First Build - Fantastic!

[Adrian]

Just completed my first DIY project.  First time soldering and everything came out right the first time.  The Crack sounds great using HD600 and Koss Pro 4AA.  This took several nights going real slow and careful.  Just starting on the Speedball.  I realize that I need a smaller "gauge" solder - 0.062" is too big.  I'm guessing a smaller gauge solder will heatup faster and make it easier to do the CB work.  Thanks Bottlehead.

[Loquah]

I'm not exactly sure of the sizes, but your reasoning is good regarding the solder. Most importantly it will also prevent having too much solder on the joints which I struggled with at times using a larger gauge solder.

PS - Congratulations on your first build!! You'll love the upgrade to the sound from the SB

[Adrian]

Thanks for your reply and comments on solder.  I found that the source input level was so high that I could not get the Volume past 9 o'clock without it being too loud (I'm old but I'm not that old!).  I had a similar problem with my Marantz 2325 receiver that I've had in operation since 1977.  I'm currently using the tape monitor out for the source input to the Crack OTL.  I installed in-line attenuators (-10dB) to drop the line level.  Now I have a much finer control over the volume and can operate the pot near and around 12 o'clock.  Lots of control at lower volumes compared to without them.
As soon as I learn hold to post pictures I will do so.

[Adrian]

Help - can't insert a photo.

[BigPete]

Help - can't insert a photo.

I use Photobucket. Just upload a pic to there. Then copy and paste the IMG link to here.
http://photobucket.com/

[JamieMcC]

Help - can't insert a photo.

If you look below the reply box there is a "attachments and other options" button you can use this to browse and upload a pic from your computer.

[Adrian]

Let's see if this works:
First pic shows the in-line attenuators (from Rothwell)

[JamieMcC]

Neat job are those some kind of spacer on your RCA inputs?

[Adrian]

JamieMcc:  Those are in-line attenuators.  They reduce the high input source line about 10 dB.  This allows me to operate the volume pot near the mid- range (12 o'clock) and give finer control over the lower volume settings.  Most source inputs today have too high a line signal and could probably go directly into an amp w/o a pre-amp.  This is a case for a passive pre-amp (selector switch and volume control only) when appropriate.

[Kris]

JamieMcc:  Those are in-line attenuators.  They reduce the high input source line about 10 dB.  This allows me to operate the volume pot near the mid- range (12 o'clock) and give finer control over the lower volume settings.  Most source inputs today have too high a line signal and could probably go directly into an amp w/o a pre-amp.  This is a case for a passive pre-amp (selector switch and volume control only) when appropriate.

Adrian,
How do you like the sound quality of your amp with attenuators? Asking 'cause I've tried 12dB once and at first I liked the control they gave me on the pot, but after few minutes of listening to my Crack with HD650, I've noticed that mids  and upper mids sounded terrible, so I pulled attenuators out and never got back to them again.
Kris

[JamieMcC]

I did try resistors in line with the RCA inputs on the insides it helped with a low volume imbalance and also gave more travel range on the pot. Once my stepped attenuator went in the resistors came out as I found I preferred the sonics without them and the stepper took care of the imbalance.  I have come across in-line attenuators before but concluded from the pictures I had seen they were much bigger.

[Paul Birkeland]

Asking 'cause I've tried 12dB once and at first I liked the control they gave me on the pot, but after few minutes of listening to my Crack with HD650, I've noticed that mids  and upper mids sounded terrible, so I pulled attenuators out and never got back to them again.

This can happen if the attenuators have a characteristically low impedance.  Unfortunately, the attenuator designer has to assume that you may be driving an amp with a 10K input impedance, so the resistors values in the attenuator are values that are low enough to accomplish this, which may not always be the greatest choice.

Building the attenuation into the Crack is pretty easy (2 or 4 resistors, depending on how much attenuation you need), and it has the advantage that you can keep the 100K input impedance (which is friendly to your sources). 

For -10dB, that's dividing 1:0.3, so you would add a 66K (68K is OK) resistor between the center pin of each RCA jack and the white/red wires that connect there.  At the volume pot, add a 50K resistor between each pair of outer lugs on each deck of the pot.

-PB

[Adrian]

Adrian,
How do you like the sound quality of your amp with attenuators? Asking 'cause I've tried 12dB once and at first I liked the control they gave me on the pot, but after few minutes of listening to my Crack with HD650, I've noticed that mids  and upper mids sounded terrible, so I pulled attenuators out and never got back to them again.
Kris

I don't think I've put enough run-time for a good sonic comparison yet.  For reference, the attenuators I'm using are from Rothwell.  I'll have to look it up cause I don't know the particulars for this attenuator.  I know I like the sound now but you have me wondering if I need to be more critical and do an A/B comparison.  Maybe I can have my wife swap them out and make it a blind test?

[Kris]

Building the attenuation into the Crack is pretty easy (2 or 4 resistors, depending on how much attenuation you need), and it has the advantage that you can keep the 100K input impedance (which is friendly to your sources). 

For -10dB, that's dividing 1:0.3, so you would add a 66K (68K is OK) resistor between the center pin of each RCA jack and the white/red wires that connect there.  At the volume pot, add a 50K resistor between each pair of outer lugs on each deck of the pot.

-PB

Thank you PB for detailed info.

I've already tried to put 270k resistors in signal input path per you sticky note in crack FAQ section, but ended up with too loud audible background noise, so I removed the resistors.
I have to try the other method you mentioned above with 68k and 50k resistors.

Thanks,
Kris

[Kris]

For reference, the attenuators I'm using are from Rothwell.  I'll have to look it up cause I don't know the particulars for this attenuator.  I know I like the sound now but you have me wondering if I need to be more critical and do an A/B comparison.  Maybe I can have my wife swap them out and make it a blind test?

I got Harrison Labs 12 dB attenuators. They were mentioned couple of times here on BH forum and people reported to have good results when matching them with crack amp, but it looks like they are not good in my setup.
I strongly suggest to pull your attenuators out and give your amp a listen without them... just don't forget to post back as I you got my curiosity now.
 
Cheers,
Kris