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KG Balanced Dynahi build discussion thread


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AC buzz or hum sounds different from gain-related hiss, at least in my experience. What does your noise sound like? If it's more AC-like, then try to rearrange your wires, as Pars suggested. Sometimes trying to keep AC wires at right angles to all other wiring helps. Also, how did you connect the front panel switch? If you're running AC to the switch and back out into the transformers or PSUs, that might extend the resulting EM field.

Shielded input cable might help reduce interference (not 100% sure about it). Sommer Galileo 238 cable, you can find it in 1m increments from various eBay sellers.

Oh, and your heatsinks look fine! They also have rounded fin edges. Mine are sharp enough that I have to be extra careful picking this beast up. If you like my sinks, though, check out Fischer Elektronik.

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Got 0.75V bias with strapped 500R parallel to 1K to get a new floor of 200R; 5-min job...

1 hour ago, Pars said:

Having the transformer(s) that close to the audio boards/pot probably isn't helping your noise floor at all. AC wiring also appears to be right over the input wiring to the left side of the pic.

Two chassis was my initial plan; however, a simple single chassis with small footprint/stack would be nice.  I did try the amp out with the trafos off the chassis (a foot or so away).  No noticeable improvement on the noise floor with trafos on-board.  

Yes, the AC/signal wiring is sloppy (so excited to get the thing humming into life).  Will  have to clean-up the wiring...:D      

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27 minutes ago, gepardcv said:

AC buzz or hum sounds different from gain-related hiss, at least in my experience. What does your noise sound like? If it's more AC-like, then try to rearrange your wires, as Pars suggested. Sometimes trying to keep AC wires at right angles to all other wiring helps. Also, how did you connect the front panel switch? If you're running AC to the switch and back out into the transformers or PSUs, that might extend the resulting EM field.

I have had tube amps with the 60Hz buzz due to AC heater and OPT interference.  This is more of gain hiss, pretty sure it's not AC hum. 

I will have to move the 32VAC wires to the GRLV boards away from the signal wires.  Right now, the heatsinks are at 42-47C after 30-min on (nominal from what I've read?).

Thanks Dr. KG and Steve for setting up the GB!       

 

Edited by Skooby
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  • 1 month later...

My Dynahi developed a problem on one channel: the offset jumps intermittently. It looks like the outer 8 output devices' bias drops from the ~0.40V I set it down to ~0.30V or lower. This causes noise, and, when the offset becomes sufficiently high, triggers the protection circuit and cuts off sound. The corresponding LED dims. The amp worked for weeks with no trouble, and developed this symptom a few days ago. The first time I opened it, the problem went away completely, and I suspected overheating. But it now occurs even after a cold start.

Any tips on how to diagnose this problem?

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If you have some clip leads (micro or mini grabbers), can you monitor the bias with the lid on?

When you say the problem now happens on a cold start, this is with the amp casing closed up?

EDIT: this is on your combined SS Dynalo/Dynahi build I take it?

Edited by Pars
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Yes, this is the combined build. The Dynalo side works fine, as does the other Dynahi channel. I checked the PSUs, they all seem to put out the right rail voltages consistently. I've not tried to get it to happen on a cold start with the lid off, but it happens fairly consistently with the lid on. It's definitely a packed case with non-ideal airflow, but the heatsinks are pretty huge and the case feels cooler to the touch than my on-board heatsink KGSSHV.

I don't have the right kind of grabbers, but I could order some and figure out a way to run a few wires out through the top vents. What do you think might be happening?

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Initially it would seem to be heat related, perhaps one of the output or bias devices cooked and is now unreliable?

This dual build would seem to have some inherent problems with potential thermal issues. I guess I didn't look closer, but in this build, only one amp is powered at a time? Including the PSUs for that amp?

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No, both amps are fully powered up all the time. Which definitely contributes to potential heat problems, though the Dynalo (and honestly all three GRLVs) run quite cool. It does seem likely that a bias device has failed, because the bias across an entire bank of output devices (not sure if the + or - side) drops. Wish there was an easy(ish) way to figure out which one, though, to minimize desoldering and part replacement.

At least I hope it wasn't an output device. I matched those fairly carefully, and don't have (matched) extras lying around.

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  • 2 months later...

Finished my Dynahi this week, a big thanks to Kevin Gilmore making this project possible. Was a more or less ;-) troublefree build, thanks to this forum i get the needed information, thanks to all. I tried to build the Dynahi in a relative small case so the challenge was to shield the trafos, i used grain-oriented-steel bands around the trafos and top covers also made from grain-oriented-steel, added 70.- usd to the BOM but was well invested, no inducted noise at all :-).

The amp is bias to 0.625 v so that the case can handle the heat. Sounds superb as the dynalo. I have a second headphone out on the back, i will use it together with the ifi iesl pro to drive my stax headphones (as my sony vfet via the iesl to drive the electrostats).

9934909_l.jpg

9934911_l.jpg

https://www.head-fi.org/gallery/album/kevin-gilmore-dynahi.1154508/

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You finde the parts here:

https://www.don-audio.com/radiation-shielding-magnetic-shielding-tafo-hum-trafo-shielding-electro-magnetic-sheets-grain-oriented-electric-sheets-electro-magnetic-foil-shielding-foil-shielding-sheets

It's a band thats wraps around the trafo (secured via cable tie) and a top plate, most of the time the band is enough, but i want to be on the secure side with the top cover. Works great and its cheaper then mu metall cans.

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  • 2 weeks later...
  • 3 weeks later...

my dynahi has a problem, i tested the offset after some hours. i can bring down the offset to around +- 2 mv,  i matched all transistors. the vf of the two leds whitout the opa is 1.75v. the problem is now when i put in the opa445 in the led on the side of the opa dims and the vf drops to 1.64v, resulting in a offset drift +-80 mv . this is the amp https://www.head-fi.org/gallery/photo/kevin-gilmore-dynahi.1871812/?regular=1  . would be great if anyone could point me to some additional measurements of have tips to solve this. took great care with soldering and measured any resistors twice, don't think it's a bad solderding or missplaced resistor. any feedback helps :-)

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thanks a lot mr gilmore, you allready answered my next question. whitout opa (i used the opa445) i have a stable offset +- 3mv around zero after a half hour, at start 20mv fast dropping the first minute to under 10mv, that's fine for me. so i will use it whitout the opa. thanks a lot for you help - it's a sexy design the dynahi. strange is that both boards have the same problem with the opa in - the offset hovers slowly to over 0.3v around zero in both direction, a bit scary with this amp. out of interest, is it possible that the servos correct the offset to much when the parts are very well matched and the offset is stable going down to near zero? other class a power amps i made have a more agil bias swing then the dynahi.

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i'm not sure if you are the first person to build that particular board or not, but the version 9 board with the to92 worked correctly, and the version you built has just the to92 changed to smt. I would use a scope and signal generator to make sure its working right. Also it has a low impedance input, so anything over a 10k pot is going to cause trouble.

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