Amp Camp Amp - ACA

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chromenuts

chromenuts

Member
Joined 2008
Paid Member
I’m not interested in having a “loud” system necessarily. However, certain types of music that I listen to (i.e. R&B) are more enjoyable to me at what I would consider a moderate level.

I have begun building the power supplies for my next amp project which is the F2/J, and will try powering the ACAs with those supplies first just for giggles.

In the mean time, I will be trying Lowther DX3 and Fostex 206e in the horns and hope I get more of what I think I want from the ACAs. It would also be an interesting time to try the tube amps again.

If any of that works out, my next step is to integrate a SLOB bass system I started a while ago with a B5 I picked up in the swap meet and temporarily drive them with the chip amp or one of my old Rotels until I can get around to building an F5.
 
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tjw59

Member
Joined 2013
MEPER said:
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.
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For my case: Heil AMT’s are rated for

Sensitivity: 96 dB, 1 watt, 1 meter

2W = 99 dB

4W = 102 dB

8W = 105 dB

Etc:


And the woofers:

91.5 dB 1 Watt, 1 meter

94.5 dB 2W

97.5 dB 4W

100.5 dB 8 W

103 dB 16 W

106 dB 32 W

Etc.

In my room 80db is plenty and happens long before the ACA reaches one watt. There is room there if we want more. Consider a power lawn mower is about 94dB. A live jazz concert is around 91 dB.

Presently, am driving the woofers with a throttled back (by the active crossover) Emotiva XPA-200 amp - which is no slouch and have them matched level wise. Intent is to build another set of ACA’s and try them with the woofers but think I am going to need the extra power. Not because I need more loudness but because the two drivers are pretty far apart with regard to the amount of power they need to stay matched in level. Almost 4.5 dB at a watt.
 
MEPER

MEPER

Member
Joined 2017
Some use Class D like the Hypex plate amp modules to drive the woofers and then use small delicate amps for mid / tweeter. I have tried to bi-amp my OB's and had a large amp to drive the woofers but I had problems getting the integration of the bass right. So far much better using only one amp to drive the speakers. Also I dit not think that the quality of the bass was better using a dedicated large amp to drive the woofers. The bass sound do get more "dry"....so a big drum sounds like "dunk!" compared to e.g. "dunkk" which to my ear was more "natural". Many experts thinks the big woofers needs an amp that can deliver a lot of current…..e.g. 20 A or more and has damping factor of > 50. I may make some more experiments…….that is part of the fun…..
 
kbergsson

kbergsson

Member
Joined 2009
MEPER said:
Some use Class D like the Hypex plate amp modules to drive the woofers and then use small delicate amps for mid / tweeter. I have tried to bi-amp my OB's and had a large amp to drive the woofers but I had problems getting the integration of the bass right. So far much better using only one amp to drive the speakers. Also I dit not think that the quality of the bass was better using a dedicated large amp to drive the woofers. The bass sound do get more "dry"....so a big drum sounds like "dunk!" compared to e.g. "dunkk" which to my ear was more "natural". Many experts thinks the big woofers needs an amp that can deliver a lot of current…..e.g. 20 A or more and has damping factor of > 50. I may make some more experiments…….that is part of the fun…..
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I use Hypex ncore 400 monoblocks in my living room system ( 2 way Carlsson OA51LE2 ). I use hypex mostly because they are good amps and can be kept constantly on as we use them for radio and streaming from phones and tablets. They deliver approx 200W into 8ohms and have quite good bass performance. However when I tried my 20-25W F6 in my living room I got just as deep but, as you describe, a much richer and satisfying bass ( not bloated at all, like when trying my PP el34 on them ). The F6 and for that matter the valve amps produced a lot better sound on the whole, but it is, regrettably, not practical to have valve amps and for that matter class-A amps turned on all the time.
 
M

Mixi

Member
Joined 2017
Mooly said:
The available output 'power' depends on the voltage the amplifier can swing into a given load. So that is one specification on its own.

The voltage gain of the amplifier tells us what input voltage would be needed to fully drive the amplifier to clipping, which is the figure our first test above determines.

The gain can be any value set by the designer and that gain will determine the input sensitivity of the amplifier.

