The STR-DB2000 is an Audio/Video Receiver Amplifier made by the Sony Corporation. This is a Class-D digital amplifier with S-Master Pro, which is no longer manufactured. The introduction of the S-Master Pro was first in 2003 making it Sony’s third-generation digital amplifier product. The improvement in this was their use of discrete output transistors and an additional digital processing stage, which they call DC Phase Linearizer (DCPL). This stage enables the user to adjust the low-frequency phase shift, which produces warmer bass.
Class-D amplifiers have huge benefits over conventional designs. These legendary amplifiers have zero crossover distortion, and produce minimal heat at the final output stage. Their sound quality is also unlike anything you would hear from a conventional amplifier and therefore they are highly sought after.
These amplifiers tend to be expensive even in the second-hand market; however, I was lucky to find one that was broken and was able to repair it. The sound quality is remarkable, because it faithfully reproduces any levels of bass and treble I feed at the inputs. The clarity of sound is also breathtaking due to Sony’s improvements in Class-D amplifier designs.
This amplifier provides seven identical channels each with a power output of 120 watts into an 8-ohm speaker load.
Traditional amplifiers require the conversion of digital input signals to analogue, however in a digital amplifier these types of conversion stages are not required, and the digital input signal usually remains digital all the way up to the last stage. The final output stage usually consists of a variant of Pulse Width Modulation (PWM) circuitry, where a digital signal drives the speaker load. The S-Master Pro uses similar technology, which Sony calls Complementary Pulse Length Modulation (C-PLM). Their version is of course better because it controls and minimises second-order harmonic distortion usually found in PWM circuits.
Class-D amplifiers are easily susceptible to damage if you short their output terminals. This is because when you have a final output transistor that is switched hard and fast, it does not take kindly to overloads. Consequently, many people sell them on eBay if they start showing Protector Code 11.
A typical output stage consists of a digital power amplifier IC (HIP2101IB), which generates a fast 1-bit pulse stream that switches a pair of MOSFET power transistors (SUP18N15-95). In the service manual, these transistors are labelled “Booster”. Their positive rail usually passes through a pair of 0.025 Ω resistors in series. For example, the positive rail for Q1653 and Q1663 is through the series pair R1633 and R1643. Similarly, Q1652 and Q1622 receive their positive rail through R1632 and 1642 series pairs. When a MOSFET transistor shorts, these resistors behave as fuses by cutting the power by going open. Therefore, if you detect a short transistor, then also look for open resistors associates with its respective voltage rail.
Digital amplifiers usually have extremely complex power supplies. In this design, they are using a switched mode power supply. One of the problems with these designs is that very few people can actually understand their operation or repair them. If the chopper transformer were to fail, then very few people in UK would be capable of diagnosing the fault.
The sound quality is of course excellent, as one would expect. 120 watts minimum RMS, with a 0.6 % total harmonic distortion makes a statement and compensates for the additional complexity of the PSU.
As you can see, this model is the S-Master Pro, which contains the S-Master Neo chipset. The electronic design of this amplifier is very bold and indicates an 'in your face' attitude. As you can see, they have thoughtfully balanced functionality, sound quality, and price.
Digital amplifiers are nice to have, and the sound quality is out of this world providing you use a good pair of speakers, however if they go wrong then they can be a nightmare to repair and consequently expensive to repair. The output transistors are on the digital amplifier (D-AMP) board underneath all the other boards, which means that you have to take the whole amplifier apart to get to them. With all the wire looms going from one board to the other, and the screws, it takes half a day of your time to take this amp apart -- assuming this is your first time and you are following the service manual.
Once you have taken it apart, you cannot take any voltage readings, because the PSU board requires removal as well. Hence, one has to diagnose the fault simply by measuring component values and seeing if they are operating within normal parameters.
Get a New Sony!
Do NOT repair this amplifier, even if you are a qualified experienced engineer with letters from the institute! Honestly, this is a complex amplifier design and definitely not for the faint hearted. At most, people check and replace the fuse on the PSU board and if it keeps blowing then it is best to sell it on eBay as spares.
Once you know that this is a big job to repair, you can happily sell it as spares or repairs without feeling guilty. The good news is that you will have room to buy a new Sony amplifier. Sony's latest amplifiers have more functions, more buttons, and more settings for you to fiddle with, and at half the price! Just think of all the fun you could have!
This is a multi-page article and in the following pages, you can see the inside of one of these amplifiers, including the MOSFET output transistor that I replaced.
This Article Continues...Sony STR-DB2000 Review
Sony STR-DB2000 Inside Look
Sony STR-DB2000 Protector Code 11
Sony STR-DB2000 Power Supply Board
Sony STR-DB2000 Back Panel Connections