After six months of acquiring this old 7.1 channel Yamaha DSP-A2070 integrated amplifier out of sheer curiosity I opened the cabinet of this huge amplifier in my off time and did some nooby analysis all by myself. Please do pardon me if there is any error in my analysis.
After about two days of tinkering with this amp plus reading the entire service manual, I reached to the conclusion that the power output claims of this amp and all those of 80's & 90's era where more truthful to their actual output capabilities than those of todays. Let me share the findings with this internal shot of DSP-A2070:
Back in 1993 Yamaha advertised this DSP-A2070 as their Top Of The Line[TOTL] amp costing $2000. On release it immediately own the coveted EISA award for the best performing home theater system. It is capable to provide 100 watts @ 6 ohms each for the main left, main right & center channels while only 26 watts was provided for the rest four channels.
One has to remember this total of max of 100X3 + 26X4 = 404 watts @ 6 ohms is available through out the 20Hz to 20KHz audio frequency range having THD levels less than 0.015%. When a company rates their amp say at 1kHz, this usually means a full bandwidth(20Hz-20kHz) measurement will be about 15-20% lower. Also keep in mind this amp weighs a hefty 21 kilos.
The Power Supply
DSP-A2070 consists of two discrete power supply units designed to satisfy two entirely different requirements.
The Smaller Power Supply
The smaller one is marked in white rectangle(pic above) situated at the extreme right bottom corner, being dedicated to power the pre-amplifer module, the Digital Signal Processing(DSP) circuits, amp's protection circuits & all the LED's.
The Bigger Power Supply
The second power supply unit consist of an humongous EI core step down transformer which can be found in the violet rectangle(pic above) being completely dedicated to the power amplifier section alone and are assisted with huge power capacitors(the biggest I have ever seen) as shown in sky blue & blue rectangles(pic above).
This transformer is over 5 inches tall, 6 inches wide and is rated at 800VA or 800 watts weighing nearly 8.5 kilos alone. I have never seen such a huge transformer in an reciever and if I compare the whole of the currently available Yamaha RX-V471, 5.1 channel receiver with 105W (6ohms, 0.9% THD) (1kHz, 1ch driven) rated power output claim, weighs a mere 8.2 kilos. So, as I found out the DSP-A2070 transformer alone weighs more than many new recievers as found today.
This transformer is assisted with four power capacitors. Those bigger pair of 4 inch tall lug type capacitors(clamped with the frame) shown by the sky blue rectangle(pic above) on the upper top corner are rated 22,000uF each and takes care of main left, main right & center speakers. This means an additional 44,000 joules of energy are stored and are readily available with the power supply in order to handle the dynamic peaks of music. Equates to 44000/3 =~ 15,000uF per channel rated at 100 watts each.
To provide an analogy my Norge 1000 stereo amp rated at 125 watts per channel uses just 9,400uF capacitance per channel. DSP-A2070 have almost two times the capacitance of Norge in order to handle the dynamic peaks per main left, main right & center speakers.
Coming to the rectangle in blue(pic above) I find the other pair of capacitors rated at 8,200uF each being dedicated to the four effect speaker channels. This means an additional 16,400 joules of energy are stored and are readily available with the power supply in order to handle the dynamic peaks of music. So we have 16,400uF capacitance for these 26X4=104 watts.
So, I ended up with a respectable 800 watts transformer and 60,400uF of capacitance dedicated to help the transformer if ever it runs out of juice at extreme high volume levels. Yamaha claims just 404 watts from all these 7 channels.
The Power Transistors
For the Main left, Main right & Center channels
The power amplifier module of thie DSP-A2070 uses discrete/solid state technology. It uses a pair of
Toshiba 2SA1302/2SC3281 power transistors in push pull mode for each of its right, left & center channels. These transistors are marked in light brown rectangles(pic above) in pairs.
Looking at their spec sheet I found out each of these transistor pairs are capable to produce 150 watts of peak dissipation thus easily pumping out a genuine 100 watts of continuous power without crossing the SOA limit. Considering the fact that these transistors have roughly 50% efficiency(actually they are more efficient) , each of these pairs will be requiring at around 200 watts of power from the power supply i order to produce 100 watts of power for each channel while the rest 100 watts being dissipated/lost as heat.
Summing up these 3 pairs of transistors for the right, left & center channel will require 200X3=
600 watts of power from the power supply to produce 300 watts of max power in total which equates to 300/3 = 100 watts per left, right & center channel, all channels being driven simultaneously.
For the Four Effect Channels
Yamaha used a pair of
Sanken 2SA1726/2SC4512 power transistors in push pull mode for each of the four effect speaker channels shown in the brown rectangle(pic above). Each of these transistor pairs can easily pump out 26 watts of continiuous power without even comming close to their SOA limit. Again if we consider these transistors having roughly 50% efficiency, each pair will require 52 watts of power from the power supply in order to produce 26 watts of power to each of the channels, the rest 26 watts being dissipated as heat.
Four pairs of transistors for thsee four channels will require 52X4=
208 watts of power from the power supply in order to produce 104 watts of max power in total, which equates to 104/4 = 26 watts for each of these four channels all being driven simultaneously.
The Heat Sinks
Even before I consider this amp is truly capable to deliver a genuine 404 watts of continious power, I had to consider how the rest 404 watts of total heat generated from all these 14 power transistors can be dissipated properly. Looking at the dual row of heatsinks, each above 4 inch tall and nearly 12 inches long I came to the conclusion that this amp must be producing a lot heat, and since it produces a lot of heat a equal amount of lot of power is produced and provided to the speakers.
Calculations
Total continuous power providing capability of the power supply = 800 watts (excluding the power capacitors)
Total power requirement from the power supply in order to produce the manufacturer claimed 404 watts = 600 + 208 = 808 watts.
At least from a technical point of view it seems this DSP-A2070 meets the demand of its power amp section in full measure and are actually capable to deliver
a true 404 watts of continuous power output, throughout the entire audio bandwidth (20Hz~20kHz) @ just 0.015% THD with all the seven channels being driven simultaneously.
Until now I have not even considered the reserved 60,400 joules of capacitance of those power capacitors waiting to lurk whenever & ever if there is more need of power. The outcome with this amount of dedicated capacitance is that the DSP-A2070 comes with full 2.0dB of dynamic headroom @ 6 ohms. Very few TOTL AVR's can ever match this figure.
This means you will never feel the amp is running out of juice and will provide 404 watts of steady continuous power @ 6 ohms with all channels being driven simultaneously and in extreme circumstances(say full volume) will jump up to 600 watts for a moment (without even considering the transformer's internal capacitance) to handle transient peaks of a complicated music composition when heard in full blast.
IMHO the points to consider about an amp's real power output capabilities are :
1) The weight of the amplifier/ AVR in question. Heavier means more power.
2) The size & weight of the transformer. Bigger & heavier means more power.
3) The amount of capacitance available from the power capacitors. More is better for better dynamic headroom.
4) The heat sink size. Bigger means more power.
5) The power transistors in use & their max power output capabilities.
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Please feel free to add your own inputs.
