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Adam: In terms of a preamp, what functionality do you really need? Do you just need a volume control? Do you need the ability to switch among components? Do you need to be able to add gain for higher volume? If you are just looking for volume control, the variable output level from many devices is perfect for input to the ACA. If you need switching or additional gain, then you need to consider an actual preamp. All of the options provided so far are great.
I built an ACA with my daughter when she was 9 and she plugs it directly into her iPod. She uses the volume output control on the iPod to control the output of the amp. The ACA drives a pair of Mark Audio CHR70 speakers that we put in a ready-made cabinet from Parts Express. This combination provides just the right amount of speaker output for her bedroom - it is loud enough for her to feel like she is rocking out, but doesn't carry too far throughout the house.
I built an ACA with my daughter when she was 9 and she plugs it directly into her iPod. She uses the volume output control on the iPod to control the output of the amp. The ACA drives a pair of Mark Audio CHR70 speakers that we put in a ready-made cabinet from Parts Express. This combination provides just the right amount of speaker output for her bedroom - it is loud enough for her to feel like she is rocking out, but doesn't carry too far throughout the house.
temp
I wired up a couple of 12V batteries (in series for 24V) to my ACA’s for fun. Does it sound better, I’m not sure, nothing super obvious, but haven’t given it a critical listen yet.
After an hour of playing the temp was ~125 degrees F, which isn’t too bad from my understanding. Reading through the thread, it seems most like a higher bias on these ACA’s, and a bias of 12.5-13 was recommended for 24V supply.
Upping the bias from 10 to 13 will come with higher heat. At what point is it too much heat and time to turn it back down? I’d rather not burn the thing up, or reduce its life by running too hot.
I wired up a couple of 12V batteries (in series for 24V) to my ACA’s for fun. Does it sound better, I’m not sure, nothing super obvious, but haven’t given it a critical listen yet.
After an hour of playing the temp was ~125 degrees F, which isn’t too bad from my understanding. Reading through the thread, it seems most like a higher bias on these ACA’s, and a bias of 12.5-13 was recommended for 24V supply.
Upping the bias from 10 to 13 will come with higher heat. At what point is it too much heat and time to turn it back down? I’d rather not burn the thing up, or reduce its life by running too hot.
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I just built a JLH class A headphone amp as a preamp. It's about $20 in kit form and is quite a decent class A amp for sensitive speakers in its own right. Good for about 1.6w and very clean sounding. It has volume and gain needed to drive an ACA from an iPhone and such.
Here is mine - built in 3 hrs and I really like the sound. As a headphone amp it sounds amazing - clear details I did not hear before.
http://www.diyaudio.com/forums/headphone-systems/159202-jlh-headphone-amp-60.html
Greetings forum members. I have fairly good knowledge around building/fixing tube amps, and I've lurked for a while, here, so I finally took the plunge and bought the ACA amps from the DIYaudiostore. Assembly was pretty straight forward, and kudos for the excellent online guide!
I have an issue I need a little help with from the experts here. My apologies if this has been answered somewhere in this 262 page thread. I tried searching for a few keywords related to it, but didn't find anything.
I was planning on using these amps to replace a pair of Eico HF30s I was using with a Kenwood L-07c II preamp. However, when I connect these amps to the Kenwood, the sound is highly distorted and very weak. I connected an iFi Nano iDSD to them, running source from my JRiver media server, and they sound fine (actually incredible!).
My first thought was that this was an impedance mismatch problem. I note that the input impedance of the ACA is "suitably high," in some of the reading I've done. However, the output impedance of the Kenwood is listed as 10 ohms, and the iFi claims to have an output impedance of >1 ohm, so I don't believe that's the issue. While the ACAs sound great with the iFi, I need the Kenwood(or other solution) because I have a turntable with a moving coil cartridge on the tonearm, and also an FM tuner I want to use as sources. Any thoughts on why the amps and the Kenwood preamp don't play well together?
Any help is greatly appreciated!
I have an issue I need a little help with from the experts here. My apologies if this has been answered somewhere in this 262 page thread. I tried searching for a few keywords related to it, but didn't find anything.
