Et tu, Brute,OCD?
first - there is no DC Offset to speak of, DC Offset usually meaning exactly the same on output of an amp
ACA having cap on output, there is no DC Offset
what you (most likely) was speaking of is - DC voltage level of inner side of output node, practically -pre-cap, or inner side of output cap
and yes, that's important for symmetrical clipping
set it either in your way - eye-balling on scope, or set by Papa's prescription
do not bother with few mV of difference between channels, you can't hear that ..........
first - there is no DC Offset to speak of, DC Offset usually meaning exactly the same on output of an amp
ACA having cap on output, there is no DC Offset
what you (most likely) was speaking of is - DC voltage level of inner side of output node, practically -pre-cap, or inner side of output cap
and yes, that's important for symmetrical clipping
set it either in your way - eye-balling on scope, or set by Papa's prescription
do not bother with few mV of difference between channels, you can't hear that ..........
thanks for clarifying DC side of the design ZM.
I know the manual says to set at 12vDC (24v rail) but I dont believe I've read or come across Papa's description of how to set this, could you point me please?
Also is it safe to "Y" feed the ACA from the one generator for simultaneously testing channels so I can scope math the difference?
I understand a few MV may not be sonically noticeable with the human ear however what I have noticed is the soundstage appears to favour the side with greater mV.
I tested this with a few different CD's, it was consistent. So I then reset the DC on each channel to 12v (forgetting symmetrical clipping) and it appeared to eliminate the soundstage favouring one side.
I settled on ~0.6% clipping... it has good depth the ACA! Now I just want to (left-right) balance that depth. I think here is where a few mV will make a difference
I know the manual says to set at 12vDC (24v rail) but I dont believe I've read or come across Papa's description of how to set this, could you point me please?
Also is it safe to "Y" feed the ACA from the one generator for simultaneously testing channels so I can scope math the difference?
I understand a few MV may not be sonically noticeable with the human ear however what I have noticed is the soundstage appears to favour the side with greater mV.
I tested this with a few different CD's, it was consistent. So I then reset the DC on each channel to 12v (forgetting symmetrical clipping) and it appeared to eliminate the soundstage favouring one side.
I settled on ~0.6% clipping... it has good depth the ACA! Now I just want to (left-right) balance that depth. I think here is where a few mV will make a difference
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Hi, my ACA has been working like a charm, putting a LOT of hours on it (it drives my computer speakers...I use my computer a lot, shocking!). I said it before, there is Z E R O background hiss, NONE, and using for near-field on sensitive speakers (with no crossover to absorb that little bit of background noise), I cannot see changing this out.
The turn-on 'whale call' doesn't bother me at all, I actually think it is cute and gives the amp personality.
On the turn-off thump, it doesn't bother me, but using the amp on some 4" full-range driver speakers. While it certainly isn't bottoming them out, it is amazing how much the cones move. Assume this is no problem?
The turn-on 'whale call' doesn't bother me at all, I actually think it is cute and gives the amp personality.
On the turn-off thump, it doesn't bother me, but using the amp on some 4" full-range driver speakers. While it certainly isn't bottoming them out, it is amazing how much the cones move. Assume this is no problem?
@ Allan
somewhat contradictory, what you're writing
setting potential of output node is trivial thing, one probe on + of output cap, second probe to GND
you need to decide which way to follow- Papa's basic (gave you safe and fast procedure), or you want to bring it to higher level, involving scope and shooting for symmetrical clipping
or THD Spectra mesuring setup, then bring it to your most liked figure
only THD Spectra measurements can give you full measure of importance of few mV up or down
do not trust your ears, when so minuscule changes are in question
somewhat contradictory, what you're writing
setting potential of output node is trivial thing, one probe on + of output cap, second probe to GND
you need to decide which way to follow- Papa's basic (gave you safe and fast procedure), or you want to bring it to higher level, involving scope and shooting for symmetrical clipping
or THD Spectra mesuring setup, then bring it to your most liked figure
only THD Spectra measurements can give you full measure of importance of few mV up or down
do not trust your ears, when so minuscule changes are in question
@ ZM
This is how I setup my ACA:
set each MOSFET drain to 12vDC (24vDC rail) as suggested in the manual.
Hook up scope and gen, null clipping using triangular wave (easier to see than sine), take note of MOSFET drain voltage's
Deduct ~0.6% from each MOSFET drain voltage and reset the drain's to their calculated result.
Tested harmonics - looked good. Sound test - YummY! Very, very good stage depth now, but images in the rear appear to favour one side just a tad - I want to fix this but only have scope and gen
Can I safely "Y" feed the ACA (left & right) from my generator?
I'm thinking if I can "Y" feed the amp, then I'll scope math (A-B) and then (if required) null the result which would indicate balance and hopefully centre the stage ?!?
Yes... I want higher level. Why eat prawns when there's crayfish to be had
This is how I setup my ACA:
set each MOSFET drain to 12vDC (24vDC rail) as suggested in the manual.
