A twisted tale about a logarithmic relay attenuator

[chalkandtalk]

There is a buffer then the pot and then a gain stage.

As in the Naim 32.5 preamp.

 

[chalkandtalk]

I have built the JT and put it in my Naim style preamp. It sounds great. Many thanks Russ and Brian. 😀

It's early days but it appears that quite a few aspects of the music are better: dynamics, bass for a start.

 

[DFroehlich]

JT kit

Hi Russ,
will the Jshua Tree come back in stock in the next time ?

 

[BrianDonegan]

The Joshua Tree is being redesigned. We will post details when things firm up a bit.

 

[Russ White]

Re: JT kit

Hi Russ,
will the Jshua Tree come back in stock in the next time ?

It will not be long.

Joshua Tree has proven to be a solid design. So I will not change it much. Just adding some refinements and design changes necessitated by my new pluggable controller design.

I am actually working on it today, and should be ready to order the PCBs in the next week or so depending on how much time I can dedicate to it.

What I have in mind should allow for both the simple control mechanism of the current JT controller (just a pot) as well as more advanced configurations such as rotary encoder and/or IR control as well as display.

Also in the work is a simple I2C relay driver board that will allow you do you existing JT boards and even Darwin. So you will be able to create a full featured preamp with this controller scheme.

The nifty part is that the controller is designed to detach from the main application board (call it a motherboard if you will) and it will have a USB connector on it. So I can disconnect the controller from the application and simply plug it into the PC and reprogram it. This makes it possible to use the same little controller for lots of different projects.

It is not a trivial project. And it may be a bit complex for some users. I will do my best to document it. I will also have some example firmware for common applications.

Cheers!
Russ

 

[robmil]

what does it look like 'ELECTRICALLY'.

Rob here

Can someone please explain what this attenuator 'looks like' electrically. I have attached a PDF of what my standard Alps in my preamp looks like 'electrically'... you all know it.

I know there are others here that would also like to know.

Thanks a billion.

R

 

[Russ White]

It looks like a series of LPADs. Each with the same output impedance so that the final output impedance is nearly constant.

Cheers!
Russ

 

[robmil]

What is an LPAD ?

cheers

 

[Russ White]

Simply put, it's a voltage divider. 🙂

 

[MrMajestic]

Any updates on the new boards? I know you have a lot on your plates, but its not beginning of may anymore 😉

 

[Russ White]

Hi MrMajestic, Life is nutz around here for Brian and I. We have both spent much more time than we ever dreamed getting our DAC project Buffalo "just right".

Lots and lots of tweaking.

That has kind of put the controller project on the back burner as we both still have regular jobs to do too.

But it is very very near ready to test. I promise. 🙂

Cheers!
Russ

 

[MrMajestic]

Hi MrMajestic, Life is nutz around here for Brian and I. We have both spent much more time than we ever dreamed getting our DAC project Buffalo "just right".

Lots and lots of tweaking.

That has kind of put the controller project on the back burner as we both still have regular jobs to do too.

But it is very very near ready to test. I promise. 🙂

Cheers!
Russ

Great, I will wait patiently for it 🙂 Keep up the good work.

 

[MrMajestic]

By the way, will the new JT have the same form factor as the old one? I ask, because Im currently planning the layout of my preamp which will use the Darwin, JT and possibly the Diamante 🙂

 

[Mazuki]

In a moment of folly, I soldered all the relays in the wrong direction.

Now I'm working on the laborious process of desoldering them. My question is: how hardy are these relays. Desoldering really heats them up, are they basically ruined afterwards?

Should I just solder them back in the right direction or save my time and buy new ones?

 

[luvdunhill]

In a moment of folly, I soldered all the relays in the wrong direction.

Now I'm working on the laborious process of desoldering them. My question is: how hardy are these relays. Desoldering really heats them up, are they basically ruined afterwards?

Should I just solder them back in the right direction or save my time and buy new ones?

been there done that.... I'd say, don't use solder wick. it will heat them up too much. The leads are very fragile. I'd use a solder pump and you should be fine. Maybe on the next boards the silk can be rotated so the text on the silk reads the same as the text on the part 🙂

 

[Mazuki]

Do you think the heat will damage the magnetics inside?

Does anyone have a Mouser part number for replacements?

 

[BrianDonegan]

The Omron part number for the relays is G6K-2P-DC5. The best price I can find at the moment (via oemstrade.com) is here:

http://www.onlinecomponents.com/product/2183307/

 

[Paulus1981]

I was hoping that there was any good news concerning the new 'tree' that you forgot to mention in this tread?

😉

I can't wait to use it in 6channel application 🙂

 

[Russ White]

There is good news. 🙂

The Joshua Tree Mark II is finished and ordered.

I should have them in my hands in a couple weeks. then we will test them and make them available.



Cheers!
Russ

 

[Russ White]

Here is the new schematic. As you can see I added a mute relay. 🙂 Otherwise it is pretty much the same circuit.

Because of the added relay the controller pin out is different from the old JT, so the old controller will not work directly. Never Fear however, as a new (better) controller is on the way too. 🙂

Cheers!
Russ