Quote from: Roly on September 08, 2014, 03:44:18 AM
I think C25 is supposed to be between the colector and base of Q1.

Yep, put it on the board correct, drew it wrong. (smashing head against wall emoticon)

Was going to work on this tonight, but got a box in the mail with the MOD Kits Trill Tremolo diy pedal in it.   

So built that instead.  :tu:

That circuit board will work fine.
A bit big maybe, but that gives you lots of room to have an "airy" layout.
It's easier to place parts and work with a big board than too small a one.

Once you have everything...
Test place the parts without solder first, following the diagram to see how things connect.
You may end up re-arranging thing so they connect easier.
I sometimes "stuff" the board several times without solder.
After looking at a parts layout for awhile I will often change it to make certain connections easier.

I think? this project has a suggested board layout at http://www.runoffgroove.com/ruby.html
ahh, yes it does. Their board is a little different in that it only has individual solder pads.
But the "packaging" on that board is pretty tight. (that's not a bad thing.)
On your board you could spread things out a bit if you wanted.

Hope you find your parts soon.
I'm excited to see what you build.   

Many here stand ready to help if you have trouble.
Please don't be afraid to ask. 

As a 'beginner" I am following this with interest.  <3)

Just a note, I checked Mouser and DigiKey for the MPF102 and both show it as obsolete and no stock.

As Roly said, just about any N channel JFET will substitute. The PF5102 is in stock at Mouser and DigiKey.

Others that would probably work are J-111, J-112, 2N3819 etc.

If you really want to stick with the MPF102, Jameco has it. 

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_26403_-1

Edit;
Amazon has it too in a lot of 6.

http://www.amazon.com/MPF102-FET-Transistor-6-pieces/dp/B007V4FS5U/ref=cm_cr_pr_product_top

Quote from: Roly on September 05, 2014, 12:29:45 PM
....you're half way to a Crystal Set.

:lmao:  :lmao:  :lmao:

Yes, I know diodes are great at rectifying RF signals... 

Amplifier stability;
So... a few changes made with stability in mind.
In order of changes made...

1. Put back original R and C values around Q1. Amp sounds good, barely audible hum (I think was always there but so slight I didn't worry about it)

2. Added C26 for RF suppression. Seems good, no more radio station.

3. R24 and C16 (near T2 on schem) are actually physically and electrically close to Q1, Q3, Q4 and T2.

4. Added R41 and C12 down by the trem circuit. This is probably the most dramatic change, so-far as stability goes. Trem still works and is quieter too. No more "thump" "thump" "thump" as it pulses.

But now have hum issue!  :grr

With all controls at 0, no guitar plugged in, amp hums medium loudish...
Start turning Vol up and hum gets quiet-er and at Vol 6 is almost gone, then increases from 6 to 10.
Quite loud at 10.

So I made a mistake when installing C6 1000uf at the buffer supply rail.
Accidentally connected C6 to -25V rail and the junction of R4 and R11 instead of ground.
(I forgot to install C6 at first... Now don't remember if hum was there before or after installing it wrong)      Rookie mistake!
Turned amp on and was greeted with a VERY loud hum.
Immediately switched off. Possible I damaged U1?
I only have the one TL072 right now, so can't try a new one to see if that's the hum problem.

The hum is quite nasty but if you can ignore it, the amp is actually quite loud and clean sounding (under the hum noise).

Also:
The gain channel may need reducing to X5 gain, as the present X10 is a bit much.

New schem with some voltages added.

Edit;
Hum is the same with or without guitar plugged in.

Here's the other changes I mentioned a couple posts above...

I followed the values in the data sheet (see pdf attached) for the 2N2148 output transistors.
The data sheet shows with 16.5 Vcc a maximum signal power output of 15 watts.
We have @ 25V on the rail.

But I'm not sure what we have for input impedance of each base.
They show 65 ohms.
Is that the impedance of the 2 transformer coils going to each base?
I'm sure that affects output power.....

Is the above for a split supply where each rail is 16.5V ?

Cuz on the right side at the bottom they show...
"Typical operation in single ended push pull amplifier circuit"
"DC collector supply voltage 16.5V"
Does that mean single supply?

I'll go check the voltages at the output....

I was initially afraid to try those R values as they are much lower than what was there originally.
Decided what the heck and... they work.
Transistors get barely warm. So little that it's hard to tell if they are warming up at all.
Everything else stays cool as well. Transformer too.

Amp is slightly louder and cleaner with those R values installed. (8 ohm speaker for now, when I get the cabinet built, it will be 4 ohm)

Edit; oops forgot to add the gain/buffer to the schem... 

Better?   

The grey wire from buffer to amp is now shielded.
At full volume not playing I can still faintly hear a radio station....

