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Old 15th September 2010, 04:20 AM   #501
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Quote:
Originally Posted by sng001 View Post
Hi OS,

Do you mean the voltage regulator that I added from the PB250?

I can easily bypass it by using the latest layout by installing only the R78 (22R) & C72. I have highlighted yellow in the attached picture.

- Stanley
What I meant is that you already lose 2v through the cascodes on the GX , so if you use the cap multipliers as well you will lose another 2-3v = 5v total. That is a lot to lose with 42v supplies. I have voltage to "burn" at 78 volts , you do not.
If you bypassed the transistors you would gain 2 volt and could add the semi's at a later date when you got a 50-55 V supply (that is what I would run your PB120 at) !!

By what this amp sounds like at moderate levels , it will be "glorious" at 4 OP pairs and 78v rails!!

OS
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Last edited by ostripper; 15th September 2010 at 04:26 AM.
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Old 15th September 2010, 04:21 AM   #502
sng001 is offline sng001  Australia
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Originally Posted by keantoken View Post
I've just tested a slew of caps in the feedback shunt network. Photoflash won, I can speak from experience now. My cap came from a clip-on flash unit, and is more powerful than what you usually find, 330V 200uF.

- keantoken
Hi Keantoken,

What do you mean by photoflash cap?

I looked thru my parts inventory, I do have a couple of Nichicon 270uF 250WV snap-on caps. They were salvaged from a switching PSU and they are pretty big - 20mm dia x 30mm tall.

I will give them a try.

Cheers, Stanley
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Old 15th September 2010, 01:31 PM   #503
sng001 is offline sng001  Australia
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Quote:
Originally Posted by ostripper View Post
What I meant is that you already lose 2v through the cascodes on the GX , so if you use the cap multipliers as well you will lose another 2-3v = 5v total. That is a lot to lose with 42v supplies. I have voltage to "burn" at 78 volts , you do not.
If you bypassed the transistors you would gain 2 volt and could add the semi's at a later date when you got a 50-55 V supply (that is what I would run your PB120 at) !!

OS
OS,

Thanks for clarifications. If the amp sounds good, I am willing to buy a new transformer.

I will etch the PCB soon & I have placed my Farnell order and some parts will be shipped from US & UK, so it will take a while.


Cheers, Stanley
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Old 15th September 2010, 02:01 PM   #504
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Hi OS,
which grade (hfe) do you choose for different transistors in the GX, please?
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Old 15th September 2010, 07:00 PM   #505
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Quote:
Originally Posted by bobodioulasso View Post
Hi OS,
which grade (hfe) do you choose for different transistors in the GX, please?
"E" for the KSA1381/KSC3503 (100-200Hfe)
"F" for the KSA992/KSC1845(300-600Hfe) I wanted "E" but had to settle for "F"

Go for these grades , or go 1 grade higher, all will be cool. I have noticed this amp is "right on" with mismatches as well (it wants to work !! )
OS
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Old 15th September 2010, 09:48 PM   #506
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Quote:
Originally Posted by sng001 View Post
Hi Keantoken,

What do you mean by photoflash cap?

I looked thru my parts inventory, I do have a couple of Nichicon 270uF 250WV snap-on caps. They were salvaged from a switching PSU and they are pretty big - 20mm dia x 30mm tall.

I will give them a try.

Cheers, Stanley
Photoflash capacitors are used in camera flash units. They can be gotten out of any camera with a flash unit inside, or the more professional clip-on flashers. Here is the wikipedia article:

Photoflash capacitor - Wikipedia, the free encyclopedia

Throw-away cameras will have the cheapest and smallest of these type of caps, clip on flashers will probably (due to more internal space and higher quality) have larger or higher quality caps. I don't know how much it matters for audio however; all photoflash caps are built to handle a dead short and I suspect this makes the difference.

If you go through with trying out the switcher caps, I'd like to hear your results too however.

- keantoken
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Old 15th September 2010, 10:29 PM   #507
sng001 is offline sng001  Australia
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Default Photoflash cap & SST grade (Hfe)

Quote:
Originally Posted by keantoken View Post
Photoflash capacitors are used in camera flash units. They can be gotten out of any camera with a flash unit inside

- keantoken

Thanks KT,

I found the following camera from my junk box. The camera still works but it does not have any slot for memory cards & I don't have the data cable, so this camera was put inside the junk box. I will open it & see what cap is used for photoflash.