I was planning on using these amps to replace a pair of Eico HF30s I was using with a Kenwood L-07c II preamp. However, when I connect these amps to the Kenwood, the sound is highly distorted and very weak. I connected an iFi Nano iDSD to them, running source from my JRiver media server, and they sound fine (actually incredible!).
My first thought was that this was an impedance mismatch problem. I note that the input impedance of the ACA is "suitably high," in some of the reading I've done. However, the output impedance of the Kenwood is listed as 10 ohms, and the iFi claims to have an output impedance of >1 ohm, so I don't believe that's the issue. While the ACAs sound great with the iFi, I need the Kenwood(or other solution) because I have a turntable with a moving coil cartridge on the tonearm, and also an FM tuner I want to use as sources. Any thoughts on why the amps and the Kenwood preamp don't play well together?
Any help is greatly appreciated!
Okay, I've had a chance to do some more experimenting to isolate the issue.
It will work fine with the Kenwood, with a tuner an with the turntable connected. The problem appears when I connect a digital source that is connected to my MacBookPro to the Kenwood preamp. To elaborate, I have the iFi, and also a Marantz SA8005 SACD/DAC. I can connect either of these to the Kenwood, and as long as I haven't connected the USB cable to them from the MBP, there is no problem. The moment I connect either DAC to the MBP by USB cable, the distorted and weak sound appears.
I'd think this was a problem with the Kenwood (and still may be), but I didn't have this problem when I was using the Eico tube amps in that configuration, instead.
More experimentation to follow.
It will work fine with the Kenwood, with a tuner an with the turntable connected. The problem appears when I connect a digital source that is connected to my MacBookPro to the Kenwood preamp. To elaborate, I have the iFi, and also a Marantz SA8005 SACD/DAC. I can connect either of these to the Kenwood, and as long as I haven't connected the USB cable to them from the MBP, there is no problem. The moment I connect either DAC to the MBP by USB cable, the distorted and weak sound appears.
I'd think this was a problem with the Kenwood (and still may be), but I didn't have this problem when I was using the Eico tube amps in that configuration, instead.
More experimentation to follow.
Ground loops, why does it always have to be ground loops?
I lifted the ground on the power to the computer, and the power to the ACAs, and voila, all is well.
This is a new experience for me - I've heard hum from ground loops before, but never distortion and weak power. Hopefully my travails will help someone else should they run into this sort of problem.
I want to comment on how pleased I am with these amps. I do plan on bumping power to 24VDC, per some of the discussion on this board, but the more I play them, the more I like them, and this is coming from a KT66/EL37 lover!
I lifted the ground on the power to the computer, and the power to the ACAs, and voila, all is well.
This is a new experience for me - I've heard hum from ground loops before, but never distortion and weak power. Hopefully my travails will help someone else should they run into this sort of problem.
I want to comment on how pleased I am with these amps. I do plan on bumping power to 24VDC, per some of the discussion on this board, but the more I play them, the more I like them, and this is coming from a KT66/EL37 lover!
Greetings fellow ACAphiles,
Sorry if this is too long a post but I wanted to get your input on some questions I have on my hopped up ACA build (build thread here:http://www.diyaudio.com/forums/pass-labs/283344-aca-concept-ii.html). For background, this is a stereo (for now - see below) fan-cooled ACA using IRFP150s for the output devices, running on 32 volts.
First an update on my progress: I got the board populated, connected it to a temp power supply, turned it on and... released the magic smoke. Specifically, the smoke came from the left channel output cap. A quick look at the board (why hadn't I done this earlier?) revealed a rather stupid mistake: the left channel output negative was grounded (only the output positive is supposed to be grounded on ACA)
.
Not knowing what other components I biffed, I decided to replace all of the input and output devices in the left channel as a precaution. The input devices are done; new output devices are on a slow boat from Taiwan and won't be getting here for a while.
