to be useful on choral music and pop vocals. Then of course came the "Lo" and "Hi" filters and Graphic EQ - but let's not go there....thank goodness my trusty Pioneer A400 has no tone controls at all.

paulsherwin · 24th Mar 2023, 10:42 am

You can usually rewire the loudness circuitry so the bass and treble boost is either on or off (that is, not dependent on the position of the volume control). This will sound exactly the same at low volumes, and if you're cranking things up you can just switch off the loudness compensation manually.

ajgriff · 24th Mar 2023, 12:07 pm

I don't know whether it helps or not but the attached partial schematic shows a similar arrangement in a 1970s Grundig radio combined with a simple switched tone control at the front end of the audio stage.

Alan

23rd Mar 2023, 9:23 pm	#1
its ur aerial Hexode Join Date: May 2009 Location: Ryde, Isle of Wight, UK. Posts: 419	AIWA A30 Amp Are any Forum members familiar with the 1980 Aiwa Amplifier model SA 30K. The one I am trying to repair and restore has a O/C vol pot on one gang . It is a 100k, two gang pot but has 4 pin connections not 3 as normal. I have disassembled the pot in the vain hope of repairing it, and the 4th pins on each gang measure as a fixed resistance of approx 4 ohms connecting to the middle slider pin. I have tried finding a circuit diagram on the net, to clarify the reason for 4 connections, but have had no success. Needless to say I can not obtain an identical part just the normal 100k two gang type with 3 connections on each section. Has any members any idea what the 4th connection is for Ken, G6HZG. __________________ Life is not Hollywood, life is Cricklewood.

23rd Mar 2023, 9:39 pm	#2
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,844	Re: AIWA A30 Amp Ken, it's almost certainly for "loudness compensation", i.e. to make the sound "richer" at low volume levels by boosting the bass, to compensate for the human ear's lack of sensitivity to quiet, low-frequency sounds (I think!). Most people would replace it with a normal 3-terminal pot and be done with it. That feature was frowned on by HiFi purists anyway.

24th Mar 2023, 7:10 am	#3
its ur aerial Hexode Join Date: May 2009 Location: Ryde, Isle of Wight, UK. Posts: 419	Re: AIWA A30 Amp Nick, many thanks for the reply, that all makes sense, because tracing back the print on the main PCB it would appear it goes back to the Loudness switch. New pot on order, so we should soon have a result I honestly don't remember seeing this arrangement before, but the memory is not what it was. Many thanks again Nick. Ken, G6HZG. __________________ Life is not Hollywood, life is Cricklewood.

24th Mar 2023, 10:17 am	#4
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,327	Re: AIWA A30 Amp This "Loudness" feature appears on many amplifiers of the period. Phiilps used them as well as a "Presence" control to boost the mid-range and was said to be useful on choral music and pop vocals. Then of course came the "Lo" and "Hi" filters and Graphic EQ - but let's not go there....thank goodness my trusty Pioneer A400 has no tone controls at all. __________________ Edward.

24th Mar 2023, 10:42 am	#5
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,941	Re: AIWA A30 Amp You can usually rewire the loudness circuitry so the bass and treble boost is either on or off (that is, not dependent on the position of the volume control). This will sound exactly the same at low volumes, and if you're cranking things up you can just switch off the loudness compensation manually.

24th Mar 2023, 12:07 pm	#6
ajgriff Nonode Join Date: May 2004 Location: Halifax, West Yorkshire, UK. Posts: 2,587	Re: AIWA A30 Amp I don't know whether it helps or not but the attached partial schematic shows a similar arrangement in a 1970s Grundig radio combined with a simple switched tone control at the front end of the audio stage. Alan Attached Thumbnails