|tedmich||6/1/2014 12:40 PM|
|Peavey JSX schematic loaded with info!|
I was looking at my JSX schematic to figure out where Peavey decided to put the (superior) NP0 vs crappy X5R/X7R ceramic caps and 1% MF versus 5% CF (in all of the preamp plate resistors) and I found that a simple PDF program (Foxit) reveals a lot of extra data on each component.
Just left click and the attributes come up.
The NPO seem to have the same cost (0.02) as the X7R, but 100k 1% MF plate resistor R11 cost 0.0049 and the nearby crappy 100k 5% CF R23 cost less than half (0.0021)
Those relays cost almost a buck but the 12AX7 costs only 0.58 (maybe per section?) The big old Illinois PS cap (680uF/350v) only costs at 3.24!
the joys of bulk purchase!
The old XXX while pretty much identical, uses MF only in the first two plate resistors, while the JSX has them in all 6, and the JSX has NP0 in most of the tone stacks.
|Joe L||6/1/2014 1:40 PM|
|Very cool! I use Foxit but don't have a copy of that schematic. Do you have a link or can you post it?|
Never mind. I looked at the bottom of the screen here and found the one you must be looking at.
|tedmich||6/1/2014 10:06 PM|
|Enzo||6/2/2014 3:44 PM|
|My plain old Adobe Reader does that. All those parts that have a yellow surround have the data. I left click on the part, and select attributes, and all that comes up.|
|roskib||6/21/2018 6:14 AM|
Hi, came across this old thread and hoping somebody can help me to identify the noisy caps to replace in the JSX 212 Combo to reduce the baseline hiss. I think it's these but need some guidance, also what to replace them with.
|J M Fahey||6/21/2018 6:25 AM|
|Sorry Billy but:|
a) capacitors are not noise generators
b) those black dots you surrounded are not capacitors anyway.
|Jazz P Bass||6/21/2018 10:32 AM|
|High gain preamp in the JSX.|
Grab a pile of 12AX7 tubes & put the quietest one in V1.
|Enzo||6/21/2018 12:21 PM|
|The black dots represent wires from the main board over to the "noise gate" control.|
"HW4" = hard wire #4
|Joe L||6/24/2018 1:11 AM|
|High impedance input gain stages are great for gain, but terrible for noise. First, research the signal and ground paths used by the early high gain designs such as Soldano's SLO. Try using Silver Mica Caps and MF resistors to see if it makes a difference but be obsessive about the ground paths. Shield everything you can to start with then remove the shielding a stage at a time to find what works to make a quiet amp.|
|roskib||6/25/2018 2:39 AM|
|Thanks Joe, the most useful response to date. Have tried valve replacement, biasing etc. Still a very noisy amp, well known issue in the 212 combo. Take a listen to the attached clip if you can. On the audio clip (mic in front of the cabinet) you will hear the noise on the Ultra channel, master volume full, nothing plugged into the amp. Then the Noise Gate control is wound up from zero to full on and back off - you’ll hear some reduction in the noise; then the channel selector is moved from Ultra > Crunch > Clean and you’ll hear the noise reduce on each channel with the gain reduction, but still there. Basically makes the amp worthless in the studio for recording which is a shame because it’s a great amp. One resolution on the Peavey forum was to "Swap out the noisegates diodes for LED's (A special type of LED, apparently used in Marshalls)" I'm keen to try that but I need to know component make/model #'s etc. to buy replacements|