Good point Extreme_Boky. If not done right, a capacitance multiplier or any other in-between component is gonna make things worse, not better.
Thanks for reminding us.
... duly noted ... I'm intent on gaining advantage from the experience of others, while sticking with a plain vanilla, standard build - especially for my first go. When I've got sufficient confidence, then I'll think about kicking the trainer wheels off.
Thanks for helpful advice.
From the ACA store page, an excerpt from the spec section reads:
Input Impedance 10 k Ohm
I've seen various rules of thumb in terms of ratios around pre-amp impedance matching but your advice doesn't include any of that quantitative detail. I'm missing the subtlety of the message I suspect...
I like to see 50K input impedance amplifier, driven by a maximum of 500ohms output impedance pre-amp. This gives a linear drive at full audio band frequency spectrum and also removes the constraints that could be imposed by highish interconnects' capacitance. So, the ratio is 100:1.
With ACA, and the same logic, you'd expect a pre-amp to have 10ohm output impedance...
With two ACA's connected in parallel, the pre-amp would need to have a 5ohm output impedance.
Let's not forget that the ACA is designed to show the virtues of the 2-gain stage, deep class A design while providing a FULL kit and a very reasonable cost. It also comes from the audio legend who pioneered class A designs. So, to expect an amp with 50K input impedance, with only 2 transistors; a second one being driven off the 1K resistor, is really unfair.
All I wanted to do was to warn you guys that ACA has its expected limitations, and as long as you are aware of them... it's all good. But, paralleling ACA's is not a good idea simply from the input impedance point of view.
The logical next step would be Alep J. That is the whole idea, to move forward and build an amp with a good input stage, correct drive for up to 2 MOSFET's, very good current source while staying simple and providing single ended pure class A goodness.
With ACA, and the same logic, you'd expect a pre-amp to have 10ohm output impedance...
With two ACA's connected in parallel, the pre-amp would need to have a 5ohm output impedance.
Let's not forget that the ACA is designed to show the virtues of the 2-gain stage, deep class A design while providing a FULL kit and a very reasonable cost. It also comes from the audio legend who pioneered class A designs. So, to expect an amp with 50K input impedance, with only 2 transistors; a second one being driven off the 1K resistor, is really unfair.
All I wanted to do was to warn you guys that ACA has its expected limitations, and as long as you are aware of them... it's all good. But, paralleling ACA's is not a good idea simply from the input impedance point of view.
The logical next step would be Alep J. That is the whole idea, to move forward and build an amp with a good input stage, correct drive for up to 2 MOSFET's, very good current source while staying simple and providing single ended pure class A goodness.
Great post Extreme_Boky. Thanks for putting the ACA scenario into perspective.
I totally agree with you. And to use a bad analogy: If I have a 1300cc budget car, there is only so much I can do to improve performance. It would be best to get a car with a bigger engine.
This is not meant as a put-down for my beloved ACA, but I have already purchased M2 boards.
I totally agree with you. And to use a bad analogy: If I have a 1300cc budget car, there is only so much I can do to improve performance. It would be best to get a car with a bigger engine.
This is not meant as a put-down for my beloved ACA, but I have already purchased M2 boards.
Ok, wait... I know very little (or nothing) about audio design, but simple math I do very well!
10Kohm at 100:1 ratio is 100 Ohms, which is, conveniently, the output impedance of a lot of PREs out there.The parallel would require 50 Ohms as per your ratios, not 10 and 5!
Best regards,
Rafa.
Just had a revelation regarding the need for a preamp with gain (for use with the ACA).
As source for the ACA, I've been using a PC + DAC + B1 buffer and 97dB speakers. The volume is quite satisfactory for 95% of my music, but then my 53% Karlsonators with dual FE25-16's are on the sensitive side of the scale.
Just now, I connected my new phone with FLAC playing capability. With all controls turned to the max, the volume is only good for near field listening. So, I understand now why some guys complain about a lack of volume. The ACA needs a bit of gain with efficient speakers, and a lot of gain with inefficient speakers.
In contrast, I recently connected an AKSA Lender Preamp with 15dB gain to the ACA and the amount of volume blew me away. I had to turn the pots on the Lender preamp right down. It goes to show that the ACA really needs a preamp with gain; exactly how much will depend on the sensitivity of your speakers.
Hint: If you have a problem with low volume on the ACA, there is a neat trick mentioned in post #5151 to increase volume past 100% using certain media players, i.e. Foobar and VLC Player.
I'm posting this for the benefit of others who, like me a year ago, isn't sure what preamp to use with the ACA. When I asked which preamp would be best for the ACA, the B1 was suggested by many - and I now realize that it wasn't the best advice for me. YMMV as they say, but maybe this post helps someone.
PS. I don't regret building the B1. I can always use it with other amps.
As source for the ACA, I've been using a PC + DAC + B1 buffer and 97dB speakers. The volume is quite satisfactory for 95% of my music, but then my 53% Karlsonators with dual FE25-16's are on the sensitive side of the scale.
Just now, I connected my new phone with FLAC playing capability. With all controls turned to the max, the volume is only good for near field listening. So, I understand now why some guys complain about a lack of volume. The ACA needs a bit of gain with efficient speakers, and a lot of gain with inefficient speakers.
