This is my first amp build and i have many grey areas ..
please advise regarding my queries with respect to excess heat and low volume as below ..
- my heatsink r of size 190mm *95mm *33mm.. is it ok .. while running it's getting very very hot .. i haven't done any mod and these r running on 19v 90w power supply.. do I need to use bigger heatsink or small fan or another additional heatsink and fix it over these 2 heatsinks ..
- volume out of the alpair 7p speakers r coming little less only .. current volume is ok for very near field ..
thanks and regards
S Sarath
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Currently i am running them from my android mobile headphone connector and volume is ok for very near field..
if we need a preamp with gain, how much gain do we need in preamp for fully driving the ACA amp.
regarding heat, after running for some 15-20 minutes i am not able to touch the heat sinks more than 1-2 sec.. Is there any thing else to check/measure (current /voltage) in the circuit to confirm every thing is normal, apart from the 10v voltage between the main gain MOSFET drain and ground?
I found an old thread where Pros. and Cons. regarding bridging of amps are listed. The "source" seem to be a Rocket Scientist called "Nelson"......but I don't know if it is "this" Nelson...….but good arguments anyway…...so people who is thinking about bridging the ACAs can have a look and decide afterwards:
http://www.diyaudio.com/forums/solid-state/148709-bridged-vs-conventional-amps-3-print.html
http://www.diyaudio.com/forums/solid-state/148709-bridged-vs-conventional-amps-3-print.html
ACA Project: square waves & power output after R15 mod
After R15 mod, I investigated square wave performance at 1KHz & 10KHz (1W power output). These waveforms did not change significantly with R15 mod.
Power Output at onset of clipping after R15 mod increased from 3.5W to 5W. That seems to follow published power output graphs by Pass Labs for the ACA circuit.
Next test will be bandwidth sweeps to determine -3dB low/high frequency performance.
dt 667
After R15 mod, I investigated square wave performance at 1KHz & 10KHz (1W power output). These waveforms did not change significantly with R15 mod.
Power Output at onset of clipping after R15 mod increased from 3.5W to 5W. That seems to follow published power output graphs by Pass Labs for the ACA circuit.
Next test will be bandwidth sweeps to determine -3dB low/high frequency performance.
dt 667
Attachments
My approach was to just try it. I loved it so both of mine stayed bridged. Might try that approach and you may or may not like what you hear! Easily fixed if not.
Yes, it is easy to try it and go back again to SE mode. But I remember that bridging amps was something we did when having party to be able to play loud and avoid clipping and burn the tweeters. The purpose was not better "quality". I was just thinking if bridging is needed if ACA was the right amp to build. It seems most go for the ACA with the purpose of bridging from beginning……..and that to me seems a little strange. Maybe because it is an easy build. But maybe some think it is for "quality" also. If it is to get balanced input as main putpose other solutions exist with a "native" balanced input circuit. But again it is a good education amp to try different things
Newbie questions: preamp needed?
Sorry if this is a repeat- searching on this thread didn't turn up what I'm looking for, which is total newbie advice.
1. I have a pair of Overnight Sensations I built. I think they're prob. something like 87dB SPL. We have them on top of our kitchen cabinets to listen in our open plan kitchen, which isn't huge (we live in the SF Bay Area where houses are like jewelry). So it's not near field, but we're also not rocking out. More for background music.
2. Current amp is some cheapy chip thing (Dayton DTA-1, "15 WPC").
3. My source is an Apple Express Modem- the poor man's Sonos. We pipe in iTunes from our iMac or more likely stream stuff off our phones (via Wifi).
Questions:
1. Do we need a pre-amp for this? What do people do about volume control?
2. Have people powered middling sensitive speakers with this?
Thanks so much-
Sorry if this is a repeat- searching on this thread didn't turn up what I'm looking for, which is total newbie advice.
1. I have a pair of Overnight Sensations I built. I think they're prob. something like 87dB SPL. We have them on top of our kitchen cabinets to listen in our open plan kitchen, which isn't huge (we live in the SF Bay Area where houses are like jewelry). So it's not near field, but we're also not rocking out. More for background music.
2. Current amp is some cheapy chip thing (Dayton DTA-1, "15 WPC").
3. My source is an Apple Express Modem- the poor man's Sonos. We pipe in iTunes from our iMac or more likely stream stuff off our phones (via Wifi).
