Remote controlled stepped attenuator/input select (balanced/

harvardian · « **on:** 7 Apr 2003, 12:48 am »

We have designed a new kit.

For details:

http://www.dipchipelec.com/apox.htm

Best Regards,

Dale

JoshK · « **Reply #1 on:** 7 Apr 2003, 02:12 am »

Very nice, looks like you've been working hard. Any ideas yet about costs? Very very intriguing.

harvardian · « **Reply #2 on:** 7 Apr 2003, 12:01 pm »

Hi Josh,

We will take some time today to work up our final BOM and guestimate costs. We are hoping to solicite pre-orders in an attempt to lower the costs significantly.

I'll re-post when some target prices are posted.

Best Regards,

Dale

Vinnie R. · « **Reply #3 on:** 7 Apr 2003, 05:33 pm »

Hi Dale,

Wow, that looks great, nice work! Cool display too!
Have you figured out the resistor values/attenuation curve?

I can see your kit connected with a DACT CT101
preamp module making an awesome preamp

Let us know when it is 100% complete.

-Vinnie

JoshK · « **Reply #4 on:** 7 Apr 2003, 05:49 pm »

Keep us posted Dale. I would definitely be interested so long as it isn't cost prohibitive. I have all kinds of ideas stirring in my head.

harvardian · « **Reply #5 on:** 8 Apr 2003, 01:03 am »

Hi,

We have posted prices.

For a balanced series 24 stepped attenuator with four inputs, the kit cost is $360.00 This does not include resistors. You can also use a TX102 type transformer.

If you only need single ended, you can subtract $72.00 as you only need one volume relay board.

Best Regards,

Dale

audioengr · « **Reply #6 on:** 10 Apr 2003, 02:57 am »

Questions:

Is this wireless remote-controlled?

What are the big Auricaps for?

Is this simply a passive attenuator or does it have active drivers?

harvardian · « **Reply #7 on:** 10 Apr 2003, 12:20 pm »

Hi,

Thanks for the questions.

The kit has three components that act together.

1) Infrared wireless remote / display / encoder board
2) Input select board (single ended or balanced) / switched grounds via relays
3) Volume attenuator - three flavors define thus far.
A) 24 step series attenuator - single ended or balanced constant impedence. (1 board for single ended, 2 for balanced
B) > 128 step shunt attenuator - variable impedence, one board for single ended or balanced.
C) Digital pot - PGA2310 or equiv.

Please see the web page for more information including schematics.
http://www.dipchipelec.com/apox.htm

If you have more questions or suggestions, please feel free post here or send us an email.

Best Regards,

Dale (Harvardian)

peranders · « **Reply #8 on:** 10 Apr 2003, 12:59 pm »

Real nice work!

What type of attenuater is it? Is it T-link constant impedance?

harvardian · « **Reply #9 on:** 10 Apr 2003, 01:30 pm »

Hi,

I forgot to answer a couple of the previous questions. The big yellow caps are "Clarity Caps" and are part of the preamp circuit (not the volume control kit). The preamp is the "Balanced Line Stage" or BrideOfSonOfZen from www.passdiy.com This preamp is not part of the kit, but demonstrates one application. I tried out the combination last night.

Here was my system:

Home brew DAC (BB PCM1702 4 in parallel per channel) with Zapfilter2 for I/V and output to balanced.
BOSOZ / APOX-2 preamp
Aleph2 clones
Watt/Puppy clones

This was the first time that I have heard the BOSOZ as well.
Compared to my passive Creek OBH12, there was a huge difference in dynamics, soundstage, and depth of music. There was absolutely no clicking noise when changing volumes with the volume control. (These speakers are pretty efficient, so I expected some pops).
There was no added hum or noise.

I am quite pleased!

Peranders,

There will be three versions of the volume board. This one is a classic series ladder with 24 taps. For my application, the volume board is on the output of the preamp and has 5K impedence. For applications where the volume is on the input, higher impedences can be built.

The second version is a shunt type attenuator using a binary decoding scheme and can have at least 128 levels using only 10 resistors.

The third version will be a digital pot and possibly a built-in gain/buffer stage.

Best Regards,

Dale

peranders · « **Reply #10 on:** 10 Apr 2003, 06:14 pm »

Have you ever considered T-link attenuater (do you know what I'm talking about?)? I made an attenuater with 8 links, 256 steps = -128 dB, 0,5 dB steps. I never made any control circuits.... but the pcb's with relays are left.

If I remember right this type of attenuater is used for RF-attenuaters.

harvardian · « **Reply #11 on:** 10 Apr 2003, 06:23 pm »

I guess that I don't know what a T-link refers to

Could you draw a picture or point me to a example.

Thanks,

Dale

peranders · « **Reply #12 on:** 10 Apr 2003, 08:52 pm »

I don't have the equations handy right know but picture this:

Rseries + R to ground+Rseries plus a load equal to the impedance.

Very low attenuation

1 ohms+1 MOhms+1ohms+ 600 ohm load

High attenuation

599 ohms + 1 ohms + 599 ohms + 600 ohms load

You can "see" 600 ohms from the input and the load can see 600 ohms towards the T-link.

Advantage of this attenuator is of course constant impedance (important in RF) and you can easy make a decade box.

Example:

64 dB + 32 dB + 16 dB + 8 dB + 4 dB + 2 dB + 1 dB these links can be chosen arbitrary with a 2 pole changeover relay

The attenuator is binary by nature.

I have formulas somewhere, maybe someone else can help?

Did I mention that this type of attenuator is very wide band, DC to MHz or even 100's or 1000's of MHz and also low noise

JoshK · « **Reply #13 on:** 10 Apr 2003, 09:07 pm »

Dale,

I am sure you are being bombarded with questions like, "why didn't you add this?", or "can I get it like this?" but I wondered if it would be too difficult to mod for a tape monitor outputs for my headphone amp? The headphone amp has a volume control so I just need an extra set of outputs without volume control. I am just a tad too novice to know how this is done to know whether it is possible.

harvardian · « **Reply #14 on:** 10 Apr 2003, 09:22 pm »

Hi Josh,

The system does have a HT bypass mode where the selected input is directed directly to the output. You could tap off the board and have a second set ouf outputs. Can the headphone amp be left in the circuit when the main amp is on? It would be tied to the input of the amp and be subjected to the preamp output.

If not, we would need to add another set of relays to swap between the main outputs and the headphone output. This would add another set of relays that all signals must pass through. If we re-spin the board, perhaps we could add. There are no more output pins on the input select board micro.

Dale

peranders · « **Reply #15 on:** 15 Apr 2003, 12:26 pm »

Quote from: peranders

I don't have the equations handy right know but picture this....

I have killed time with deriving formulas but here is a shortcut.

http://members.home.nl/myrnout/elek/eatten.html

harvardian · « **Reply #16 on:** 15 Apr 2003, 01:04 pm »

Hi Peranders,

Great link. Thanks.

Let me see how we could implement.

Dale

peranders · « **Reply #17 on:** 15 Apr 2003, 07:42 pm »

The implemention is rather easy, just connect a couple of T-links and terminate with specified load. For audio it's not necessary to have correct source impedance.

You connect and disconnect each link with a 2 pole change over relay.

If you look at the Java script (view source), you can see how you calculate if you want to make your own calculations (with Excel)