[rsaavedra]

Speaking of cases, I have a problem finding any decent metallic cases here in Venezuela. The only available ones have inapropriate dimensions, and are extremely horrible anyway

. Not sure if I will be able to find aluminum panels to build the enclosure myself. Also wondering if wooden enclosures would be too bad an idea. Some amps don't have metallic enclosures after all, for example the Audio Valve RKV MK II. Even the Berning Microzotl has some glass walls, not a full metal jacket so to speak. In my case it's a Dynahi, I know those heatsinks heat up a lot and will have to breathe, but assuming sufficient vents how about a wooden enclosure that I could build myself? I wonder it wouldn't help against EMI though. Any suggestions/recommendations?

 

[rsaavedra]

Today I found some nice connectors and a nice cable for the umbilical cord between my two enclosures:

Interestingly, I did find the speakon connectors in one local store, but they only had the cable connectors, not the chassis mountable ones, so couldn't use them. I liked these ones too anyway.

Despite the overall thickness of the cable, it is really very flexible. The wires in it are 16 awg btw. This will be much better than the 22 awg wires in the microphone cable I have.

 

[luvdunhill]

I'm not sure if this is the best place to ask this, but I wanted to see if it would be possible to use PRP resistors on a Dynahi board. As you might know, there are a lot of holes in their 0.5 W line. So, I'm trying to understand if it's possible to substitute. Here's my analysis:

schematic value 500R used at the emitter of 2sa1145. sub to 510R. seems reasonable, this will decrease the current a tad.

schematic value 20R. strange, as I found a schematic that uses 10R, but the 20R is mentioned in djgardner's BOM. anyways, my choices are 18R and 22R, 18R seems fine here.

schematic value 300R. used at collector of 2sc2705/2sa1145. Closest value is 270R or 330R. I'm not so sure about this one.

schematic value 30K. use at base of 2sa1145... choices are 27K or 33K...

schematic value 5K, used at collector and base of 2sc3381/2sa1349 and into OP27. Closest value is 5K1... seems reasonable to me, but again I'd like your opinions.

If this isn't feasible, then I'll just use vishay-dale resistors, but I'd like to give it a try. I know some of these values are available in Holco, but I'd like to stay with the pretty red ones

Thanks guys!

 

[DigiPete]

If you don't get help here, go to the DIY area of headwize. There is a Dynahi amp build thread there.

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif I'm not sure if this is the best place to ask this, but I wanted to see if it would be possible to use PRP resistors on a Dynahi board. Thanks guys!

 

[Pars]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif I'm not sure if this is the best place to ask this, but I wanted to see if it would be possible to use PRP resistors on a Dynahi board. As you might know, there are a lot of holes in their 0.5 W line. So, I'm trying to understand if it's possible to substitute. Here's my analysis: schematic value 500R used at the emitter of 2sa1145. sub to 510R. seems reasonable, this will decrease the current a tad.

should be fine

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif schematic value 20R. strange, as I found a schematic that uses 10R, but the 20R is mentioned in djgardner's BOM. anyways, my choices are 18R and 22R, 18R seems fine here.

the actual resistance is 10 ohms... done by paralleling (2) 20 ohm resistors for better power handling.

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif schematic value 300R. used at collector of 2sc2705/2sa1145. Closest value is 270R or 330R. I'm not so sure about this one.

not sure on this one... I'd probably try both

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif schematic value 30K. use at base of 2sa1145... choices are 27K or 33K...

I would think that would be OK
Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif schematic value 5K, used at collector and base of 2sc3381/2sa1349 and into OP27. Closest value is 5K1... seems reasonable to me, but again I'd like your opinions.

that would be fine

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif If this isn't feasible, then I'll just use vishay-dale resistors, but I'd like to give it a try. I know some of these values are available in Holco, but I'd like to stay with the pretty red ones Thanks guys!

I'd use Roederstein MK3s if I could get them... PRPs are nice also... my dynalo uses a mix of these since the common values (10K, 1K, etc.) are unobtainable in Roederstein.

 

[luvdunhill]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif not sure on this one... I'd probably try both

heh, and what would be my litmus here?

 

[Kruemelix]

Hello,

just wanted to know whether the planned internal wiring of my Dynamight will be correct. Hope everyone understands everything. The input ground of all amplifier boards and the ground of the balanced input jacks are connected due the internal structure of the attenuator.

Thomas



P.S. I still don't know how important a good ground wiring is. By using a seperate PSU case, is it possible to connect the ground of the two power supplies and the ground wire of the power supply for the attenuator already in the PSU case together and lead only one ground cable out? Or shall I realize a uncompromising star wiring (don't know the exact english word) which will result in many ground wires from the PSU to the Amp case where the connection point will be.

