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Warpspeed -An Optocoupler Volume Control

Up and running battery pack...the diy cable is a repurposed CAT6 with connectors for an SLA battery supply.
 

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What are the range of resistances that your "engine" allows for the series LDR and shunt LDR? There is only one example of each in the spreadsheet, 30r for series and 35M for shunt. These predict -0.04dB through the attenuator and result in an impossibly high 118dB of SPL at 1m.
If I swap these values: 30r to shunt and 35M to series the spreadsheet predicts -95dB through the attenuator and <0dB SPL 1m from the speaker.
Are these valid LDR values for your "engine"?
 
Another pearl of a discovery from my local library -John Williams and the Boston Pops Orchestra's, "It Don't Mean A Thing If it Ain't Got That Swing". Special guest vocalist is Nancy Wilson (Cassandra Wilson's mom?).

The music is very dynamic, high levels never hurt the ears, light and airy big band sound -a lot of swing with the brass!...recorded in 1994 at the Boston Symphony Hall using Sony's 20-bit SBM technology says the literature.
 
To answer several queries, here's a brief description of the completed Warpspeed (pics above)...

*It has a switchable Balanced/Unbalanced functionality; XLRs Pin 1=Signal Gnd, Pin 2=+, Pin 3=-
*2xQuad matched Silonex optocouplers
*Unbalanced has 1 input with 2 outputs paralleled for bi-amping; XLR pins 3 and 1 are shorted via a switch for Unbalanced
*It can be DC powered with an SLA battery at 12V with 5Ah or more capacity
*The power switch and power indicator flank the volume control in front
*The feet are machined black chrome stainless steel; the 'Squid is now in copper; the chassis body is anodized extruded aluminum; the volume knob is a 1.75" lathe-turned aluminum; the connectors are gold-plated Neutrik; silver on copper alloy contacts on switches; wire is silver-coated copper in PTFE (Teflon) insulation on 'Squid; and panels are cherry finished in oil and wax from an OR craftsman...planted a cherry tree this year to replenish:D.

Due to 2x quad matched optos being harder to come by, and my desire to get the product right, this Balanced/Unbalanced version is available as a completed unit only. Please email or PM for availability...Thanks!
 
Warpspeed Att Chart Updated

Last night I got the chance to verify my approximations on the Attentuation Chart (now version 1.3 attached) with measurements on all 3 digital Sources I mentioned a while back (a Toshiba, 2 Sony). The computed versus the measured values are validated and are very close.

The data and computed values are below the chart. Vary the Source Vout pk and it's corresponding Source Out Z and you'll find the measured is very close to the computed (Warpspeed Output Attenuation values). The data also shows the effect of going from a 200-ohm Source Z to 600 ohms and 900 ohms. Although the largest change is about 4dB (going from 200R to 900R) the subjective sound level difference is not much...for 200R I have to dial it down to about 10:30 as opposed to 12:00 for the 900R Source which are both comfortably loud.

The test is a simple 200mVrms, 1kHz test tone played on the Sources while measuring the output of the Warpspeed with a true RMS capable AC voltmeter. Since I already have the data with the unloaded Sources, it was just a matter of plugging in the measured values. Difference in measured values versus with an amp connected on the Warpspeed is very low at less the 1mV.

Btw, I've mentioned before that one of my amps is with 33k input impedance is actually 23k, it can be outright measured from the inputs because there is no input cap and is also the value reflected on the Aleph 3 manual.

I've also added more values on the drop-down list...let me know if you have any particular values you want added.

:warped:
 

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Dear Blues. I currently use LDR attenuator in my system and really like it. Few questions with regards to your kit:
I have LDR's placed in small boxes with RCA in and out connectors that are directly connected to the inputs on my power amps and are controlled from the central box by feeding necessary current to them. Can the same be done with your kit?
A also noted while playing with LDR parameters that sound quality can vary a great deal depending on the Rtot. of voltage divider. I managed to find an optimum for my system with my present attenuator but I am a bit concerned whether I will be able to achieve the comparable sound with your kit. (I read feedback in your thread but still cannot imply anything with regards to this).
 
Hi Alex, it comes with a construction manual with recommendations that the LDRs (optocouplers) be soldered directly on the IN/OUT connectors, and be powered with a battery supply (or tap from a clean/quiet DC supply as long as it is +24V or less).

The LDRs when operated at lower resistances, and coupled with a solid power source(dual-VCCS in the 'Squid) will have minimal or no R drift. Download and play with the Att Chart and input your system's specs to see some data...
 
