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AudioSector LM3875

Posted 12th August 2013 at 09:55 AM by MagnumOpus

My first completed build. I used an Alps in a box for this one before I finished my awesome B1.

It's a tight fit, and I get some noise from the toroid, but it's hardly audible and not at all when the music is playing.

Takman Resistors, Toroidy transformer, DH Labs and Kimber hookup, Connex RCA's. Its not the most powerfull amp, but it drives my PSB Image B6 just fine and then some. The most awesome sound I have ever had in my own house, and I actually don't miss a thing. I would put it in a bigger chassis and perhaps get some copper to further shield the toroid instead of building another amp.

But I have pcb's for a Zen v9, so that's it
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Digital input section completed!

Posted 12th August 2013 at 06:56 AM by dvb projekt

Now the digital input section is completed!


Click the image to open in full size.


Wave I/O for USB input --> SPDIF/AES input board --> FIFO --> Isolator board -->
Dual Clock board with Crystek CCHD-957 clocks (powerd exclusive from a A123 Systems LiFePo4 cell) -->
Ianīs I2S to PCM V2.0 Module --> Red Baron



Because i use two Red Baronīs parallel, i added two additional U-FL connectors for DR and DL.


Click the image to open in full size.


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Variable output impedance tone control

Posted 6th August 2013 at 04:43 AM by homeskillet (Journey to the Center of the Circuits of Homeskillet)
Updated 28th August 2013 at 01:49 AM by homeskillet (It's a goofy idea and best left alone.)

Aug. 27th, 2013 edit:
Tapping the output transformer as a balanced secondary is totally goofy as was determined by Osvaldo de Banfield and Cnpope (Chris) here:
http://www.diyaudio.com/forums/tubes...madness-2.html

I'll leave it posted here just to show that I'll try just about anything and to show that it's unwise.

Aug. 7, 2013 edit:
I was just looking for the Hawksford and Mills current amp paper on google and I found this very blog post so I thought I would point out a potential drawback to the following feedback technique. Hawksford and Mills claim that using a sense resistor to the ground return from the speaker introduces a distortion similar to "interface distortion" in voltage amplifiers.

There is very little I could find about interface distortion.

As far as I can see it, this feedback scheme may introduce back emf from the speaker and feed it back to the amp...
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Old

Little Big Amp - page 2

Posted 5th August 2013 at 04:34 AM by homeskillet (Journey to the Center of the Circuits of Homeskillet)
Updated 5th August 2013 at 06:49 AM by homeskillet (added a bit of plate to plate feedback)

Continued after some listening and more tinkering from here:
http://www.diyaudio.com/forums/blogs...e-big-amp.html

It seemed lacking in the high end so I added a bit more capacitance to the bypass cap on the cathode resistor on V1.

This picked the high end up nicely. I then hooked the speaker up to the 16 ohm tap and used the 8 ohm tap as the feedback center tap. This resulted in a bit more output and I like the sound just fine.

The volume seems to increase after it's turned on a while. Also, it needs a B+ fuse in the event that V1 doesn't draw then V2 will have no bias and will draw tons of current and then will dump tons of current into it's cathode resistor.

The schematic posted here is updated with voltages and values done to the best of my ability and it sounds very nice. It's not a finished design but great for experimenting.

I will be setting this aside as my curiosity is leading...
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Old

Passive fiilters - musings on inductors and topologies

Posted 5th August 2013 at 12:58 AM by abraxalito
Updated 5th August 2013 at 01:02 AM by abraxalito

I've spent many hours recently poring over webpages and catalogues of inductors, looking for the best bang-for-the-buck in relation to anti-imaging filter inductors.

The gold standard, where performance is uppermost and cost and size are subsidiary, looks to be still the gapped ferrite pot cores I started out using. Their disadvantages are they need to be custom wound, not being available off-the-shelf, and their consequent higher cost. They also produce relatively bulky filters when a dozen or more are called for in a design. I've found nothing to beat them in performance, particularly accuracy and repeatability of their value and in terms of achievable Q (I've seen 500-plus in some cases on my meter).

I do hanker after a more portable and easier to replicate design though hence my investigations into cheaper alternatives.

Right down the bottom of the pile are the bobbin-wound coils, available in a wide variety of values here, at stunningly affordable...
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Old

The non passive pre becomes interesting

Posted 3rd August 2013 at 09:03 AM by hbc

Lots going on, my making things mojo has been busy. I have been reading 6 moons, and was interested by the idea of the directly heated triode preamp which sounds quite well apparently, and also repelled by the thought of using a huge output tube, slightly. So after some thought, I realised that the old battery radios used the directly heated ones, so a few weeks later some 3A5s were winging them selves to me.

Oh, (sigh) I had spent some time tweaking it first (the not passive pre) the most exciting feature was that the copied guru circuit pulled the output cathode to the HT rail when the heater is turned off! (I have big reservoir caps and small bleed). To be fair guru circuit is direct coupled so things are all over the place, but Anyway.

I decided to graft in the 3A5 in to this circuit, which was simple in principle, but ended up with a complete redesign of the power supply several times, as the addition of that one little tube hugely increased the heat generated...
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Old

Little Big Amp

Posted 3rd August 2013 at 04:55 AM by homeskillet (Journey to the Center of the Circuits of Homeskillet)
Updated 5th August 2013 at 05:34 AM by homeskillet

Hi. Here continues the tinkering continued from the forum post:
http://www.diyaudio.com/forums/tubes...-feedback.html

I took out that EF184 and the plate to plate feedback loop since I read that devices with a more stable performance without feedback sounded better once it was applied than devices that rely on feedback for their very operation. This seemed about right and I was tiring of the sound a bit.

The plate to plate feedback was the only way I could find to stabilize the EF184 and 6550 in this basic configuration and give any reasonable results and wiring it satisfied my curiosity so apart it came.

I replaced V1 with a 12AT7 and wired it in parallel since I figured it could use all the help it could get to drive the 6550.

The global feedback is my first attempt at current feedback. It's basically part of my first attempt at feedback at all.

I...
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