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Discrete transistor line amplifier stage

Posted 16th April 2013 at 02:18 AM by rjm
Updated 16th April 2013 at 01:23 PM by rjm

Over the last couple of years most of my interest in audio has been with transistors. I've been slowly teaching myself to read and understand the circuits.

Circuits like this one for example. Not hard, but still a bit too complicated for me to understand without the helpful wikipedia markup attached.

Instead I've looked at primarily at the schematics I have for discrete audio preamplfiers, 1970's vintage typically. Based on what I've learnt so far, I've done up a "test mule" in LTSPICE, shown below.

It's not a circuit you should build. It's for pedagogical purposes, though it does actually work reasonably well - in simulation anyway. Its just a simple starting point to observe how the different parts interact under simulation.
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Old

Progression - A Low Power Desktop Amp

Posted 9th April 2013 at 10:06 PM by BuildMeSomething
Updated 13th April 2013 at 10:21 AM by BuildMeSomething

Power supply boards are on their way, as is a full Digikey order for this project. However, no LME49722, which are currently out of stock. Due to that and wanting to keep to a 1 x psu & 1 x amp layout, the amp board underwent a quick re-design. It's now duel mono layout, utilising two LME49990.

Ordered LT1033/LT1085 for the PSU, these should give 3A each [typical]. Plus, six 4,700uf caps to help out. The plan is to run the rails at +/-15Vdc, with a 120VA 2x15V toroidal transformer.

Will place an order for the prototype amp boards on Saturday, just before I go on holiday.

Update (13-04-11): The PSU PCB's still haven't arrived, Plus UPS failed to deliver my Digikey order, this is now in limbo as they're saying "A correct street name is needed for delivery" ... I've talked to both Digi-key & UPS (U.S.) and they have the correct full address, UPS (UK) I can't get hold of... my translation is "Delivery driver can't read a map!"...
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Old

Ultra Low Distortion Class B Amplifier

Posted 9th April 2013 at 07:40 PM by alexcp (My DIY projects)
Updated 12th May 2013 at 04:49 PM by alexcp (Added better photos)

I built this one a while ago but could not find time to post.

This is a Class B power amplifier that follows the Ultra-LD Mk.3 amplifier design published by the Australian Silicon Chip magazine in 2011, which in turn draws heavily from the concept of a Blameless amplifier devised by Douglas Self. I used a different power supply and speaker protection, and changed the grounding scheme vs what was published.

The distortion at 1 kHz is below my measurement capabilities, and the amplifier does sound very nice, although it seems to give more sibilance than my Class A amplifiers.

The acid test I use is the dual CD "The Very Best of Placido Domingo" album published by EMI Classics. Many amplifiers I have heard cannot deal well with Domingo's tenor, esp. on louder and higher tones. Class A amps, particularly those using simple internal structure like the Zen series, perform well in this test. This amplifier seems to do better than any other...
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Burning Amp BA-3b (Balanced)

Posted 9th April 2013 at 07:10 PM by alexcp (My DIY projects)
Updated 2nd November 2013 at 12:17 PM by alexcp (Added better photos)

Big, hot, and heavy! Just completed it and adjusted for distortion, have not had yet a real chance to listen to it. (Update: I have listened to this amp for some time, and it seems to be a keeper, at least for now.)

The build is in a 4U/400 case from modushop; each side has two 200mm heatsinks, each holding six MOSFETs (three complementary pairs) and a biasing circuit.

The construction is dual mono (separate transformers for each channel) with CRC filtered +/- 18V rails, quiescent current is 3A per channel. Eight Mundorf MLytic® HC High Current Power Caps and two 300VA toroids occupy the most of the chassis, while the actual electronics is mounted on the sides.

Now I need a balanced preamp. I contemplate building some variant of BoSoZ, but am also thinking about a SuperSymmetric balanced preamp using JFETs or tubes...

UPDATE: No- and low-feedback amplifiers have no (or little) control over output errors and thus poor PSRR. On this premise,...
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Old

My aha! moment - loadline optimization

Posted 9th April 2013 at 12:07 PM by alexcp (My DIY projects)
Updated 9th April 2013 at 12:32 PM by alexcp

I build myself a Millett's Hybrid Headphone amp, originally published in AudioXpress issue 11, 2001.

The amp uses low-voltage 12AE6A tubes for voltage amplification and BUF634 solid state buffers to drive the load. Each tube houses two diodes (unused) and a triode, here loaded with a CCS. The whole thing runs off a 24VDC power brick and consumes maybe 150mA after the tubes heat up.

The DC operating point of the triode can be adjusted with a multiturn trimpot. The original AudioXpress article talks about the influence of the operating point on the sound and suggests to trim for symmetrical clipping, then adjust for the subjectively best sound.

The aha! moment came when I connected the amp to my sound card and looked at the distortion spectrum. On small signals (~300mV output into 300 ohm) the distortion is 2nd harmonic only. The operation point can be trimmed to the point where the the 2nd harmonic goes into the noise floor! I've read about this but...
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Old

Adding TentLabs XO2.2 low jitter clock to exposure 2010S CD player

Posted 9th April 2013 at 11:03 AM by alexcp (My DIY projects)
Updated 12th May 2013 at 04:58 PM by alexcp (Added photos, links)

I added a TentLabs XO2.2 low jitter clock and a separate power supply for it to my exposure 2010S CD player. The process was very straightforward - see the pictures.