Thanks for the quick answer, Blues. Does this means that I can solder part to the in/out connectors in the box for the monoblock driving my left channel and another one for the right channel standing 4 feet away?
I know that resistance with my current setup varies a little and I can measure it but I don't really hear it. I can also easily live with small mismatches between resistance values of optocouplers.
The reason why I am considering another option is because I am interested in higher levels of attenuation. Even -40db is still pretty loud for my setup. On my current DAC I was able to decrease its output attenuation level by another 10db so I am good for now, but I ordered another player which will not have such a feature.
My knowledge of electronics are minimal therefore forgive me if something said further will expose my ignorance. Your spreadsheet contains data for attenuation levels that are achievable with my current 'classical' attenuator and calculated for input peak voltage of 0.2828V which I believe is slightly too low as for standard unbalanced output.
Also, what to my understanding makes difference in my system is amount of current provided after attenuation: when it is right the system sounds really sweet, if there's too little it goes to the 'dark side' and when there's too much is gets too sharp/bright. You probably will understand my concern with regards to this.
 
I have not tried >3.28ft interconnects...but unless you have some funky, high capacitance/inductance cables I don't see any problem. I always recommend on unbalanced systems, to make source-preamp-amp interconnects the shorter runs and on the amps(even with monoblocks)-speakers the longer ones...induced noise on line out signals will be amplified further as it goes thru the amps.

Volume level will go from dead silence, very soft, soft, medium, to loud, and very loud so you're covered. The 0.2828Vpk on the spreadsheet is variable just change it to your Source's spec. It is just there as an example per my test with my own Source (scroll down for the details). Have a read to have an idea about the design on the article (FTL-Fiction or Fact?) posted at the start of the Thread.

Here are some pictures of a newly completed unit getting a workout with Kodo (taiko drums) which is also my tribute to the Japanese people's resiliency and discipline in the face of tragedy and hardship. Picked up the cd in Akihabara during my visit in '98...very warm and respectful people.
 

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Your attenuators look really gorgeous! Fine work and nice pics. And thanks for answering. Just to clarify: my interconnects are ~ 2ft. The boxes attenuate signal right before it is fed to the amplifier. This way I have no need for another pair of interconnects between source and power amps at all. It is just DAC->RCA interconnects->Attenuator boxes(sitting right on the RCA inputs of power amps)->Power Amps(monoblocks)->Speaker Cables->Speakers. I could've send the pictures but I doubt that they will explain the idea any better.
My source was factory preset as 2Vrms (Benchmarkmedia DAC). My amplifiers are Kenwood L07 M with input sensitivity 1V. That is one of the reasons I don't want another set of interconnects to the power amps: even with very good ones it is difficult to keep signal undistorted at that level.
Now, If I put 30R source impedance with 2.8284 Vpk the figures in the spreadsheet do not look very reassuring even with amps Z 10K which is much lower than my amps (can look it up but as far as I remember it is close to 30 or 50K).
Anyhow, even current -40 db attenuation for this setup is pretty darn loud as the minimum volume setting. As I explained before this is not a problem for me at the moment but it might require some tweaking in the future that's why I was curious about your kit.
 
I think I now see where controlling it separately on each monoblocks comes in (I take it you have separate attenuators on each amp?)...you can choose to locate the Warpspeed closer to the DAC and run (how long?) interconnects to each amp.

My system goes totally silent at about -100dB and from there increases nicely in sound level. So like I said you are covered. -120dB is achievable at max CCW.

Email/pm me and we can discuss it more...
 
I have only LDR's in the boxes. A pair in each box. They are controlled by the central box with volume and balance knobs and of course with all the nitty gritty required to regulate power.It feeds the necessary current to attached boxes trough the cable. Must say this makes a big sonic difference in my system. Anyway, I sent you PM.
 
Updated Spreadsheet v1.4

The Attenuation Chart is now v1.4 which includes a page with volume level scenarios(also interactive) if the Warpspeed is used for Headphones volume control.

The Warpspeed's output impedance will now come into play because of headphones' generally low impedances. A buffer after the Warpspeed is recommended, and a B1 or a DCB1 can be employed.

Since you are a DIYer, build a 1/4" headphone jack to RCA adapter and you are ready to plug your high-end headphones into your B1 or DCB1 output RCAs. Enjoy!

:warped:

ps. -No reason not to give a listen to a direct Warpspeed to headphones connection though and decide if a buffer is really needed.
 

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