So you could have a 100wrms into 8 ohm amplifier with a gain of 30db and another amplifier of identical output that is a just a unity gain buffer. Both have the same output capability, but both have very different input sensitivity's.
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thanks for that explanation ... with a bit of a delay.
so basically as soon as i know the output rating and the gain i can calculate the input sensitivity, right? and then i guess it's down to choosing a source that can deliver that input V so the amp is used to it's max.

is there a quick formula to calculate input sensitivity from the power and gain?
 
D

deathtube 667

Member
Joined 2010
ACA Project: bias current after R15 mod

First, I needed to add some 1 ohm power resistors after the FWBR to get the correct 19VDC supply rail.

Took bias current measurements post R15 mod (2.2k resistor) after 15 minute warm up:

Zero input signal = 1.32A, 1W = 1.27A, 2W = 1.24A, 3W = 1.21A

The lower supply rail did cause THD to increase slightly but nothing that deviated very much from the Pass Labs data. :cool:

dt 667
 
M

mraudioguru

Member
Joined 2014
kstagger said:
Any word on the shipping timeline? ie - parts still looking to ship by July 31st? With my metalwork in I'm starting to get antsy to build these.
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From the DIYSTORE website:

AMP CAMP AMP KIT - PRE-ORDER STATUS PAGE
UPDATE - JULY 25TH 2018

Batch 1: Your chassis should now have shipped. As of two weeks ago we starting sending a what-to-do-when-you-get-your-shipment email to customers once their chassis started shipping. If you missed that email, all that information is included in our new FedEx problem reporting guide (basically, don't throw away any packaging and check you got what you ordered within 10 days of receipt).

Parts kits? As they say "The best-laid plans of mice and men often go awry". This pre-order gave us the opportunity to move to an improved logistics facility so that we can better serve you in the future. We consumed much of our breathing room in July with this move, which is ongoing. After thinking we were 2 weeks ahead of schedule, thanks to some heel-draggingly-slow results from our old fulfilment company, it looks like about half the kits should start shipping from July 31st and about half from August 7th.

We do apologize for the inconvenience but please know we have been working very long coffee-fueled 16 hour days to both get these kits out as well as bringing our level of service for future orders up to the next level (of price, delivery speed, and reliability).

At this stage we'll say that any particular parts kit from batch 1 has a 30% chance of shipping by July 31st, 50% by August 7th, and 20% by August 14th.

Batch 2: Everything is on track for shipping on September 15th
 
astromo

astromo

Member
Joined 2017
RafaPolit said:
I hate to be the math geek, but those chances are wrong! (Which is actually good news! :) ).

The correct chances should be: 30% chance of shipping July 31st, 80% by August 7th, and 100% by August 14th.

Your chances cannot dimish as time goes by, unless you really have lesser chances of getting one after August 7th. ;)
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Feel free to be a maths geek. In this place, I reckon nerds are definitely allowed.
:cheers:
 
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sarathssca

Member
Joined 2014
sarathssca said:
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?
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Last weekend took the amp to native and play it with sony ss-rv900 speakers (3 way speaker) from Sony Hi-fi setup. Though the hi-fi setup was rated at 150w+150w, got decent (but not much loud, may be little louder would have been better) sound from ACA played with mobile as input source. But when played it from a laptop (vnc player) got nice loud volume from the ACA amp driving the these speakers .. :)..

5w amp looked very nice loud with speakers rated at 150w each..

Now may be need to get a nice preamp for the ACA amp with gain, as with laptop as source ( seems which has good gain compared with mobile phone) sounded loud enough and some updates to handle the excess heat that my amp is generated with my given heat sink..
 
S

sarathssca

Member
Joined 2014
Mixi said:
do you have a sensitivity rating for these speakers? the watt rating (150w + 150w) really doesn't mean a lot in this context. also, bear in mind that mobile sources usually have rather low outputs. have you tried it with a CD player?
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don't have sensitivity info of those speakers..
only tried with mobile and laptop as inputs so far.. with laptop as input its nice and loud.. looks like the wattage numbers are deceptive.. after hearing the 5w amp sounding nice loud on it..
 
chromenuts

chromenuts

Member
Joined 2008
Paid Member
sarathssca said:
Now may be need to get a nice preamp for the ACA amp with gain...
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I think this has been mentioned more than once previously by some builders who felt it allowed them to get the most out of their ACAs...I was wondering if the pumpkin preamp would be a good choice with speakers that require a little help. I love my TB W8 1808, it they need a little more help with the ACA in my opinion.
 
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