Hook up scope and gen, null clipping using triangular wave (easier to see than sine), take note of MOSFET drain voltage's
Deduct ~0.6% from each MOSFET drain voltage and reset the drain's to their calculated result.
Tested harmonics - looked good. Sound test - YummY! Very, very good stage depth now, but images in the rear appear to favour one side just a tad - I want to fix this but only have scope and gen
Can I safely "Y" feed the ACA (left & right) from my generator?
I'm thinking if I can "Y" feed the amp, then I'll scope math (A-B) and then (if required) null the result which would indicate balance and hopefully centre the stage ?!?
Yes... I want higher level. Why eat prawns when there's crayfish to be had
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I believe you ! See the graphs I uploaded in post 576 of this thread. That was almost 9 years ago with the very first version of the ACA. When I first built the ACA and measured the THD, I just adjusted the pot with an oscilloscope for symmetrical clipping. I wasn't getting graphs consistent with what Nelson was getting, until I started adjusting the pot for DC Voltage at the Drain of Q1. The THD graphs started matching very close.
We’re working on getting you another bag.
Should be shipped tomorrow!
We have never combined 2 kits worth of parts in one bag. Too confusing for our simple minds..
Should be shipped tomorrow!
We have never combined 2 kits worth of parts in one bag. Too confusing for our simple minds..
ZM, LoudThud
well yesterday I ran the ACA on the scope, couldn't see anything abnormal or an imbalance unless I went to frequency extremes, so I decided to adjust the right side MOSFET drain voltage down to what the left channel is set at being 11.88v. Ran some CDs and it made no difference, however in the process I noticed I had filtering engaged on the DAC, I turned this off and BINGO.. my stage was centralised properly across the channels. Bloody thing, I need a new DAC
So all good.. this little ACA thingy sounds lovely with -0.6% drain voltage. Good instrument spacing, good stage depth and quite airy, its actually surprisingly dynamic too, brass instruments are right on the money! So thats it, I'm all finished with the ACA now.. it will eventually live in my shed once I build my F5... I've now all parts bar the heat sinks. Still undecided though, I may still go with mono blocks
I can see a lot of questions coming up during Friday night drinks in mi shed with the ACA knockin out tunes
well yesterday I ran the ACA on the scope, couldn't see anything abnormal or an imbalance unless I went to frequency extremes, so I decided to adjust the right side MOSFET drain voltage down to what the left channel is set at being 11.88v. Ran some CDs and it made no difference, however in the process I noticed I had filtering engaged on the DAC, I turned this off and BINGO.. my stage was centralised properly across the channels. Bloody thing, I need a new DAC
So all good.. this little ACA thingy sounds lovely with -0.6% drain voltage. Good instrument spacing, good stage depth and quite airy, its actually surprisingly dynamic too, brass instruments are right on the money! So thats it, I'm all finished with the ACA now.. it will eventually live in my shed once I build my F5... I've now all parts bar the heat sinks. Still undecided though, I may still go with mono blocks
I can see a lot of questions coming up during Friday night drinks in mi shed with the ACA knockin out tunes
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Keeping my fingers very crossed that the Naim Uniti Atom Headphone Amp/Streamer/DAC/Pre-Amp will be a big hit driving ACA monoblocks via XLR cables. Been using Apple TV and Cambridge DAC magic with Nutube pre-amp. Everything apart from the pre-amp should be a step up. No way of knowing if Nutube pre-amp has been doing a better job than the pre-amp built into the Naim will do especially since the name has XLR built in. Parcel tracking received - should be a musical weekend.
Looks like it has unbalanced outputs as well. Between the two, we like ACA mono blocks using paralleled output. While using the unbalanced inputs over the XLR input.
Point to this otherwise meaningless blathering is try it in every configuration you can. To get those XLR outputs requires a minimum of three more components. One being phase inversion and then two additional chips to act as line drivers. (In the source, not the ACA)
And it cancels all of those nifty harmonics. If the balanced setup sounds kind of dry and lifeless - it is just the nature of balanced audio feeds. In the broadcast industry which uses balanced audio pretty exclusively, there are companies that have made lots of money making boxes to re-create the harmonic energy lost in the balanced audio process.
Something to chew on while you wait! Cool you can change a cord and see which one floats your boat. Look forward to seeing which one you choose but encourage you to try both.
Point to this otherwise meaningless blathering is try it in every configuration you can. To get those XLR outputs requires a minimum of three more components. One being phase inversion and then two additional chips to act as line drivers. (In the source, not the ACA)
And it cancels all of those nifty harmonics. If the balanced setup sounds kind of dry and lifeless - it is just the nature of balanced audio feeds. In the broadcast industry which uses balanced audio pretty exclusively, there are companies that have made lots of money making boxes to re-create the harmonic energy lost in the balanced audio process.
Something to chew on while you wait! Cool you can change a cord and see which one floats your boat. Look forward to seeing which one you choose but encourage you to try both.
Thank you for your words of wisdom, I'm just starting this hobby. I should probably do a bit more studying so I can understand more about what I'm putting together, like the ACA I just finished. Maybe my next build will be the ACA with integrated power supply!