Anyway, I started looking into transformers for the PSU. I built a simple unregulated CRC (4 X 3,300uf caps, 3 X 0.47R resistors), hooked it up to my Variac, and determined that 20 volts from the Variac will produce the desired 32 volts after rectification and filtering. This 20V, 200VA transformer from Antek seems to fit the bill, and is reasonably priced. Since it has two secondaries, I figured I would make the amp dual mono rather than stereo.
This means my PSU umbilical will have four wires for the amp (+ & -, X 2), plus two for the fans.
So here are my questions:
1) Is a ground wire between the amp chassis and the PSU chassis necessary or desirable?
2) Should the wire pairs in the umbilical be twisted?
3) There will be a separate 12V transformer in the PSU for the fans. Does this need to be filtered in any way or can I connect directly to the rectifier?
4) The Antek transformer has two primaries (see linked image). Do I just connect these to the IEC module in parallel? (the module includes IEC, switch, fuses, and EMI filter).
5) Anything else I'm missing?
Thanks...
Sorry if this is too long a post but I wanted to get your input on some questions I have on my hopped up ACA build (build thread here:http://www.diyaudio.com/forums/pass-labs/283344-aca-concept-ii.html). For background, this is a stereo (for now - see below) fan-cooled ACA using IRFP150s for the output devices, running on 32 volts.
First an update on my progress: I got the board populated, connected it to a temp power supply, turned it on and... released the magic smoke. Specifically, the smoke came from the left channel output cap. A quick look at the board (why hadn't I done this earlier?) revealed a rather stupid mistake: the left channel output negative was grounded (only the output positive is supposed to be grounded on ACA)
. Not knowing what other components I biffed, I decided to replace all of the input and output devices in the left channel as a precaution. The input devices are done; new output devices are on a slow boat from Taiwan and won't be getting here for a while.
Anyway, I started looking into transformers for the PSU. I built a simple unregulated CRC (4 X 3,300uf caps, 3 X 0.47R resistors), hooked it up to my Variac, and determined that 20 volts from the Variac will produce the desired 32 volts after rectification and filtering. This 20V, 200VA transformer from Antek seems to fit the bill, and is reasonably priced. Since it has two secondaries, I figured I would make the amp dual mono rather than stereo.
This means my PSU umbilical will have four wires for the amp (+ & -, X 2), plus two for the fans.
So here are my questions:
1) Is a ground wire between the amp chassis and the PSU chassis necessary or desirable?
2) Should the wire pairs in the umbilical be twisted?
3) There will be a separate 12V transformer in the PSU for the fans. Does this need to be filtered in any way or can I connect directly to the rectifier?
4) The Antek transformer has two primaries (see linked image). Do I just connect these to the IEC module in parallel? (the module includes IEC, switch, fuses, and EMI filter).
5) Anything else I'm missing?
Thanks...
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I will take a stab at this and the ones who know more can jump in if I'm wrong....
this is my 3rd year reading and playing....
1) Is a ground wire between the amp chassis and the PSU chassis necessary or desirable?
All chassis (metal boxes with electricity in them) should have safety earth, (not audio ground)
might not be critical for the amp at 32v but why not?
A good place for audio ground is a star ground at or near the smoothing caps, many examples in this forum.
but with two boxes you might want to put the star in the amp section and a nice large wire to the power supply.
4x3,300uf seems kinda low, check F5 PS example. (scaled down for lower amp draw)
or that was for testing and you are doing a larger for use?
2) Should the wire pairs in the umbilical be twisted?
some say no on DC, I like to, light twist for neatness.
3) There will be a separate 12V transformer in the PSU for the fans. Does this need to be filtered in any way or can I connect directly to the rectifier?
do not understand ..... transformers connect to rectifiers then to caps..
when using fans I find that some caps and bypass caps are needed for noise. (electrical noise)
4) The Antek transformer has two primaries (see linked image). Do I just connect these to the IEC module in parallel?
YES
5) Anything else I'm missing?
for me the Antek put out more voltage that the spec's say 1-2v on my power here at 117-120v
but yes 20v should be good
Nice project and good luck
what i played with today, its been a few years and thought I would try some of the mods.....
this is my 3rd year reading and playing....
