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Amp Camp Amp - ACA
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Old 1st October 2018, 11:21 AM   #6181
semmyroundel is offline semmyroundel  United Kingdom
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Quote:
Originally Posted by NealJ View Post
Sorry, I'm a novice so can't comment on the suitability of something I haven't tried.



If you have the Cmoy's already, why not swap the headphone jack for RCA jacks and swap the R3 resistor to 2K ohms to get x6 gain. Have a look at Tangents website for more info.
Many thanks again NealJ, I can assure you, I'm even more of a novice!
I'll defo check that Tangents website.
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Old 1st October 2018, 11:30 AM   #6182
Toaster is offline Toaster  United Kingdom
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Heh! My memory is working just fine! The original MS specs back then used a different standard, and it's that misleading figure that comes up on web searches. The sensitivity of the Pageants won't be more than 90dB, using the standard 2.83V (1Watt into 8 Ohms) input. I have one of the old digest format Hifi Choice magazines with measurements somewhere... I also owned a pair back in the day, and the DSB208 is a nice drive unit.
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Old 1st October 2018, 12:25 PM   #6183
twocents is offline twocents  South Africa
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Amp Camp Amp - ACA
Quote:
Originally Posted by maxijazz View Post
Hi,
I have just built my first ACA 1.6. I do have MeanWell 24V power supply, but it outputs only 22.5V, when measuring with my DMM.
My concern is, what should be bias voltage? 12V or 50%x22.5V=11.25V?

Cheers,
Max
Hi Max. Congratulations with your build. Many of the Meanwell power supplies have an adjustable output range. So, it might be possible to adjust your Meanwell to give 24V (if you want that) with a small trim pot. Give us the model number and we can check that, or you should easily spot the trim pot. However 1.5V extra will probably not make much difference.
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Old 1st October 2018, 07:53 PM   #6184
RafaPolit is offline RafaPolit  Ecuador
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For an 'uninitiated' like me... what prevents one from turning the ACA into a Headphone AMP? I mean... if I were to control the volume through a PRE, what is it 'not good', or at least 'not optimal' in driving a Headphone with a Power Amp such as the ACA?

Is it just that you would need to drop the volume down considerably on the PRE, therefore perhaps affecting sound quality? Is it just not something used often because of the lack of volume control?

I'm curious (and, as may now be obvious, preparing to build a Whammy :O )

Thanks, best regards,
Rafa.
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Old 1st October 2018, 07:57 PM   #6185
semmyroundel is offline semmyroundel  United Kingdom
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Quote:
Originally Posted by Toaster View Post
Heh! My memory is working just fine! The original MS specs back then used a different standard, and it's that misleading figure that comes up on web searches. The sensitivity of the Pageants won't be more than 90dB, using the standard 2.83V (1Watt into 8 Ohms) input. I have one of the old digest format Hifi Choice magazines with measurements somewhere... I also owned a pair back in the day, and the DSB208 is a nice drive unit.
Sorry Toaster, didn't mean to offend, I was just going on printed spec.
I have been amassing DSB208 units for a while, as I've always liked the speakers but found that seventies' design of broad (wide and shallow) as opposed to the narrow and deep designs of today to have a papery bass.
So... I've decided to redesign the cabinets, hence amassing the drive units.
I was told (on this forum) not to mess with the volume of the cabinets or indeed the porting.

B*llsh*t
You may remember, with the exception of the tweeters, which I seriously doubt are affected by cabinet design in the same way as the bass/mid units, the three speakers in the range ALL used the same drive units and varied greatly in cabinet size and porting.
I was not convinced that the Festivals were the best as some claim, though I've only owned the carnivals and pageants.
So... in keeping with a nod to the design of the Q Acoustics Concept 20's, I'm going to redesign the cabintes, heavily braced and with a gel liner as the above speakers have.
Who knows what they'll sound like?
Who cares? It's just a bit of fun!
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Old 1st October 2018, 08:23 PM   #6186
poseidonsvoice is offline poseidonsvoice  United States
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Amp Camp Amp - ACA
Rafa,

There is nothing wrong with using the ACA as a headphone amp in all honesty. You can get more gain too if needed by adjusting the feedback resistor. The output impedance is low enough for all headphones, particularly those that are difficult to drive (ie 30 ohms, etc...). Have at it if you want! Just wire a 10K Alps pot or equivalent and away you go.

