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Old 6th October 2012, 10:11 PM   #11
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Since I didn't want to go back inside again, I decided to throw almost everything at my 5200: IEC connector, RCA sockets, caps, resistors, wiring, jumpers....

It now has 2x 15000uF in place of the original 2x 6800uF per rail, as well as 0R25 in a CRC (68000uF + 0R25 + 15000uF + 15000uF per rail) for over 7 times the original PS capacitance. For inrush protection, it already had a 2R5 NTC on the switch pcb, which is enough to prevent the stock fuse from blowing at turn on.

Since I didn't have the schematic, I decided to change only the emitter resistors from 0R1 to 0R07 and leave the circuit otherwise mostly unchanged (except for different type caps and resistors here and there).

Next I would like to add some inductance in a CLC for the PS and modify the cover so it fits over the new heat sinks.

With the extra heat sinking added, I have the bias set as high as I dare: 0.4A (5W of class A into 8 Ohms), but it takes over an hour to reach a stable temp and sound its best. It keeps sounding better with more and more bias, so I suppose it's time to move on to real class A amps....
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File Type: jpg Adcom 5200 ADS2.JPG (280.3 KB, 255 views)
File Type: jpg 5200 close ADS3.JPG (238.5 KB, 251 views)
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Old 22nd December 2012, 09:11 AM   #12
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Andersonix

Thank you for your comments about the service info and biasing. My 5200 is working well, runs reasonably cool, and I really like the way is sounds. So much so that I swapped it in place of my ST70 tube amp and my whole system sounds better. I was amazed! Who would have thought a $25 broken beater amp from eBay would end up replacing my main system amp.

I did add a small PC type fan under the 5200 which forces air up through the heat sink fins. It is just glued on with some RTV and it works very well. Anyway, I am enjoying the amp and really appreciate folks like you sharing your experiences.

Best regards
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Old 26th December 2012, 08:54 PM   #13
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jsfinusa: Indeed there is some potential bottled up inside the 5200!
If you're confident in the state of your thermal insulators (and its location is cool enough) I suggest aiming for about 0.25-0.30A of bias with the stock heat sink. And since the HS is mounted to the bottom panel for extra heat rejection, raising the amp with some taller feet (like the 1.5 inch tall ones from ApexJr that I'm using) helps air get underneath. I had left myself the option to add two small fans (stuck on with double-sided foam tape to prevent noise), but I don't think I need them for now.

Updates to my 5200: As cooler weather descended, I adjusted the bias to 0.5A (that's 8W of class A), and it improved even further (with possibly some margin for even more bias -- I will aim for 0.65A next time).

Finally, as planned, I connected a couple of 9mH (~0R6 DCR, 19AWG) inductors from ApexJr in place of the 0R25 resistors to make a CLC: Ripple on the rails went from about 4mV to about 2mV, and rails went from +/-40.6V to 39.1V. CLC (CLcc, really) is 68mF + 9mH (0.6DCR, 19AWG) + 15mF + 15mF. The improvement in the highs and low level resolution from this quiet PS was beyond my expectations. Let's just say this amp is no longer the bottleneck in the system...

But it's clear this will never be a great bass amp: Bass is slightly mushy and impact-less compared to my hot-rodded Acurus with paralleled output transistors and similar PS. But that's alright, as it was primarily intended to drive just the ESL panel in my hybrids, which it does really well -- without the 'distortion alert' lights flashing too much!

More pics to follow when a new cover is completed.
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Old 28th March 2013, 10:46 PM   #14
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Default Quarterly Update

For you DIY cheapskates following along at home and working up the nerve to re-cap your own little Adcom, the perfectly fitting 15mF 50V Panasonic caps that I used for my 5200 are on sale for about $3 at AllElectronics (see attached), which is less than half the 'retail' price. If memory serves, the 535 also takes this size caps (30mm Dia, 50mm H).

I have now dialed up the bias to 0.7A (over 15W of class A into 8R), and now the HS runs hot, so hot that I can barely hold it for 10 seconds. And after about an hour it sounds glorious, despite the PS ripple going up again to ~4mV. So now I'm battling to get the ripple down again, and thinking about working in some more caps into the new cover (see attached), so that it will have a total of 128mF per rail -- 9.4 times the original! Also I want to find a tin can to put the transformer into.
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File Type: jpg Adcom Feb update.jpg (327.5 KB, 198 views)
File Type: png Screen Shot 2013-03-28 at 12.56.34 .png (116.6 KB, 186 views)
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Old 14th November 2013, 09:06 PM   #15
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I have a 5200 which my sister is using at the moment, pristine condition and I am the only owner, since back in 97 or something. I bought it as a combo with the GFP 345.

I have since moved on to other equipment but would like some input; I am no electric DIY guy yet, but am very interested in turning up the bias and possibly add more HS. Would you recommend this and how is the bias turned up - do I need to de-solder anything or is it possible to 'adjust' it in some way?

If I could turn up the bias to get a couple of watts in class A, I might use the little amp again in either my main system or a secondary one..
Am a complete novice in doing this though so maybe it's not recommended without help from someone experienced? btw it's the 220v version as I am in the UK at the moment..
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Old 24th November 2013, 02:04 AM   #16
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Yes, it is possible to turn up the bias without soldering anything. With stock heat sinking with the cover on in a cool place in the rack, I reckon you can go up to about 0.25A bias (which will give you 2W of class A into 8 Ohms).

I recommend you have a more experienced person helping you, as those single turn pots are very jumpy, and you could blow the output transistors. Note that the Adcom service manual for the 5200 has the bias check wrong as it's copied verbatim from the 5300 service manual. Setting the voltage at 20mV as printed will set the bias current at 0.20A (as the source resistors are 0.1 Ohm in the 5200, not 0.33 as in the 5300.)

You need a volt meter to measure voltage across one of the 0.1 Ohm source resistors. Don't do this by 'feel'!

Last edited by Andersonix; 24th November 2013 at 02:08 AM.
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Old 10th December 2013, 09:00 AM   #17
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hello
Prompt what electrolytes can be put in place regular power supply, without replacing the transformer?
Regards Ivan
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Old 16th December 2013, 09:58 AM   #18
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Ivan,
I replaced the 4 on-board power supply caps with Panasonic ECO-S1HP153DA from Digi-Key. They are 15,000uF 50V caps that are a perfect fit: 30mm Dia, 10mm lead pitch, and 50mm tall.
I would have gone with some caps with larger capacitance, but couldn't find any in 30mm Dia. The PS rails are about + and -42VDC, so replacement caps need to be at least that voltage rating. Hope that helps!

PS. In case it wasn't clear, I am still using the stock transformer which came with the amp.

Last edited by Andersonix; 16th December 2013 at 10:03 AM.
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Old 12th January 2014, 08:00 AM   #19
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Thank you for the answer.
Unfortunately in the free market in Ukrane 15,000 uF 50V 30mm diameter not have to 12000uf is 22,000 but the diameter of 35mm. Suggest that gave replacement input capacitors WIMA MKP10 2.2uf? Whether they can be removed by placing a jumper if I have a pre-amp?
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Old 4th February 2014, 11:24 PM   #20
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I did not use 35mm Dia caps because it looked like they were not going to fit, especially after I squeezed in larger input DC-blocking caps. (I used 2u2 WIMA that I had on-hand. See pics in post 11)

You may choose to bypass the input caps, as long as you accept any consequences of what happens upstream to the signal! I did not want to push my luck any more than I am already...
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