My ODS schem. What do you think?

[Mostro]

Hi guys, I´m slowly making the schem for a planned ODS build. Not trying to make a clone of a particular one, I just did a patchwork of different schems that are here, taking whatever parts I thought would work for me. Of course, except Youtube vids, I´ve never heard an original one (or a clone, for that matter) in person. so it´s all guesswork. Specs: 50 watts, 6L6´s, included FX loop, no FET input, relay switchable OD and PAB. Possibly a combo. I want nice cleans (not necessarily fender-like, I like fat sounds, not a single coil player) and full, rich OD, not a super high gain thing (not a metal player).
This is my first draft schem:

[IMG:160:110]http://i68.photobucket.com/albums/i5/Morocotuco/th_Humble-Over-Driven-Special-V10_3.jpg[/img]

[IMG:160:110]http://i68.photobucket.com/albums/i5/Morocotuco/th_Humble-Over-Driven-Special-V10_2.jpg[/img]

[IMG:160:110]http://i68.photobucket.com/albums/i5/Morocotuco/th_Humble-Over-Driven-Special-V10_1.jpg[/img]

I´d very much appreciate your opinions. Any obvious mistakes?

I have many questions/doubts but I´ll post them later with more time.

Thanks for reading!

[markusw]

Looks nice!
I would move the anti-popping resistor R42 to the other side of C38 or wire it in parallel with C38. At the current position it doesn't prevent popping.
You might also lower R42 to 4M7 but I don't think it would change the sound.


Peace,

Markus

[Mostro]

Thanks Markus. So, that´s an anti popping R? Nice to know...
C38 and R42 were added ´cause i saw them on some of the schems or read about it, can´t remember. Supposedly they make for a better OD tone with non HRM amps? Not too sure about that parts, might include them or not.
I just realized that I forgot to draw the PAB and OD switches, relays control and footswitch... I´ll update later.

[markusw]

Thanks Markus. So, that´s an anti popping R? Nice to know...
C38 and R42 were added ´cause i saw them on some of the schems or read about it, can´t remember. Supposedly they make for a better OD tone with non HRM amps? Not too sure about that parts, might include them or not.
I just realized that I forgot to draw the PAB and OD switches, relays control and footswitch... I´ll update later.

C38 reduces the bass content hitting the OD and makes the OD smoother. You might want to add sockets for it to try if you need/like it. You might even go lower to 5n....or skip it....depending on taste

[alvarezh]

Hi mostro, your 330uF PS filters are usually associated with the 100W version. My 50W had as per the originals 100uF. By following suggestions from this forum I went up to 140uF that was the closest value I could obtain (100+40 sprague atoms), although the recommended value is 150uF.

Happy building!

[Mostro]

Hi alvarezh! Good to see another spanish speaker here (you do speak spanish in Dominican Republic, right?) I´m from Argentina.
So you have 70 uF in your first filter node, or 140 uF in total? I´ll change the schem to get 100 uF in total, so 220 + 220 in series. I´m gonna use radial caps, can´t get axials here.

[alvarezh]

Spanish…yes! A rocker here from Merengue land who saw Jimi Hendrix at the Inglewood Forum in April 1969 (I saved my ticket too).

Check out the schematic for serial 101. The original had two 100uF, and there is a note in blue specifying 220uF for the 100W version. The guys here suggest using 150uF for the 50W and 300uF for the 100 Watter.

About the schematic: it should be on the FILES section of the forum, I have it in my computer. The heading says "ODS-101-NON-HRM". If you can't find it, Google it specifying "The Amp Garage", I find it easier to find things that way than through the forum's search. If you still can't find it, I will try to post it, but I have never uploaded anything before, so I will be learning and can't guarantee success.

BTW, I need to learn how to dance Tango, but not many of your country's girls around here to teach me, I guess a trip down your ways would solve that!

Hope this helps.

[Structo]

For a 50w power amp you may want to try a different NFB resistor, R64.
6K2 or 8K2 can work well.

[dcribbs1412]

By following suggestions from this forum I went up to 140uF that was the closest value I could obtain (100+40 sprague atoms), although the recommended value is 150uF.

Hi alvarezh
Was the difference noticeable...just finishing up a 50 watt and wondering
about this...so you are running 2x100uf and 2x40uf on your 1st node?
so this would up the total to 70-75uf as opposed to 50uf with 2x100uf original

Darin

[alvarezh]

Hi Darin, on your second build already? Ah, yes, your backup rig, we all need one right?