Most headphone amps are 8-15dB in gain.

The ACA should have GOBS of power for pretty much any headphone setup. The only thing to see is if the noise is low enough (I think it is 15 uV with the Meanwell 24V, which is low but not uber low. The best I’ve seen is 1uV from other headphone designs).

A good experiment is to hook up an ACA to a pair of Klipschorns. If it’s quiet there, then you’re good!

Best,
Anand.
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Last edited by poseidonsvoice; 1st October 2018 at 08:31 PM.
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Old 1st October 2018, 08:31 PM   #6187
oc11 is offline oc11  United States
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Quote:
Originally Posted by RafaPolit View Post
For an 'uninitiated' like me... what prevents one from turning the ACA into a Headphone AMP? I mean... if I were to control the volume through a PRE, what is it 'not good', or at least 'not optimal' in driving a Headphone with a Power Amp such as the ACA?

Is it just that you would need to drop the volume down considerably on the PRE, therefore perhaps affecting sound quality? Is it just not something used often because of the lack of volume control?

I'm curious (and, as may now be obvious, preparing to build a Whammy :O )

Thanks, best regards,
Rafa.
Hello Rafa, as far as I am concerned a preamp is a preamp. We can define it further as a separate component in the chain carrying the signal from the source to the speakers. This chain contains an origin for the signal (your CD player, computer, what have you), it contains an amp and speakers. Between the amp and the source, you can insert any number of components as you may need or wish to insert for any reason you may want to insert them. There are, of course, a pile of interconnects involved. Now, while it is true that all of these modify the signal to some degree, the final product is what you and your ears have to evaluate: Does it sound good, is it detailed, is the musical stage nice and lifelike?

I believe the amp and the speakers are the keys to the music you hear. Everything else just produces the signal and processes it to some degree, including the interconnects, before it gets to the amp. You can make all kinds of adjustments to your setup, most importantly the volume must be adjusted, and then judge the results with your own ears. You cannot go by what someone else says it sounds like or should sound like, your ears are the final judge of your setup. If it pleases you then it does not matter how many components you have placed between the source and the amp.

The concept of signal purity and of minimalistic handling of the source are valid concepts, however, it takes a lot of time, effort, and money, to realize these. If you saw the movie "Gandhi" there was a scene where one of the rich people supporting Gandhi was telling a reporter: "You cannot imagine how expensive it is to keep him living in poverty."

If you want fine music and can get it from a cheap headphone amp used as a preamp, using its volume control to adjust the level, before sending it to your amp and speakers, then that is exactly what you should do.

Personally, I am a lot more interested in posts that talk about changing the value of the input resistor of the ACA as a way to increase the power output of the amp, than upon a discussion of the merits or lack of merits of any kind of intermediate components used.
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Old 1st October 2018, 08:34 PM   #6188
maxijazz is offline maxijazz
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Quote:
Originally Posted by twocents View Post
Hi Max. Congratulations with your build. Many of the Meanwell power supplies have an adjustable output range. So, it might be possible to adjust your Meanwell to give 24V (if you want that) with a small trim pot. Give us the model number and we can check that, or you should easily spot the trim pot. However 1.5V extra will probably not make much difference.
I am not going to make any changes, now. I do have second ACA unit i still need to build in spare time. Since i will use both units for monoblock operations i might need to adjust output voltage to match both supplies.
Model number of the Meanwell is GST120A24.

Thx,
Max
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Old 1st October 2018, 08:45 PM   #6189
MEPER is offline MEPER  Denmark
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The only thing I would be concerned about using a "real" power amp as headphone amp without any voltage divider at the output would be safety. If something goes "mad" it could be bad for the hearing and/or headphone…….
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Old 1st October 2018, 09:32 PM   #6190
plsvn is offline plsvn  Italy
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Quote:
Originally Posted by nycavsr2000 View Post
A good experiment is to hook up an ACA to a pair of Klipschorns. If itís quiet there, then youíre good!
hooked up mine to a pair of Klipsch Cornwall and itís *dead* quiet
canít say the same about my beloved 2A3 SET
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