Dynahi questions (which item to buy?)
Mar 27, 2006 at 4:38 PM Thread Starter Post #1 of 18

Kruemelix

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Hello,

just a few questions concerning the Dynahi:

- Do the HS-TWS heatsinks also fit for the amp board? IMHO they should, right?
- How do I insulate the transistors from the heatsink? Any mouser/digikey numbers?
- Mouser had no 3,57 kOhm resistors left for the PSU, do the 3,48 kOhm ones also fit?
- Where to get all the transistors for the amp board and the 0,33µF capacitors parallel to the rectifier diodes from?

More questions following soon,

Thomas
 
Mar 27, 2006 at 6:13 PM Post #4 of 18

Pars

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Quote:

Originally Posted by Kruemelix
- Do the HS-TWS heatsinks also fit for the amp board? IMHO they should, right?


I believe they do, but haven't used them.
Quote:

Originally Posted by Kruemelix
- How do I insulate the transistors from the heatsink? Any mouser/digikey numbers?


Look at the Berquist silpads on Digikey. Sorry, I don't have PNs handy.
Quote:

Originally Posted by Kruemelix
- Mouser had no 3,57 kOhm resistors left for the PSU, do the 3,48 kOhm ones also fit?


Yes, the spec'd resistor value is 3.5K... 3.48K is closer than 3.57K.
Quote:

Originally Posted by Kruemelix
- Where to get all the transistors for the amp board and the 0,33µF capacitors parallel to the rectifier diodes from?


Transistors from B&D Enterprices (bdent.com). Make sure you ask for same gain classification for any PNP/NPN pairs. The caps should be a stacked film or monolythic ceramic... try P4669-ND
(Digikey) from the Dynalo parts list
 
Mar 28, 2006 at 1:06 AM Post #6 of 18

dgardner

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Quote:

Originally Posted by Kruemelix
Do the HS-TWS heatsinks also fit for the amp board?


The origin of the HS-TWS heatsinks stems from the fact they were cheap, readily available, and about the right size. They are not special in any particular way. If you can scrounge for alternatives, you might want to look for something with roughly about 0.8 C/W to 1.2 C/W or lower, per board. Each dynahi amp board is mono and dissipates about 15W on the output stage. Hope this helps.
 
Mar 28, 2006 at 1:32 AM Post #7 of 18

grasshpr

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Quote:

Originally Posted by Kruemelix
- How do I insulate the transistors from the heatsink? Any mouser/digikey numbers?


I used this part from digikey for the OPA541AP op amps: BER180-ND
This is for the PSU. For the LM338's you can use any TO-220 type sink pads.

The output transistors for the dynahi do not need to be insulated since they are plastic backing. You could however get any type of TO-220 sink pad, but that may be a waste of money.

Hope this helps
 
Mar 28, 2006 at 3:33 AM Post #8 of 18

amb

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Quote:

Originally Posted by grasshpr
I used this part from digikey for the OPA541AP op amps: BER180-ND
This is for the PSU. For the LM338's you can use any TO-220 type sink pads.



I used the BER107-ND for the OPA541s, and BER219-ND for the LM338s.

Quote:

The output transistors for the dynahi do not need to be insulated since they are plastic backing. You could however get any type of TO-220 sink pad, but that may be a waste of money.


The heatsink pads help heat conduction by providing better contact between the transistor and the heatsink (because they are slighly pliable and fill the
microscopic voids on each surface). If you don't use pads, then you apply a small dab of heatsink compound goo.
 
Mar 28, 2006 at 3:47 AM Post #9 of 18

grasshpr

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Quote:

Originally Posted by amb
I used the BER107-ND for the OPA541s, and BER219-ND for the LM338s.


The heatsink pads help heat conduction by providing better contact between the transistor and the heatsink (because they are slighly pliable and fill the
microscopic voids on each surface). If you don't use pads, then you apply a small dab of heatsink compound goo.



Right, a little bit of goo is nice to have as well. A bit messy though...
I did try working the dynahi with and without the pads and found very little difference. For me, most important part was providing enough torque for the mounting screws onto the heatsink.
 
Mar 28, 2006 at 11:08 AM Post #11 of 18

Kruemelix

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almost completed my order I am still missing the following things:
- CAP - Monolithic Ceramic, 0.33uf, ??V ---> are the P4669-ND @ digikey ok?
- 0.1uF 50V ceramic Z5U radial

any proposals? (sorry, but I don't want to buy a wromg item)

Thanks,

Thomas

EDIT:
- how much (or less) gain can a Dynamight handle? 1,5? 2?
- 10k or 25k attenuator for a Dynamight?
 
Mar 28, 2006 at 12:49 PM Post #12 of 18

amb

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Quote:

Originally Posted by Kruemelix
- CAP - Monolithic Ceramic, 0.33uf, ??V ---> are the P4669-ND @ digikey ok?


It is my opinion that 0.33µF is excessive capacitance as rectifier snubbers. I personally used 100pF monolithic ceramic 100V axial lead caps on my build (Digikey 399-1812-1-ND or Mouser 80-C410C101J1G). This is the same as what Tangent specifies for the STEPS supply. Btw there is nothing magical about 100pF. Anything in the 100pF to 680pF are common for snubber applications.

Quote:

- 0.1uF 50V ceramic Z5U radial


If you're referring to those on the PSU board, I actually used 0.1µF 50V X7R monolithic ceramic axial lead caps (Digikey 399-4484-1-ND or Mouser 80-C412C104K5R). The X7R ceramics are slightly superior to the Z5U grade, and the axial leaded version fit the board nicely.

Quote:

- how much (or less) gain can a Dynamight handle? 1,5? 2?


