DIY Simple Active Preamp

[Russellc]

please reread my quote of NP "The pc boards are on order, and when they arrive I will present it complete."

and he posted that in the F5 thread just a few mins ago

Mr Pass just dropped another crumb/hint: "It will have more gain.":thmbsp:

Russellc

 

[HypnoToad]

May be system dependant, I find mine clean, but hardly sterile. Mine is warm with lots of bass. What amp and speaks are you using? I do tend to favor my pre with gain in some instances. I need to throw together the J-fet BOZ!

Russellc

Maybe it is a mismatch in between the Phonoclone 3 and power amp of the CR-1020. It is very good but just doesn't have the same musicality of the op amp based preamp. It has good bass but I wouldn't call it warm.

 

[Woody1911a1]

Mr Pass just dropped another crumb/hint: "It will have more gain.":thmbsp:

Russellc

yesss , a very good thing as far as i'm concerned . i'd moved on past the F5 because it just wasn't doing it for me , but i need a good excuse to revisit it .
personally i found the sound very sterile and lacking any warmth . maybe a rebuild with some tweaking .

i just recently finished a couple builds of the swordfishy/aspen Fetzilla and i'm just amazed at the sound so the F5 is going to have to step up a few notches to get back in my system .

cheers Woody

 

[skywave-rider]

...

I have been listening to the B1 a lot and I find it just too clean and sterile, the sound stage and "musicality" of the simple preamp is better IMO. But that may just be mental illness on my part....

Well. Good thing you did not post that over on DIY....hahaha. Once, after hearing JBL Everests, I was asked to post my opinion of them on another forum. I made a few comments. Bad idea...hahaha. I had to skim past a lot of responses from people who probably never heard the things. I've since heard them 3 times more...I pretty much had it correct from the beginning.

So, I respect your opinion.

Now I want to hear your Simple preamp for myself.
:tongue:

 

[HypnoToad]

I took the Simple Preamp and did as I said, removed the two 1k5 input resistors. Changed the feedback loop resistors for a pair of 10k / 8.2k on each side. Then I removed the old ratshack 100k dual pot and put in the two 25k pots I was using for the BI Buffer Preamp and viola.

Here it is the all singing and dancing Super Simple Preamp with less than 20 components on the board.

It has an AD823 in it but a OPA2134, LME49720, LM4562 or just about any two channel op amp will work IMO. Maybe even a twin single channel op amp version would be good. Depends what sort of sound you like.

The new pots made a world of difference the gain is about right and can be easily adjusted by changing out the 10k / 8.2k combo, you can either increase the 10k or lower the 8.2k.

It has a slightly warm tube like sound, that I attribute to the AD823, that you could listen to for hours and never feel you are missing anything, the detail and sound stage is first class.

 

[ghazzer]

Here are the values that I measured from a 5k "volume" pot that I ordered from one of our favorite parts suppliers. Scroll down for the plots. They said it was a 10% pot, and they were mostly right. I didn't do this very precisely - just turned the shaft a little and took another measurement.

Glad I didn't save another buck and get the 20% one ! ! !

My conclusion is that I want a stereo volume pot with gangs that are within at least 1% of each other. 1% stepped attenuators (23 steps) from Hong Kong are ~ $25, and conductive plastic ones go for about 3 times that. Both are advertised as "make before break" so there should be no speaker popping as you adjust the volume.

The 5k pot will give 20X finer adjustment than say a 100k pot, so I'm wondering if it would be practical to finese the position of the gain pot to get to the range taht you want. That is, if the preamp design calls for a 25k gain resistor, could you put a 5k pot between two 10k resistors?

 

[HypnoToad]

Here are the values that I measured from a 5k "volume" pot that I ordered from one of our favorite parts suppliers. Scroll down for the plots. They said it was a 10% pot, and they were mostly right. I didn't do this very precisely - just turned the shaft a little and took another measurement.

Glad I didn't save another buck and get the 20% one ! ! !

My conclusion is that I want a stereo volume pot with gangs that are within at least 1% of each other. 1% stepped attenuators (23 steps) from Hong Kong are ~ $25, and conductive plastic ones go for about 3 times that. Both are advertised as "make before break" so there should be no speaker popping as you adjust the volume.

The 5k pot will give 20X finer adjustment than say a 100k pot, so I'm wondering if it would be practical to finese the position of the gain pot to get to the range taht you want. That is, if the preamp design calls for a 25k gain resistor, could you put a 5k pot between two 10k resistors?

I have found the 25k pots to be very good for this design the 100k dual gang was way off. A 25k 1% stepped dual might be the ticket as well if they have those for a reasonable price.

