Search found 5468 matches

by mediatechnology
Wed Sep 05, 2007 9:47 pm
Forum: Pro Audio Design
Topic: Dynamic Equalizer
Replies: 4
Views: 16721

Dynamic Equalizer

There was a post today over at Prodigy-Pro that reminded me of this: Larry Blakely while at dbx presented an AES paper "A Variable Frequency Limiter/Compressor/Expander" which was given the working model number dbx169. I don't think it was ever built but it was a frequency-selective dynami...
by mediatechnology
Wed Sep 05, 2007 12:00 pm
Forum: Pro Audio Design
Topic: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp
Replies: 80
Views: 353547

Re: Using the THAT1646 As A Power Transistor Pre-Driver

sender: I haven't actually tested the maximum input range and it does depend on supply voltage. A very good question. I'm assuming that you're going to be using the unbalanced "common-mode" drive using the paralleled sense +/- pins as input and taking the output from both pins 1 and 8 in p...
by mediatechnology
Mon Sep 03, 2007 6:22 am
Forum: Pro Audio Design
Topic: Precision M-S (Sum/DIfference) Matrix Uses No Resistors
Replies: 5
Views: 27248

Re: Precision M-S (Sum/Difference) Matrix Uses No Resistors

Roger gave me an idea for something to try. We've had a lot of people ask about adding a variable width control and I've been somewhat concerned about it's effect on precision. The centertap ground pots in Rick Chinn's design also complicate building. I want to explore a way to subtractively vary &q...
by mediatechnology
Sat Aug 25, 2007 10:22 am
Forum: Pro Audio Design
Topic: Precision M-S (Sum/DIfference) Matrix Uses No Resistors
Replies: 5
Views: 27248

Re: Precision M-S (Sum/DIfference) Matrix Uses No Resistors

Roger I did receive it and want to look it over. The layout is the one with balanced I/O and the inverter in the middle which allows the actual matrix to be either -6 or 0 dB compensation for "build-up" gain. What I need to run some more experiments on are the choice of THAT1240 and 1246 a...
by mediatechnology
Tue Aug 21, 2007 8:49 am
Forum: Pro Audio Design
Topic: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp
Replies: 80
Views: 353547

Re: Using the THAT1646 As A Power Transistor Pre-Driver

Thanks Keith. I want to find a way to operate it closed loop with a "helper" op amp next. But with the distortion so low as it is (with the final buffer operating Class-A without global or local feedback) I'm tempted to just quit and leave it alone. For a portable version (stereo would pul...
by mediatechnology
Mon Aug 20, 2007 5:23 pm
Forum: Pro Audio Design
Topic: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp
Replies: 80
Views: 353547

Re: Using the THAT1646 As A Power Transistor Pre-Driver

I just rebuilt this little circuit on it's own protoboard with a better heatsink. The idle current as measured through the V+ lead is 60 mA. So with 36 V supplies this little baby is burning off 2.2 watts Class-A while it's doing nothin'. https://www.ka-electronics.com/Images/jpg/energy_star.jpg Nah...
by mediatechnology
Sun Aug 19, 2007 8:47 pm
Forum: Pro Audio Design
Topic: Why A GSSL and SSL Compressor Aren't Exactly the Same
Replies: 2
Views: 23057

Re: Why A GSSL and SSL Compressor Aren't Exactly the Same

Thanks ghengis. I don't know of any that sum L+R as audio ahead of the detector. Not to say that there aren't some that do. Roger, in the original Pico Compressor, did provide this as a build option but I don't know of anyone that's used it. Most that we've heard of used true power sum. I agree that...
by mediatechnology
Sun Aug 19, 2007 7:24 pm
Forum: Pro Audio Design
Topic: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp
Replies: 80
Views: 353547

Re: Using the THAT1646 As A Power Transistor Pre-Driver

I just thought about the offset and why we're not seeing it. In a conventional output, lets use a 990 as an example, we have a bias string that looks like this: https://www.ka-electronics.com/Images/jpg/JE-990_Bias.jpg CR9 and CR10 set the Vbe delta for the output devices. But the anode cathode volt...
by mediatechnology
Sun Aug 19, 2007 5:50 pm
Forum: Pro Audio Design
Topic: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp
Replies: 80
Views: 353547

Re: Using the THAT1646 As A Power Transistor Pre-Driver

I lowered the pullup resistor to the bias diode to 1K. With a 68 ohm load I now see 1 KHz open loop distortion figures of -100 dB at 2nd and 3rd at 10V P-P. The Iq is roughly 80 mA.

I'm thinking that 68 ohms is a realistic load for 32 ohm headphones with a 27R buildout.
by mediatechnology
Sun Aug 19, 2007 5:15 pm
Forum: Pro Audio Design
Topic: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp
Replies: 80
Views: 353547

Re: Using the THAT1646 As A Power Transistor Pre-Driver

Thanks Roger. No I didn't see much offset which is surprising. Maybe I got lucky "matching" random transistors. For a line driver you can't beat the bare 1646 or a 1646/transformer configuration as you've shown us. The open loop distortion performance driving 30 ohms is not spectacular: I ...