Search found 304 matches

by terkio
Tue Sep 24, 2019 3:33 pm
Forum: The Peabody Lounge
Topic: Engineering malpractice
Replies: 8
Views: 5637

Re: Engineering malpractice

Changing the anode. Can't you just destroy the old one and fit a new one someplace, all it needs is electric contact with the tank's metal. I think any chunk of zinc is a good enough anode. I know of a heather that blew up because of the pressure relief valve. The manual, from a new heather, the ver...
by terkio
Tue Sep 24, 2019 12:01 pm
Forum: Build
Topic: VCA Multiplying DAC.
Replies: 6
Views: 23704

Re: VCA Multiplying DAC.

You mentioned that the THD specs for the DAC8812 weren't specified for operation at reference levels >5V. That may be because Vcc max is 5V and though the maximum for the reference is +/-18V the distortion performance of the FET(?) switches probably degrade rapidly. It is unlikely the gates are boo...
by terkio
Fri Sep 20, 2019 12:37 pm
Forum: Build
Topic: VCA Multiplying DAC.
Replies: 6
Views: 23704

Re: VCA Multiplying DAC.

I was afraid of such a limitation from the FET switches control voltage. It's even worse, their 0.0005% thd spec is at 5V peak TO PEAK. So the AD5545 may be better since this one mentions being AC able for Vref +12 V -12 V. May be not, that is 24Vpp able, but they don't give a thd figure at this lev...
by terkio
Fri Sep 20, 2019 10:05 am
Forum: Build
Topic: VCA Multiplying DAC.
Replies: 6
Views: 23704

Re: VCA Multiplying DAC.

I need at least: +30dB -10dB gain range and 50 KHz a bandwidth.
by terkio
Fri Sep 20, 2019 7:46 am
Forum: Build
Topic: Audio RMS versus Peak
Replies: 21
Views: 59566

Re: Audio RMS versus Peak

Ok thanks, this thread can be closed, title topic is fully answered.
I opened a new thread for VCA Multiplying DAC.
by terkio
Fri Sep 20, 2019 7:41 am
Forum: Build
Topic: VCA Multiplying DAC.
Replies: 6
Views: 23704

VCA Multiplying DAC.

I am on a VCA design where I need high headroom, high accuracy ( resolution and stability ) I am thinking to use 16 bits MDACs. DAC8812, AD5545. From TI, AD they look the same. The data sheets give -104dB THD at 5Vpp. That is 0.0005%. How do they perform at higher levels ? The AD5545 only mentions A...
by terkio
Tue Sep 17, 2019 7:05 pm
Forum: Build
Topic: Audio RMS versus Peak
Replies: 21
Views: 59566

Re: Audio RMS versus Peak

I think it is a good trick for analog VCA. Their exponential transfer curve mostly makes H2 harmonics, H2/H1going higher with signal amplitude. The trick zeroes H2/H1 lowering the THD figure, but unfortunately does nothing about H3/H1. The results about bridged amps was not from commercial PA, this ...
by terkio
Tue Sep 17, 2019 2:28 pm
Forum: Build
Topic: Audio RMS versus Peak
Replies: 21
Views: 59566

Re: Audio RMS versus Peak

THD cancellation. With a differential topology, if the two legs are exactly the same then you have cancellation of all even harmonics. This is from theory and applies at any level. This theoretical result I have seen effective in bridged power amps. Cancellation of even harmonics does decrease THD, ...
by terkio
Tue Sep 17, 2019 11:20 am
Forum: Build
Topic: Audio RMS versus Peak
Replies: 21
Views: 59566

Re: Audio RMS versus Peak

I looked at a fully balanced configuration, using two VCA circuits as suggested. Compared with balanced to unbalanced input stage, one VCA, unbalanced to balanced output stage. I like the fully balanced for a nicer output stage and the harmonic 2 cancellation and a better S/N. The drawbacks: Cost of...
by terkio
Sat Sep 14, 2019 2:23 pm
Forum: Build
Topic: Audio RMS versus Peak
Replies: 21
Views: 59566

Re: Audio RMS versus Peak

mediatechnology wrote: Sat Sep 14, 2019 2:08 pm I never get timeouts.
How does that happen?
I am extremely slow at typing on a smartphone and checking stuff. I got logged out.