Yes on your calculation, it's supposed to tighten the bass. I suggest using the original 100uF. If you feel you need a tighter bass, just up those caps to 150uF (for your 50 watter) or as close to that figure as you can get, but it should not be overdone. I am not an EE, but it does take more time to load higher capacitance capacitors which could have an adverse effect. Also, since more energy is demanded from your transformer it could run hot or perhaps even fail on the long run. To summarize, I would not go above the previously posted recommended modded values (which BTW were posted by reputable an knowledgable members of the forum) unless the numbers have been crunched to assure proper operation. As those modded values stand, I have not had any problems, nor have I read here that anyone has either.

Mostro was showing on his above schematics 330uF for C19 and C20, those values are recommended for the 100 watters, it's just way too much for the regular power transformers used on 50W amps.

Here is an excellent book on the subject:

http://www.amazon.com/Designing-Power-S ... 0956154514

Cheers.

[dcribbs1412]

Hi Darin, on your second build already? Ah, yes, your backup rig, we all need one right?

Actually its an old build(my first) I've gone back to update and clean up
with things I've learned here...afterwards is sounding much better
I may experiment with these cap values on an upcoming build

Thanks for the info and link

Darin

[alvarezh]

Cheers!

[Mostro]

OK guys, I made the corrections suggested by all of you. Thanks!
This is the current schem:

[IMG:160:110]http://i68.photobucket.com/albums/i5/Morocotuco/th_Humble-Over-Driven-Special-V11_1.jpg[/img]

[IMG:160:110]http://i68.photobucket.com/albums/i5/Morocotuco/th_Humble-Over-Driven-Special-V11_2.jpg[/img]

[IMG:160:110]http://i68.photobucket.com/albums/i5/Morocotuco/th_Humble-Over-Driven-Special-V11_3.jpg[/img]

Now the questions.

1) In the OD pre triodes, there´s a 25 pF cap from anode to cathode. I guess to avoid oscillations and/or tame the high end. In some schems I´ve seen it as a 250 pF one...quite a difference. Wich one should I use?

2) Regarding the "master" pot, since I´m including a Dumblelator, I´ll have as many as four level controls in some configurations (for example, in OD I´ll have the OD vol, the master, the send level, and the return level). Too much... In some thread I read that you can replace the master pot with a fixed voltage divider, as drawn at the right of the pre schem, between points A and B, and use the loop Ret level as a general master. Fine and dandy, but....... I have a switch to activate/deactivate the loop, so with the loop out I´ll have just the clean volume for controlling the clean level and the OD vol for the OD level. Would that work OK?

3) About the footswitching of the relays: As drawn, I don´t think the relay switching will work, because the led´s and their resistors will take the voltage down, and it might be not enough to make the relays switch. I´ve never used relays, so I´m not familiar with their operation...I got this particular section from a file that´s called "100W in the style of #183", but that doesn´t have the current limiting R´s, and says "Mod´d "Silk Road" Footsw." Other schems have a 5 conductor link, that would allow a separate led´s power feed, but those have a capacitor included, I don´t quite get them. Is there a way of getting switching and leds with a 3 conductor cable? Or, my schem will work?

3b) After giving it some thought, maybe I can use an LM317 adjustable V regulator for the relay power, and tune it to give me 12V with the led´s and associated R´s in line. Of course some schem modification needed. That would let me use just a 3 conductor cable and jacks instead of the MIDI-type connectors. Doable?

4) About the power supply, is the Dumblelator power supply OK? I´ve seen people add nodes from different places, for example, after the choke. But I think that in B+3 I´ll have less ripple.

5) Also, is the 150K resistor at the end of the power supply chain needed? I saw it in some schems as a suggestion if no FET input used. Does it compensate for the reduced current draw?

6) Regarding all the jacks: Do you guys use non-isolated jacks for the input(s), loop, speaker out(s), like Switchcrafts? Grounds through the chassis? In some schems/layouts I´ve seen the grounding is through the chassis, with like 4 or 5 ground points. So no star grounding... Is that just tradition? Cause most writings I read about grounding advise against using the chassis for ground. I´m thinking of making mine star grounded. We´ll see.

That´s what comes to mind now. Surely I´ll have more questions in the future!

Thanks for the help.

[wicker]

Some people keep mentioning (there's even a thred) that they have problems with bass on their amps, most guys do not set bass more that 11 oclock cos the amp sounds too bassy, I had it also in my amp, witch is clean only machine, I have added 10n cap between anode and eq, that helped a bit, I find amp now better balanced, you might try that.