How should I integrate this remote volume control?

I will shortly be building a diy remote volume control kit:

http://www.altronics.com.au/index.asp?area=item&id=K5026
[IMGDEAD]http://www.altronics.com.au/images/prod/K/K5026.gif[/IMGDEAD]

It controls a 20k pot.

I'm currently using an integrated amp, which has pre-out/main in, and I have inserted Behringer Ultracurve in between pre and power amps, which means I can use it to provide more gain. This makes me think, should I bypass having a normal preamp? Could I insert this 20k motorised pot before or after Ultracurve?

It has a +12 and +22 dbu setting which as I understand, alters the gain ...

I have a non working ESP preamp (the one with tone controls), which I could get working and insert it in there perhaps ... (but don't really want the tone controls now) ...

If I inserted this motorised pot in without any preamp, would it then be a passive line level attenuator? I have never been clear on what is the difference with those apparently expensive passive attenuators!
 
It's a good value kit and I've done a few. Never could get the mute to work properly as too touchy on adjustment so the track was cut as suggested in the instructions and the pot varies in quality.... have had a real good one and others crappy. I ended up getting one of the 16mm Alps that Peter Daniel was selling and was very cheap and sounds good.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=57626&highlight=

Just wire it in after the selector and before your pre out. You can try passive or with your active pre in the existing location. Passives are a strange beast and when they sound good they are great but when they don't.... er.... awful. Impedance matching and all that stuff. The only amp I've ever had luck with a passive was the GC.

Here's a layout but has an active pre.... igonore that and it's a passive.
 

Attachments

  • opa627 in case all view.jpg
    opa627 in case all view.jpg
    49 KB · Views: 467
Ok I've built the kit, grabbed some remotes to see if one of them can control it. Fortunately yes, one of them does :)

However ...

I then programmed the signal that worked into my learning remote, and then tried it. It worked as well, but only for a short time! :( I disconnected from the power, and after half a minute tried again and it worked for a few moments, then stopped working again. This happened yet one more time ...

but now it doesn't seem to work at all!

Any ideas?

Yes - it has adequate power 12V going to the terminals
Yes - all the connections seem fine

One strange thing - there was a spair MKT cap left over, did you find that as well? Also, does that chrystal thing have a polarity?
 
Should be 3 100nF MKT's on the PCB. If they are all there, then surplus. There is another 10nF MKT for the motor filtering. 4MHz Crystal can go in any direction.

Just double check the wires running to the motor as sometimes the fine wires break. Once I solder these on I put heatshrink over the joint to act as a sort of strain relief (put the heatshrink on the wire before soldering).

If it happens again, check the voltage at the input terminals and pull out IC1 and measure the voltage between pin 5 and 14 on the socket for roughly 5V.
 
ahhhh that's the cap I was talking about ... so how do I put it in?

I tried it out in my system passively, after the switchbox and before preamp, and it sounded terrible. Apart from very unsteady changes in volume, which seemed to change almost randomly, the overall sound was terrible - distorted like a very cheap amp (ie. 1w) and speakers turned up to their limit. TV speakers would sound good in comparison!

It appears I'll have to do a diy preamp! ... I did one as one of my first electronics projects, however it didn't work :(

Any ideas why it might sound so bad?
 
paulspencer said:
ahhhh that's the cap I was talking about ... so how do I put it in?

I tried it out in my system passively, after the switchbox and before preamp, and it sounded terrible. Apart from very unsteady changes in volume, which seemed to change almost randomly, the overall sound was terrible - distorted like a very cheap amp (ie. 1w) and speakers turned up to their limit. TV speakers would sound good in comparison!

It appears I'll have to do a diy preamp! ... I did one as one of my first electronics projects, however it didn't work :(

Any ideas why it might sound so bad?


Sounds as if you have too much gain in your system. Maybe you should try without that Behringer, or preset that for a comfortable range on the remote control.

Jan Didden
 
How can there be too much gain? If that were the case, surely the amp would be clipping. However, in this case, the sound is distorted at any volume when the pot is included as a passive attenuator. Not distorted as in the peaks being clipped, but distortion as in the entire signal sounds like AM radio on a cheapie clock radio!

Rabbitz, what do I need to do with that 10nf MKT cap?
 
The 10nF goes across the motor terminals.... see the pic below.

Too much gain really can make the sound sound harsh and ill defined. Had a Rotel pre amp attached to an AKSA and the Rotel must have had a zillion dB gain as it was full bore about 9 o'clock so I put in a dividing network to attenuate the signal which was OK until I finished my pre amp with 6dB of gain.

Try the passive first with only the source > pot > power amp without any other electronics. Then add one active thing at a time.

Just double check you have the pot wired correctly... looking from the front:
Right pin is IN
Centre pin is OUT
Left pin is GRD
 

Attachments

  • alpha 20k pot.jpg
    alpha 20k pot.jpg
    61.8 KB · Views: 230
paulspencer said:
How can there be too much gain? If that were the case, surely the amp would be clipping. /B]


Doesn't quite work like that but I believe you can overload the power amp with too much voltage in... so it's not clipping as such. Make sure your Behringer doover is set to the lowest gain as 22dB is a HUGE amount of gain..... a virtual power amp.
 
I got the wiring wrong then ...

I treated centre as GND and the end pins and in and out! I'll have to fix this and try it again, thanks :)

Question: is there any real purpose to a preamp except for gain and volume/balance control?

Suppose I don't need the gain and balance ... what do I lose by not having a preamp?

Put another way ... what is hard about getting a passive pot right compared to a preamp? How is it different?
 
paulspencer said:
IQuestion: is there any real purpose to a preamp except for gain and volume/balance control?

Suppose I don't need the gain and balance ... what do I lose by not having a preamp?

Put another way ... what is hard about getting a passive pot right compared to a preamp? How is it different?

Aside from gain, preamp can provide two things, high impedence to the previous stage, and adequate current (low impedence) to maintain the voltage signal into the next stage - in other words, a buffer. The usual rule of thumb is that the input impedence of a stage should be at least 10 times the output impedence of the previous stage. With that ratio you shouldn't have gross distortion, but a higher ratio might sound better. Add a buffer to your volume control, and you have a "preamp" with no gain.

Sheldon
 
In theory a pre amp only needs a volume control which a passive can do but there are problems with matching the source and amp impedance and driving the low level signal cables especially if they are longer than 1m.

Passive when working is very yummy and I have 2 amps working that way which are LM3875 chipamps with the pot inside with the power amp. I've tried it with bipolars and it didn't work for me and ended up with a rolled off response such as loss of some bass, so active was the way to go and I just used a simple design using a OPA2134 op amp for 6dB gain.

I don't completely understand it and if I did I probably could have got the others to work.

Best bet is to try and listen..... only way to find out.
 
Oils ain't oils and the same with pots.

Channel balance, tracking, noises, pops, farts, feel, sonics, noisy motors.... they're all different. PD has a good thread in the Chipamp section and don't confuse this Alpha with the one in the thread as it's a different beast. 2 of mine were unusable (they were to be replaced anyway) due to poor sonics and clatter but 1 was a beauty but a noisy motor, whirrrrrrr.... made on Wednesday :D

That's why earlier in this thread, I suggested the Alps pot that PD was selling..... about AU$22 shipped and very nice and great value. If you're happy, stick with the Alpha.