Was thinking when it's all said and done I will strip the chassis and blast it.
(I have a blast cabinet) and a nice paint or even powder coat?
The original anodizing is stained and discolored on much of it.
If I could find a place local that does anodizing, that might look nicer than paint.
(if not too expensive)

"Frank-In-The-Box"  :lmao:

I deliberately left the wires long cuz I knew I'd be making changes... I guess that's not really necessary.  :loco
Can change stuff even if wires are the "correct" length and if too short... wires are (relatively) cheap and can be replaced.

I'll correct the lead dress tonight. 

BTW that white wire from the buffer to amp is the signal. If I touch it I get a radio station... 
I'll definitely shield that one.

I have six colors of wires I use like this...

Red - power + OR -
Black - ground
Green - tone
Blue - trem
White - signal
Yellow - used for speaker out and misc. signal

Output transistor wiring.

Black - base
Red - emitter
Green - collector

Thanks again for all your help Roly. Very much appreciated. Just wanted to say that publicly.  :dbtu:

Got the buffer/gain board done. Works a treat! 
X10 gain seems to be plenty for now. (maybe too much, but the rest isn't "quite right" yet...)

Got some other things done too, will update later, for now some pictures....

Excess wire lengths will be trimmed later, got some new pots on order.

Quote from: Roly on September 02, 2014, 01:27:50 PM
Half rail.

Got it, I'll fix the schem.

Quote from: Roly on September 02, 2014, 01:27:50 PM
The second doesn't make sense.

Right, I meant in general for other designs...
I haven't looked at enough SS amp schematics to have a grasp on what the "normal" design conventions are for clean and gain channels.

Quote from: Roly on September 02, 2014, 01:27:50 PM
You can probably go up to x100 before it oscillates like crazy.....
.....discover that the guitar pickups are slightly microphonic .......

.......try a few different values and see how far you can push the envelope.

Yep, I've had that from pickups that are not potted, and even some that are....

Ok, I'm guessing R8 10K is the one I increase to up the gain?

Fuzz;
Right, 1 to 10k + diodes to ground, seen that lots. 

Another rambling random thought...

Some of this stuff (electronics) is slowly coming back to me. 
Big difference in just copying something out of a book or wherever,
compared to actually understanding what the circuit does and being able to apply it to other stuff.

Edit; I'm getting this wired up right now (sans fuzz circuit) and I noticed something....

Do we still need R7 100K from pin 7 of U1b?

We originally used the 100K on the output of the buffer to get the trem to work.
R7 is not needed for that here.

Now, I can see that with nothing plugged in at all,
it provides a ground path for J1 suppressing any noise from an otherwise open jack.

Correct?

(see, I'm lookin at stuff and trying to understand how it works  )

Quote from: Roly on September 01, 2014, 01:51:21 PM
I wouldn't be content with that 'tho, tamed, but not yet unconditionally stable.

Yeah, seems like lotsa tweaking still to do...
If I knew how to use/apply some of the math I've been reading, I'm sure it would go much easier/faster. 

Anyways....

Keeping up to speed here...

1. Input jacks now insulated, and grounded to Vol pot ground. Which goes to board near Q1, not ideal but works.
1a. Existing Input buffer presently grounded on input jack, so, ok.

2. Bypass caps C14, C15 now 10uF and 47uF.
With the 100uF at C15 tooo much bass response, maybe if I played a Bass Guitar. :lmao:
(sows ear heh heh heh  )

3. New schem of input buffer(s).


--------------------------------------------
Random thought(s), feel free to ignore....

Ever has there been such effort and re-engineering expended on such a (started out as) piece of crap amplifier...
Only a fool or insane dummy would do such...   :duh  :lmao:

The end result (if we ever get there) Is going to be soooooo coooool!  8|

More random thought...

How about a "Fuzz" circuit for J3?
Re-purpose those germanium transistors I pulled off the board. Yeah! Built in Fuzz Face!  :lmao:

Could label the front panel...

1. Normal
2. High
3. Fuzz

Sorry... I can't help it... the Muse is with me and I'm just inspired...

besides... i have this huge (95x47cm) stripboard for mounting the input buffer(s) and reverb brick, (when we get there)
and all this room near the input jacks...

Fun Fun Fun... 

Edit; does that R5 1K go to ground, or the half rail?
I drew it to the half rail but thinking it goes to ground...
Oh wait, I figured it out.. corrected schematic...
This look good?

Oops, C7 is backwards.

Is there a convention for an input gain stage like this?
Buffer first then gain? or vise versa? Does it matter?

Yet another question...
Can we safely increase the gain of U1b? As configured its X10, can we go higher?

I have a guitar that I really like, it plays great but has very low output. I don't want to change the p-up's
This is why I keep wanting to add a High gain input to this amp.

For the record, the guitar is a 60's Teisco/Silvertone and I want to keep it "stock"
I'm a small guy and these guitars have a short scale and are very light, easy for me to play.
I don't use it all the time, simply because of the low output.
I know I can stick a pedal in front and get gain that way, but I don't (like to) use pedals much.
My main guitar is one of those Made in Mexico Nashville Tele's, great guitar.

