The MONGREL (supersym II)

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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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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
 
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
 
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 !! :D )
OS
 
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
 
Photoflash cap & SST grade (Hfe)

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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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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SST grade

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
 
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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Ready to ROCK !!

All 4 pairs are installed and tested , just have to do a little millin' on my heatsinks. Lined the NJW0281/0302 pairs up at 4 -1/2" - 114mm (pix 1) and the
MJE15032/33 drivers at 4" -102mm. These amps look like they were made for the heatsinks (pix 2) . A lot of precision drilling and tapping , I use 6-32 allen head bolts with load spreaders and strange orange insulators that came from the genesis stealth.

All set for tommorrow's FULL power test from hell. 2 paralleled speakers per channel , same as the "supersym" test. With the GX's higher gain I will most likely approach the speakers "death zone" :D

OS
 

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OS,

You are truly welcome. I'm glad it arrived and survived. I consider it a paltry dues for all the good you share with us. :up:

It is a funny transformer , I wonder who "yuki" is ?? I will share more now that I have the PCB problem "licked". I share a lot , but there is something strange afoot. Many download my designs but do not give any feedback. I would be more than glad to help with any aspect of something I designed.

Next , I need to redesign a simple soft-start , I will share the whole experience here. I will use the little salvaged microwave trafo and a few other simple parts (darlington , simple RC delay) to make a compact , reliable unit.
I don't want this one to rely on the main power supply to be triggered but to be enabled by the AC line directly AND to be self powered.

BTW , Ed ... i see you are a speaker man. I eventually want to design a 12" peerless 3-way super speaker to match my amp. It would need to be most robust , as my amps can easily spit out 500w peaks.

OS
 
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Top dog !!

This is what I will be dealing with tomorrow(below). I am even impressed (very hard to do) at the professional look of this amp. I am glad there will be no "finger crossing" or any other B_S to look forward to as I have already biased and listened to the units ... NO SURPRISES.. :cool: Except maybe some awesome headroom and superior stereo imaging (I have only heard these in mono so far :( )
OS
 

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OS, I have downloaded some of your stuff and appreciate what you share. I am not there yet with prefabricating my own pcb. I have been researching on it and in the process of looking for a used laserprinter now. From what I read in your previous posts is that I should be looking for a HP printer due to the toners lower temperature? I have been thinking for some time now of going your route and build a universal PSU and try different amp builds. This DIY does get costly and this is what I've experienced with the different builds that I have done or attemted to finish. This includes and not limited to 3 amps (SkA 150, Blames ES both done, Lynx 60%), 2 Linestages (Heretical 90% finished, Aikido 50% finished), just got done with DCB1 buffer.

The funny part with me is that new things always pop up and I tend to jump from project to project so the finances for parts are always jumping around also.

I used to have a Dodd TUBE amp and preamp, I sold both for about 4k a few years when I stumbled to this site thinking I could have more for less. In the long run I figure I will probably spend more but at least I'm getting an education at the same time, plus I really enjoy it, and I get to try different flavors.

Thanks for what you share, and I will definitely be looking at your progress with this amp and will look forward to building your designs in the future. Too bad you don't offer boards but this is DIY....
 
The funny part with me is that new things always pop up and I tend to jump from project to project so the finances for parts are always jumping around also.

Thanks for what you share, and I will definitely be looking at your progress with this amp and will look forward to building your designs in the future. Too bad you don't offer boards but this is DIY....

That is the reason for the "mongrels". Once you get your power board and power supply done and bolted in , you don't have to go broke and build all those projects anymore. I will eventually have Voltage boards up to A "ZX" , if I wanted to , I could even turn all of mr. carlos's DX amps into voltage boards and run them at 60 or 200w+.

Each voltage board costs less than $10 , so DIYing can be less expensive. Also , my FR-4 is "bulletproof" you CAN NOT lift a pad from my military grade PCB's .... you have to scrape it off.

I will be selling boards in october (GX,AX,BX,CX , PB250/60- PS100) all made by me , not chinese board house stuff.
Below is the AX , I had to take parts out to finish my GX's , but it sounds golden. It is still the champ in Wahib's simulation "shootout".

OS
 

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