KG Balanced Dynahi build discussion thread

[sbelyo]

I've decided to use two sigma22's for the psu. One for each channel. How much DC current will one channel draw?

I'm guessing it's based on what the load of the amp is so I'll be using it with 32 to 300 Ohm headphones

[kevin gilmore]

Each balanced board should pull 600ma on each of the power supply lines.

[sbelyo]

Perfect... Since I'm planning on using Grado's along with high impedance cans will I need to adjust the gain?

[Victor Chew]

Nice work Vortex. Any further progress with the casings?

Any suggestions, on implementation of a switch between high and low impedance cans?

[sbelyo]

I'm going to use the opa445 so I can omit the 7815 and 7915 regulators correct? If so, do I have to jumper the holes for the regulators or can I just leave them unpopulated?

[kevin gilmore]

You have to jumper across the regulators

[sbelyo]

got it. we don't need them because of the opa445 can handle the 30 volts with no problem right?

[kevin gilmore]

opa445 can handle up to +/- 45 volts

for the 7815 you jumper pins 1 and 3

for the 7915 you jumper pins 2 and 3

[sbelyo]

Got all my parts and boards ordered... Parts Bill so far is around $500 but this includes PRP resistors and a pair of Sigma22 board along with their components as well.

My plan is to put the PSU and xformer in it's own case so there's some added expense in that. By the time I buy 2 cases, panels from FPE, and a volume control I would think I'm into it for just about $1K

Could it be done for less, yes but I'm letting FPE and Par-metal do all the casework. I just don't enjoy that part anymore plus I want a gold point attenuator this time around. I figure go big, or go home

[Victor Chew]

Got a bunch of J74BL from my local shop and have been matching them. IDSS readings are between 13mA to 20mA. These are too high and are obviously fakes.

Also got a bunch of K170BL and the IDSS is between 3mA to 5mA. The spec sheet says 6mA to 12mA for the BL and 3mA to 6mA for the GR, These are obviously not BL grade, and may be GR grade badged as BL.

[luvdunhill]

what's the voltage you're testing them at? iirc, the datasheet numbers assume 10V.

And, in case you are curious... "rebadged" == "fake... avoid"

Edited May 25, 2012 by luvdunhill

[Victor Chew]

I followed the instruction here - http://www.diamondstar.de/transistor_matching_jfet.html

Edited May 25, 2012 by Victor Chew

[flecom]

Using a Dynahi to drive speakers is a bad idea IMHO unless you have huge heatsinks and a PSU which can handle the load. Even two Sigma22's will struggle to keep up so why not just build a F5 for speaker use with its super simple PSU?

I have run speakers off my dynamight, works fine... although I am using some bigger power supplies... I have even run some GS-124 laser galvos with it in a pinch and it worked great hehe

[JoaMat]

/

Edited November 12, 2015 by JoaMat

[Victor Chew]

I got mine from Lil knight. You might want to PM him and check if he's got any left.

[JoaMat]

Thanks Victor. I PM:ed him a few days ago and so far no reply - but of course only a few days have elapsed. No question that Tran is a great board supplier for the DIYers.

Edited September 19, 2012 by JoaMat

[Victor Chew]

Hey, no worries JoaMat.

I think Tran still has exams and what not to attend to. His replies may not be immediate, but he eventually does attend to them. He is a reliable chap.

[TMoney]

I've got a set (2x amp and 2x PSU) that I'm probably not going to get around to building anytime soon. If you can't get a hold of Lil'Knight in the next week or two let me know.

[JoaMat]

Thanks a lot TMoney,

be in touch.

[sbelyo]

I need help deciding the gain and volume control values. I know that when you go blanced the gain is doubled.

My first question is, what is the default gain when following the parts list?

what resistors control the gain?

I have Grados as well as high ohm cans so I need to find some sort of balance between gain and volume control knob sweep. Normally I use a 50K volume control but that only gives me less than half the knob sweep when using my grados with my original Dynahi. For that build I left the gain stock. I believe it was 10 or 11 I can't remember.

[sbelyo]

I'll be using a 10K balanced volume control. Balanced gain will be 10 by changing R52, R56 to 50K and C1, C3 to 5 pf.

[dubiousmike]

I'm cobbling together the parts for 2 channel dynahi (on the '04 boards) and was hoping you guys might be able to provide a little guidance regarding GR vs. BL grade transistors.

Amb happened to have a couple of 2SJ109BLs on hand recently, so I went ahead and ordered those up. I also already have a pair of 2SK389's (that I got along with the boards a while back), but I just noticed they are GR grade. I also have a line on some 2SA1349's and 2SC3381's (through the diyaudio forums), but I understand they are also GR grade.

Am I stepping in it if I use this combination in the same amp?

[StrawHat]

I've just started building this amp and wanted to share with everyone since this thread hasn't seen much activity.

 

I decided to start populating the pcb's while I wait for the transistors for the amp boards.

 

Power supplies are almost finished but I wanted to ask Dr. Gilmore if we should still leave Q9,Q10,Q24,Q14,Q15,Q26 unpopulated or the fix suggested on post #25 solves this issues.

 

 

[Victor Chew]

Kevin said that once you add the 1k resistors the current limit transistors won't blow up. So I guess the transistors in questions can be populated.

I am halfway through my build. Faced some problems with the bom and had to reorder parts unfortunately.

Edited January 25, 2013 by Victor Chew

[StrawHat]

Thank you! May I ask you what transformer will you be using?

I still have to decide VA rating and secondary voltage.