nj pheonix
Lunatic Member
Scott as I understand the page I posted, They want you to swap the positions of the caps and the resistors (change the value of both ) and add jumpers.
BIG-TIME BREAKTHROUGH!!! Here's the fix (finally!) for the Loudness switch that works for both the ST-40 and the ST-70 and completely changes their sonic character, emphasizing the obvious fact that, as implemented, it was a clear design and/or documentation error. First of all, get a schematic, and see for yourself--it just cannot work as designed. I finally got fed up with two problems that both these amps exhibit (especially with high-sensitivity speakers)--one, all their volume is dialed in within about the first 20% of the volume control's rotation, which exacerbates a problem inherent in the part itself--an imbalance favoring the one side at low settings, and two, the stock Loudness switch performs more like a bad Mute switch which cuts the volume but doesn't add any real bass. The ST-70 is rather short of bass anyway, and this just makes that worse. Well, guess what, it ain't the guts--it's the stupid-ass Loudness switch design. Here's how you fix it:
1. We have to reverse the positions of the resistors and capacitors on the Loudness switch, and change their values, as well as add two jumpers to the switch with this change, so bear with me. The .2mfd @ 10vdc capacitors are becoming .022mfd @ 400vdc 716P Orange Drops, and the 2.7K resistors are becoming 22K. And their positions on the four-gang switch are reversed--the resistors go from the switch to the ground points on the chassis-mounted terminal strip (where the caps were), and the caps are mounted on the switch body itself (where the resistors were).
2. Now we add two jumpers that, looking at the switch from the rear, connect the bottom left tab to the middle right tab of the left-most DPDT switch section and another jumper in the same position on the right-most DPDT half. Think of the four gang switch that EICO used as though it were two DPDT dual-gang switches side-by-side (although this function could be performed correctly by a single DPDT switch, as in any Scott 299 circuit.)
So, from the rear the Loudness Switch looks like this:
Top
1 4 7 10
2 5 8 11
3 6 9 12
Rear View
The new jumpers go from 3-to-5 and 9-to-11.
3. And while you're at it, replace the 68pf ceramic caps with silver micas. Keep all stock wiring intact!
BIG-TIME BREAKTHROUGH!!! Here's the fix (finally!) for the Loudness switch that works for both the ST-40 and the ST-70 and completely changes their sonic character, emphasizing the obvious fact that, as implemented, it was a clear design and/or documentation error. First of all, get a schematic, and see for yourself--it just cannot work as designed. I finally got fed up with two problems that both these amps exhibit (especially with high-sensitivity speakers)--one, all their volume is dialed in within about the first 20% of the volume control's rotation, which exacerbates a problem inherent in the part itself--an imbalance favoring the one side at low settings, and two, the stock Loudness switch performs more like a bad Mute switch which cuts the volume but doesn't add any real bass. The ST-70 is rather short of bass anyway, and this just makes that worse. Well, guess what, it ain't the guts--it's the stupid-ass Loudness switch design. Here's how you fix it:
1. We have to reverse the positions of the resistors and capacitors on the Loudness switch, and change their values, as well as add two jumpers to the switch with this change, so bear with me. The .2mfd @ 10vdc capacitors are becoming .022mfd @ 400vdc 716P Orange Drops, and the 2.7K resistors are becoming 22K. And their positions on the four-gang switch are reversed--the resistors go from the switch to the ground points on the chassis-mounted terminal strip (where the caps were), and the caps are mounted on the switch body itself (where the resistors were).
2. Now we add two jumpers that, looking at the switch from the rear, connect the bottom left tab to the middle right tab of the left-most DPDT switch section and another jumper in the same position on the right-most DPDT half. Think of the four gang switch that EICO used as though it were two DPDT dual-gang switches side-by-side (although this function could be performed correctly by a single DPDT switch, as in any Scott 299 circuit.)
So, from the rear the Loudness Switch looks like this:
Top
1 4 7 10
2 5 8 11
3 6 9 12
Rear View
The new jumpers go from 3-to-5 and 9-to-11.
3. And while you're at it, replace the 68pf ceramic caps with silver micas. Keep all stock wiring intact!
k oddly enough after ordering pieces for this, I end up having everything on hand except the mica 68pfs, which didn't prevent me from doing mod /fix . Not to offend the purists, but I really like the result. it fixed the volume control issue and acts like all the loudness controls I've encountered before. Bass at low volume just slightly boosted (at least not as heavy as some loudness controls I've encountered). All in all a success . This thing is starting to sound awfully good!
