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DIY Simple Active Preamp

Wow,
That was fast!
I'm like a blind man hunting for fish in a muddy pond with a spear here. This should at least get one eye free. Thanks for the info, the insight, the details and the speed
 
omishra said:
With default schematic as above, it is -
Rf = R27, R29 = 10K
Rg = R28, R30 = 8.2K

output = input x A, gain

gain, A = (1 + Rf/Rg) where Rf = 10K and Rg = 8.2K
= 1 + 10/8.2
= 1 + 1.21
= 2.21

output = input x 2.21 times

with swap Rf = 8.2K and Rg = 10K

Gain A = 1 + (8.2/10)
= 1 + 0.82
= 1.82

output = input x 1.82 times

Now you can experiment lowering Rf to something 4.7K or increasing Rg to 15K or higher. :)
Click to expand...

Absolutely correct. However, x 2.21 is 6.9dB and x 1.82 is 5.2dB, ie not very much difference between the two.
Also, both gains are pretty low, so I wouldn't expect a "hair trigger" volume control problem. Is the volume control a log pot? The correct values of resistors being used?
 
Grainger49 said:
omishra,

Thanks, I edited my post. I don't want incorrect information to linger here. We always called the resistor to ground Ri, but Rg makes sense here.

The resistance values you are giving are not what is in the first schematic. There must have been some changes in the 400+ posts.
Click to expand...
No problem! Please keep sharing your thoughts, we all value it.
 
OK Rf @ 4.7k
Rg @ 10k
restored 250k to 100k (default value)(I was thinking if this became 50K , maybe less this might be another option to tamp down the signal, or is this a bad idea).
definite improvement.
From a practical point of view how far can i go in each direction?
Is there a point where you throw the circuit out of the linear portion?
Or, can you tweak it indefinitely? Until you find the gain you like?
 
Rf = 4.7K and Rg could be 10K to 47K. We can get meaningful gain still slightly greater than 1.
Otherwise make voltage divider of 12K+12K at each input - 12K inline to inputs and 12K as shunt to ground.

Sent from my E6 using Tapatalk
 
There's only a few dBs gain as it is. You could go down to unity gain by having Rf as a link (zero ohms). There should really be any need to go below unity by having an attenuator at the input.
The real question is why is the volume control so twitchy? Is it a log (audio taper) pot? If it's a linear pot you're bound to have problems.
Does the power amp have an excess of gain? More than 30dB in the power amp would make the volume control twitchy.
Really, there shouldn't be a problem if the pre-amp has only 6dB gain. There must be a problem elsewhere.
 
Here are a couple more pictures of my SSP.

It´s not perfect optically, but it´ll do :)

I´m really looking forward to using this in the future !

Thanks again to Hypnotoad for starting this thread!
 

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Based on this article I'd guess this is a commercial Log pot
http://sound.westhost.com/pots.htm

One way starts at 0, 47,121,221,440,781,1.25k,1.85k,2.6k,3.7k,5.19k,7.38k,10.66k,15.75k,21.8k,27.82k,34.31k,39.8k,44.49k,47.77k 50k
0ther way 0,5.6k,10.4k,15.85k,22.34k,28.36k,34.4k,38.46k,42.25k,44.93k,46.43k,47.53,48.27k,48.87k,49.92k
 
Using a DVD player as an input source (as a CD player) using a 3116 chip amp as an amp (if it's important I can tell you which board. I'd have to look).
I have used both of these pieces with other amps speakers preamps

Unless there's some kind of incompatibility I'm unaware of.?
 
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ChipAmps have high gain. You might want to make an attenuator at the output of the Simple. Say a 22k in series with another 100k to ground. That makes the source impedance about 50k.
 
nj pheonix said:
Based on this article I'd guess this is a commercial Log pot
http://sound.westhost.com/pots.htm

One way starts at 0, 47,121,221,440,781,1.25k,1.85k,2.6k,3.7k,5.19k,7.38k,10.66k,15.75k,21.8k,27.82k,34.31k,39.8k,44.49k,47.77k 50k
0ther way 0,5.6k,10.4k,15.85k,22.34k,28.36k,34.4k,38.46k,42.25k,44.93k,46.43k,47.53,48.27k,48.87k,49.92k
Click to expand...

The first step should attenuate by 60dB. The second step, 52dB. Third step, 47dB. That doesn't seem at all bad to me.
One quick and simple thing you could try is to put a resistor in series with the pot/stepped attenuator. A 50k resistor would cut the whole lot down by 6dB. 100k would cut down the whole lot by 10dB. Of course, you would never be able to get up to the maximum gain, but maybe that wouldn't be a problem. Or you could have the the resistor switchable for hign and low level listening.
 
nj pheonix said:
Using a DVD player as an input source (as a CD player) using a 3116 chip amp as an amp (if it's important I can tell you which board. I'd have to look).
I have used both of these pieces with other amps speakers preamps

Unless there's some kind of incompatibility I'm unaware of.?
Click to expand...

Many regular amps have enuff gain to take the output of that player directly thru a pot, dunno about the chip amps. My Sure chip amp seems relatively insensitive. Otherwise, for a line amp stage I'd say 12-15 dB is sufficient gain for most purposes.

Sent from my SM-N900V using Tapatalk
 
Ok tamped down the input . 10k in series 15k to ground (I would've used 12ks as suggested but I had none) . Not quite enough gain. I had rg at 33k. Now that I'm in experiment mode, I left leads long and paralleled 22k across for 13.2k @rg. I'd guess this is pretty close. Very good control of gain through the attenuator. I have listen a bit and see what I have now. Thanks all for getting me this far!
PS all the add ons make this pretty ugly as it sits. Once its dialed in it'll have to be cleaned up a bit!
 
nj pheonix said:
Using a DVD player as an input source (as a CD player) using a 3116 chip amp as an amp (if it's important I can tell you which board. I'd have to look).
I have used both of these pieces with other amps speakers preamps

Unless there's some kind of incompatibility I'm unaware of.?
Click to expand...

:D Just Added a 100K Alps Pot
(genuine Not Clone although that shouldn't matter as the Chinese 'Alps' Clones are of 'Just Fine' Quailty and besides Alps No longer makes the Blue cased Pot)
to MY 3116 d2 Blu/black pcb Chi Fi amp...
So I could have some Volume control from my CD/dvd player direct input.
Spliced into/between input RCAs and Amp, it Works "perfectly".. period.
And I'm Picky, having been doing this Audio Nonsense and Diy components Lark.. since early 70's.
Sometimes (more than sometimes actually) Simplicity has Dominion.
 
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I'm using a 10k Noble black box stepper as the level control element in my passive controller since the mid 1980s. Works pretty well with most sources and amps.

Sent from my SM-N900V using Tapatalk
 
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