[MoodySteve]

RK40 will be next-to-impossible to find.

I am using an RK27 currently but, once I have built a slightly larger case, will have the room to substitute some others. I already have a Noble 50k on hand to try.

I've seen someone suggest AVC and TVC - those are MONSTROUSLY expensive.

There's a relay-based attenuator project going on at DIYAudio here>>> diyAudio Forums - New project : R-2R Attenuator With Remote Control V2 - Page 1
but bear in mind that this volume controller consumes almost as much current as three ß22 boards (500mA).

 

[digger945]

It is capable of using either, with the same end result.

 

[rhys h]

Quote:

Originally Posted by digger945 /img/forum/go_quote.gif It is capable of using either, with the same end result.

Ahh i see. Part of my reasoning for choosing somthing like the joshua tree, instead of somthing based on a PGA23** & encoder was the fact i like the feel of a standard pot (too lazy to write firmware all over again). This also allows me to use a standard notched volume knob, volume will allways be the same after poweron and the lack of a need for a display to show the volume level etc.

Joshua tree will work out the same price as a nice stepped attenuator. I know what im choosing

 

[digger945]

I totally look forward to your listening comments. I have never heard a negative comment about the JT, but I think there are plain few of them around.
I agree with you, and if it were available at this moment, it would probably be high on my list.

 

[amb]

I would advise against an external pot or attenuator. The wiring from the pot to the amp board(s) should be kept as short as possible, not only to reduce interference, but also to avoid stereo crosstalk and high frequency rolloff (due to capacitive coupling). The high-Z nature after the pot makes these concerns quite real.

 

[pabbi1]

Noble alert - HIGH probability of funkiness.

IFF confirmed as good, might be quite a snag, but at 100k.

 

[adamus]

Rhys, I am building something at the moment which is similar to your requirements.

In a hifi2000 case, i have installed a relay based input selector which will be controlled by IRremote volume (balance Alps).

However, i think i probably go for a 'lightspeed' ldr attenuator for the signal (controlled by the alps).

I wil probably go active with the preamp too, maybe a cathode follower (bipolar or CSS loaded, maybe even choke loaded) or something solid state like jisbos or some simple diamond buffers. Hopefully this will negate the negatives AMB rightly points out. What ever i do, it will be unity gain.

 

[rhys h]

Quote:

Originally Posted by amb /img/forum/go_quote.gif I would advise against an external pot or attenuator. The wiring from the pot to the amp board(s) should be kept as short as possible, not only to reduce interference, but also to avoid stereo crosstalk and high frequency rolloff (due to capacitive coupling). The high-Z nature after the pot makes these concerns quite real.

Would there be anything wrong with using a simple unity gain buffer after the attenuator before the beta in this case, to avoid the high Z signal? How would this fit in with using the beta22 directly after the buffer?


R

 

[rhys h]

Adam, i have seen the lightspeed over at diyaudio, it looks intresting but im not really certain on its design. I will give the thread another read and see whats what.

Thinking about it, if i was to use the external joshua tree, i could go overkill and use a motorized alps to control the relays

 

[rhys h]

New JT Information / images have been posted

Joshua Tree - A Twisted Log Attenuator

 

[amb]

Quote:

Originally Posted by rhys h /img/forum/go_quote.gif Would there be anything wrong with using a simple unity gain buffer after the attenuator before the beta in this case, to avoid the high Z signal? How would this fit in with using the beta22 directly after the buffer?

Yes, a unity gain buffer immediately after the volume pot will eliminate the high-Z and its associated problems, but you have to ask yourself this question: What's the point of building an amp as elaborate as the β22 when you will be inserting more (most likely inferior) electronics directly ahead of it?

 

[rhys h]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Yes, a unity gain buffer immediately after the volume pot will eliminate the high-Z and its associated problems, but you have to ask yourself this question: What's the point of building an amp as elaborate as the β22 when you will be inserting more (most likely inferior) electronics directly ahead of it?

I dont quite understand your post, i will be using my β22 as a headamp primarily, but also as a preamp for my firstwatt f5, at what part would i be using inferior electronics?

If i was going to use a buffer, i was thinking of a simplified Pass B1.

 

[amb]

Quote:

Originally Posted by rhys h /img/forum/go_quote.gif I dont quite understand your post, i will be using my β22 as a headamp primarily, but also as a preamp for my firstwatt f5, at what part would i be using inferior electronics? If i was going to use a buffer, i was thinking of a simplified Pass B1.

What would you use as the buffer for your volume pot? Would that bit of extra electronics be worthy of β22? Read through the "tech highlights" section at the β22 website. Your buffer will have to be at least as good as the β22 itself in order not to degrade the chain. Will it be fully complementary? Will it be cascoded in all stages? Will it have all those current sources for high PSRR? The list goes on and on...

Edit: missed the bit about the Pass B1. With all due respect to Mr. Pass, and his B1 buffer is a fine circuit, but my point about the β22's topology and design still stands. Also, adding yet another active amplification stage (whether it's unity gain or not) will always add noise/distortion/phase shifts, etc.

 

[rhys h]

Quote:

Originally Posted by amb /img/forum/go_quote.gif What would you use as the buffer for your volume pot? Would that bit of extra electronics be worthy of β22? Read through the "tech highlights" section at the β22 website. Your buffer will have to be at least as good as the β22 itself in order not to degrade the chain. Will it be fully complementary? Will it be cascoded in all stages? Will it have all those current sources for high PSRR? The list goes on and on... Edit: missed the bit about the Pass B1. With all due respect to Mr. Pass, and his B1 buffer is a fine circuit, but my point about the β22's topology and design still stands.

So would you reccomend against using the B1 in such a situation? I have found it to be a very nice buffer in previous experience, but obviously i dont know how it would match up with the beta.

R

 

[amb]

The B1 is a nifty, simple buffer, and so is the JISBOS, for example. But I would not advocate adding a JISBOS ahead of the β22 simply for the purpose of making the volume control external.

As I eluded in my edit above, I'd avoid adding yet another amplification stage unless there is a really good reason for doing so.