Mods to Your Amps

[markw51]

Just picked up a 9444a and wow what a power house. I'm using it for home stereo and planning a few audiophool upgrades. What have you done, if anything?

[gearfreak]

Just picked up a 9444a and wow what a power house. I'm using it for home stereo and planning a few audiophool upgrades. What have you done, if anything?

What I have not yet accomplished with the 9442a is to replace the pots with stepped attenuators. I took one look and decided 'maybe another day'. Either too hard to get to or were board-mounted, or both, I forget now ...of course you may be more skilled/able to get to them more easily in the 9444.

bfish lists the dc offset/bias adjustments in this thread:
9444A

You can also search on 'anniversary series' or similar as these are often referred to.

e.g.
Anniversary amp caps

[markw51]

What I have not yet accomplished with the 9442a is to replace the pots with stepped attenuators. I took one look and decided 'maybe another day'. Either too hard to get to or were board-mounted, or both, I forget now ...of course you may be more skilled/able to get to them more easily in the 9444.

bfish lists the dc offset/bias adjustments in this thread:
9444A

You can also search on 'anniversary series' or similar as these are often referred to.

e.g.
Anniversary amp caps

What I've done so far is to bypass the pots, since I already have a volume control with the Schiit passive preamp I'm using. I've done the bypassing in a half assed fashion by shorting the connections on the circuit board for the wiper and the top terminal of the pots. The better way is to connect the wire to the pot wiper directly to the input terminal on the pot but that will take some work. Maybe in the future.

I've also removed the old power cord and installed an IEC connector for using different cords.

Next is to double the size of the fan resistor to slow it down. Too loud and it should still run very cool for home use. Then eventually replace the power supply filtering caps. I suspect they are getting a little dry.

[endeeinn]

I don't have an Altec 9444a but it is a 30+ year old amp and the electrolytic caps should be changed. When I did my first amp I did everything but the power supply caps (because of the expense - 4 x 22000uf 63v at $125 the set) but I did add bypass caps to the power supply caps and was disappointed with the results. The amp simply lacked the punch I thought it should have. I went back took out the power supply caps and measured them. Three of them ran from 6000uf to 12000uf and the other one was near the low side of spec but still out. I changed them and the amp came alive with all the dynamic punch I could hope for. Needless to say when I did the other amps I did the PS caps along with the others and it was much easier (except on the budget) since everything was apart anyway. Most modern caps are much smaller than they were 30 years ago so most should fit without a problem but be sure you measure the physical dimensions your power supply caps to be sure the replacement will fit within the current space. Another thing that may or may not be specific to my amp ... the bias setting trimmer pot was a cheep single turn pot that made setting the bias a test of patience as it was very touchy and after a lot of playing it still was not right on so I replaced them with burns 10 turn trimmer pots now setting bias is a breeze and I can get it right on without effort. My advice, once you dig in and start taking things apart do it all at once.

[markw51]

I don't have an Altec 9444a but it is a 30+ year old amp and the electrolytic caps should be changed. When I did my first amp I did everything but the power supply caps (because of the expense - 4 x 22000uf 63v at $125 the set) but I did add bypass caps to the power supply caps and was disappointed with the results. The amp simply lacked the punch I thought it should have. I went back took out the power supply caps and measured them. Three of them ran from 6000uf to 12000uf and the other one was near the low side of spec but still out. I changed them and the amp came alive with all the dynamic punch I could hope for. Needless to say when I did the other amps I did the PS caps along with the others and it was much easier (except on the budget) since everything was apart anyway. Most modern caps are much smaller than they were 30 years ago so most should fit without a problem but be sure you measure the physical dimensions your power supply caps to be sure the replacement will fit within the current space. Another thing that may or may not be specific to my amp ... the bias setting trimmer pot was a cheep single turn pot that made setting the bias a test of patience as it was very touchy and after a lot of playing it still was not right on so I replaced them with burns 10 turn trimmer pots now setting bias is a breeze and I can get it right on without effort. My advice, once you dig in and start taking things apart do it all at once.

All very good advice. I plan to do it just like you said.

[markw51]

I'm having a heck of a time getting the filter capacitors off the input board. That's where the low current power supply is. A 40 watt iron was not hot enough to melt the solder on the PC board where two 1000 mfd caps are soldered. They have thick, twist on type terminals. Going to the store tomorrow to find a hotter iron. Also the components on this board are soldered on both sides of the board. Messed up some of the copper traces but have been able to work around it.

I removed the screws holding in the main board but there are some push on type connectors holding some single wires and they do not come off so I will try to replace all the caps leaving those wires connected.

Replacing the big can capacitors was no problem and also installed a power resistor to slow the fan down for less noise.

[endeeinn]

I'm having a heck of a time getting the filter capacitors off the input board. That's where the low current power supply is. A 40 watt iron was not hot enough to melt the solder on the PC board where two 1000 mfd caps are soldered. They have thick, twist on type terminals. Going to the store tomorrow to find a hotter iron. Also the components on this board are soldered on both sides of the board. Messed up some of the copper traces but have been able to work around it.

I removed the screws holding in the main board but there are some push on type connectors holding some single wires and they do not come off so I will try to replace all the caps leaving those wires connected.

Replacing the big can capacitors was no problem and also installed a power resistor to slow the fan down for less noise.

I use the older non-digital version of the Hakko - FX-888D and it does fine with those large globes of solder, just have plenty of solder wick to soak up all that solder and then you'll be able to twist or cut the terminals to remove them.

[magnarc]

Just curious, (and not starting a cap brad war), what brand caps did you use?

I've four 9444A to check over at some point....

[markw51]

Just curious, (and not starting a cap brad war), what brand caps did you use?

I've four 9444A to check over at some point....

Nothing special. Just brand name stuff - Panasonic, Nichicon and so on. All from Digikey. There is one capacitor in the audio chain as far as I can see. Its a 10 mfd electrolytic from the output of the input board. I replaced that with a Panasonic film cap. Its rather large but got it to fit on the board.

I found the caps on the low voltage power supply difficult to remove because it is a two sided board and the bigger caps have thick terminals. I ended up just yanking them out, leaving the connectors on the board and then removed from the other side. That's probably the wrong way but it worked for me.

Also be advised there are four 100 mfd, 100 volt caps that are missing from the parts list of the service manual. I discovered that only after installing all the caps I had and seeing there were four more. I had to order them separately.

[markw51]

I'm pleased to report that I finished the refurbishment. It was a big job but am pleased with the results. The 10 mfd cap following the input board into the main board was replaced with a Panasonic film cap but it sounded like hell so I took it out and replaced it with an electrolytic as was the original. Sounds much better. I was surprised by that. My total investment is about $200, including the purchase price for the amp. I'm quite certain I would not be able to beat that in the consumer hifi world for what I have now.

I plan one more change. I ordered a LM4562 op amp and will use it to replace the NE5532 op amp in the input section. Some guys claim the LM4562, which was specifically designed for audio, is sonically better.