Hi soundroi,
Q1 is hard to answer without the thing in front of me.

Q2, well as it's a rack it implies that you are plugging into another Amp.
IF the 2 units are *grounded chassis* then there will be an earth loop created.
This is a common mistake when linking equipment together.
With high gain preamps not helping the situation.

You have to lift the *Signal common* from the *mains Safety ground*
to fix it. IF you have no idea what is being said then Get pro advice before messing with Chassis earth wiring.
Doing it the wrong way can have fatal conciquences.

The safest/cheapest way to *test/fix* if you have this issue is *cut* the common wire on one end of the audiocable that joins the 2 units. If the hum is greatly reduced then you most certainly have a ground loop happening.
you will then have to deside which way to go.
just something to consider.
Phil.

Quote from: Enzo on January 29, 2010, 11:16:01 PM
That's why I get the big bucks here.  DOuble my pay, please.

Solder is a weak link alright.  Check solder on each and every control and jack, plus all the rectangular cement power resistors - those 5 and 10 watt things.  They vibrate and break their solder.

Crate uses those Cliff style jacks, and the cutout contacts on those is a weak link.  I automatically measure the resistance of each cutout contact.  If it is more than half an ohm it needs to be cleaned or burnished.  If it measures like 1 or 2 ohms, it will probably work fine, but the very fact the resistance is up that high means the contacts are not pristine, and 2 ohms at the moment can turn into 2000 tomorrow.

Good come back Enzo, LOL.
But I think Fonzy holds the copyright on thumping juke boxes to get them to work.

Those cliff sockets USED to have a pressed carbon stud imbedded in the tang so as to make proper contact but I've not seen them for many years.
Now it's just a pressed metal tang with a bump protrusion for contact, really no better than the cheap stuff.
Phil.

hi callanbrown,
ok, then *Enzos* likely on the mark. :tu:

Start hunting the solder side of PCB board for cold solder joins or cracked tracks.
Good light, a keen eye, oh and some patience.

Since RoHS the solder compounds have changed, good for the planet but not so good for long term reliability. This new solder stuff tends to *Shrink* away from joins
over time and any hot running components just speeds up this shrinking issue even more so.

Also most stuff is PCB mounted and things like input sockets and pots often crack at the solder pads.

Good hunting, Phil.

Thanks Magnus,, I've got the sound.
Now I just need to make my circuits look as professional as your's  

Just adding the schematic for the DDC as the PhAbbtone circuit is already on this site. The DDC is the only thing not posted, the rest is gear purchased s/hand.

Please note I own the original Nobels SST1 and it's now beyond fixing,
I've just taken the bit that works well and refined it.

I think it's important that I state it's not entirely my design, So I can't claim any originality here. I've just tweaked it and made it a lot more dynamic and returned the bass response for use with a real speaker.
Being a headphone unit they most likely wiped a lot of bass.

Although this will be old school teck to those in the know it is certainly capable (with the aid of a simple tone stack *Before* and Graphic *After*)
To capture many different tonal signatures that a lot of guitarists are chasing.  

The interesting thing is the rather low R2 68k, most circuits would use a much higher value here. in real world testing hanging 1Meg resistors on the front end may well do little.
Sure you get more bandwidth but then it gets killed off via the cabsim.

Thing is you just amplifiy more hiss and hum and get closer to oscilation,,
so it's a dog chase tail.
Have fun, Phil.

If *Audio signal* is in sync with channel led issue then likely the switching relays or power supply to same.
Just my guess?
Phil.

Hello Zappacat,
There is no magic size it's not the space shuttle the word you need to concentrate on is *ABOUT* this wide *About* this deep.

You only need to look at the massive variations in what has gone before.

Guitar speakers are low compliance drivers and as such do not depend on box size.
If this where not so then every open back guitar amp combo on the planet would sound horrorbillus.

Close the back of the cab and the sound will tighten and focus a little more.

