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Metaxas Solitaire III Bias
Metaxas Solitaire III Bias
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Old 25th November 2018, 04:13 PM   #11
Depaj is offline Depaj  France
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I'll go easy on them and see what they give back.
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Old 26th November 2018, 01:05 AM   #12
AKSA is offline AKSA  Australia
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Depaj,

Look for a small cap around 47pF or thereabout between a base and collector of the VAS, which is typically in the centre of the schematic/layout. It will connect directly to the bias generator. Metaxas did not reveal his schematic, but if you can post a detail picture of the pcb it should be possible to identify the lag compensation cap. Often these caps are silver mica, or polystyrene, or even ceramic NPO.

Hugh
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Old 26th November 2018, 07:11 AM   #13
Depaj is offline Depaj  France
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Could it be c4 that is marked on the board but isn't there (in the description of the circuitry on their website it says that because of the very fast output transistors (60MHz) there is no need for lag compensation).

DSC_1494.jpg
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Old 26th November 2018, 07:38 AM   #14
RM is offline RM  Norway
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You can see them between Q14-R14 and Q15-R15. One is labeled C5. I believe they are 10-22pF. They can be increased to 56-68pF. In my opinion 100pF is too much.

R
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Old 26th November 2018, 11:18 AM   #15
AKSA is offline AKSA  Australia
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There is the issue:
Quote:
description of the circuitry on their website it says that because of the very fast output transistors (60MHz) there is no need for lag compensation
A more silly comment I have not seen.... even 400MHz transistors need compensation, 60MHz devices are SLOW.

Hugh
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Old 26th November 2018, 11:32 AM   #16
Depaj is offline Depaj  France
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Quote:
Originally Posted by AKSA View Post
There is the issue:

A more silly comment I have not seen.... even 400MHz transistors need compensation, 60MHz devices are SLOW.

Hugh
Sorry I misread, they were talking about the zobel network, I have a translated version and there were some errors in it.

The cap has just written 11 on it so I guess that would be 1 x 10 = 10pF, I can get some 56pF or 68pF 65V 2.5% styroflex caps from a distributor here in france, does this look like a good option ?
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Old 26th November 2018, 12:07 PM   #17
RM is offline RM  Norway
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Yes.
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Old 30th November 2018, 08:54 AM   #18
Depaj is offline Depaj  France
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I replaced the caps and am testing the amp now with an 8ohm load but still with the dim bulb (200w bulb so it can take a little power). I set bias at 10mV for now just for some testing but I did find some differences between the 2 x 4 outputs in parallel (the bias voltage ranges from 9 to 11mV without signal so some devices are conducting a little more than others). The difference amplifies with output : at 12W into 8ohms I read from 89mV all the way to 101mV on different emitter resistors. As I said I have two mono blocs, one original, the other has the new outputs, emitter resistors and drivers I mentioned before, both have these differences, are they acceptable ?
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Old 30th November 2018, 09:55 AM   #19
RM is offline RM  Norway
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The "old" ones used to have 2SA1095 & equivalant. These are superior from a heat transfer point of view, which really is of paramount importance considering the piddling, god I love that word, heatsinking on these amps. 2SA1227 & its equivalent are stellar performers, I used more than 3K pairs of these in the late eighties, still have a few left.
But I would still opt for the former given your special circumstance.

I have forgotten, what is the value of the resistor between the emitters of the driver transitors? It should be quite low.

I wouldn`t be surprised if Hugh also agreed on this notion. From our different conversations ages ago I seem to remember we shared many opinions on the Metaxas brand of amps.

R
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Old 30th November 2018, 10:05 AM   #20
Depaj is offline Depaj  France
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Hello RM,

I think you misunderstood, I have one example that has its original transistors the 2SA1227 and complementary indeed and the other one as I said in my first post has undergone some changes :

Quote:
Originally Posted by Depaj View Post
A few weeks ago a friend brought me his two mono blocs from Metaxas (Solitaire III). A previous tech plugged them in to a 230V mains outlet when they were configured for 110V mains so... lets just say there wasn't much left of the fuse and most of the small signal transistors shattered to pieces.
I changed most of the small transistors, replaced the main caps that vented and all the power transistors (2 were shorted so I replaced the whole bunch with MJW 1302/MJW3281) and drivers (MJE15030 ans MJE15031). All the other transistor are original references.
The 2sa1227 aren't available any more that is why I went for the on semi.

The drivers have 27ohms between their emitters.

My actual question was : is the difference of bias current between the different paralleled outputs going to be a problem or should I be just fine ?
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