[Kruemelix]

After collecting 2000$ for a sft-audio balanced Dynahi, I realized that even with my poor electrical skills a selfmade-Dynahi shouldn't be too difficult. Soldering station, multimeter and other basic equipment are avaliable, so at least at this point there are no problems, am I right? And in case the Dynahi wouldn't work at the first attempt (what I suppose), I have still some electrical engineers as acquitances who would surely help me

Nevertheless, there are still some questions left:

- I just had a look at the Dynahi PCB/PSU part list when I realized that even with a DACT stepped attenuator and a good enclosure the price for a balanced Dynahi won't reach the 1000$ limit. So I have still 1000$ left to spend for better parts. Which upgrade would have the greatest effect? Better caps (like Black Gates or Elna cerafine), better resistors (0,1%), better matched transistors(which will result in buying more of them), a better attenuator or even anything else? Could someone make any proposals? Concerning the 1000$ left: That doesn't mean that I HAVE to spend this money on better parts, but if these would improve the sound noticeable, I have no stoppages to do so (I remember KG's Dynahi with his high-end parts). At this point: Is it really possible to hear sound differences between different resistors?

- Concerning the attenuators: I first thought in the DACT CT2 stepped attenuators with a seperate gain swich (any proposals for a good one?) - but after some people complained about only using the lowest 4 steps, I thougt about a stepped attenuator with 36 or 48 steps. Are there also good ones avaliable?

- The transformator: What about the Avel (www.avellindberg.com) 40/2780 one? It is encapsulated and has 130 VA. At an input of 230V, this will result in 34,5V output, right? (230/120 * 18V). Is this ok for the Dynahi PSU? I saw that you can use anything around 30-36V even if I don't understand why... What means "flying lead style"? That you can install them also outside of a circuit board?

- The circuit boards: where to buy them except from sft-audio (18$ are a bit too much)
Should I simply ask here in the forum?


Thank you for your answers and sorry about my awkward English,

Thomas

 

[dgardner]

Quote:

Originally Posted by Kruemelix After collecting 2000$ for a sft-audio balanced Dynahi, I realized that even with my poor electrical skills a selfmade-Dynahi shouldn't be too difficult.

If you have not done a few successful DIY amp projects leading up to this, you may have more trouble than you think.

Quote:

Originally Posted by Kruemelix I just had a look at the Dynahi PCB/PSU part list when I realized that even with a DACT stepped attenuator and a good enclosure the price for a balanced Dynahi won't reach the 1000$ limit.

Don't forget that you will probably need two complete power supplies, a power supply box, and heatsinks for four amplifier boards. This expense is not insignificant. Figure at least $200-300.

Quote:

Originally Posted by Kruemelix Which upgrade would have the greatest effect? Better caps (like Black Gates or Elna cerafine), better resistors (0,1%), better matched transistors(which will result in buying more of them), a better attenuator or even anything else?

I've built two balanced dynahi's from the ground up and the greatest impact on performance is very good construction techniques. Very close attention to wiring and grounding is required.

Quote:

Originally Posted by Kruemelix Concerning the attenuators: I first thought in the DACT CT2 stepped attenuators with a seperate gain swich (any proposals for a good one?)

I've used a four pole DACT CT2 with good results.

Quote:

Originally Posted by Kruemelix The transformer: What about the Avel 40/2780 one? It is encapsulated and has 130 VA. At an input of 230V, this will result in 34,5V output, right? (230/120 * 18V). Is this ok for the Dynahi PSU? I saw that you can use anything around 30-36V even if I don't understand why... What means "flying lead style"? That you can install them also outside of a circuit board?

You will need two complete dynahi psu boards for a balanced dynahi. One psu board will suffice if you build a single-ended dynahi. Thermal analysis shows that a 30VAC secondary is about as big as you want to go, unless you use giant heatinks.

Quote:

Originally Posted by Kruemelix The circuit boards: where to buy them except from sft-audio (18$ are a bit too much) Should I simply ask here in the forum?

Bare boards for the amplifiers and psu might be obtained by posting WTB (Want to Buy) messages in the "For Sale' forum.

 

[Kruemelix]

concerning the transformators: the reason I am asking is that at the transformator groupbuy they also used 35V ones. Furthermore, at the discussions in the Dynahi PSu thread someone said that a 30V transformator might be too less. That's why I am wondering whether they will also fit...

Thanks

Thomas

 

[Pars]

I'm guessing that many of the people in the transformer group buy have very hot running PSUs

which is why I didn't go in on it. Dan has built at least two Dynahis, as well as several Dynalo/Mids, and he knows what he is talking about. Many people made the same type of mistake on Dynalos, going for 24V + tranformers where an 18V transformer is perfect. What did your sft Dynahi have in it, or didn't you look?

