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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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It is currently 21 Aug 2019, 22:54

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PostPosted: 22 Apr 2019, 06:42 
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Matt, have you run it past the frequency and distortion analyser? It would be interesting to see how it performs although the ears are the ultimate test.

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PostPosted: 22 Apr 2019, 07:18 
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Woodo wrote:
Matt, have you run it past the frequency and distortion analyser? It would be interesting to see how it performs although the ears are the ultimate test.

Most Ds are extremely low distortion until you get to near there max wattage. Then they jump to about 10% distortion. Figures of 0.03% to 0.05% are typical at low wattages.

But Matt love to see how it looks under test.

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PostPosted: 22 Apr 2019, 12:21 
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Woodo wrote:
... have you run it past the frequency and distortion analyser?
Actually, I never even considered it. The module is rated for THD+N at 0.05%/1W & 0.5%/8W @ 1KHz (SE mode, 8Ω load). This is well below the capabilities of my test equipment. Here are the distortion plots by frequency at 1W and 5W from Sure.
Attachment:
AA-AB32231 THD+N by Frequency.jpg

This is pretty typical for these amps. The low frequency distortion rise is due to the AC coupling of the PWM and the rise in the higher frequencies is almost entirely due to the chosen modulation frequency (310KHz). Once designed and put into production, the unit-to-unit performance of these little class-Ds doesn't really change much.

Overall the sound is very good. I will say that it doesn't have any of the warmth or character of my tube based SE amps. However, as a companion system for my workshop where acoustics are what they are and are often interrupted by the whine and rumble of heavy machinery, this amp seems ideally suited to the task. :)


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PostPosted: 22 Apr 2019, 17:07 
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Agree with the lack of warmth that’s where (in my case any rate) a 6SN7 tube preamp makes its mark. My big Ds sound thin at a friends house because he really has no preamp but back home there is no thinness. Also my woofers don’t cross into the horns until 1100hZ so more of the upper bass lower mids are boosted by the woofers.

Matt’s D Class tested even lower than thought with the typical rise in the upper frequencies. I don’t think all Ds have this rise at least not that early. From what I understand a lot have a 400khZ clock. Not sure it would make much difference.

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PostPosted: 27 Apr 2019, 14:57 
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One more postscript to this project.

So what does one do when their new amplifier has an input sensitivity of about -11dBv for full output and the old school digital receiver feeding it has an output of around 6dBv? Compounding this problem is that the inexpensive audio control in the amp has poor channel-to-channel tracking at very low settings.

Well, if you're me, the answer is to slap together a little attenuator box. So I grabbed an old ethernet transfer switch box that was in my stash, ripped the guts out of it, drilled four holes, and wired up a little 10kΩ volume pad. Here's what it looks like.
Attachment:
Front.jpg

Attachment:
Back.jpg

Attachment:
Guts.jpg

As it will be sitting under the work bench, I didn't even bother with paint. It does the job. Although I might update it with two single potentiometers so I can do a little balancing at the same time. The work shop has pretty funky acoustics.


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PostPosted: 27 Apr 2019, 19:25 
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Suncalc wrote:
One more postscript to this project.

So what does one do when their new amplifier has an input sensitivity of about -11dBv for full output and the old school digital receiver feeding it has an output of around 6dBv? Compounding this problem is that the inexpensive audio control in the amp has poor channel-to-channel tracking at very low settings.

Well, if you're me, the answer is to slap together a little attenuator box. So I grabbed an old ethernet transfer switch box that was in my stash, ripped the guts out of it, drilled four holes, and wired up a little 10kΩ volume pad. Here's what it looks like.
Attachment:
Front.jpg

Attachment:
Back.jpg

Attachment:
Guts.jpg

As it will be sitting under the work bench, I didn't even bother with paint. It does the job. Although I might update it with two single potentiometers so I can do a little balancing at the same time. The work shop has pretty funky acoustics.

Recognise the box. I think the term is re-purpose these days and why not for a lab based unit. The second latest Class d I built was housed in an enclosure made for another amp which never got finished. Apart from a few odd holes in the bottom which no one will ever see from the outside it looks shmick. And saved me about $100 and help cut the clutter in my work room.

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