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DIY Simple Active Preamp

Back in action

I put in a new IC, electro caps and installed diodes for the -/+ input (reverse voltage protection.) :nono:

Working fine on batts. Now investigating the PS. (Had hum with it.) I suppose it's possible that the filter caps are NG. I may have another PS to try.

Here's the guts with room to move-in. Transformer I/O would fit.
I won't use solid hookup wire any more.

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The other supplies I have are not the right voltage, So I rewired-in the home-brew and rigged a temporary AC ground to its chassis. Buzz greatly reduced. So I'll get some 3 conductor wire tomorrow and make up a permanent hookup.

Currently running on + - 15v, minus .7v.

I think the SSP will be back in the rack soon. :thmbsp:
 
Potentiomer question

Given the same type, (brand/model) do pots of different values have a different sound? Or does the value merely change the feel of the attenuation around the rotation in a given circuit?

A 25kOhm log is ideal for the SSP circuit, as stated by the designers, but if I go with say a 50kOhm, would I get a more gradual increase from infinity to say 12 or 1 o'clock? I feel that currently (20k stepped attenuator), the volume is up a bit quickly, not bad, but could be more gradual.

More importantly, does a different value change the sound, irrespective of attenuation "feel?" And how would it change?
 
skywave-rider said:
. . . A 25kOhm log is ideal for the SSP circuit, as stated by the designers, but if I go with say a 50kOhm, would I get a more gradual increase from infinity to say 12 or 1 o'clock? I feel that currently (20k stepped attenuator), the volume is up a bit quickly, not bad, but could be more gradual. . . .
Click to expand...

To this, no. If both pots are log taper you would get the same volume at 12:00 on both pots. However they would load the source differently. As long as you are above 10k ohms it should be safe for any source.

As for higher resistances, the higher the more stray noise you will pick up.
 
Could s-r achieve the desired finer adjustment by using a 5K pot between two 10K resistors? Loading would be the same. Might have to experiment to find out where to put the pot to get the desired volume range (5-5-15, 15-5-5, etc).
.
 
dodog said:
Reverse voltage protection against installing the voltage/wiring backwards?
Click to expand...

Yes!
Sorry, I missed your question last time I checked the thread.

All's working well. I am currently deciding on whether or not to install transformer input. Then it goes back in the rack.
 
Just wanted to alert you guys that my cheapo stepped attenuator (Ebay) is starting to crap-out. In between steps getting crunchy, as if dirty. Wow....I'll probably put in an Alps after the transformers arrive. Or maybe the lightspeed will be ready.
 
I was listening to my HTMCPS that is connected to a Super Simple Preamp and thought their was a little harshness in the upper midrange with my new to me B&W speakers.

I have them going into the power amp section of my Yamaha CR-1020, the pre in the Yamaha is no slouch but everything opens up using the Super Simple Preamp.

I tried swapping the AD823 op amp for a OPA2134, the harshness disappeared but it was too laid back for my liking.

I then looked in my op amp stash and found a pair of LME49710's, they are single circuit version of the LME49720. I put them in a dual adapter an put it in the preamp.

Wow what a revelation, the harshness was gone and the soundstage had widened but is not quite as 3d, but with even more detail. Bass is a little tighter and more extended, voices are much sweeter IMO.

So if you want to try something good give the LME49720 a go, you might be surprised.
 
That's interesting. I've felt that the bass was a little loose on my SSP, so on the next order I place, I will pick up an LME49720.
Thanks.
 
HypnoToad said:
.......
So if you want to try something good give the LME49720 a go, you might be surprised.
Click to expand...

Fasterdamnit was extolling the virtues of the LME49XX0 series in the CNC thread, so I built mine with an LME49720 and an OPA2134. That was very nice until I blew both of them by probing around with my NTM o'scope. I replaced them with the same and am still happy with the sound.

I am building an SSP (MM version) and have planned to use the AD823. Maybe I'd better spring for some more opamps so I will have enough to roll around.

What is your opinion on combinations of the opamps and speaker selection? Would the harshness be resolved if you switched back to your previous speakers? I suspect that you were acclimated to that system and only detected a problem when you switched speakers.

One other factor seems to be that lots of us just like to play around with our toys!

Enjoy - - -
.
 
ghazzer said:
...

One other factor seems to be that lots of us just like to play around with our toys!

Enjoy - - -
.
Click to expand...

True! I am actually in the process of installing transformer input. Haha.
This project is cheap fun for tweakers.
Regarding the sound, in my case, I don't have harshness in the mids, just a more robust LF.
 
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100 uF/10 uF cap differences aside, am I seeing this correctly that HT's design has the caps on the input, before the opamp, and Omishra's has them after the opamp? Will this make any difference?
 
Electrically, they are both the same. Both PCBs have these caps tied to ground and the + or - rail. I suspect that the difference was created by the auto layout features of whatever S/W program was used, and the selected parameters.

One school of though says that these caps shound be as close (physically) as possible to the power pins of the IC. This often boils down to choices between which improvements can reasonably be implemented, and at what cost.

My 2¢
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