Experienced one slight mechanical - not electrical - problem. When trying out parallel mode (and I am loving the sound), when tightening a jumper in the speaker jacks through-hole, one jack was not tightened down enough to the back panel and rotated. I will have to go back in and add some lock washers and probably even solder the nuts to the threads.
I do not want to think about what would happen if the jack rotated further and pulled off a bunch of wires from their terminals...
I do not want to think about what would happen if the jack rotated further and pulled off a bunch of wires from their terminals...
Thanks to everyone for previous advice and help!
Now I will try adding led vu meter kits that require 12v supply.
Where would be the optimal place to draw 24v or 12v for the vu meter circuits? Would the switched power lead be safe for 24v supply to transformer?
I do use external speaker protection unit to protect from excessive DC to the speakers and I plan to check the DC levels prior to connecting speakers.
What should I expect DC levels to be at the speaker outputs for a healthy, unmodified ACA amp?
I plan to reference the speaker level outputs at the boards for the vu meter input signals (they are designed to support speaker level input).
If I decide I want to try to "calibrate" the vu meters I will try using my scope, sending in a 1 khz signal to just below clipping amplitude and see if I can get the LEDs to match (although it was pretty easy even for my ears to detect clipping of the amps when it happened- like someone was playing a guido!).
For active cooling I just decided to sit the amps on computer laptop type cooling fan platforms. The platforms are silent to my ears, wide enough to push air through the heat sink fins with good air flow, and dirt cheap.
As always, thanks for any and all advice for this hair-brained scheme 😉
Now I will try adding led vu meter kits that require 12v supply.
Where would be the optimal place to draw 24v or 12v for the vu meter circuits? Would the switched power lead be safe for 24v supply to transformer?
I do use external speaker protection unit to protect from excessive DC to the speakers and I plan to check the DC levels prior to connecting speakers.
What should I expect DC levels to be at the speaker outputs for a healthy, unmodified ACA amp?
I plan to reference the speaker level outputs at the boards for the vu meter input signals (they are designed to support speaker level input).
If I decide I want to try to "calibrate" the vu meters I will try using my scope, sending in a 1 khz signal to just below clipping amplitude and see if I can get the LEDs to match (although it was pretty easy even for my ears to detect clipping of the amps when it happened- like someone was playing a guido!).
For active cooling I just decided to sit the amps on computer laptop type cooling fan platforms. The platforms are silent to my ears, wide enough to push air through the heat sink fins with good air flow, and dirt cheap.
As always, thanks for any and all advice for this hair-brained scheme 😉
UPDATE for the VU meter effort:
I have tried a few different analog vu meter boards and meters, and digital LED. I am using the low level inputs to the boards. They all work but they all have two problems:
1: not sensitive enough. At their most sensitive settings (using whatever pots are available on the boards), when powering my relatively insensitive Pioneer speakers, the volume must be set somewhat too loud to get a visible response on the meters. This is true for either led or analog boards/meters.
2: dynamic range insufficient. When I increase the volume enough to get any response from the meters, they tend to max out well before the music peaks seem to indicate they should.
Note that I am testing with a chifi LM1875 gainclone amp (which sounds quite good in general) since I did not want to risk a $350 ACA amp while experimenting. The gainclone amp is advertised at max 30wpc and I am supplying with only 20v so power output of the gainclone should be close to what I would get from my pair of mono ACAs.
All the boards have "high level" inputs but I have not tested that approach yet and may not, since it seems higher risk of damaging amp or speakers if something goes wrong.
As usual for chifi DIY devices, I have no documentation to indicate if the devices are logarithmic or linear response. My guess would be linear given the cheap prices. This could be part of the problem.
I have tried a few different analog vu meter boards and meters, and digital LED. I am using the low level inputs to the boards. They all work but they all have two problems:
1: not sensitive enough. At their most sensitive settings (using whatever pots are available on the boards), when powering my relatively insensitive Pioneer speakers, the volume must be set somewhat too loud to get a visible response on the meters. This is true for either led or analog boards/meters.
2: dynamic range insufficient. When I increase the volume enough to get any response from the meters, they tend to max out well before the music peaks seem to indicate they should.
Note that I am testing with a chifi LM1875 gainclone amp (which sounds quite good in general) since I did not want to risk a $350 ACA amp while experimenting. The gainclone amp is advertised at max 30wpc and I am supplying with only 20v so power output of the gainclone should be close to what I would get from my pair of mono ACAs.
All the boards have "high level" inputs but I have not tested that approach yet and may not, since it seems higher risk of damaging amp or speakers if something goes wrong.
As usual for chifi DIY devices, I have no documentation to indicate if the devices are logarithmic or linear response. My guess would be linear given the cheap prices. This could be part of the problem.