 

[HypnoToad]

yesss , a very good thing as far as i'm concerned . i'd moved on past the F5 because it just wasn't doing it for me , but i need a good excuse to revisit it .
personally i found the sound very sterile and lacking any warmth . maybe a rebuild with some tweaking .

i just recently finished a couple builds of the swordfishy/aspen Fetzilla and i'm just amazed at the sound so the F5 is going to have to step up a few notches to get back in my system .

cheers Woody

Care to elaborate more on the swordfishy/aspen Fetzilla, sounds interesting.:yes:

 

[skywave-rider]

...

My conclusion is that I want a stereo volume pot with gangs that are within at least 1% of each other. 1% stepped attenuators (23 steps) from Hong Kong are ~ $25, and conductive plastic ones go for about 3 times that. Both are advertised as "make before break" so there should be no speaker popping as you adjust the volume....

No popping.

 

[ghazzer]

I bought this and it measures very precisely from gang to gang. I also bought an Alps, it has some variations.

Cheap, too.

Please share your measurements with us, for both.
.

 

[Pio1980]

Have you tried a 'bypass' parity check with one of the high-output phono stages direct-driving the power amp thru the same grade/type control vs thru the simple pre to see if it actually helps or hinders the system re transparency and natural ease of listening, ect?

 

[HypnoToad]

Have you tried a 'bypass' parity check with one of the high-output phono stages direct-driving the power amp thru the same grade/type control vs thru the simple pre to see if it actually helps or hinders the system re transparency and natural ease of listening, ect?

Using just the pots in a passive setup, no, I have heard that a passive setup up "sucks the life out of the sound" not sure if this is true or not. But that's why I went active.

I could just remove the batteries and the op amps then run jumpers from the output of the pots to RCA + output jacks? To see what difference I have.

 

[Pio1980]

Using just the pots in a passive setup, no, I have heard that a passive setup up "sucks the life out of the sound" not sure if this is true or not.

Quite the opposite, most preamps suffer from WTMS (Waaaay Too Much Schtufff) (and of generally compromised sonic merit) in the signal chain of custody and do that to excess. That's why I've abandoned recievers and integrateds for total separates that I've personally vetted.

 

[HypnoToad]

Quite the opposite, most preamps suffer from WTMS (Waaaay Too Much Schtufff) (and of generally compromised sonic merit) in the signal chain of custody and do that to excess. That's why I've abandoned recievers and integrateds for total separates that I've personally vetted.

That's why I wanted to make it as simple as possible, but will try what I said in my previous post to see how it works out.

 

[skywave-rider]

Please share your measurements with us, for both.
.

No can do. I used my Fluke multimeter. But it's simple enough, for the cheap stepped attenuator, the resistance on each step was equal to the resistance on the corresponding step on the other gang. What else can I say? : )

 

[skywave-rider]

Using just the pots in a passive setup, no, I have heard that a passive setup up "sucks the life out of the sound" not sure if this is true or not. But that's why I went active.

I could just remove the batteries and the op amps then run jumpers from the output of the pots to RCA + output jacks? To see what difference I have.

I think the way to do that is to connect the phono pre directly to your power amp, which hopefully has pots. If not, you are screwed because using just a pot without a buffer will change the sound IMHOP.

 

[Pio1980]

I generally avoid PAs with input level pots as an indication of sonically compromised design philosophy (TMS syndrome again), unless they are the premium pots which never happens.

 

[Pio1980]

I think the way to do that is to connect the phono pre directly to your power amp, which hopefully has pots. If not, you are screwed because using just a pot without a buffer will change the sound IMHOP.

It probably depends on the drive capability of the stage and configuration re output resistances/capacitors vs loading. Regardless it'll sound better, worse, or pretty much the same, just try it. Aside from that I don't see how input pots would be any different than pots at the stage's output.
Experimentally I found that typical carbon track wiper pots fuzz things up relative to using the 'good stuff'. Another passive component that gave trouble were some gold-plated selector switches, one nasty example just made the clear direct sound disappear. The point is to get a result that doesn't sound like anything other than the clearest most direct conduit to the source content.

 

[HypnoToad]

Okay I got home and made some short leads with alligator clips on each end and removed the op amp and batteries. I connected the wiper of the pots to the + output RCA's so the signal was only going through the pots and there was still the 100k loading resistors at the outputs. So basically what came in went through the pots and out again.

I was surprised by the sound it was bassy, clean and very clear, however the 3D sound stage had collapsed inward, and the upper mids to the treble seemed thin, it sounded recessed and flat. Even though the detail was there, something was missing. It was like some of the life was gone.

I then put it back the way it was and everything was back in balance, it sounded more musical, the 3D sound stage was back.

So IMO it sounds better with the simple preamp as is than with just the pots and loading resistors.

 

[Pio1980]

Outstanding! Proof is in the result. I am trying to convince myself to try the e-Bay line stage I built last year before going nuts with strain gauge carts