eighteen (ROG) to jimbob

[mat]

Hi jimbob,

I finally sorted out why my new 18 did not had the overdrive the earlier did....... well i'm kind of ashamed of it.... it was wired properly :oops:

:x In the earlier version the 2n2 cap between the 15k resistors was not connected into ground - result: more treble and little more gain in my ears.  :shock:

Also the 470k+820 was straight into ground - not trough 8k2 as it supposed to be - result: noticeably more overdrive with the volume pot!!  :shock: ...........    :lol:

It feels somewhat more open with these "mods" and i'm going to keep it that way. Maybe some pro would shed some light to me and tell what those components primary job is on the circuit ? Would be nice to know.

Thanks,
mat

[petemoore]

http://runoffgroove.com/eighteen.html

[petemoore]

http://runoffgroove.com/eighteen.html
the 2n2 cap between the 15k resistors was not connected into ground - result: more treble and little more gain in my ears.
  This cap shunts highs to ground [rolls off highs].

[jimbob]

Great!- im going to go back over mine and see if i can make any difference.

thanks,

jim

[petemoore]

The 8k2 should alter gain and distortion of that stage, and the one after it for that matter.
 To tet the difference, and I would check voltages just for kix if nothing else, clip a jumper across the 8k2, eliminating its resistance path, I think how you had it wired, and you can make better conclusions as to what's what with that, and if you like the mod, put the wire through a switch...
 I boarded the 18 today,   , decided to give that one a try. Has alot of guts compared to the 4 gain stage Supro. had a bug in the tonepot wiring, and pulled a 2n2 or two, deciding whether and which to put on a switch and value changes.
 Took me a while, I ran top of board wires about 3/8'' between Drain and the next cap for biasing...I soldered one lug of a 100k pot to the V+, then found the ResistorS to hit the bias points, and replaced them one by one, then rechecked the voltages...I ran them all a bit high for a time and that was cool, but the stated voltages on the schematic sound better.
 I had to substitute a 1meg for the tonepot, and didn't really try to figure out the difference it would make, will sub in the 5ook there...
 Hafta say the amp Emulators ROCK [once again!!!}, I'm really getting to appreciate tha tubey overdrive tones they get.
 Biasing without trimpots this time was a bit of a pain, but all the Jfet circuits I use seem to work really well without alot of 'messing about with it...of course I socketted all but three caps..

[jimbob]

I completely went back over mine trying this and that until i finally got something i really really like! The 8.2k were changed to 10k's, the out 2n2 changed to 332, 820's were changed to series-ed 800's. A lot of minor diff but i realized that these projects really have a lot of leway and room for changes I did notice that it sounds great w my tube amp versus my SS. I add a little gain channel boost to it and WOW! Its sounds great! Im really not going to mess w it now. Turns out my original problen was that my 820(800) was connected to the 470k then ground when it should have been connected to a diff 470k and then to the 8.2k(10k) and ground. And i had a loose lead going to the middle j201. I did go through a lot of diff j201's to see what sounded better--now that took some time.

Good luck all

jimbob

[mat]

Ah! Sorry, I forgot the link... :oops:

mat

http://runoffgroove.com/eighteen.html

[mat]

Hi petemoore,

Ok that is it what it's for, thank You for the info - now i can try different values and know what to expect for it to do  

mat

http://runoffgroove.com/eighteen.html
the 2n2 cap between the 15k resistors was not connected into ground - result: more treble and little more gain in my ears.
  This cap shunts highs to ground [rolls off highs].

[mat]

Hi,

Thanks again for the great tips. I have just started the hobby and these tips are so valuable to me, thanks!

What kind of caps despite the electros did You use on this one ?

mat

The 8k2 should alter gain and distortion of that stage, and the one after it for that matter.
 To tet the difference, and I would check voltages just for kix if nothing else, clip a jumper across the 8k2, eliminating its resistance path, I think how you had it wired, and you can make better conclusions as to what's what with that, and if you like the mod, put the wire through a switch...
 I boarded the 18 today,   , decided to give that one a try. Has alot of guts compared to the 4 gain stage Supro. had a bug in the tonepot wiring, and pulled a 2n2 or two, deciding whether and which to put on a switch and value changes.
 Took me a while, I ran top of board wires about 3/8'' between Drain and the next cap for biasing...I soldered one lug of a 100k pot to the V+, then found the ResistorS to hit the bias points, and replaced them one by one, then rechecked the voltages...I ran them all a bit high for a time and that was cool, but the stated voltages on the schematic sound better.
 I had to substitute a 1meg for the tonepot, and didn't really try to figure out the difference it would make, will sub in the 5ook there...
 Hafta say the amp Emulators ROCK [once again!!!}, I'm really getting to appreciate tha tubey overdrive tones they get.
 Biasing without trimpots this time was a bit of a pain, but all the Jfet circuits I use seem to work really well without alot of 'messing about with it...of course I socketted all but three caps..

[mat]

Hi jimbob,

Congratsulations for Your findings! I think I'll try those out myself too.

Do You think that it is safe to change the trannies or caps while power is on, or is there a chance to break something. Havent tried yet with power on.

mat

I completely went back over mine trying this and that until i finally got something i really really like! The 8.2k were changed to 10k's, the out 2n2 changed to 332, 820's were changed to series-ed 800's. A lot of minor diff but i realized that these projects really have a lot of leway and room for changes I did notice that it sounds great w my tube amp versus my SS. I add a little gain channel boost to it and WOW! Its sounds great! Im really not going to mess w it now. Turns out my original problen was that my 820(800) was connected to the 470k then ground when it should have been connected to a diff 470k and then to the 8.2k(10k) and ground. And i had a loose lead going to the middle j201. I did go through a lot of diff j201's to see what sounded better--now that took some time.

Good luck all

jimbob

[petemoore]

I think i'ts safe, I did numerous changes witht he battery connected.
 However I have blown actives...but there was some 'other' wiring error involved...
 I used film caps for everything except the Lectro caps. I'd have to re-look at the values to tell you.
 The signal path caps are like the schemtic, rolloff caps adjusted to taste including eliminating the second 2n2.

[jimbob]

I changed my trannies out with it on and connected to the amo. ! sec its got sound, next its quiet--next theres sound. I had to rebias some of them though.

[jimbob]

Also the 470k+820 was straight into ground - not trough 8k2 as it supposed to be - result: noticeably more overdrive with the volume pot!! Shocked

I cant believe i did newarly the same thing! It gets confusing in that area.

[mat]

Thanks petemoore/jimbob    for your input.

I think i'll manage with this one for now on, thanks

mat

I think i'ts safe, I did numerous changes witht he battery connected.
 However I have blown actives...but there was some 'other' wiring error involved...
 I used film caps for everything except the Lectro caps. I'd have to re-look at the values to tell you.
 The signal path caps are like the schemtic, rolloff caps adjusted to taste including eliminating the second 2n2.