Buy or build?

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#2
buying is almost always cheaper when mass produced consumer electronic product is the subject
diyers can't buy raw parts, often not even just case and PS for the finished, delivered cost of commercial audio amps

Geddes used a Pioneer Home Theater amp from Costco to demo his speakers
 
#3
Building is more fun but a lot of work.

One advantage of DIY is that when you get bored you can modify for usually a lot less than buying a complete new amp.

But I like the idea of having something unique in the world. 🙂
 
#5
jacco vermeulen said:
You're implying that an Emotiva can not be modified if one gets bored with it ?
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Didn't mean to imply that. But you would need to understand the circuit fully to make any meaningful changes. (IMHO, topology changes are far more significant than adding some higher quality components)

It most likely can be modified but in DIY the options are potentially greater. 🙂

There's no way a power amp like that can be DIY'd for the same amount, not even close. And then it would have next to zero resell value.
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Agreed. DIY can be very expensive but it is a great hobby. Second hand blown amps can help keep costs down though.
 
#6
Past year 2000 construction, one runs the risk that a commercial amp is all surface mount components, which makes modification that much more of a problem. Old burnt up junk amps from the eighties and nineties are more likely to be easily modified to make them better. Assuming one tests the power transformer for proper AC output.
Switcher power supplies are convenient when carrying to gigs, but not convenient to repair if they are blown. Not an easy design for a newbie to repair. Transformer amps are more of a sure thing.
 
#7
Thanks for your feedback

Before I add two XPA-3 to my shopping basket (-: I would like to know if there is a ready amplifier kit out there that can compete with emotive at a much lower price. Remember I need 6 channels. 2 x 100w, 2 x 50w and 2 x 10w can do it
 
#10
Geddes tested for low level linearity, bought amps for $150 at Costco

Geddes doesn't seem to think "transparent" audio electronics is hard to do, and good enough electronics can be had very cheaply

his waveguide speakers, selling for $3k each, were demoed with < 3% of a pair's price in his mass market consumer amp


Quote:

Originally Posted by gedlee
You can believe it or not, but its true. I tested about five amps that I had and the Pioneer was the best.

People always take my statements out of context. Once one has good electronics - and clearly price and "personal perception" don't correlate with good - then the only thing that matters is the speaker and the room (source material being a given). I have never said that any piece of junk electronics is fine. Only that very inexpensive and readily available electronics place the electronics into the "insiginificant errors" category.

I know that this is not a popular position and it's not one that I have always held, but I have studied this problem intensely and this is my conclusion. It is, by the way, the same one as held by Flyod Toole and Lauri Fincham and a whole host of other well know audio researchers. It's amp designers and marketers who seem to hold contrary beliefs

Quote:
Originally Posted by gedlee
No hardly - I don't "favor it", but I was severly chastized for using it at RMAF when, in fact, no one really knew if it was any good or not. It works just fine as my measurements show. I would not use this amp for many applications, but it suited my point at the time, which was that loudspeakers account for 99% (well you could argue 98%, but you get my point) of the audio systems sound quality.

The amp is a Pioneer DSX-V912 - a receiver. The point is that it was on sale at Costco for $150.00. I bought several of them for home theater use. I used my test to measure the amps and they were quite good actually. Especially for chip amps. I was measuring a lot of chip amps (a survey of capability) and most were pretty bad. As a chip amp this unit deffinately stands out. It compared quite favorably to a very well engineered discrete amp that I also use.

I also tested several other receivers and they were almost universally bad.

Quote:
Originally Posted by gedlee
Crossover distortion is a particularly insideous form of nonlinearity because it happens at all signal levels and there is no comparable mechanism in a loudspeaker to mask it. The question was asked if I have a way of identifying crossover distortion in an amplifier.

Yes, I do.

You see the situation with crossover distortion is that the % distortion increases with falling signal level. This is exactly why it is so audible since this is directly opposite to our hearing.