 

[Kruemelix]

nobody who could help? A "yes" or "no" will be enough

 

[amb]

Run the unbalanced headphone jack ground return wires separately from the amp board grounds back to the PSU. As far as your attenuator goes, you do not mention what it is, and whether the "ground" on it going back to the PSU is shared with signal ground. If you put the PSU in a separate case than the amp, it could really complicate matters if the grounds are shared.

I suggest you read my post in the dynahi thread at headwize about grounding concerns and why separate amp and PSU cases are a good thing, but in my situation the volume control is an Alps RK40 pot, so there isn't an issue with having to run power supply lines to it.

 

[Kruemelix]

thanks amb, I found your artile at headwize and read it. The problem I had was that I didn't look neither at a schematic nor at a PCB of the amp. Now that I had a look at the schematic, you better replace "Out 2" in my picture by the GND pin at the amp board. So our two proposals are almost the same, except the fact that you are realising a better "star wiring" (still don't know the exact name), right?

But another major problem occured: I thought the amp boards were already built completely when I saw the 2sk389 and 2sj109 missing. After a little bit of searching I realized that they are almost everywhere out of stock or only avaliable at insane prices (15$ a piece). Is it possible to use 2sk170 and 2sj74 instead of them? Of course I will have to match them (even if I don't know exactly ho to do so with JFETs).

Furthermore, with the qouted wiring above, I can use the balanced output only with balanced inputs completely, right?

Thomas

P.S. I just realized that the grounds aren't tied together (attenuator is a V-03 from diyclub.biz

 

[amb]

Quote:

Originally Posted by Kruemelix /img/forum/go_quote.gif thanks amb, I found your artile at headwize and read it. The problem I had was that I didn't look neither at a schematic nor at a PCB of the amp. Now that I had a look at the schematic, you better replace "Out 2" in my picture by the GND pin at the amp board. So our two proposals are almost the same, except the fact that you are realising a better "star wiring" (still don't know the exact name), right?

Yes, the idea about running separate wires for the unbalanced headphone jacks' ground return back to the PSU ground is so that the small signal ground reference from the amp boards won't be modulated by the higher output return currents.

Quote:

Is it possible to use 2sk170 and 2sj74 instead of them? Of course I will have to match them (even if I don't know exactly ho to do so with JFETs).

2SK389 and 2SJ109 is obsolete (Toshiba has stopped making them quite some time ago), and the shrinking supply of unsold parts are being horded at high prices.

You can use matched 2SK170 and 2SJ74 in place of 2SK389 and 2SJ109. They are equivalent devices (except for the fact that the former are singles and the latter are duals). See the "device matching" page of the β22 website about how to match them. You will need a fairly large number of them to achieve a good match, though, which probably makes even less sense than buying the 2SK289/2SJ109s at their high prices (if you could find them).

Quote:

Furthermore, with the qouted wiring above, I can use the balanced output only with balanced inputs completely, right?

If you use an unbalanced input (feeding only the + and GND input pins on the XLR), and you also ground the - input, then you can still use the balanced output jack. The signal won't be truly differential, but it will work.

Quote:

P.S. I just realized that the grounds aren't tied together (attenuator is a V-03 from diyclub.biz

I suggest running a separate ground wire back to the PSU for this board since it contains relays and digital circuitry. I don't think there is a need for the ground on this board to be connected to the amp ground at all. They could remain completely independent.

 

[Kruemelix]

After around 12 hours of working (only enclosure), I finally finished my Dynamight. Checked everything twice, plugged in and runs stable for around 15 minutes now. Thanks to Pars and Amb who helped me a lot during the building process.

Thomas

P.S. first DIY project for me

EDIT: now around 1 o' clock in the morning....

 

[Kruemelix]

ok, first problems appeared:

when I plugged in a headphone, I heard nothing. After some measurements, I found out that the controller board of the attenuator (V-03 from DIYClub) seems to be damaged - the input resistance never goes below 100k. Might be the microcontroller.

Another problem occured: Without any input signal/load, the voltage drop over the 20 Ohm output resistors is around 1V - makes 100mA per transistor. Furthermore, the heatsink is getting damn hot after some minutes. Thus, I never have plugged in my Dinamight a longer time. How can you adjust the output current?

 

[Pars]

I would short the input of the amplifier to ground when setting up or verifying its operating points. The 20 ohm resistors are in parallel (2 in || for 10 ohms), so that would be your current calculation for the output devices. There is another build thread on Headwize as well if you aren't aware of it. I still haven't

 

[Kruemelix]

ok, after a month I got back again on the Dynamight, adjusting the output current of each of the output transistors to 75mA. Nevertheless, the heatsinks (HS-TWS) are still getting very hot - you can barely touch them with bare hands. Is this normal? Are the heatsinks undersized?

Thanks,

Thomas