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Old 30th September 2018, 10:09 AM   #6151
damkel is offline damkel  Denmark
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Quote:
Originally Posted by Alan4411 View Post
damkel

Here is a way to test your ACA is amplifying correctly. I just tried it on mine and this is what I did.

Used my mobile phone and went to this site for the 1 kilo Hertz test tone, it is a bit louder than some. YouTube

I turned my phone's volume to maximum and measured the AC voltage at the head phone socket playing the tone. Mine is 0.43 volts AC. Yours might be more or less, just note what it is.

Then I plugged the phone into my ACA and measured the output at the speaker terminals. (No speakers connected.) I get 1.622 volts AC.
If I connect my speaker (8 ohms) and measure I get 1.57 volts AC.
Again yours might be different just note it.

So on my amplifier for an input of 0.43v ac I get 1.57v ac out.
3.6 times amplification and you should get something similar if all is well.

Hope that helps.
Hi Alan

First thank you for trying to help me.
I am sorry I have not replied before now but I went down with stress and Star Trek was about all I could manage.

I am a bit better now so I have tried measure the voltages as shown.
The output from the phone fluctuates a bit but on average 0.37v.
Out ACA without speakers 1.4v.
Out ACA with speaker 1.17v.
This gives an amplification of 3.2 and not that far from your 3.6 and probably well within measurement uncertainty.

So I guess the conclusion is that my ACA is OK which is good news.

I connect the ACA to my desk speakers and used my phone as input. Really low output. Then I used the output on my pc (not laptop) and that changed everything. Suddenly I got a sound level that was usable.

So... how do I know if a preamp is usable?
How much gain is required?
None of my present gear works and I before buying (or building) a preamp I would like to be sure I am doing the right thing.

A nice sunday to all you ACA'ers :-)
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Old 30th September 2018, 11:28 AM   #6152
semmyroundel is offline semmyroundel  United Kingdom
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Originally Posted by Sledge93 View Post
I built v1.6 a week ago. What a sweet little amp. Great detail and the bass is amazing. I don't blast music any more and I can't believe this drives my MMGs to a satisfying level. I've had a rash of amps pass through this system and this rivals the best I've had (Audio Research CA50 and Pass Aleph 5 come to mind). I'm thinking of buying another and running them in parallel mono mode.
Hi, does this mean that you can effectively get a 8w+8w amplifier ?
I had this idea of buying two parts kits and installing them side by side in the same chassis, each being driven by one RCA, naturally they wouldn't be balanced, but at least I'd get double the power.
Or am I missing something?
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Old 30th September 2018, 11:32 AM   #6153
MEPER is offline MEPER  Denmark
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If you need more power than 8W into 8 ohm why not consider some of the more powerful alternatives? …...there is a bit more work to do but then you get an amp that was designed for its purpose...…..
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Old 30th September 2018, 11:37 AM   #6154
semmyroundel is offline semmyroundel  United Kingdom
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Originally Posted by oc11 View Post
Semmyroundel, there are any number of preamps, including those labeled "headphone amps" that can serve your purposes very well and give you 6 dB gain. You have to do your due diligence and check the net to find them. Let me suggest that you check two offerings of Schiit audio, I am not connected with them, just like their name and their prices:

1. Jotunheim, a DAC /headphone amp (can be had without the DAC) with balanced outputs. Swith selectable gain as follows, high gain of 14dB, low gain of 6dB. The low gain is more defined and precise.

