[jkarhan1]

What standard is the HT pasthru on the GK-1. SPDIF?  Will it support/allow current standards to pass (Dolby....yada...yada...)
And.... Does the sub out have a crossover. If it does not.   What would you guys recomend to for a crossover? (assuming your sub has none)

[AKSA]

Hi jkarhan1,

You are referring to digital standards;  the HT bypass was designed ostensibly for audio, however.

It works this way.  When the HT Bypass is selected on the remote, whichever source is selected - and one of the sources can of course be HT processor - is passed directly to the output.  The output of the GK-1 is connected, of course, to the power amplifier, an analog component.  The GK-1 is NOT turned off, so this is actually an excellent way to do a component AB test.

The earth of the source is switched as well as the signal 'hot'.  The earth of the GK-1 is left floating, so that with this regime the source earth, GK-1 earth and power amplifier earth are all connected.  The earths of the other (non-selected) sources are not connected to this system (viz, they float), and this applies both to the manual switched version as well as the relay, remote version.  For any inputs not used, shorting RCA plugs are supplied to banish all traces of hum.  This system is also used by Mark Levinson on his Red Rose gear.

The sub-out does not incorporate a filter.  It is configured so that the sub-out signal is taken from the wiper of the gain pot, just after the gain block and immediately before it enters the tube.  The purpose of this is to process the sub-out before its bass is softened by the tube, an issue with tube equipment.  Tube bypass for very low bass is a GOOD idea.

My suggestion is a third order (18dB/octave) filter.  It could be discrete or IC-based, either is just fine.  I may supply something optional for just this purpose in the future.  It will be discrete, and single ended.

Hope this helps,

Cheers,

Hugh

[jkarhan1]

Hi Hugh,
I might have missed this in your reply. But, here goes. Does the HT signal also go thru the Sub out?
Joe

[AKSA]

Hi Joe,

Yes, it does, but the sub out in this situation is controlled by the preamp volume control, a useful feature.

Sub out does not carry a low pass filter;  that is assumed to be in the active subwoofer box.

Hope this helps,

Cheers,

Hugh

[fred]

The low pass filter within my subwoofer is turned off, because it is also used by my HT processor - which does the filtering (for its signal).  Therefore it seems like a good idea for me to install a low pass filter connection from my GK-1R to my subwoofer.

Since Hugh suggested a third order filter, I did a GOOGLE search and found this description and calculator:

http://www.the12volt.com/caraudio/cross18db.asp
http://www.the12volt.com/caraudio/crosscalc.asp#ccc

I plugged in my requirements (4 ohm speakers, 85Hz cutoff) and it calculated that I need to use the following values: L3: 11.2 mHy, C3: 622.6 ufd, L4: 3.74 mHy

I, of course, know absolutely nothing about electronics, so I'd appreciate it if someone who DOES could tell me if this will work  - and if not, what I should be doing.

[AKSA]

Fred,

The HT Bypass out and Sub-woofer out of the GK-1 are in fact high impedance outputs.  This means they deliver the necessary voltage to an amplifying device, but not much drive.  In truth, the outputs are taken in the first case direct from the input of the GK-1, bypassing it effectively so the drive depends on the grunt of the input device to the GK-1, and in the second case, the sub-out, output is taken from the wiper of a 22K cermet pot (M version) or 50K pot (remote version).

Consequently, the low impedance low pass filter you envisage would be much too difficult to drive.  You need the high impedance filter which is integrated into your active sub.  These normally have input impedances of around 10K minimum, and usually 20K, and sometimes 30K.  The higher the better.

Sometimes active subs are designed to run straight from the speaker output of the amp.  If this is the case, you have no option but to connect it to the output of your power amp, and let its internal circuitry do the rest.

If however it is designed to be driven from line (or preamp output) level, then you are in luck, and the GK-1 should accommodate it well.

Hope this helps,

Cheers,

Hugh

[fred]

Oops.  I had listed the 4 ohms impedence of my main speakers, not the sub.  My sub indeed uses a line level input, but I'll have to research what the input impedence is.

In order to use the low pass filter built into my sub, I have to flip a switch on it.  Then flip it back to disengage it for HT mode (the subs low pass  must be disengaged for HT because I rely on the bass management feature of my digital processor to send the low frequencies from all 5 HT channels to my single sub.  It's not appropriate to use the sub's low pass in this already-filtered environment).

Flipping the switch does not appeal to my lazy nature (the same nature that drove me to buy a GK-1R). This is why I hope to build a low pass filter external to the sub itself; ideally built into the GK-1R.  

Is the circuit in the link I previously  posted correct?  Does the calculator in the other link provide usable values for capacitor and inductors?  For 20000 Ohm impedence, the calculator says to use: L2= 53K mHy, C2: .066 uF, L3: 56.2K mHy.  Am I on the wrong track entirely?

Gracias et Vielen Dank

[AKSA]

Fred,

You expose my design weakness with these questions on filters.  Not my game really.

However, a couple of points.

The sub-out on the GK-1 is not merged into one output for a single sub.  It's left as discrete left and right channel, and is a tap on the wiper of the volume control - a high impedance (meaning:  low drive) point.  Obviously, to combine them AND create a separate low pass filter in the GK-1 you will need additional active circuitry.  I must admit this was not something I had expected when I designed the GK-1;  I was trying to oblige those who wanted a sub-out, but didn't give it perhaps the thought it warranted because at the time I was close to completion and not thinking too hard about integrating a high fidelity component with a HT application.  This is not to decry either technology, but they are very different beasts.

In order not to mix the left and right channels, you'd need a buffer for each channel between the sub-out and the filter.  Then you'd need a low pass active filter of at least 18dB/octave, possibly integrated into an emitter follower, or maybe an IC.  The output from this would then be a single channel, integrating both bass components of each channel, and could then be passed to your sub amplifier.

However, you mentioned your active sub had a filter on it already.  Do you really need another?  And do you know the input impedance of your active sub?  They are typically 10K, but it could be as high as 33K.

Cheers,

Hugh

[fred]

you mentioned your active sub had a filter on it already. Do you really need another?

The filter in my sub is switched off.  This is common for HT systems, because the HT processor performs bass management.  This process is performed by a digital signal processor, and consists of "filtering" low frequencies (typically < 80-90Hz) from all channels (5-7 channels), and combining with the LFE (low frequency effects) channel with output going to the LFE connection (designed to be connected to a self-amplified sub).  Consequently, it is inappropriate to filter the signal again.  By the way, the built-in filter in my sub is only second order (12dB/octave).  I CAN, of course, simply flick a switch to engage/disengage the built in filter.  I was simply trying to avoid the exercise, if practical.

And do you know the input impedance of your active sub? They are typically 10K, but it could be as high as 33K.

Alas, no.  I have looked through the documentation that came with the thing and searched the manufacturer's (Velodyne) website.  I have sent them an e-mail, but have not received a reply yet.  Are input impedences, a constant - not frequency dependent?  Regardless, I gather that the passive filter I envisioned is not possible.

I now realize my desire is probably not practical.  At this point, I don't even know that it will be necessary to use the filter; what's the real harm if the full range signal is sent?  I'll judge this by listening comparisons - when the GK-1 is completed.  At worst, I'll live with flicking the switch - really a small price to pay for what I'm getting.