BTW, Kevin Gilmore used a Penny and Giles pot (not a stepped attenuator) in his Dynahi (at least the one I saw and listened to) These can be had in a 4 gang version which would be quite suitable for a balanced Dynahi. Only drawback is they are pricey (~$400USD for a stereo pot). Kevin used to use Goldpoint stepped attenuators, and he likes the P&Gs better. YMMV.

Chris

 

[dip16amp]

I built my balanced dynahi over eight months ago for less than $500 (not including case or volume control). With the extra money you should get a good balanced source for it. I use a Benchmark DAC1 which is also my volume control.

Transformers are normally rated at full load so you also have to look at the no load voltage output and determine what your load will be and what the voltage you will end up with. I use four 28 volt transformers rated at 56 VA each but they have a no load voltage of about 34 volts AC. My wall voltage stays between 119 and 120 VAC rms. With the dynahi load, they still put out over 32 VAC rms. Using separate transformers for each AC input keeps the heat down on each one. They are barely warm.

After the rectifier diodes, the DC voltage is about 40 volts so I adjust the output of the LM338 to 35 volts. It has a five volt drop across it and it only needs two volts so that has a three volt margin. The opa541 outputs 30 volts and also has a five volt drop across it with a two volt margin.

Higher voltage transformers will need to dissipate the extra voltage into the heat sinks. The output current is constant with the dynahi so the input AC voltage variation is what you would have to decide on how much voltage margin and heat you end up with. A power conditioner would also help minimize AC voltage variation from the wall.

 

[skyskraper]

Quote:

Originally Posted by Kruemelix - The circuit boards: where to buy them except from sft-audio (18$ are a bit too much)

you want to spend more money but the base cost of the pcb's is too much?

in all seriousness though there are lots of bits and pieces that will start to add up and eat up your 2k. you're lucky that you have a large wiggle margin with your budget already.

agree, buy a better source, if you don't have enough to get the source you want, then buy another pair of cans or a bottle of cognac

 

[Edwood]

You should take a look at the Dynahi PCB group buy threads, look at how many people bought Dynahi Boards.

Then look at how many people have completed one Dynahi amp.

-Ed

 

[sft]

That's all Kevin's fault because he forget to lay the position for power-on indicator LED.

just kidding...

seriously, Dan have done a great paper work for dynalo, this is unselfish and geat work IMO. i learn a lot from that and I think it's very helpful to build dynahi.

 

[Kruemelix]

Hello,

First, thank you for all your impressions - it helped me a lot!
The only part lists I found was at djgardner.com, but these two lists also appeared several times here on head.fi.
Here they are:
http://www.djgardner.com/headphone/g...nahips/BOM.pdf
http://www.djgardner.com/headphone/g...nahips/BOM.pdf
Are they ok or are there some things where you say: Well, ok but it could be done better.
I personally do not want to exchange just randomly some parts for higher quality ones - with my poor electrical skills I doubt that this would have a positive effect.
But I saw that also KG used 0,1% (or were it 0,05%?) resistors and high quality caps. Ok, it's KG

but he will have his reasons to do so.

Thank you for your impressions,

Thomas

P.S. I have around 5-10 electrical engineering technicians in my circle of friends, so I hope I will finish my Dynahi

. And because of the PCBs, I just read that at the group buy the costs were around 5$ each, so if someone will sell me some boards for 10$, it would be fine. That's the reason why I thought that 18$ are a little bit too much. Well, if no one is selling the boards, I will have to buy them from sft...

 

[skyskraper]

well the quantities the boards were ordered in for the group buy were huge, pricing in smaller quantities is far pricier. and there was a discount given coz it was the second order put through for the layout. for something the size of th dynahi board, in small quantities, the $18 per board is pretty reasonable. considering they have to keep it in stock from their own pocket, etc.

 

[dgardner]

Quote:

Originally Posted by Kruemelix But I saw that also KG used 0,1% (or were it 0,05%?) resistors and high quality caps. Ok, it's KG but he will have his reasons to do so

If you work in a research lab or in a big company engineering lab, you will have ready access to high precision parts. High precision resistors don't necessarily sound better, but they help get certain sections of the circuit that require matching components to matchup better.

 

[dip16amp]

If you have access to a good six digit meter you should measure and match 1% resistors by hand. Only a couple of resistors in the PSU need to be low temp coeff ones.

 

[Edwood]

Is it more important to precisely match the resistors in the amp section or the transistors?

-Ed

 

[dip16amp]

You should measure and match resistors and transistors as best as you can to get as close as possible to the calculated design values. Then you will know if your measurements differ, what to adjust to correct it.

 

[Blorton]

Quote:

Originally Posted by dip16amp If you have access to a good six digit meter you should measure and match 1% resistors by hand. Only a couple of resistors in the PSU need to be low temp coeff ones.

And this is exactly why I haven't started my dynahi yet. I'm slowly stocking up on lab equipment. A good bench meter is next on the list, followed by a scope.

But the pcb's sure are pretty to look at!

Cheers!
Dan