So moving the front panel in by 3/4 inch will not effect the sound.

Speaker cloth should not lay flat on the baffle board,, you need to raise it slightly off the board as the cloth will flap againt the board.
You need to put a small moulding all the way round the front outer edge.
see drawing.

Cheers, Phil.

Kikey and rowdy,, Re http://www.ssguitar.com/index.php?topic=1177.0
I don't think that circuit would be current drive?
Anyone care to elaborate,,,Headscratch?
Phil.

Oh just a little warning about mains voltage when working on any open chassis.

These things often have no shrink wrap on the mains terminals and it's Dead easy (pun) to inadvertanly grab the chassis and your finger can touch the bare Mains wires.

If I'm working on something like this My first port of call is a roll of 2 inch wide masking tape and I tape over all the bare mains terminations as it's just so easy to have a momontary lapse of reason.

So work safe. 0:)

No watches, finger rings or dangle neck chains. Never work in bare feet.
I'm on a concrete floor so I also stand on a 20 mm thick solid rubber Matt.
Phil.

Oh you are to kind. 

Learn as much as you can absorb about Power supplies it will open a lot of doors for you.
Very good stuff here by people who have far greater understanding than myself.
http://www.ssguitar.com/index.php?topic=60.0

Phil.

Hi Zappacat,
                  Looks like the secondaries are Red/Black/Red.
On the end of those wires is a white plug.
So set DMM to read ACV and you should get 25VAC between two reds and the black.

If low or no reading then yep it's probably a blown tranny.
If the tranny has gone *short circuit* (which will/should blow the mains fuse) then it will probably hum like crazy and get hot very fast.

My guess the smoke maybe comming from the rectifier section.
(that bank of electro caps where the 3 primary wires terminate on the white plug)
Most likey cause of smoke is a dud filtercap.
If big filter caps go open then you just get a lot of hum but the amp still works,
but if they go *Short circuit* then bang they blow the fuse.

Without being able to test everything your best bet is to replace all those big caps and replace the diodes to be safe.

Put it back together bit by bit.
Rebuild rectifier section then isolate it from the rest of the Amp.
Test it on it's own and establish your working volatages are right.
Then connect the poweramp back up again,,(Use the mains light bulb trick before you power it all up again).
Good find,, looks like it will make a lot of noise.
Cheers Phil.

Hello kikey,

If it interests you I've built a lot of these things and had little success.

The best I ever got was experimenting with a small noname amp.
By running the mains (primary) through a 40Watt light bulb did wonders for the compression.

This allowed the *clean channel* to sound much more like a  compressing output stage of a tube amp.
Like a vast majority of SS amps the clean is *Super clean* and the drive has vastly to much distortion.
There are few SSamps that produce that *middle ground rattle* that Valves do so well.
You need to trial a few different wattage light bulbs to get more or less
compression.

BTW don't try this trick on Amps with a whole lot of switching circuitry as
things may well go all haywire once the light bulb starts to sag the supply.
Do it with simple Amp designs, preferably really simple discrete component types.
My best guess is that chipamps have to many current source/mirrors an all the fancy hi fi tricks. They maywell be *To accurate* You need chaps like Teemu and J M Fahey to explain the indepth stuff.

Re the Lenard stuff,, Very good ground work on your part and it's well explained.
My beef with these chaps who know so much more than little ol me.

***They never bother to show a *REAL LIVE TEST*.
ie a shootout between Valve an SS

I do not doubt their ability to understand the maths but in all my testing of
things that make these claims very few have ever really worked as implied.

I cite my Maxiverb Reverb circuit as example;
My desire to build a simple Spring Reverb took me on a wild and wooly roundabout.
The Overwhelming Opinion on driving Reverb transducers was to use *Current Drive*.

