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Is the Dynalo still a good choice?
May 14, 2011 at 1:58 PM Post #31 of 45
Could the 20k pot requirement be circumvented with a 10K pot and a 10K resistor hooked in-line with the pot, connected via a "gain switch"? With the resistor connected (switch on) you have basically the second half of the 20K pot; with the resistor detached (switch off, direct connection) you have the bottom half of the 10K pot. Am I doing this right?
 
May 14, 2011 at 1:58 PM Post #32 of 45
Yep, 20k pots are tough. You can get a 50k blue velvet and an epsilon 27 for mounting from AMB. The only RK27 at 20K I could find was motorized and linear. I managed to find a dual 10k RK27, but Mouser doesn't specify if it's linear or audio (log) taper, so it's probably linear. Ebay turns up a few, but I'm always a bit skeptical (though the seller has decent feedback).
 
May 14, 2011 at 5:40 PM Post #33 of 45
There's always waiting for AMB's δ1, or getting involved in someother group buy for a resistor based attenuator.
 
I'm a tiny bit skeptical about the gain, I'm using a γ1 as my source. I'll give the 11x a go with my RK27 50K pot and see if I can handle it fine. If not I'll switch to ether 8x or 6x gain... I'd rather not have to change out the 10pF silver mica cap for a alternative. I'll also play show and tell.
 
Well great... Now I want to build a resistor based attenuator, thankfully I don't have the money for one right now.
 
Hopefully I can help with your pre-planning along the way.
 
May 15, 2011 at 11:36 AM Post #35 of 45
I wouldn't worry about finding a 20K pot too much. 10K or 50K will work just fine. Michael Percy sells the TKD (my favorite reasonably priced pot) in a 20K or 25K, but I've always used 50K in my Dynalos.
 
I couldn't find the source of the quote by me posted, but I have always used the stock gain. I normally don't use Grados however, but AKG K601s primarily (and Shure SRH840s or modded Fostex T50RPs) and have never had a problem with the gain being too high (and putting me in the low range of the pot rotation). You could always socket the gain resistors.
 
May 15, 2011 at 5:07 PM Post #36 of 45


Quote:
pars said:
I wouldn't worry about finding a 20K pot too much. 10K or 50K will work just fine. Michael Percy sells the TKD (my favorite reasonably priced pot) in a 20K or 25K, but I've always used 50K in my Dynalos.
 
I couldn't find the source of the quote by me posted, but I have always used the stock gain. I normally don't use Grados however, but AKG K601s primarily (and Shure SRH840s or modded Fostex T50RPs) and have never had a problem with the gain being too high (and putting me in the low range of the pot rotation). You could always socket the gain resistors.
Click to expand...


OK, thanks for the info. I think I will socket the resistor and order several different gains and see which one works the best.
 
Hopefully I'll be receiving more funds today and I'll make my order. Thanks for your help guys. 
 
May 16, 2011 at 11:01 PM Post #38 of 45
Motivational pictures,
Is it bad that I want to sell it for money to build more headamps?
If cost was a factor, with mistakes and repurchases, I believe the total is somewhere around $293 canadian, which, for a world class amp is not much to ask for. Although, without the mistakes I made with the amp should be nearly half that cost. If you need any transistors, send me a PM, I've got about 200 transistors waiting to be used that I can't find a match for.

 
As for gain, I can comfortably listen anywhere from 9:00 to 11:00 depending on what I'm doing. That being said, I might lower it to about 8x.
 
May 17, 2011 at 4:34 PM Post #40 of 45
Here is a budget Dynalo with power supply in one box I'm building for my brother, gain is setting at 2x (for Denon D5000).
The power supply includes ~10,000 [size=x-small]µF Sikorels (my favorite PS capacitor). [/size]
[size=x-small]Most parts are from my parts bin, from there the resistors cocktail.
smily_headphones1.gif
[/size]
 
 
[size=x-small][/size]
 
May 17, 2011 at 5:08 PM Post #41 of 45


Quote:
justin w. said:
What is the DC voltage on the output of each channel, before and after the servo has adjusted?
Click to expand...



90% of the time the offset stays below 1.0mV, occasionally the DC servo overshoots and can get as high as 2.6mV (which is the highest I've seen). Compared to my last Dynalo build with a standard LM3xx supply, It's much more stable. I would only worry about having excessive DC at the output if I used a direct coupled source, but alas! I don't have one.
Damn, now I want to build a new DAC already, I have to sell the Dynalo!
 
May 18, 2011 at 2:09 PM Post #42 of 45
[size=x-small]The unstable problem of your previous Dynalo build on a self-etched PCB (as you posted in the other forums a while back) has probably to do with the PCB layout itself (signal routing, LCR characteristics…).[/size]
[size=x-small]Your recent Dynalo is built on a professionally made PCB, which has been proven to work properly for years and that makes the different.[/size]
[size=x-small]Better power supply can reduce the noise floor further, which is of course a good thing.[/size]
 
[size=x-small]The Dynalo I’m building for my brother (in post #40) is using a LM317/337 based power supply on perfboard and it works just fine, no audible noise at all.
smily_headphones1.gif
[/size]
[size=x-small]Without the DC servo circuit, the DC offset can be dial down to +/- 3mV on both channels, which is acceptable to me.[/size]
[size=x-small]With the opamp installed, the offset is further down to +/- 1 mV and it remains rock solid at that low level for hours now (while I’m typing this post).[/size]
 
May 18, 2011 at 6:32 PM Post #43 of 45
I blame my ignorance more then the board. I let the problem get to my head and create frustration beyond what I've ever experienced before.
 
Ironically, using a PSU that has inaudible noise causes you to notice the amount of noise in the recording during quite sections... thankfully It's not as annoying as the computer noise out of my PSU.
 
Does adding the heatsinks add to thermal stability and ultimately a more stable offset?
 
May 19, 2011 at 4:24 PM Post #44 of 45
From experiences, closely matched and thermal-bonding of the input JFets does contribute to the stability and help to lower the DC offset of the amp. 
(not only on this build but generally on all the amps I have built in the past)
 
I'm not sure about the tiny heatsinks used on the output transistors of this Dynalo build, but it does reduce the heat a bit and that counts.

 
May 27, 2011 at 1:21 AM Post #45 of 45
OK guys, it's been a while, and I appreciate everyone stopping by. I learned a lot researching this amp, but I ended up getting more funds than I anticipated, so I'll be building a M^3 instead. It's better documented (since I've only built one amp before), and I've always wanted one, so I'll be building that instead.
 
Ferrari, your builds are beautiful.
 
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