This freeware might do the job: Low-Cost Audio Testing Techniques Using a PC | Suite101 .
A User Manual and the software can be downloaded from: http://audio.rightmark.org/download.shtml
The 9444B Service Manual calls for an oscilloscope, tone generator and distortion analyzer, unlike the 9444A which can be serviced with a multimeter. Basically, the fundamental stripped waveform from the distortion analyzer is sent to the scope and... analyzed. Are there alternate procedures for these adjustments? I have software oscope, tone generator and spectrum analyzer, the only thing I'm lacking is a distortion analyzer with output. My options:
1. Purchase a distortion analyzer - I was outbid on a HP 331A today.
2. Build one - http://sound.westhost.com/project52. htm
3. Call Ira - does he post here? If he doesn't, I'm hesitant to ask him for free advice.
4. Ask the smart people here for advice - Help!
This freeware might do the job: Low-Cost Audio Testing Techniques Using a PC | Suite101 .
A User Manual and the software can be downloaded from: http://audio.rightmark.org/download.shtml
Last edited by mah; January 18th, 2013 at 08:04 PM.
Opinion is only as valid as its verifiable supporting evidence.
Thanks mah, I RTFM and played with Rightmark, as far as I can tell it does not have the capability to output fundamental nulled distortion signals in realtime.
I was hoping that someone would know of a simpler method of making said adjustments, possibly with a multimeter. For example, the 9444A service manual shows no less than 5 methods of adjusting bias-the simplest is done powered off and only requires a screw driver!
Last edited by _88; January 19th, 2013 at 08:07 AM. Reason: typing is hard
FWIW Most service folk's are eager to help.Whether they can help you for free with advice (If you do the Work) or if you have to send it in to them for a fee..
If you can't find what you need I wouldn't hesitate to call Ira.He may have one of these simple solutions for you.
Where did you get a 9444A service manual?Originally Posted by _88
Audio_by_Goodwill
Michigan, USA
^ I found it online, it's missing a few pages, but it shows DC offset and the 5 ways to adjust biasI tried to attach it, but at over 2mb, it's too large
Suggest me a hassle free way to upload it.
Thanks. I'll call Ira for free advice as a last resort.
I just looked at the 9444A pdf, it's 10 pages, the first 2 are cutsheet. Pages 1-6 are missing from the Operators Instructions. Page 11 is missing from the Service Instructions, which is most likely just the cover sheet if it's printed like the 9444B O&SI manual. I have pages 1-20 for the 9444B, which appears to be complete. I wish the pages were numbered 1 of 20, 20 of 20, then we would know for sure. PM me your email if still interested.
edit- just found 6 addendum pages for the 9444B and AP2600A
Last edited by _88; January 19th, 2013 at 01:38 PM.
My progress:
Current Limiting - used the oscilloscope in Visual Analyzer. The test requires the amp be driven hard to check for asymmetrical clipping. Channel 1 clipped evenly, then 8 ohm 200 watt dummy load started making funny noises. I rechecked both channels with a 12 ohm 1100 watt hot plate (complete with tea kettle), both looked good. Now I get to build a proper water cooled 4 ohm load with water heater elements and repeat check by the book - yay!
LF cancel and bias - I think both can be checked with free software. The brainstorm:
SweepGen sine wave > sound card L out > amp/dummy load > voltage divider (100k lin pot) > sound L in > Spectrum Lab super-dooper notch filter > sound R out > sound R in > Visual Analyzer o'scope
Spectrum Lab allows for building custom filters - the bad news - it's been almost 20 yrs since I've fired up a C compiler. If I fail as a code jockey (highly likely), I'll probably build Rod Elliot's DA design posted above with only two filters - 60Hz and 1k.
Visual Analyzer - Visual Analyser 2011 XE
Spectrum Laboratory - DL4YHF's Audio Spectrum Analyser
SweepGen - Audio Tools - from David Taylor, Edinburgh
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