Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Quickie => Topic started by: underdawg on March 06, 2013, 02:49:44 AM
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NOw that my preamp is up and running the gain is way to much. I can only get 2 stepped positions out of noble volume control, which is 100k. What is the best solution to get the gain down to gain more volume control?
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Add two 100K resistors between rotary switch terminals A and B and the input of the potentiometer. Do you have a link to the Noble control you bought? It may be likely that 100K isn't enough.
You can also pad the inputs of your amplifier, which is the best way to go IMO, but often the least accepted.
-PB
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............I can only get 2 stepped positions out of noble volume control, which is 100k. What is the best solution to get the gain down to gain more volume control?........
Are you sure the control you have is logarithmic, "audio", taper not a linear taper?
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sorry dont have a link, the paper with the noble is a small manual but it contains just the electrical specs and all the measuremnents of physical construction. I will add the resistors to the rotary switch a&b. If not enough volume movement gain then ill add to the potetiometer inputs. Thank you for the idea's. Maybe I will try some pads on the amps also first , check the sound, I assume just a resistor - what value to pad the amp input?
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............I can only get 2 stepped positions out of noble volume control, which is 100k. What is the best solution to get the gain down to gain more volume control?........
Are you sure the control you have is logarithmic, "audio", taper not a linear taper?
no idea on that one, the manual state its is a noble audio volume control.
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what value to pad the amp input?
Try this in the amplifier:
-----input---->
|
|
100k
|
|---------->output
10K
|
|
----ground-----|
There may already be a resistor there, if it's over 100K, you can just leave it there if you want to, if this is a solid state amp and that resistance is pretty low, then I would advise leaving it in place and using it as your lower resistor in the picture above.
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My amps are Odyssey Stratos Monoblocks regular edition at the moment- Klaus is sending me ann upgrade kit for them which I will do and then rebias the amps., no zobels or anything else on speaker terminals, Ill have to check the boards more closely. Ill try that circuit you gave me. I have not installed the pcjj upgrade yet to the quickie , I really enjoy the sound now except for the over whelming gain.
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Well, the Quickie is a very, very low gain preamp (around 7dB), the Odyssey Candela that could be a companion product to your amplifier has twice the gain by comparison.
It looks like your amps have ~22K input impedance, but no specified sensitivity. You can lift the wire leaving the center pin of each RCA jack on the back of the amp and add a 100K resistor to start (feel free to check with Klaus on this one).
A lot of the time the sensitivity issue can be the combination of pairing a sensitive amplifier with sensitive speakers, and in this instance I'd imagine your loudspeakers are well over 90dB efficient.
-PB
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I tried the circuit above you gave me and it did work but it took to much gain away, 2 volume positions to 5 positions but then no more gain if I contined on the volume control-noble ap25, when plugged in direct its way to much gain from the quickie only 2 volume positions before blasting me out of the room literally, my hafler modified preamp solid state, my cary preamps which are tube work fine. My musical design tube also worked fine in this system. I am not sure maybe I have something wrong in my circuit in the quickie? I did try diferent tubes which made a difference in the gain of the quickie also. My speakers are 90db Vmps Super tower R's I think, not the 7 footers but the 5 foot speakers in this system with 2x 15s, 1 12 and other drivers in each cabinet. I guess over the weekend ill try the quickie in my other system, cary cad 100s in triode mode, but speakers are 90db also cabbasse 8 inch woofers and tweeters.
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Try installing the stock pot.
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Sage advice from PB - built it stock first - get it to work - then mod away.
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Ok ill install the stock pot this weekend.
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Dam Eric, I have to second that thought. My first 'Q' had all kinds of changes that I made to it and it held me up. I will be getting the new 'Q' today, and I promise to be a good boy this time.
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Hey UnderDawg, I feel your pain... I had a very similar problem in my setup. way, way too much gain... PJ helped me with some calculations and I installed a voltage divider with some tantalum resistors at the amplifier input.
here is the thread about my issue/Paul's suggestions
http://www.bottlehead.com/smf/index.php/topic,2049.msg15833.html#msg15833
here is a voltage divider calculator
http://www.raltron.com/cust/tools/voltage_divider.asp
good luck
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yes we tried that but it took to much gain away :)
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ok I am sad. Thank you paul the stock volume control works alot better than the noble.The only isssue I have left is switching between sources causes a loud pop or bump, any ideas? Still have not installed the pcjj yet as I am trying to get the original working perfectly.
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The bump comes from the rotary switch, and will quiet down a bit after some use.
Sorry that the Noble pot wasn't up to snuff, but this is why we always advocate that you build the kit stock first.
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fair enough ill keep on eye on the bump, should i wait for it to meelow out or install the pcjj now?
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Something that is seldom discussed in audio circles but well known in the recording industry is the "exercising" of pots and rotary switches. Every once in while it is a good idea to run pots and rotary switches through their full range a few times to clear off any crud that might have built up. Exercising that switch will help to burnish the contacts and quiet it down a bit.
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Doc, would that apply to the plastic strip pots as well as to the carbon track ones? And do you think that a sealed pot would require this as well?
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I can't think of any reason not to do it to any pot. Sealed pots should, in theory, not need it (or at least need exercise less often). Why not do it anyway?
I have just installed a couple of CTS conductive plastic sealed pots (283 series) in my new guitar. Small, quite nice feel and very quiet. Interesting to note the rated lifetime for the similar 282 series is 2 million cycles. I'm guessing 283 is log and 282 is linear, but not sure about that.
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If my DAC puts out a 2V signal, and I turn the Quickie up all the way, what will the signal to my amp be?
Best regards,
Adam
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The answer to this question depends on a few other parameters, and they are (I'll probably miss one or two here!)
1. The load seen by the Quickie (input impedance of your power amp(s).
2. PJCCS, Choke, or Resistor plate load
3. Freshness of batteries
4. How much THD is acceptable?
Under ideal circumstances (PJCCS/no load), I think you'd get maybe 10dB of gain out of the Quickie, which would get you 6V out. This seems tight in terms of compliance within the PJCCS, but I would want to test it myself to see what happens. With a stock Quickie, that would drop to ~4V. With decreasing load impedance, the output impedance of the Quickie will become a factor, and the voltage present at the input of your amplifier will decrease more.
The good news is, you can play a 60Hz tone through your DAC and measure the AC voltage out with your meter. This won't tell you much about distortion, but it's a start!
Having made too many assumptions, I just performed the measurements. I can get 11dB of gain with 0.7V in and 1.5% THD with the PJCCS and no load. This drops to an even 1% at 8dB of gain. Unfortunately, my testing setup won't generate 2V of signal, and our low-noise/low-THD testing amps aren't finished yet, so that's all I can report.
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Thanks, Paul. Much appreciated. I can't find input impedance specs. for my headphone amplifier. I will be using the Quickie with the PJCCS.
But you're already answered by question, so I'm all set. Thanks!
Best,
Adam