Mechanically thats more difficult that it looks to be. It may be possible to get a movement that will do this but getting the pin to move the next decade one step requires some tricks. If you look at watch movements that do this they are not as simple as they seem. I have wanted to do this for years. There is a mechanism in the old Fluke differential voltmeters that works this way-
An externally hosted image should be here but it was not working when we last tested it.
I have a couple and the mechanisms are not smooth. They have a bigger problem with more digits but the core issue is the same.
Depends on the architecture. If its 1 dB steps and 10 dB steps you still need six or more steps on the 10 dB level. The mechanical device to do this is one of these: Berg but they are very expensive. Electronically it can be done with some sequencing of relays but the clicks and pops suggest you would be better off with different solutions. Or all relays if you go there.
Re. those TKD stepped attenuators:
Did anyone ever try to contact their local TKD sales reps? Considering the price of a unit I guess they might still be interested in selling even a single unit directly. I read about a DIY fair here in Germany last year where the German TKD representative was present; this tells me they ARE interested in DIY sales.
Did anyone ever try to contact their local TKD sales reps? Considering the price of a unit I guess they might still be interested in selling even a single unit directly. I read about a DIY fair here in Germany last year where the German TKD representative was present; this tells me they ARE interested in DIY sales.
Of course you can get TKD pots cheaper than $800 from the manufacturer, and more local sources. We did, but they are still too darn expensive for most people. However, our customers are not 'most people'. It is the same with auto tires, etc. If you want the 'best' be willing to pay for it.
Once, about 20 years ago, we used an Alps dual pot that we got from Radio Shack for $2.79 and it was actually pretty good. Not great, but pretty good. Kind of like a bargain tire for your car.
Once, about 20 years ago, we used an Alps dual pot that we got from Radio Shack for $2.79 and it was actually pretty good. Not great, but pretty good. Kind of like a bargain tire for your car.
I have gone from 2 knobs for vol plus 2 switches to control their range to a single Alps pot covering the full range, I wouldn't go back to the old system. Does it sound better? It doesn't sound any worse, I have not done a DBT. Ergonomics is important, I wouldn't rush to the next room to change a record even if it sounded better with the turntable out of the listening room.
On an early product I used a rotary switch and inserted a series resistance in one channel or the other with .5 dB steps. Centered it was out of the circuit. Cranked all the way to one side or the other it was 3 dB. Total correction was 6 dB in effect. If the program was worse than that it has real problems. If the system needs correction a balance control is the wrong place to fix it.
john curl said:
Thanks, that sums up the situation nicely.
I am going to try fixed series resistors feeding the tops of the stereo pot then connect the arms of a mono lin pot across these with the wiper earthed. Maybe no better than stereo pot in series with the vol pot but a good single pot should be cheaper than a ganged pot.
fredex said:
There is a good chance that more than gain will be different between the channels. If you have any cathode degeneration it should reduce the unit to unit variations a lot. If they remain the tubes must have big intrinsic difference that will also show in different frequency responses.
Early on the feedback effects of cathode degeneration were used in instruments to reduce the instability of gain etc. Tek tube scopes don't have feedback in the conventional sense on the fast amplifiers however careful design usually ensure they meet spec. with tube variations. Another possibility is tube end of life cathode aging.
- Status
- Not open for further replies.