In contrast, I recently connected an AKSA Lender Preamp with 15dB gain to the ACA and the amount of volume blew me away. I had to turn the pots on the Lender preamp right down. It goes to show that the ACA really needs a preamp with gain; exactly how much will depend on the sensitivity of your speakers.
Hint: If you have a problem with low volume on the ACA, there is a neat trick mentioned in post #5151 to increase volume past 100% using certain media players, i.e. Foobar and VLC Player.
I'm posting this for the benefit of others who, like me a year ago, isn't sure what preamp to use with the ACA. When I asked which preamp would be best for the ACA, the B1 was suggested by many - and I now realize that it wasn't the best advice for me. YMMV as they say, but maybe this post helps someone.
PS. I don't regret building the B1. I can always use it with other amps.
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Yes, I reported the same findings a few pages ago. With a DAC / PRE with little gain and the 'standard' line output of 2V, I get average volume and decent sound. With a PRE that can output 4V into the line (albeit I don't have access to its gain value per-se) the volume is enough even for 4 Ohm speakers in a living room, and the sound is full of body, detail and bass.
I said the same: make sure you pair the ACA with a nice PRE (with some gain) and you will be surprised!
Rafa.
I said the same: make sure you pair the ACA with a nice PRE (with some gain) and you will be surprised!
Rafa.
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I have to say that the B1 is a great preamp/buffer. The sound is exceptional, and as others have mentioned, transparent. With the right DAC (with gain) and efficient speakers, the B1 can be a good match for the ACA.
Not to worry, Rafa. That's how I understood it too. I'm sure you didn't mean any offense, and none taken.
I just felt the need to mention that the B1 is a VERY good preamp/buffer. I have been enjoying mine for a year now. But with the music player on my phone, it is not sufficient.
For those who like building kits, and are using your ACA as a stereo amp, I can recommend the Transcendent Sound Masterpiece preamp with an upgraded volume control. It is more difficult to build than the ACA kits, as it is all point to point wiring using terminal strips, but it does sound great. No balanced outputs though.
while I have all the sympathy for all things overkill and exaggerated ......... be aware that ACA and mentioned preamp are on two opposite sides of bulllllshitttting , not even mentioning difference in numbers of solder points for desired result
upgraded volume control ....... volume control is chapter all by itself , and usual "upgraded" criteria is ......... sometimes cheapest Piher pot is working better than superduper megadollar thingie , made of holco and whatnot , mounted on most expensive Elna switch
to cut with rant ........ for ACA , as preamp , best to look at something more in ACA's spirit ......
and no - I'm not thinking about preamps from my cousine , they also not belong in ACA idea
upgraded volume control ....... volume control is chapter all by itself , and usual "upgraded" criteria is ......... sometimes cheapest Piher pot is working better than superduper megadollar thingie , made of holco and whatnot , mounted on most expensive Elna switch
to cut with rant ........ for ACA , as preamp , best to look at something more in ACA's spirit ......
and no - I'm not thinking about preamps from my cousine , they also not belong in ACA idea
Zen Mod - at a recent event another of Nelson’s designs that requires a hearty front end -i.e. F4- was apparently quite nicely served by an Aikido . Too many things going on that day for me to hear every rig, but by all accounts it was very well received by those who did. As for 300B pre-amps, I’ve never heard one, but if so inclined, I guess at approx half the price of Doc and PJ’s BeePre, Bruce’s could be considered a bargain?
I'm not writing about price .......
anyway , no one stopping you from your heart's desires , nor I intend to .....
however , Aikido driving gain-less OS is much more logical thing than luscious and luxurious tube preamp driving ACA
if you take ACA as VW Beetle , and it is in every possible positive way of observation , it doesn't belong in company of Jaguar E-type ......... maybe more fun , maybe some of performances on same level,while other ones in favor of E ........ but Beetle is gonna bring you several spins around globe more than E type
anyway , no one stopping you from your heart's desires , nor I intend to .....
however , Aikido driving gain-less OS is much more logical thing than luscious and luxurious tube preamp driving ACA
if you take ACA as VW Beetle , and it is in every possible positive way of observation , it doesn't belong in company of Jaguar E-type ......... maybe more fun , maybe some of performances on same level,while other ones in favor of E ........ but Beetle is gonna bring you several spins around globe more than E type
Oh, I think we agree. I’ve own/built more than a few tube pre-amps since getting back into this DIY thing, and - here’s the flame bait- as nice as some of them where, there’s nothing inherently majik about the type or price of any component itself. It’s all about circuit and implementation.
Ok, wait... I know very little (or nothing) about audio design, but simple math I do very well!
The parallel would require 50 Ohms as per your ratios, not 10 and 5!
Best regards,
Rafa.
It did seem a bit low to me as well...
I was referring to the cheap VC upgrade that is offered as an add-on. It doesn't sound different, but tracks better between channels at low volumes.
Here is why I like the Transcendent kit:
- is extremely quiet and sounds very good.
- has gain.
- is not too expensive (relatively speaking), and is accessible to people like me who do not have much understanding of circuit design.
- doesn't poop out into low impedance amplifiers like some of the other gear I've tried.
I am generally interested in trying new projects, especially during the long winters where I live. I've built the B1 buffer, which sounds nice but does not have gain and thus is not a good match for the ACA and my speakers. Do you have recommendations that are more in line with ACA spirit that can be built reasonably easily by people like me (who don't have much electronic design understanding)? I would be particularly interested in a balanced design that would play well with the balanced bridged ACA.
Thanks