1) Is a ground wire between the amp chassis and the PSU chassis necessary or desirable?
All chassis (metal boxes with electricity in them) should have safety earth, (not audio ground)
might not be critical for the amp at 32v but why not?
A good place for audio ground is a star ground at or near the smoothing caps, many examples in this forum.
but with two boxes you might want to put the star in the amp section and a nice large wire to the power supply.
4x3,300uf seems kinda low, check F5 PS example. (scaled down for lower amp draw)
or that was for testing and you are doing a larger for use?
2) Should the wire pairs in the umbilical be twisted?
some say no on DC, I like to, light twist for neatness.
3) There will be a separate 12V transformer in the PSU for the fans. Does this need to be filtered in any way or can I connect directly to the rectifier?
do not understand ..... transformers connect to rectifiers then to caps..
when using fans I find that some caps and bypass caps are needed for noise. (electrical noise)
4) The Antek transformer has two primaries (see linked image). Do I just connect these to the IEC module in parallel?
YES
5) Anything else I'm missing?
for me the Antek put out more voltage that the spec's say 1-2v on my power here at 117-120v
but yes 20v should be good
Nice project and good luck
what i played with today, its been a few years and thought I would try some of the mods.....
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You don't need much fan to cool this - I used a tiny (40mm) one and the temp of the heatsink was barely warm. A simple 7812 regulator fed by the main PSU DC is fine as long as it is <35v. Put 7812 on same heatsink to draw off the excess heat from dropping the voltage. This way a simple single 32v smps can be used and don't have to mess with transformers, rectifiers and cap banks.
Am trying out the R15 2.2k (used 2k)
and changed the feedback value, 200k now and will try some lower values, 150k, 100k
also want to bypass the output cap and see if I can hear or measure any difference.
I do see more gain when raising the voltage, with a square wave input I get 1/3 more at 24v
My 4 fans are perhaps a bit overkill... but they'll be running at a nice, lazy pace.
But where's the fun in that?
Besides, I've already cut the traces so I'm committed to
(dyslexic for dual mono)
based on Rudy's example I drew this up
single sided with one jumper wire
Using 120k feedback resistor
Added Wilma MKS2 4.7uf film bypass cap, helps mids and Highs sound better.
two rail caps - noticeable help with bass tightness
and 1uf film to snub fan noise.
Now I have to find a power brick that is not noisy,
two Dell ones 6A & 7.7A are 3 prong and terrible if amp is connected to a usb DAC
and lifting the ground is only partially helpful
A Compaq one is nice but under powered @3.16A, so runs hot and may not last long.
Hi all
Just finished my 4 channel ACA to power my active horns and I've got a couple of questions.
First there is a bit of a buzz from the speakers when they're first turned on, as my horns are going to be active i hope this buzz energy hasn't got to much power to damage my mid and tweeter drivers. Also a small pop on switch off. Concern?
Secondly was the heat sink temp, after about 1/2 hr on idle the heat sink temp got to a bit over 50 deg C. Is this too hot?
Other than these questions this would have been the easiest aml project I've ever done, no power supply makes it easy!
Just finished my 4 channel ACA to power my active horns and I've got a couple of questions.
First there is a bit of a buzz from the speakers when they're first turned on, as my horns are going to be active i hope this buzz energy hasn't got to much power to damage my mid and tweeter drivers. Also a small pop on switch off. Concern?
Secondly was the heat sink temp, after about 1/2 hr on idle the heat sink temp got to a bit over 50 deg C. Is this too hot?
Other than these questions this would have been the easiest aml project I've ever done, no power supply makes it easy!
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noise at turn on normal, use delay if needed. Ebay or make one. or just manual switch.
Pop at off, normal can try adding a cap to the power rail, 10,000uf or so, may cause SMPS to be mad.
orientation of sink not optimal, (up). might be OK looks close to too hot. sinks look small for 4 channel.
all discussed in this thread, have you tried to search?
May find better answers...
Looks nice!
Enjoy
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