DIY audio blog for projects, schematics, PCB's, designs, electronics, mods


LME49810 HIGH-POWER By Bis. High-End

Here is a great realization of LME49810 based power amplifier by a fellow forum user – Bis. He had incorporated some minor tricks in his design to improve the sonic performance of the amplifier. Despite the fact he is using this amp for professional purposes, the sonic performance is excellent.
Thank you Bis for sharing this great project with us.

Tubes: 12B4 Single Stage Preamplifier.

The 12B4 tube has a lot of followers. They can swear that this is the most transparent sounding preamplifier ever. I will hold my thoughts about this claim. However it’s a simple, minimalistic and offers the shortest signal path possible.
Due to it’s internal construction and typical characteristics the 12B4 offers almost no PSRR. This calls for a regulated power supply. The tube loving path is of course a tube voltage regulation. A modern approach is to combine the voltage stabilization with a solid state constant current source. Here is a general idea of how this might look like:


uPC1237 Amplifier/Speaker Protection Module

uPC1237 is a well known IC used for protecting the speakers form DC as well as amplifiers from over current. Almost any Sony amplifier starting from the lower range and right up to the higher-end ES series are using this chip.

So I thought was a good idea to make a stand alone module which could be used by the DIY community.

To start of, here is the datasheet of the uPC1237:

One important aspect is that this IC could be used to prevent the output devices from over current. This happens when a load too low is introduced at the amplifier’s output or a short circuit is present. Most power amplifiers have a dedicated circuit built in them, to monitor the current flow trough the power transistors. This part of the schematic is forcing the current to stay within the recommended SOA of the devices.

It is a common situation where in case of a short circuit at the output, the output transistors get damaged “to save the fuses” which is absolutely unwanted fact.

Using uPC1237 for over current protection allows the designer to drop the SOA limiting elements in the power amplifier. This will save space on the PCB, lower the cost of the project and increase the reliability.

Due to some patent issues one can not find a recommended schematic to do the current limiting job in the uPC1237’s datasheet. There is no built-in circuit either. However all you need is to monitor the current flow trough one of the emitter resistors at the output of the power amplifier. According to the datasheet pin 1 must be driven above 0.67V. This is the threshold. Rising the voltage above 0.67V will trigger the relay opened. Using a current source will require the pin 1 driven with current above 110uA.

This is what I use in my amp to do the job:


Now the schematic of the module itself. It can be downloaded HERE


A few words about the PCB. Now I wanted to have a rather non standard approach here. I needed a module which could be mounted directly on the rear panel and bolted through the speaker terminals. I’ve seen this type of modules around the eBay. However those were using small current relays not suitable for more powerful amplifiers. For my project I wanted to have a good quality DPST relay with at least 10A rated current. Those can be quite bulky so the PCB is quite large. However, reliability is more important than the cost of the PCB. The devices protected by this module can be quite expensive so no cheap tricks here.

Here is the relay – OMRON – G4W PCB Power Relay

Those are available for purchase from Farnell in Europe:

This is what the PCB looks like:


The relay is located between the mounting pads to keep the paths equal and at the same length. The mounting pads are of 15mm diameter. The mounting holes are at 5.5mm. Those can be drilled to a larger diameter if necessary. My speaker terminals have 5mm threads and fit just fine.

A PDF file of the PCB is available for download here:

PLEASE NOTE – this project is provided to the DIY community for free. It’s free for personal use. Any commercial usage is prohibited.


Universal I2S interface. Line + cable

Here is a way to make an I2S output from your CD player. This one includes a reclock option inside the CD player.

Universal i2s interface

This idea uses a standard cat5 network cable. I personally don’t like the idea of reclocking the I2S bus and then sending it over the cable. A way better solution would be to include a low clock source inside your DAC. This source could have two outputs. One used to make the reclocking and feed the DAC chips with clean clock. The other output could be sent out over the same cat5 cable (using the 4th pair inside the cable) to the transport. This would make the transport a slave to the DAC and will practically eliminate it as a source of any troubles.

Discrete I/V For Current Output DAC’s. AES Publication.

Here is an article by AES, describing a very interesting solution for the I/V stage. This one is fully discrete and includes LPF and emphasis equalization. For current output DAC’s like TDA1541A and PCM63 etc.

Abstract- A family of current-steering transimpedance amplifier circuits is presented for use in high-resolution, digital-to-analogue converters.  The problems of achieving accurate current to-voltage conversion are discussed with a specific emphasis on digital audio applications.  Comparisons are made with conventional virtual-earth feedback amplifiers and the inherent distortion mechanisms relating to dynamic open-loop gain are discussed. Motivation for this work follows the introduction of DVD-audio carrying linear PCM with a resolution of 24 bit at a sampling rate of 192 kHz.

1 Introduction
This paper investigates the design and performance requirements of the transimpedance amplifier used in association with a current-output, digital-to-analogue converter (DAC) [1].  The principal motivation for this work stems from the extreme resolution requirements determined by the advanced audio specification available in digital versatile disc (DVD) applications [2]. Following a theoretical discussion, two principal circuit topologies are presented, the first based upon wide-band, current steering circuit techniques enhanced by input-stage error correction [3], while the second incorporates dual operational amplifiers with nested differential feedback and an embedded low-pass filter.

Current-steering transimpedance amplifiers for high-resolution digital-to-analogue converters – >>>[LINK]<<<

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