I wouldn't go below 5, and even at a gain of 5 you should change the 33pF compensation capacitor to a 47pF to ensure stability. See this post on headwize.com. Also keep in mind that for a dynamight in balanced configuration, the effective gain is twice that of the amplifier gain, so if you set the gain to 5 on each amp, the real gain as seen by the headphones is 10.

Quote:

- 10k or 25k attenuator for a Dynamight?


You can use anything between 10K and 50K. The "10KΩ" resistor going to ground at each input should be increased to at least 10x the value of the pot or stepped attnuator, so if you use a 10KΩ pot/attenuator, that resistor should be at least 100KΩ. I used a 50KΩ Alps Black Beauty RK40 pot, and a 1MΩ resistor at the input to ground.

For a dynamight you will need a four-gang pot/attenuator to control all four amps simultaneously.

Also, I recommend that you add a series resistor between the output of the pot and the input terminal of the amp. I used a 475Ω resistor but up to 1KΩ is also fine. This resistor provides a little buffer to prevent the input FET's gate from shorting directly to ground at minimum volume, and also provides a small buffer between the driving source and the input FET when the volume is set to maximum. Without this resistor the amp may misbehave. See the schematic diagram of the dynahi and psu with all part values as I built it (including wiring):

My dynahi page
Amp schematic
PSU schematic

Edit: There are also dynahi-specific build discussion threads at headwize.com that you should peruse:
dynahi amp thread
dynahi psu thread
 
Mar 28, 2006 at 2:52 PM Post #13 of 18

Kruemelix

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Quote:

Originally Posted by amb
It is my opinion that 0.33µF is excessive capacitance as rectifier snubbers. I personally used 100pF monolithic ceramic 100V axial lead caps on my build (Digikey 399-1812-1-ND or Mouser 80-C410C101J1G). This is the same as what Tangent specifies for the STEPS supply. Btw there is nothing magical about 100pF. Anything in the 100pF to 680pF are common for snubber applications.


k, I will use the 100pF you quoted above

Quote:

Originally Posted by amb
If you're referring to those on the PSU board, I actually used 0.1µF 50V X7R monolithic ceramic axial lead caps (Digikey 399-4484-1-ND or Mouser 80-C412C104K5R). The X7R ceramics are slightly superior to the Z5U grade, and the axial leaded version fit the board nicely.


Yes, I meant them...

Quote:

Originally Posted by amb
I wouldn't go below 5, and even at a gain of 5 you should change the 33pF compensation capacitor to a 47pF to ensure stability. See this post on headwize.com. Also keep in mind that for a dynamight in balanced configuration, the effective gain is twice that of the amplifier gain, so if you set the gain to 5 on each amp, the real gain as seen by the headphones is 10.


would there be any problems if I place another 1,2kOhm resistor in parallel to the existing one in case the Dynamight is way too loud?

Quote:

Originally Posted by amb
You can use anything between 10K and 50K. The "10KΩ" resistor going to ground at each input should be increased to at least 10x the value of the pot or stepped attnuator, so if you use a 10KΩ pot/attenuator, that resistor should be at least 100KΩ. I used a 50KΩ Alps Black Beauty RK40 pot, and a 1MΩ resistor at the input to ground.


just one question: At which position of the volume knob you are listening? I fear that a Dynamight becomes way too loud, especially with my L3000 (ok, there are also other headphones like the K1000, but...)

Quote:

Originally Posted by amb
For a dynamight you will need a four-gang pot/attenuator to control all four amps simultaneously.


jep, I know.

Quote:

Originally Posted by amb
Also, I recommend that you add a series resistor between the output of the pot and the input terminal of the amp. I used a 475Ω resistor but up to 1KΩ is also fine. This resistor provides a little buffer to prevent the input FET's gate from shorting directly to ground at minimum volume, and also provides a small buffer between the driving source and the input FET when the volume is set to maximum. Without this resistor the amp may misbehave. See the schematic diagram of the dynahi and psu with all part values as I built it (including wiring):


huh? You mean in series with the output of the pot?

My dynahi page
Amp schematic
PSU schematic

Edit: There are also dynahi-specific build discussion threads at headwize.com that you should peruse:
dynahi amp thread
dynahi psu thread[/QUOTE]
 
Mar 28, 2006 at 3:18 PM Post #14 of 18

amb

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Quote:

Originally Posted by Kruemelix
would there be any problems if I place another 1,2kOhm resistor in parallel to the existing one in case the Dynamight is way too loud?


The original dynahi schematic has 1.2KΩ and 100Ω for the feedback resistors, which makes a gain of 13. In balanced mode that doubles to 26.
basshead.gif


In my build, I increased the second resistor to 200Ω and kept the first at 1.2KΩ (actually, 1.21KΩ) for a gain of 7. Depending on whether you use 100Ω or 200Ω for the second resistor, if you put two 1.2KΩ resistors in parallel you'll get a gain of 7 or 4, respectively. As I said previously, you should avoid going below a gain of 5, and should consider changing the 33pF to 47pF for any gain less than 9. I still have 33pF in mine but will change to 47pF when I get around to it.

Quote:

just one question: At which position of the volume knob you are listening? I fear that a Dynamight becomes way too loud, especially with my L3000 (ok, there are also other headphones like the K1000, but...)


I use Sennheiser HD600 and get good range of control with the gain of 7. Depending on how hot the source is and the recording level, the pot is usually near center of its travel. Now my amp is a dynahi, not a dynamight. With a dynamight the doubled effective voltage gain means that at any volume control position the sound will be 6dB louder than unbalanced mode for the same headphones and source.

Quote:

huh? You mean in series with the output of the pot?


Yes, have a look at my schematic and you'll see it (link in my previous post).
 

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