IMHO моды - скользкая тема...
у нас они не оч популярны - так как на пост СССР паяльник у каждого второго в тумбочке - все "умные" - денег не многие дадут. Вот в Европе и штатах это довольно популярное дело - отправлять усилители на модинг - те же fjа, фридмен, и т.д.
Замодить усилитель что б он звучал иначе - не проблема, что б хозяину при прослушивании нравилось больше чем было - тоже не проблема. Проблема как этот усилитель потом будет звучать в пачке, или при снятии микрофоном и т.д.
Поэтому моды должны проверятся временем и достаточно большим колл-вом людей (Кеп привет).
по поводу фридмана, на одном из форумов посвященных усилителю Jca20H и его модом
один товарищ выложил схему мода Фридмана, которую он сделал по фото моденых усилителей
вот она -
http://img225.imageshack.us/i/friedmanmarsha.jpg/на сколько она верна - не известно.......
вот комментарии человека, чья схема (они вперемешку про jca20 и про фридман мод)
For the brown eye mod, just skip the 3rd gain stage in the schem above.
The hairy brown eye mod has 4 gain stages, and is not applicable to the JCA20H
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Here we can see a circuit between the cathode follower and the tonestack.
This is most probably the "Saturation switch", which includes the stuff that is covered in black.
In the JCA20H, the stuff covered in black are probably 2 diodes plus a couple of resistors instead of a pot.
We can also get clues about the cathodes for the gain stages.
For the brown eye mod, just skip the 3rd gain stage in the schem above.
The hairy brown eye mod has 4 gain stages, and is not applicable to the JCA20H
The JCA20H preamp is based on the Atomic 16 which is a modded jcm800.
A main part of the brown eye mod is that all 3 gain stages have bypass caps.
I'm far from an expert, but this is what I have come up with just by looking at the pics of the modded board, and with some educated guesses.
1st gain stage cathode R looks like 2.8k with a small black electro cap piggybacked, probably .68
1st gain stage anode looks to be changed from the stock 220k. going by the pic it looks like 330k, but this value seems too high?
from the 1st gain stage the signal goes to a poly cap (probably .022), then into a voltage divider (looks like 88k/88k)
then into a 33k which is directly connected to pin2. that makes the gain pot just a variable 1M resistor to ground forming a voltage divider with the 33k input grid resistor into the 2nd gain stage.
2nd gain stage cathode also looks like 2.8k bypassed with a little electro cap (probably .68 again)
2nd gain stage anode seems to be the same value of 100k, just changed to a carbon film resistor.
From there, it looks the standard marshall stuff (.022, 470k/470p, 470k to ground) heading into the 3rd gain stage.
the 220k going into the next gain stage seems to have been jumpered.
3rd gain stage cathode looks to be a 820R bypassed with another electro cap which looks bigger than the other 2 previous bypass caps, the value could be anywhere from 22uf to 330uf. This can be tweaked to taste.
3rd gain stage anode looks to be 100k bypassed with a silver mica cap, probably 120p to 470p.
input R is 33k
slope R is 33k
NFB is 47k
The stuff going on between the first and 2nd gain stages are the toughest to figure out just based on the pics provided.
If we could get clearer pics that would be awesome!
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Glad to see this thread moving forward.
I have a friend who got one of these BE modded JCA20H with the Sat switch.
I was able to take a peek inside.
Here is what I found:
First stage:
Anode - 220k in series with 100k // 500p -- very interesting!
Cathode - 2.7k // .68 -- standard marshall
then into 2n2 coupling cap then into 68k/68k voltage divider.
then into 33k which is soldered straight to the grid of the next gain stage
Second stage:
anode - 100k
cathode - 2.7k // .68
then into 2n2 coupling cap
then into the standard 470K/470K divider with 470pf treble peaker (it think the actual value in the amp was 500p silver mica)
3rd stage:
anode - 100k
cathode - 820 // 22u
Tone stack values changed to stock marshall -- slope R 33k, treble cap 500p mica
Also, there is a "fixed depth" mod installed -- it looks like a 4n7 cap in series with a 100k resistor.
That's all I remember off the top of my head.
Hopefully that'll get you in the ballpark.
I will be able to take pics over the holidays and i'll post em here
I'm really interested to find out what is hidden in the SAT switch, the stuff that is covered in the black stuff.
It is most likely a jose master, but I have heard that the jose master does not use diodes like everyone thinks.
ссылка на трид
http://acapella.harmony-central.com/showthread.php?2639458-Jca20H-Mod-thread-and-owners-club.цена на фридман мод от 300-500, типа мод 300, +регулятор с сатурацией 50.... ну и тд . петля 200
с одной стороны дорого - с другой - идея стоит денег, ну и цена у них и у нас имеет разный вес.
Тут важна обоюдная сатисфакция - кому от проделанной работы и полученных деньгах, кому от нового звука своего усилителя. Алелуя...
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