It will work great without mods.
The distortion will almost vanish @32ohm and above. So will the output power but you don't need much for cans.
You can consider reducing the bias current somewhat, but keep the 24V supply voltage.
One interesting consideration is the output polarity. Some people find the inverse polarity objectionable, I don't.
I run a Zen Lite as a HPA and it also inverts phase.
One way is to have a pre-amp which inverts first and then everything is sweet.
The distortion will almost vanish @32ohm and above. So will the output power but you don't need much for cans.
You can consider reducing the bias current somewhat, but keep the 24V supply voltage.
One interesting consideration is the output polarity. Some people find the inverse polarity objectionable, I don't.
I run a Zen Lite as a HPA and it also inverts phase.
One way is to have a pre-amp which inverts first and then everything is sweet.
my hd 650 is 300ohm, i guess there is no need for reducing the bias current.
how to convert from speaker output to 3.5mm
Very easy, just wire your amp output to the 3.5 mm socket, L to L, R to R, common ground.
Mount the socket on the front panel for convenience.
Or if you don't want to spoil the look of the amp keep the socket at the back.
Just do not connect speakers to the posts.
You'll find wiring diagrams all over the net.
I would recommend wiring a 6.5 mm socket with a lock, like this one:
P0064 6.35mm Chassis Mount Heavy Duty Metal Jack Socket - Altronics
and then a 6.5 to 3.5 adapter.
Mount the socket on the front panel for convenience.
Or if you don't want to spoil the look of the amp keep the socket at the back.
Just do not connect speakers to the posts.
You'll find wiring diagrams all over the net.
I would recommend wiring a 6.5 mm socket with a lock, like this one:
P0064 6.35mm Chassis Mount Heavy Duty Metal Jack Socket - Altronics
and then a 6.5 to 3.5 adapter.
For 300 ohm you might benefit from a higher voltage, lower current design.
Think of a tube HPA.
Still worth trying the ACA.
Just make yourself a 3-wire fly lead from the speaker output to the socket (loose) and try your HD 650.
If you like the result make the change more permanent.
Or if you are like me use it that way for as long as you can.
Nothing's more permanent than the temporary measures.
If you are going to drive headphones - remember that the speaker posts are backwards!
Remember on the the ACA the red posts are the common, and the black posts are the individual channels.
If your headphones have the grounds tied together (like 97% of the headphones do, using a TRS plug) you need to put the 2 speaker reds to sleeve, right black to ring, and left black to tip. The suggestion of making an adaptor cable to go from speaker posts to a female TRS jack is very good.
(The posts are inverted to help with output phase but more importantly to allow for the self-bridging feature if building them as monoblocks.)
Remember on the the ACA the red posts are the common, and the black posts are the individual channels.
If your headphones have the grounds tied together (like 97% of the headphones do, using a TRS plug) you need to put the 2 speaker reds to sleeve, right black to ring, and left black to tip. The suggestion of making an adaptor cable to go from speaker posts to a female TRS jack is very good.
(The posts are inverted to help with output phase but more importantly to allow for the self-bridging feature if building them as monoblocks.)
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Does the same thing apply when hooking up a REL sub to the speaker posts? The REL has a red and yellow lead for the positive connections and a single black wire for the ground. Do you put the red and yellow on the red speaker terminals or switch them to the black because of the internals of the ACA?
Thanks.
It might be a box like this you what. It interfaces from banan speaker plug to stereo female jack. Inside the box is a 8 ohm load resistor pr. channel to ensure proper load of amp (original made for tube amp) and across 8 ohm load resistors a voltage divider is made which reduces the signal so it fits to headphones. Also it protects a bit in case of short circuit....
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Hi, I am building two aca and would like to run stereo thru them using the XLR input. They will both be in a single enclosure. I am confused about mirrored pairs and making sure the phase is correct. Is wiring each as a monoblock the right move? Would someone point me to a post or help me understand how to wire two aca as a stereo pair, please.
XLR:
pin 1 ground
pin 2 positive
pin 3 negative
so for example you can do:
pin 1 common ground to both channels
pin 2 Left
pin 3 Right
look here:
How to Wire an XLR to Two RCA Connectors
I'm sure other members will come up with different and likely better suggestions.
pin 1 ground
pin 2 positive
pin 3 negative
so for example you can do:
pin 1 common ground to both channels
pin 2 Left
pin 3 Right
look here:
How to Wire an XLR to Two RCA Connectors
I'm sure other members will come up with different and likely better suggestions.
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AFAIK, if you stick to the building guide, you will have your ACAs prepared for monoblock (bridged) operation —one left channel, the other unit the right channel?
Confusing answer.
The question was running stereo ACA with the XLR connector as input to both channels, Left and Right.
Otherwise you are right, the guide covers the option.
Hi.We want to make bridged ACA amplifier with RCA input to eliminate output capacitors.(4 ACA board in one case but not balanced amp,RCA input.May also build B1 buffer inside of amp)My friend told that we can not make a DC protect circuit to protect speakers.We want to make a delay circuit when start up and save speakers for any DC if one block of amplifier damaged.Is it not possible?
It may be possible. You could use an opamp as a type of servo. This would sample the DC voltage at the output of amp 1 and then using that as a reference bias amp 2 to achieve the exact same DC output conditions.
Two resistors and two caps plus one opamp.
The problem (imo) with bridging the ACA is that because the output impedance is so high, the load affects the absolute output voltage of 'amp 1' and then we use that altered voltage as the input to amp 2.
I think it would be better to do the phase splitting at the inputs using an opamp... however
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Hi.Because of i think this amp is one of the best (full n channel, i am excited ) and also gain is good i also wanted to make it better(without output caps) and also more power would be good.But i see damping is 10 and when making bridge it will be 5 and i think it is a bit low.My FR speakers are 86dB 4 inch and i think it needs more power to fill the room (i will make F.A.S.T and bottom frequency will be supplied by active preamp though) .If make balanced DF will be 5 again right?And can we make it without output coupling caps if make balanced?(if not i will use elna silmic 3300uf 50v caps which i bought in the past)Thank you and best regards
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