One could therefor ***** crossover distortion by looking at THD as the signal level goes lower, which is a typical measurement. The problem is that virtually all of these THD versus level measurements are THD + noise. When this is the case, the rise in THD at lower signal levels is actually the noise and NOT the distortion, but it is impossible to tell which is which. SO this test actually masks the real problem. One would have to track the individual harmonics of the waveform, but then the noise floor is still an issue.

Hence the measurement problem is one of noise floor and how to measure distortion products down below this floor.

This is done by averaging. But normal averaging can only lower the noise floor so much - down to the noise power. But if I have a signal and I average this signal sychronously then I can raise the net signal to noise level. This too is common. But if the signal does not exactly fit the time base then I need to window it and the resultant spectral leakage makes this sychronous averaging less effective.

I use a signal that exactly fits into the time base of the A/D taking the data. This means that I don't have to use a window and I can sychronously average a signal to noise ratio that is about 20 dB better than a simpler test could achieve. This means for example that the input signal needs to be something like 976 Hz, not 1000 Hz, which doesn't exactly fit the window.

I actually had to generate the input wav file in FORTRAN using quad precision, special random number generators and rounding techniques, because the test signals needed to have a 120 dB dynamic range - very difficult with 16 bits.

I use a signal that starts out low and goes up in level. I plot out the results as the signal drops into the noise floor. This test shows vast differences in amps that measure identical with standard tests.

It also shows that my Pioneer amp - you know the "really crappy" one that I get crticized for using at RMAF - is an extremely good amplifier. As good as the best that I have tested with this technique.


basically if you're serious about improving audio reproduction with finite time and knowledge - don't build amps - just buy cheap adequate ones, spend the time and dollars on speakers and room
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#11
MartinAndersen said:
Remember I need 6 channels. 2 x 100w, 2 x 50w and 2 x 10w can do it
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That makes a difference, imo.

There's a near linear relationship between power output and most of the hardware, the costly part :
- For power devices, Pd total is 4-6 times the power number in 8 ohm
(6 OnSemi devices of 150W Pd each, per 200W channel of the XPA-3, makes a factor of 4.5)
- For the transformer, it's a minimum factor of 1.5 for class AB
(the 3 channels of the XPA-3 do not load the transformer simultaneously, so it can get away with 1.375 , 825VA divided by 600W)
- A twice as powerfull power amp channel requires twice the size heatsink.

For the electrolytics, linearity can also be assumed between output power and stored energy in the lytics.
That does not equate to two times the cost for twice the power though.
Stored energy is C times V squared, divided by 2.
The cost of an electrolytic is somewhat linear with C times V.
Means that a twice as power full amp channel raises the cost of the power supply electrolytics by ~50 percent.

In practical numbers, compared to 600W (3 * 200W), 160W total power output per side (100W+50W+10W) requires :
- less than half the number of power devices
- 2/3 less transformer VA
- 3/4 less heatsink.
Plus a third less expenditure in electrolytics for the power supply.

Downside of 3 channels with different power levels is that they require 3 power supplies instead of 1.
Upside is that they'd be completely separated, neither of them can influence the other amp channels through the power supply.
 
#12
In dollars and cents :

With 40% added, an XPA-3 will cost you ~$1100, €1000 at the current exchange rate.

With a 100W/50W/10W setup you'd have no requirement for 3 heatsinks, the 50W and 10W channels can be mounted on one heatsink.

You'd also have the option to go class A for the 10W amp, AB for the other two, or even class D for the 100W channel.

€300 buys a really pretty amp case, including heatsinks (several sources, e.g. hifi2000 in Italy)
€300 will easily cover the cost of the power supply (300VA +160VA + 50/80VA toroidals, plus electrolytics and bridge rectifiers)
€100 will cover the cost of PCBs.
€100 for the components on the boards
Leaves €200 for the auxiliary parts.

Largest hurdle to take would be collecting the PCB's.
There've been plenty of design projects with board group buys on this forum in your 100/50/10 range.

One example is the 10W class A hybrid by Glen Kleinschmidt a number of years ago, valve input with bipolar transistors.
I use a pair of them to drive the array speakers of a rewired HK Soundstick set (way nicer than chip amps, imho :clown: )

To find out which boards are available at this moment, you'd have to search/ask.
 
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