An being only a novice I could only assume it was me making all the mistakes. I would probably qualify as being the builder of nearly all the reverb circuits on the net, as well as what circuits I found in books. :duh

10 years latter I built my Maxiverb stand alone Reverb.
Finally I got one that delivered the sound,,, an guess what?
YEP **Voltage Driven**. which just leaves most C drive circuits sounding like toys. (Listen to my PhabbTone Demo Clips,, the reverb is on *1* 8|)

I can only assume the Cdrive maths they use is correct BUT there is something missing in their equations.
Armed only with limited knowledge all I can come up with is this observation.
Current drive or not *Without voltage not much can happen*.

Re The 90% increase to the speaker mentioned on Lenard page might not be talking about *What you Hear*, in other words it might imply to the novice that you get almost *double the wattage*,,, (or SPL is doubled).

I don't think that is what is meant but I'm not the expert.

In all my experiments with these ideas there is a drop in output power or SPL.
Again,,I'm not the expert and may have missed the *Oh I see bit*.
Don't get me wrong Kikey,,I'm quite happy to give you all that I learnt from
experamenting with such ideas.
If you have an idea in your head that you can't let go of,,
then just *DO IT* and damn what others say.
I had to do that with my reverb and that's hard to do when all the experts point the other way.

Sadly that lil' amp with the light bulb is long gone,, I sold it but I may have some schematics down in the shed. Having moved twice since then I can't promise much.
have fun, Phil.

 You should have quit while you where ahead, LOL
Well at least you know it works.

OK with no electronics skill just go hunting for cold solder joins.
These are often hard to spot but with good light, a keen eye,, and some logical deduction you can pick them.

The pots are often mounted directly onto the PCB and can be a stress point leading to cracked solder points or even cracked tracks.

The switch that engages the chorus effect may not be making proper contact, try jiggling it on off a few times. Some of those push on buttons are cheap and nasty devices and I've found quite a few give trouble after ten years or so.
Wish you luck.
Phil.

 Just check the data sheets on those Reg's.
I believe it is unwise to use BIG caps *After Regulation*

The data sheets I've read suggest only 10 uF Max.

2meg on the input might be prone to noise?

Might be wise to label the reg as *7815 and 7915* as the inexperienced here might try to build it using incorrect parts.

Other than that yep good ideas :tu:
Phil.

Hello Destroid,

Re this; "I really want to keep my options open in terms of Solid State since I want an amp that'll **sound the same recorded as it does live**."

My setup would qualifiy in that regard,

http://www.ssguitar.com/index.php?topic=1446.0

Of course you would have to build it DIY.
Phil.

Hello billyjoe, Sigh

This is the very reason you go in circles:
I quote
"What about a 470k resistor on tube 2 where the trace was cut?
I'm going to try this.The solder is there.
I see it on a lot of Hiwatt amps including the sa412.
This should cut down the gain somewhat?
I'm going to try it tomorrow just to see what happens.
Dumb idea maybe but what the hell.Why not?
What about a 68 k resistor on tube one? A grid stopper. What exactly is that?"

Everything you just mentioned will be solved via ****DELETION OF V1****
So If you don't get the JOKE now you probably never will.

Here is a way to quickly delete V1 from the signal path with minimum work.
_________________
BUT ***READ THIS***First;

I am only going on a rough drawing you posted of this PCB layout so I have no way of knowing if it is *Accurate*

If you have no idea what I'm talking about don't do it!!!
If you don't know why the WARNING is there then YOU DOn'T HAVE THE Knowledge and therefore I will *ASSUME* you are inteligent enough not to touch it, RIGHT!!
So get someone to help you with it.
____________
If this works well and the amp has much less hum problem then you just might be
interested in persuing my first comment and suggestions.

If you persist in making it complicated then YOU  *Not I*  will have to endure the
frustration and pain of such pointless complexity.

Get V1 OUT and work from there.

Till that happens you are just shooting arrows with no target.
Have fun and don't do something you may not live to regret. Wink Phil.