A twisted tale about a logarithmic relay attenuator

[Erlend Sæterdal]

Impedans

I am interested in the volume control but I think the impedans is all too low for my purpose. 🙁

 

[Beefy]

I know that this post is old but I'm looking at LOG attenuators and just wanted to offer a comment.
While the individual spec for the I/O pins above is correct, the absolute total for the PIC16F685 PIC
is 200 mA for all the ports. Your calculation:
20mA * 14 (all on) = 280mA........

So just to confirm what is being said here (and in Brian's original post three years ago), a balanced Joshua Tree would draw over 0.5A of current?

 

[MikeBarton]

So just to confirm what is being said here (and in Brian's original post three years ago), a balanced Joshua Tree would draw over 0.5A of current?

for the relays (there are 8 per JT and for balanced mode you will need 2JT's), the calculation would be:

5v / 237ohms = 21mA * 8 relays * 2 JT's = 0.33A

This is ofcourse a worse-case scenario, so 0.5A is in the right ball-park.

I was planning on using my own encoder along with MCU board. If I want to integrate it with your relay driver board what do I need to know?

as mentioned, you need to drive the relays to ground using a ULN2803. This sinks all the current so your pic won't melt 😉
Coupled to a 74HC595, the code to control a JT (using SPI) is surprisingly simple.

Mike

 

[BrianDonegan]

We use I2C rather than SPI, but, same difference. It's pretty simple. The trick is the hysteresis and averaging to prevent constant value changing.

 

[MikeBarton]

We use I2C rather than SPI, but, same difference. It's pretty simple. The trick is the hysteresis and averaging to prevent constant value changing.

Brian
I would assume though that you use the hysteresis averaging because you are using an analogue pot, if sjalloq wants to use an encoder instead, then I don't believe this is an issue.
Mike

 

[BrianDonegan]

Brian
I would assume though that you use the hysteresis averaging because you are using an analogue pot, if sjalloq wants to use an encoder instead, then I don't believe this is an issue.
Mike

Correct.

 

[Keyoke]

Hate to revive an already lengthy post - but is there a 'fixed' schematic available? I didn't see one on the twisted pear site, and the ZIP (on page 4 or 5 i believe of this thread) is no longer a valid link...

 

[thor2]

Cut the crap!! Software isn't my business! My main focus areas are:
- Digital to analog conversion (Which was my special during my education)
- Analog electronics (Also my special)

I know your special is more like this: http://web5687.web04.talkactive.net/homepage/kbhifi/gallerier/moede_01_02_08/klubforforamp.jpg

I am more into making electronics like this: http://img522.imageshack.us/img522/7730/pict2819vm3.jpg

For those who don't know Erlend Sæterdal, please feel free to ask me. His intentions isn't what they look like 🙄

But let's have some of the users of Diyaudio decide... Guess you have to make a bunch of fake profiles, to wote for you (Like all the other forums).

http://web5687.web04.talkactive.net/homepage/kbhifi/gallerier/moede_01_02_08/klubforforamp.jpg
There is no reason to laugh about this Hurtig.
Printed on the front plate is a completely full volume with the remote control: volume, phase switch, mute, four memories for volume setting , input select, max output setting, sleep timer, etc.
perhaps it is not so nice, but it is far above your level,
A closer look here:
http://tkhifi.homepage.dk/javapro/Ir_system1_3.jpg
It is built around an AVR controler.
and the sound of this preamp is fabulous

 

[novec]

Is the firmware posted anywhere?

 

[Erlend Sæterdal]

Cut the crap!! Software isn't my business! My main focus areas are:
- Digital to analog conversion (Which was my special during my education)
- Analog electronics (Also my special)

I know your special is more like this: http://web5687.web04.talkactive.net/homepage/kbhifi/gallerier/moede_01_02_08/klubforforamp.jpg

I am more into making electronics like this: http://img522.imageshack.us/img522/7730/pict2819vm3.jpg

For those who don't know Erlend Sæterdal, please feel free to ask me. His intentions isn't what they look like 🙄

But let's have some of the users of Diyaudio decide... Guess you have to make a bunch of fake profiles, to wote for you (Like all the other forums).

????????????????????????????

 

[thor2]

Is the firmware posted anywhere?

no it is only made for Copenhagen Hi-Fi Club Hvidovre and myself
maybe sometime in the future I release the code.

I wrote only to show Hurtig that we are not totally stupid and hopeless in Copenhagen Hi-Fi Club Hvidovre.
which he is apparently think.

 

[novec]

Sorry, my bad. I was asking for the JoshuaTree firmware, before I realized that the Volumite is controlling everything. I would never get in the middle of a Hurtig fight 😉

 

[thor2]

Very wise!, sorry I misunderstood what you meant when you wrote right after my speech.

 

[Adrculda]

Any updates on the AC1 and AC2 ????

 

[ThuyTN]

Russ,

Not sure if there's a reply here but I'm thinking of raising the input impedance of the JTA to at least 25k because my source is pretty hot. What resistors should I change?

Thanks

 

[AndrewT]

my source is pretty hot

do you mean it is overheating?

 

[ThuyTN]

Sorry, I meant it has high output impedance, 1k-1k2 ohm.
Tried to search a lot but still couldn't find the calculator for the JTA. Would appreciate if someone could give me a hand on this.

 

[Russ White]

Really you might consider a buffer (there are lot of options here). The JT is designed to be used from a low impedance (<100R) source. Even doubling the resistor values would not yield very good results, and produce a lot more noise/distortion.

 

[ThuyTN]

Posted my question in TPA's forum but no help there so I guess I should ask here for better advice.

I've just finished populating the boards and wired it to my headamp. Now the problem is I couldn't set the pot to mute. Right after I turned on the music, the sound is already very loud, even when I already turned the pot all the way off and I had to adjust the master volume in Foobar2k. When I turned the pot, the relays clicked but the sound is not louder, just the same. I already set the switch on the relay driver to off.
My guess is something wrong with the cable from the relay driver to relay board. Somehow I broke the connectors so I just soldered the wires directly to the pins on both boards.

Any idea on this? Would be great if someone could provide me the correct wiring.

 

[BrianDonegan]

Posted my question in TPA's forum but no help there so I guess I should ask here for better advice.

I've just finished populating the boards and wired it to my headamp. Now the problem is I couldn't set the pot to mute. Right after I turned on the music, the sound is already very loud, even when I already turned the pot all the way off and I had to adjust the master volume in Foobar2k. When I turned the pot, the relays clicked but the sound is not louder, just the same. I already set the switch on the relay driver to off.
My guess is something wrong with the cable from the relay driver to relay board. Somehow I broke the connectors so I just soldered the wires directly to the pins on both boards.

Any idea on this? Would be great if someone could provide me the correct wiring.

Sounds like you have the audio wired incorrectly. Could you post a pic?