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Towards a better DAC - introducing the HEC

Posted 14th June 2010 at 04:16 AM by abraxalito
Updated 8th September 2011 at 03:05 AM by abraxalito

Doug Self's comprehensive work on power amplifiers has been an inspiration to me over a number of years. In it, he coined the notion of the 'blameless amp' as one which was beyond reproach, measurements-wise. So I pondered over running with the notion of 'blameless DAC' along the same lines. Initially this sounded attractive, even though not entirely original. Google found a reference to it already here on diyaudio but could not show me the actual posting.

I decided on reflection that the 'blameless DAC' would be not such a good idea. That's partly because for me, measurements are not the goal of audio design. Enjoyable sound is what does it for me, not vanishingly low THD figures. So a 'blameless DAC' could only be blameless if measurements are God, so to speak. For someone like me for whom auditory experience is all, I decided I'd need another term for my DAC project.

I've settled instead on the term 'highly evolved converter' or HEC for short. This recognises...
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New scope...

Posted 2nd June 2010 at 04:59 AM by abraxalito
Updated 5th March 2012 at 02:52 AM by abraxalito

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Bought this (well not quite this one, mine has Chinese text on the panel) little puppy yesterday as my old UNI-T was just getting too frustrating to use. In particular its triggering ability is almost useless, giving way too much jitter. That added to the trig level encoder being majorly unreliable (its just over a year old) and lots of apparently self-induced noise on the trace meant I decided to bite the bullet. And boy I'm glad I did - its like getting a new pair of HD800s to replace my aged Sony CD3000s, everything is much clearer.... (and no, I haven't made that particular upgrade yet).

About six months ago I first noticed the younger sibling of this scope in a shop window in the local electronics market. I was blown away - a widescreen scope? That screen was drop dead gorgeous! This pic really doesn't do it justice so hopefully I'll post up one of my own pics soon.

Having been immediately...
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Salas Shunt v1.2 notes

Posted 27th May 2010 at 01:00 PM by klewis
Updated 27th May 2010 at 01:11 PM by klewis

The ones I posted as symmetric 1.2 in page# 190 can do for +/-24V. Those are the ones that Bill initially tested for supplying his OP AMPS. There is a Q2 2N5459 JFET which is 25V VDS max that will set a 30V absolute max Vin given that it sits on 1.85V and there is a Vgs and R1 drop above it. Respect that Vin max. That Q2 must have 7mA or more IDSS for the cascode to work efficiently for a 7-9mA 2SK170BL Q9 under it with the given R4 (220R). If you want to feel free from Vin restrictions or choosing JFETS, you can do the BJT cascode left side. See post #2432 for negative example.
Making an additional positive one like those for 5V, only needs R13 1k trimmer to be 5k trimmer so it can go that low.
R1 is changing current setting, by 0.6V/R1=CCS current. Steadily predictable because that 0.6V is Q7's Vbe. Does not vary significantly per part or batch as with Leds Vf.
As for Vref and output caps subjective preferences, as Andrew said.
Good luck!
...
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Tweaking electronics sound quality in active speakers

Posted 24th May 2010 at 12:39 PM by abraxalito
Updated 25th May 2010 at 04:24 AM by abraxalito

My main listening system has been based on Fayou XPE active speakers for over six months now. I bought my first pair of Fayou speakers a year earlier than that, the lower-spec'd B2 models. The B2s are now my main PC speakers, connected to an Asus Essence ST. After getting the B2s, it was only a matter of hours before I had them open, poring over the implementation details. I noticed that the grounding to tweeter and bass/mid was shared so sliced into the board to give each unit its own dedicated ground path. I also tweaked the high current paths to the main PSU caps to ensure no impedances in common with the audio signal grounds. After these mods, the sound was highly enjoyable.

When I first heard the XPEs I considered them not to be quite as good sounding as my (tweaked) B2s, but given their superior amplification and bass/mid driver, figured they were ripe for hot-rodding. Their construction also suits tweaking much better as all the electronics is easily accessible on the...
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A New Comer to Audio

Posted 17th May 2010 at 09:49 AM by borispm

Hi everyone. This is my very first post. I am not really new to audio but I am very new to DIY audio.

I have a pair of MB Quart standmounters with a cheapo Marantz receiver and they sounded great until I heard something high end, and that's why I've joined this DIYaudio, where I can explore more about audio (especially a very special group of fullrangers).
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Krell KSA150 - Low distorted output after heated up

Posted 16th May 2010 at 07:51 AM by wabun

my Krell sings well when turn on, but left channel has low distorted output after play for 3 songs..turn it off and let it cool down, turn on again it sings normal again ! but after play for 3 songs, the left channel has low output again...unable notice any damaged component, any good suggestion how could it happen and what is the cure ? Thanks..
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Rating: 2 votes, 4.50 average.

Cathode Follower

Posted 14th May 2010 at 11:40 PM by Miles Prower

AC Coupled CF

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In this schemo, Rk is the normal cathode bias resistor. Rl represents the tail load in parallel with the load impedance. Rg is the control grid DC return. The CF gives excellent high frequency performance since Miller Effect is absent, and the Cgk sees very little current since the grid and cathode are always at nearly the same potential. This makes the Cgk effectively smaller than its static value. The main component of input capacitance will be the reverse transfer capacitance: Cgp. With small signal triodes, it is easy to present a Hi-Z, Lo-C load to the driving stage. This isn't just helpful at RF.

This is another circuit which has lately come under unjustified criticism within certain audiophile circles. Much of this is unjustified on the basis that the CF is a negative feedback circuit. This view that all NFB is all bad does have a basis in fact. It has...
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Rating: 2 votes, 5.00 average.

Demystifying the Cascode

Posted 14th May 2010 at 11:25 PM by Miles Prower

Basic Cascode

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This is what the schemo of the cascode looks like. Rk serves to establish the Q-Point bias for the lower triode, and Rg is its DC grid return. Rp is the passive plate load. The voltage divider connected to the grid of the upper triode establishes its Q-Point bias.

So why would you want to do this? What you have here is a cascade of a grounded cathode stage driving a grounded grid stage. The GC topology has the advantage of a Hi-Z input. However, its high frequency performance is impacted by a high Cmiller that only grows worse with increasing voltage gain.

The GG topology avoids Cmiller for excellent high frequency performance, but it suffers from a Lo-Z input. It's not very often that a Lo-Z input is desirable. However, you can combine the two in a manner that work together. The Lo-Z of the GG stage loads down the plate of the GC stage, reducing its gain...
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Some more progress on my Baby Huey PP EL84

Posted 4th May 2010 at 09:24 PM by Bas Horneman (Bas Horneman's diyAudio.com blog)

Unfortunately the paintjob is slowly chipping away on the edges...
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Old

Active inductor substitutes

Posted 3rd May 2010 at 01:45 PM by DougL
Updated 14th September 2010 at 06:34 PM by DougL

Here is a circuit I like.
Not excessive voltage drop, no absolute expectations on voltage or current.

http://aquinaudio.webspace.virginmed...act_choke.html

A link to the discussion in the Tube Forum

http://www.diyaudio.com/forums/tubes...ml#post2173626
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