Hi OS,
I salvaged the SSTs from the JVC PCBs, most of the A970 & C2240 are GR grade (Hfe 200-400) and four C2240 are of BL grade (Hfe 350-700).

Can I just use the BL grade in Q1 to Q4 & GR grade for the rest?


Cheers, Stanley
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Old 15th September 2010, 10:31 PM   #508
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I must truly thank Ed LaFontaine for the "Yuki" trafo(pix 1). It gives a rectified 45-0-45 , which is just perfect for small amp development. (Pix 2 ) is the second amp being tested on "Yuki" (this trafo has a little japanese guy on it - strange) , and finally on the "Monster" (78-0-78VDC).

Some would wonder why I go sooo slow. Besides being a braindead redneck , I want to be sure that any offering by "mongrel labs" is top notch and very safe to build. Another reason is that to determine thermal stability in the real world is a bit harder than in simulation. Heating and cooling , with hairdryers ,lighters , and cold mornings may seem primitive ... but it works!! Electrical stability- longterm is important if you want your project to last for DECADES.

The GX/PB250 has a preferable tendancy to hold its current source , and main bias settings regardless of voltage , Main Vbias drops a little as you reach 70+ volt rail levels ... but this is good. Wiper failure on any trimmer would set the amp in a safe , if not underbiased mode. This is definitly not a "burning amp" , in fact it is a "green amp" using 18ma per rail (GX1.2VB - 78V).

SNG001 - your C2240/A970 is the EXACT semi luxman used ... so you will have a perfect match.


OS
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File Type: jpg 2ndtest.jpg (174.0 KB, 458 views)
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Last edited by ostripper; 15th September 2010 at 10:36 PM.
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Old 15th September 2010, 10:41 PM   #509
sng001 is offline sng001  Australia
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Default SST grade

Quote:
Originally Posted by ostripper View Post
SG001 - your C2240/A970 is the EXACT semi luxman used ... so you will have a perfect match.


OS
Thanks OS,

I just want to make sure that I understand you correctly:

Q1 -- KSC1845 bipolar transistor or 2SC2240 BL grade
Q2 -- KSC1845 bipolar transistor or 2SC2240 BL grade
Q3 -- KSC1845 bipolar transistor or 2SC2240 BL grade
Q4 -- KSC1845 bipolar transistor or 2SC2240 BL grade
Q5 -- KSC1845 bipolar transistor or 2SC2240 GR grade
Q6 -- KSC1845 bipolar transistor or 2SC2240 GR grade
Q7 -- KSA992 bipolar transistor or 2SA970 GR grade
Q8 -- KSA992 bipolar transistor or 2SA970 GR grade


Cheers, Stanley
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Old 15th September 2010, 10:54 PM   #510
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Quote:
Originally Posted by sng001 View Post
Thanks OS,

I just want to make sure that I understand you correctly:

Q1 -- KSC1845 bipolar transistor or 2SC2240 BL grade
Q2 -- KSC1845 bipolar transistor or 2SC2240 BL grade
Q3 -- KSC1845 bipolar transistor or 2SC2240 BL grade
Q4 -- KSC1845 bipolar transistor or 2SC2240 BL grade
Q5 -- KSC1845 bipolar transistor or 2SC2240 GR grade
Q6 -- KSC1845 bipolar transistor or 2SC2240 GR grade
Q7 -- KSA992 bipolar transistor or 2SA970 GR grade
Q8 -- KSA992 bipolar transistor or 2SA970 GR grade


Cheers, Stanley
Yes , optimum. Having this circuit running at so many voltages and environmental conditions, I would say it would also work well with 2n5551/5401 or even BCxxx at lower rail voltages. VERY forgiving topology. Of course , the closer you approach the baseline design (luxman M120a), the more closely the sound will match the original.

Be sure to test all your salvaged components before using them .
I would try to use the same grade throughout the amp , even as I included the "LS adj" , the level shifter adjust to compensate for any mismatch.

OS
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Last edited by ostripper; 15th September 2010 at 10:58 PM.
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