The exposure 2010S CD player has an easy internal layout, where most of the components sit on a large PCB.

The original clock is based on the 74HC04N chip located in the middle of the PCB, to the left from the three white power connectors connecting the toroidal transformer. A close-up picture shows the crystal resonator wrapped in a black heat-shrink tube, two 33pF capacitors on each side of the resonator (those with black dots on top), and a resistor R75, which also serves in the circuit. The oscillator is built on the single invertor (pins 13 and 12 of the IC).

The original clock is generating 16.9344 MHz at 5V CMOS levels.

To install XO2.2, I removed the resonator and the capacitors, leaving the resistor in place. I connected the signal cable from XO2.2 to the...
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Old

What? - A Low Power Desktop Amp

Posted 6th April 2013 at 09:52 PM by BuildMeSomething
Updated 9th April 2013 at 08:31 PM by BuildMeSomething (Updates)

2] Basically, this is me trying to do a 2-layer PCB layout based on the LPUHP circuit schematic.

I'm using FeePCB for laying out. Not hit any problems with the software yet and it produces Gerber RS247X files. The parts library is none specific, so I'm having to generate footprints from datasheets as I go.

Notes:
1) Untested PCB design [should work though].
2) 2-Layer PCB.
3) 2 channels per board [16 x LME49600].
4) LME49722 with 4x gain.
5) Up to +/-18VDC rails.
6) Separate regulated power supply.
7) Utilise a 10K Alps RK27 for volume control.
8) 8 Watt into 8 Ohm [based on 2VRMS input].

Aim is to create 1 x power supply & 1 x amp board of a small enough form factor to fit in a desktop friendly case. With an output of 8 Watt into 8 Ohm load, for up close & nearfield listening in a small room.

Why the LME49722. Its drop in replacement to the nice 49720 but will run on +/-18VDC,...
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Old

Why? - A Low Power Desktop Amp [LPDA]

Posted 6th April 2013 at 09:34 PM by BuildMeSomething
Updated 26th April 2013 at 11:26 AM by BuildMeSomething

1] I hold opc's "The Wire" series of headphone and power amps in high regard. Small form factor, simple no nonsense designs and killer performance. God bless that man

I'm fortunate enough to have a few pieces at home. Primary, is the SE-SE headphone amp that gets used for both music and late night movies... Also, under construction is the A/B Power Amp, utilising two 55V/45V DPS-600 smps. This should provide over 100 Watt per channel into 8 Ohm load. Nice, but way to powerful for my spare little room.

opc designed a Low Power Ultra High Performance [LPUHP] Amp giving 16 Watt into 8 Ohm @ 1% THD. This was based upon the headphone amps he'd designed, using the same LME49990 opamp, but paralleled 8 LME49600 buffers.

Unfortunately I didn't have the funds to get both the A/B Power Amp and LPUHP Amp. Plumping for the former...



My little spare room is just that... Its 3m[w] x 2.9m[L] x 2.4m[H] and is full of...
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Old

My Ikea Blanda Bowl Build Diary

Posted 6th April 2013 at 08:56 PM by mondogenerator

So upon seeing many nice Blanda bowl projects here on DIYAudio I thought it about time I had a try and see what all the fuss is about!

About a year or so past I went through a phase of buying the nicest small wide-band drivers I could. Whether I achieved this is subject to the readers' opinion

So I have a pair of Mark Audio Alpair 5, and a pair of Tangband W3-1285SG. Both of these drivers were available to me in the UK at a very similar price-point and they both fall roughly into the 3" wide-band category. (Shown in the following picture alongside some Tangband 2" drivers)

Click the image to open in full size.

I chose to buy the 20cm Blanda bowls in bamboo. Gross volume works out at ~2 litres. Factor in stuffing or denser absorbent and I guesstimate a 1 litre volume.

This is really too small for the Alpairs, but the 2 dB rise towards the cut-off wasn't...
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Old

Tube-I-zator V3.0 - Out of production

Posted 5th April 2013 at 04:28 PM by dvb projekt
Updated 16th September 2013 at 06:16 PM by dvb projekt

Tube-I-zator V3.0

Click the image to open in full size.

The evolution brings the following changes:

- Anode PSU with Salas SSHV Shunt Reg. onboard
- External B+ Input for usage with other Anode PSU
- Heater PSU with C-R-C filtering
- Heater PSU with Softstart circuit
- Heater PSU Power LED

Thanks to John (-ecdesigns-) for the following suggestions!

- Grid stoppers to prevent unwanted oscillations
- Bias current injection for TDA1541A usage
- Pull-down resistors to keep the coupling cap output at GND-potential

Still on the Module:

- Heater switch for 6N2P or 12AX7 usage



An example for a balanced use (e.g. Bufalo II), you could see HERE.



The PCB has the following data:

Material: FR4 - 2mm
Layers: 2
Board size: 193x157 mm
Surface
...
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