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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old Yesterday, 08:57 PM   #32121
Hans Polak is offline Hans Polak  Netherlands
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Join Date: Mar 2005
Location: Blaricum
Quote:
Originally Posted by Tournesol View Post
- I think a problem exists. DC offset in the output. Means the need to adjustments to minimize-it. In an industrial production, it has some cost and drawbacks.
- What are the artefacts you are talking about ?

On an objective and technical point of view, if there is no phase turn at 10Hz, and no increase of distortion (but the contrary) with the servo, could-you justify this assertment ?

https://www.diyaudio.com/forums/atta...zzi-schema-gif
Here, the unusual* servo I use in this project.(See attachment)
The original audio signal is canceled in the comparator, before to be filtered and the remaining DC error applied.
Is here any luck we could notice a subjective and noticeable impact on the sound character ?

* No patent pending ? ;-)
A bit retarded reaction, but just flying through the postings of this endless thread, I came across your suggested servo system, meant to remove DC from the output from the PA.
However to my opinion that is not what this topology is doing.
It should be seen as an Active Error Feedback or AEF, correcting distortion components caused by the PA, see image below.

When increasing the BW of the LPF in your schematic, it will do a very effective job of error correcting over the whole audio range, but DC at the input will come out as the same DC, not at all what a DC removing servo is supposed to do.

Hans
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File Type: jpg AEF.jpg (80.7 KB, 83 views)
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Old Yesterday, 09:40 PM   #32122
DPH is offline DPH  United States
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Join Date: Dec 2008
Location: West Coast USA (somewhere)
Quote:
Originally Posted by simon7000 View Post
How are the bearings? Do the wheels wiggle? Are there any in the blade guides?

Can the saw cut a straight line in plywood?
Haven't tried the latter and we need to get at least one fresh blade as a dull one will invariably fail. The guides were known to need replacement/modernization. The frame/bearings are smooth and solid, no undue rattles or vibrations when we fired it up -- but we'll go through the whole thing and make sure it gets set up square.
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Old Yesterday, 10:15 PM   #32123
Bonsai is offline Bonsai  Europe
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Join Date: Jul 2003
Location: Europe
Quote:
Originally Posted by Hans Polak View Post
A bit retarded reaction, but just flying through the postings of this endless thread, I came across your suggested servo system, meant to remove DC from the output from the PA.
However to my opinion that is not what this topology is doing.
It should be seen as an Active Error Feedback or AEF, correcting distortion components caused by the PA, see image below.

When increasing the BW of the LPF in your schematic, it will do a very effective job of error correcting over the whole audio range, but DC at the input will come out as the same DC, not at all what a DC removing servo is supposed to do.

Hans
This is a bit like AFEC which I’ve used and is very effective at reducing overall distortion. 10x reduction, removal of DC offsets and a 30 dB improvement in PSRR

Here is a practical implementation Ovation High Fidelity - Model 1721

Here’s the write-up voverimg the technicalities Augmented Feedback Error Correction (AFEC)
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Old Yesterday, 11:38 PM   #32124
scott wurcer is offline scott wurcer  United States
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Join Date: Jan 2004
Location: Belmont MA
Quote:
Originally Posted by simon7000 View Post
Now why would you need to replace parts others think are fine?
Maybe because they failed pathologically, Hallmark used a particularly bad 1000uF/10v cap to store the rectified AC (the pre-2005 ornaments were a real hack depending on the divider string of lamps right off of the mains). The cap leaked, failed, and a replacement worked fine.
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Old Today, 12:34 AM   #32125
Ultima Thule is offline Ultima Thule  Europe
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Join Date: Jan 2004
Location: PKS, Finland
Quote:
Originally Posted by scottjoplin View Post
pico's posts are consistently off the wall
Come on slyjoplin, get a life, no need to of your average ~10 posts/day regurgitate 9 PC opinions without substantial input on this forum.
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