2. Asgard 2 headphone amp with preamp outputs switch selectable as follows: high gain 15.6dB, low gain 3.5dB.

Both of these can be had with UK specific plugs and voltages. I imagine there is any number of other similar products out there, you just have to find them.
Hi, thanks for that reply-taken in the helpful vein that it was intended.
But, and it's a big but, this is a DIYaudio forum is it not? Why would I want to buy $280-$400 worth of pre amp?
I was hoping to find a way of doubling the power in stereo, that would be sufficient for me.
As I've said, I'm hoping that the bare bones 8wpc will suffice once built, as I'm hard pressed to follow an electronics wiring diagram, even the tripath amp that i built (and it works fine except on tuner) I built by sight and layout. Once parallel paths had been created on the circuit board, I was no longer able to test the resistors on the board, only prior to soldering.
Such is my limited ability.
Anyway, I still appreciate the reply, it's all good.
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Old 30th September 2018, 11:59 AM   #6155
MEPER is offline MEPER  Denmark
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You will probably be surprised what 5-8 Watts can do......I was…..and I don't need more power. But just of interest I have started building the MoFo and also got the M2X PCBs so I have something to "play" with in the future...….
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Old 30th September 2018, 12:05 PM   #6156
semmyroundel is offline semmyroundel  United Kingdom
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Originally Posted by MEPER View Post
You will probably be surprised what 5-8 Watts can do......I was…..and I don't need more power. But just of interest I have started building the MoFo and also got the M2X PCBs so I have something to "play" with in the future...….
Thanks and yes, it seems clear that I'll have to try it without doubling up, as Nelson said: "the first watt is the most important" I shouldn't lose sight of that I guess.
BTW, for those in Europe, that 2u chassis is only €84 from modu shop plus 15 for delivery.
Granted, you have to tap the threads, but that's part of the fun of DIY
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Old 30th September 2018, 12:07 PM   #6157
semmyroundel is offline semmyroundel  United Kingdom
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Also, I wanted a wooden case, but still ordered the chassis. What I'll do is veneer the outer so that it looks like wood, but still has a metal chassis underneath.
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Old 30th September 2018, 12:33 PM   #6158
astromo is offline astromo  Australia
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Quote:
Originally Posted by MEPER View Post
If you need more power than 8W into 8 ohm why not consider some of the more powerful alternatives? …...there is a bit more work to do but then you get an amp that was designed for its purpose...…..

I agree with this. If the ACA doesn't have enough grunt for your tastes, there are plenty of Pass Class A options to choose from.


My personal philosophy was to use the ACA to dip my toe in the water and establish my sense of capability. Then, of course, I've been bitten. So, the next step that I'm planning is an Aleph J. From the sounds of what you're after, the Pass amps on offer that can deliver in the 25 W pc range would probably fit your bill.



My thinking is that my learner ACA monoblocks will head down to my studio and drive some bookshelfs and get low down drive separately from a sub. The Aleph J will ultimately be the main unit in my living room where there's more space to fill.


That said I could happily live with the ACAs where they are (those 15 W monos drive wonderfully well) but, meh, why do that? Why stop at just 1 build?
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Old 30th September 2018, 01:07 PM   #6159
Alan4411 is offline Alan4411  Wales
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Quote:
Originally Posted by semmyroundel View Post
I had this idea of buying two parts kits and installing them side by side in the same chassis, each being driven by one RCA, naturally they wouldn't be balanced, but at least I'd get double the power.
Or am I missing something?
The answer is yes or no*.

Mono 'bridged' or 'balanced' mode (2 ACAs) gets more power out for 8 to 16 ohm impedance speakers so say 14 - 15 watts. They can effectively swing more volts.
'Parallel' mode (again 2 ACAs) gets more power into lower impedance speakers. 4 ohms or so. Could be 15 watts. This is because there is double the current available.

* So the answer depends on the speaker impedance as much as anything.

There are puts and takes for either mode and it is covered here https://cdn.shopify.com/s/files/1/10...ation_RevA.pdf in the build guide.
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Old 30th September 2018, 01:22 PM   #6160
JimT is offline JimT  Canada
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Quote:
Originally Posted by semmyroundel View Post
Hi, thanks for that reply-taken in the helpful vein that it was intended.
But, and it's a big but, this is a DIYaudio forum is it not? Why would I want to buy $280-$400 worth of pre amp?
I was hoping to find a way of doubling the power in stereo, that would be sufficient for me.
As I've said, I'm hoping that the bare bones 8wpc will suffice once built, as I'm hard pressed to follow an electronics wiring diagram, even the tripath amp that i built (and it works fine except on tuner) I built by sight and layout. Once parallel paths had been created on the circuit board, I was no longer able to test the resistors on the board, only prior to soldering.
Such is my limited ability.
Anyway, I still appreciate the reply, it's all good.
If you want an inexpensive DIY fix.. Reduce the feedback to get more gain. You can do that in the ACA by changing R12 from the 39.2K found in later versions of the ACA to the 68.1K found in the earlier version.

Jim
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