Here are the latest changes.

1. Added insulated input jack, grounded jack on Vol pot.

2. 2N2907A's for Q1, Q3, Q4.

3. For Q1, R6-180K, R7-18K, R9-27 ohm (basically adjusted the bias to have approx 1/2 the supply Voltage on the base)

4. For Q3, R21-5.6K, R22-2K

5. For Q4, R23-1.5K C15-47uF

What killed the squeal was mostly the changes made around Q3 and Q4.
esp. R21-5.6K
I guessed that the original R21-330ohm sets the gain there,
so thought I would attempt to lower the gain.

Stuck a 10K in for R21 and got no squeal but very little volume.
Got out the R substitution box and started trying different values.
4.7K was no squeal but very loud and harsh sound.
5.6k tamed it.

Not sure how all the other changes affect things, but for reference I added the voltages measured around Q3, and 4.
What voltages should we be seeing there?
What would be considered "normal'?
Should I do something with R20-6.8K?

Amp now sounds "OK" fairly loud at Vol 10. "almost" clean at low Volume.
Tone ranges from quite thick to almost ice-pick.
All that can be tweaked as we go...

It's getting there.... 

HAH! I killed it!!!!  :dbtu:

No more squeal!!!!

More later.... 

Alright, I got the ground changes done.

1. Installed an insulated jack for the speaker. Ground of this now goes direct to main filter cap.
2. Short lead from main filter cap to chassis.
3. PS + and - now go directly to the board from main filter cap. Each go to the end of their respective traces near the PA section.
4. All 4 pot grounds now go direct to board near their respective circuitry.
5. Input jack is *not yet* insulated but I ran a jack ground wire all the way back to the main filter cap anyway.
If there is a loop, this is where it will be.
6. Input buffer is still grounded to the input jack. (mounted on it actually)

Test conditions;

C14 and C15 bypass caps on the driver transistors removed. All else just like the schem shows.

When I first fired it up I thought something was wrong, or I had made a mistake somewhere...
It was soooo darn quiet.
If I thought it was quiet before, now it's dang near silent. Barely even any hiss.

Sounds good, clean, low volume, about bedroom level. No squeal. Any settings.

Installed both bypass caps C14 and C15 (not sure how their values affect gain, if at all) used 1uF for C14 and 10uF for C15.

Test;

Squeal is back but character has changed. Due to value change on the caps?
Tone 10, Vol 2, squeal starts and is harsher and nastier than before (more high freq).

Tone 0, Vol 10, No squeal, Thick pleasant distortion. LOUD! Could gig with that sound! Crunch Rhythm only, not a good lead sound.
Bring Tone up to 2, squeal starts... nasty nasty nasty.

Next up, insulate input jack, play with C14, C15 values, see what happens...

I'm also working on a few things in parallel here...

I do make changes to the amp one at a time.

This is just my latest idea for the 3 inputs.

Normal Input is just a copy of what I already have.
High Input has a gain of 10. I lifted the circuit from an app note somewhere.
Low Input is obvious...

Will this work? Any obvious flaws?
I know the passive mixing of the three 10K resistors is not ideal...
Does the Low Input need a coupling cap?

Quote from: Roly on August 31, 2014, 05:54:38 AM

grounding paths. 

Ahhh Ha Ha Ha ...hahaaa gaspchokesnortcoughwheeze....

Sorry... I just spewed hot coffee out my nose and all over the keyboard....

Yes, grounding paths,,, harrumph...

I actually know about star grounds etc. as I have Kevin O'Connors excellent books the TUT (The Ultimate Tone) Series 1 thru 5.

http://www.londonpower.com/audio-design-books

He writes extensively on the subject of grounding in tube amps (and other).

Too bad I read stuff without sometimes actually comprehending/understanding/retaining what I'm reading... (embarrassment)
perhaps a touch dyslexic....  :duh

In my defense, it's been a long time since I read those books and I never actually applied anything from them.
Your mention of star grounds triggered my memory. (such as it is)

Anyways... this amps grounds are probably about as random as you can get.
There are 2 sorta "L" shaped ground tracks on the board. Both originally had separate leads to ground.
One to the input jack ground, the other to one of the pots body.
I jumped the 2 tracks together so as to have one ground lead from the board.
The main filter cap ground goes to the speaker jack ground near the PS.
So the chassis is the ground path for *all* other grounds.

I will correct this before I go any further.

Thanks for the link to your site on grounding.  Great stuff!

BTW I've been reading (and actually understanding and learning ) the ESP Basics Articles on Electronics and Amplifiers.
Good stuff, easy to understand.  Learning lots and have been applying what I'm learning on breadboard circuits. 

Will report on how the ground issue/correction goes...
Stay tuned!

Oh, also BTW this amp has never had a hum issue, quite quiet actually, so I never considered it to have a ground problem.  :loco