Questions:
1. Do we need a pre-amp for this? What do people do about volume control?
2. Have people powered middling sensitive speakers with this?
Thanks so much-
My motive was not to be louder or more powerful. Exploring active crossovers, purchased one that only had balanced I/0. The DAC that drives said crossover is also balanced. The (2) ACA's drive Heil AMT's and are odd birds in that they are as close to a resistor as I have ever seen a load be without being a resistor. There is no measurable (by my equipment, anyway) reactance and that is true from around 650 cycles out to way beyond what we humans could ever hear. While I don't have any numbers to back my observations up. We hear exceptional clarity using the ACA's in this way. Not to say we did not hear it using them with the passive crossovers. Using it however in the differential mode made it in our case that much better. Even if measured numbers would disprove it - we like it!
Yes, it is easy to try it and go back again to SE mode. But I remember that bridging amps was something we did when having party to be able to play loud and avoid clipping and burn the tweeters. The purpose was not better "quality". I was just thinking if bridging is needed if ACA was the right amp to build. It seems most go for the ACA with the purpose of bridging from beginning……..and that to me seems a little strange. Maybe because it is an easy build. But maybe some think it is for "quality" also. If it is to get balanced input as main putpose other solutions exist with a "native" balanced input circuit. But again it is a good education amp to try different things
The ear should always be the winner
My purpose building the ACA was another.......I wanted to compare low power SE tube amp with SS SE amps. Before I looked into the Pass forum I did not know they existed. It is a bit of a speciality........I wonder how many HiFi shops selling Solid State Single Ended amps.......
The ear should always be the winner
My purpose building the ACA was another.......I wanted to compare low power SE tube amp with SS SE amps. Before I looked into the Pass forum I did not know they existed. It is a bit of a speciality........I wonder how many HiFi shops selling Solid State Single Ended amps.......
An interesting goal...in my DIY floundering so far it has been difficult to find an “apples to apples” comparison in audio amplification.
My romantic ideas from when I was too young and poor to own any tube equipment had me struggling to hear and see that beautiful glow that I must have been missing, only to discover the dilemma of matching equipment properly.
My KEF 104.2 speakers just weren’t efficient enough to be driven by the pair of 25W Quicksilver Horn Monos I managed to come up with. I did have a brief period of bliss using the KEFs with a Counterpoint SA12 hybrid...until one of the channels went up in smoke.
It took me a while to put together a set of horns (Oris 200) to try with the Quicksilver amps. When I did, I still came up short because the Tang Band W8-1808 I put in them still sounded dull and muted to my ears. I thought their 93dB sensitivity in the horns would work out fine...turns out their manufacturer rating is a bit “ambitious”.
In response to that failure I built a LM3875 chip amp and found that they melded pretty well with the TBs in the horns. I got some really nice midrange for lovely vocals. The top end gave me some harshness, but it wasn’t unbearable most of the time. There was a definite hole in the bass response. I only had a subwoofer to supplement the bottom end and had tried fudging things by setting its crossover point as high as possible and allowing the TBs to just roll off.
Now I have built the ACAs. They are an earlier mono block unbalanced version with the R12 and R15 changes in place using Semisouth R100 in the Q1 position and the Meanwell 24V SMPS supply.
My first observation was that the ACAs had an enormous increase in bass response over what the LM3875 was able to provide. In fact, I had to lower the cross over point of my subwoofer and reduce its output quite a bit in order for the system to be tolerable to listen to.
After listening to the ACAs for a couple of months now I have found that I am able to enjoy them on the TB/Oris combination with quite Jazz especially with female vocals that I like to listen to. Unfortunately, as soon as I put on anything that requires some “stones” like R&B etc I find myself trying to turn the system up as a means of attaining the response I want.
It seems my system is still mismatched. I am pushing toward trying more efficient drivers and resolving a better low frequency system.
There is no doubt that efficient speakers with "nice" impedance opens up for a lot of possibilities using low power amps. Efficient speakers means large magnets and cone area. My experience is that such speakers are a lot more dynamic than "hard to drive" speakers. A must to reach real high-end sound which can simulate live music experience. Speakers are the first place to start. I am also surprised by the bass response of the ACA. My version was able to give usable response down to 3 Hz. At 2 Hz the output signal was "gone". They are great for live music. Pipe organs also.
My next build is the MoFo…...it is a bit more powerful….....but don't know if it can be called a powerful amp in absolute terms......probably not......but relative to the ACA it probably is. Then I can compare.......
Even with ACA my OB speakers can get everything in the room to rattle.....I also have my 180 Watt Nad M3 but the sound is "hard" and not as dynamic as my low power SE amps.........strange!!
Even with ACA my OB speakers can get everything in the room to rattle.....I also have my 180 Watt Nad M3 but the sound is "hard" and not as dynamic as my low power SE amps.........strange!!