Posted 9th January 2013 at 10:41 AM byrjm Updated 21st January 2013 at 07:12 AM byrjm
The $50-from-China-via-ebay NJM4556-based headphone amp, pictured below, fails the "Is thing thing on?" test. With 16 ohm, 104 dB/mW headphones there is a faint-yet-audible background hiss when the unit is powered up and the volume is turned all the way down. The hiss increases only slightly as the volume is turned up (input disconnected).
The output noise of an op amp is normally estimated from the input-referred voltage noise density multiplied by the gain, and the current noise density multiplied by the gain and the sum of the input impedances on the inverting and noninverting inputs. The NJM4556 datasheet does not give a figure for current noise, but a reasonable guess is 1 pA/sqrtHz. The voltage noise density is estimated at 8 nV/sqrtHz.
This is the continuation of my personal journey to build my first tube amp.
It was a very happy day yesterday when the first mono bloc powered up and produced music. I was pretty comfortable that I had not made mistakes that would result in smoke, but really did expect some issues with hum, grounding or tube substitution. But nothing! Hum was barely audible with my ear on the speaker or from the chassis. And music played! My first test flight was one channel only driven by a Sony Walkman on a small Totem speaker. Even under these conditions the sound was pretty good, and really started to open up after the first 60 minutes. I was like a proud father
The first picture shows the pair with a Rotel CDP in the middle for scale.
I will not be able to fully know the sound until both are wired, broken in and hooked to the good speakers and source. I think they will be amazing. Already better than the very respectable chip amp they replace. There is a switch...
Posted 6th January 2013 at 02:32 PM bysuwaned (tube audio friends suwaned)
Updated 1st July 2013 at 11:25 PM bysuwaned
Preamp cleo4 Triodedick's
The First falling in Love with TUBE, when i had heard the preamp B406 my friend.
I have build the first Project tube , preamp B406 single stage.
Preamp with Phillips B406 and Phillips D3a with output line transformer Hasimoto HL10K_600.
rectifire Valvo AZ1.
Thank you for your Help and advised my Friend "The_Manta" and my friends_audiotube.
Posted 5th January 2013 at 05:50 AM bysuwaned (tube audio friends suwaned)
Updated 18th January 2013 at 04:49 PM bysuwaned
i have set krell CDT DM-1 , dac studio and preamp.
i cann't used my set because my dac is fail.
the problem it can't locking when i connecting with CDT. i think this must fail at board digital input and filter.
there are to old.
i can not find what wrong? i see krell's pcb is complex and closed. this is dificul.
i have tried check board pcb digital.but no have meansure intrument like digital analyser. become i not know how?
my be jitter or digital reciver or xtal or ect problem.
I think “ why I did not try to use part of the DAC Krell was still good: power supply and the overall analogues by replacing the digital part of the DAC”
When I see there is a chart on Web andrea ciuffoli DAC. with a detailed explanation of the parts that can be used. to replace the digital
board from my Krell...
Robert Harley reports no correlation with listening so I deduce from this that the test method isn't looking for the right thing. My own gut feel is we need a multitone test waveform rather than a single sinewave as a sinewave has a crest factor quite unlike music and if a sine provoked the condition we'd see it on the 'N' part of a THD+N vs level test.
Having said that, of course we do indeed see something weird going on - on Weiss Medea's implementation of the ESS Sabre. The THD+N plot versus level shows kinks which most certainly are not increased THD at various levels, so can only be noise floor modulation. See a critique I made on WBF here - http://www.whatsbestforum.com/showth...l=1#post133677...
Posted 23rd December 2012 at 03:07 AM byfas42 Updated 23rd December 2012 at 03:11 AM byfas42
As 'threatened' in a comment in abraxalito's blog I'm going to kick off posting and linking to some samples of sound generated by myself, at the moment examples of replay on my system, recorded using a very basic technique.
I'll probably regret it, but I'm going to put up a rough and ready trial run, to give a smell of what I'm aiming at. It's full of problems, but it gives some good indicators of what I'm dealing with, and hopefully some feedback will help me for future runs.
The system is my 'dud' HT all-in-one setup, heavily tweaked, and the recording device is a Fujifilm S4000 camera, which does HD video rather nicely, with mono 44.1/16 audio thrown in - that's handy. To maximise sound quality and minimise card storage used, hopefully, the lens was covered while recording, yes, no pics! Unfortunately, signal to noise is poor and the automatic volume control keeps falling over its feet, but you can't get everything for that sort of money ...
Posted 10th December 2012 at 11:42 PM byStormrider
David Hafler (RIP) must have sold tons of these amps... There are always a wide selection of different models on ebay, but the DH200 and DH220 seem to be the most common. I have three of my own (2 P230's and a P125) that I cycle in and out of use. I've repaired and rebuilt several for other people, and yet I keep running into more of them. The most recent being Brokencrank's DH200, which I have documented below for reference, and to have a place to put my notes. I don't claim any of the info below to be gospel, just my experience. I also don't claim this to be a step by step guide to resuscitate your old Hafler. A basic understanding of electronics and amplifiers will be required. Know what you're doing before you do it, and you will make less mistakes. If you have questions, ask!*
Note: All of the component reference numbers (ie. R3, C14, Q10, etc...) I mention will be based on the schematics available in the manuals at Hafler.com. Because...
Google+ has always been a "quiet room" where like-minded people got together to talk about things, away from the noise and chaos of facebook.
The problem was that it was difficult to find said like-minded people. They were there, but for the majority you had no way of knowing that.
Well, now Google has fixed that by introducing "communities". It's a user-created hub, a digital meeting room ~ salon ~ lounge ~ front porch, a designated gathering place associated with a certain hobby, interest, or topic.
This feature is brand new, so I have no idea whether it will work. It could, like facebook, devolve into noise and spam... or it might be useful and worthwhile. I think its worth a shot, anyway.
I created the group, but it is free and open. It's not mine in the sense I don't intend to use it as a platform. I have my own G+ page for...