Finished First DIY amp - ghost note etc.

[fretwizard]

Hello all.

I finished my first very first build a few days ago:
thread is here: http://forum.metroamp.com/viewtopic.php ... 1&start=45" onclick="window.open(this.href);return false;

EDIT: I've solved all my voltage problems, but I'm starting noticing some ghost notes. go to next page.

You can look at the pics on page 3-4.

The thread title has nothing to do with it anymore (it was mainly about choosing parts) and it was started last year so, I thought I could make a thread that would be more visible for help/advice. Especially because I never owned a marshall-type amp before and I don't know how noisy it is normally.

SCROLL DOWN FOR THE CLIPS.


It is a Ceriatone 100w Super lead kit. With a few differences.
The circuit board is this:
http://www.ceriatone.com/images/layoutP ... iatone.jpg" onclick="window.open(this.href);return false;

But.. it has external bias test points (and the bias pot is not on the board) and triode-pentode half power switch on the back. You're gonna see from the pics that the back of the chassis is very crowded in wires. Nik sent me a temporary layout for those parts.

There is also a passive fx loop, but I'm gonna do it when I will add a master volume.

Ceriatone's chassis has changed now, also it is smaller than the classic 100w chassis.

I chose Magnetic Components transformers mainly for price and also because of the clips recorded by Curt Granger...
PT http://www.classictone.net/40-18053.pdf" onclick="window.open(this.href);return false;
OT http://www.classictone.net/40-18026.pdf" onclick="window.open(this.href);return false;
Choke http://www.classictone.net/40-18058.pdf" onclick="window.open(this.href);return false;

Also, after suggestions from a few users in the other thread I also incorporated star/Larry grounding. (thanx JimiJames and julkke)
Based on this thread: http://forum.metroamp.com/viewtopic.php?f=45&t=31328" onclick="window.open(this.href);return false;
With the heaters center tap routed under the control pot up to grounding point N°1.

I don't have a cabinet yet so I'm using a board covered in aluminium foil and I keep the chassis on it. So I can definitely say that the squeal I had when all the controls were at 10 is gone.
It only squeals when I get too close with the guitar but that's obviously normal.

Now to the voltages.

[fretwizard]

Voltages

I checked my wall voltages every 2-3 measurements and used a variac to make sure it was 240VAC, -/+ 3 or 2 volts.

With no power tubes installed and bias pot at minimum, tonestack is at minimum too

____pin-1___pin-2___pin-3____pin-4____pin-5____pin-6____pin-7______pin-8____pin-9
V1__165v____0v_____1v________2.8vac___2.8vac___202v____0v________1.7v_____2.8vac
V2__171v____0v_____1v________2.8vac___2.8vac___306v____170v______176v_____2.8vac
V3__214v____12v____43v_______2.8vac___2.8vac___208v____14v_______44v______2.8vac

V4__GND____2.9vac__501v____496v____-47v_____498v_____2.9vac____GND ---------
V5__GND____2.9vac__501v____496v____-47v_____498v_____2.9vac____GND ---------
V6__GND____2.9vac__501v____496v____-47v_____498v_____2.9vac____GND ---------
V7__GND____2.9vac__501v____496v____-47v_____498v_____2.9vac____GND ---------

__________________________________________________________________________________________________________

After I installed the power tubes I biased to ~62.5% (i guess it's a bit cold). As soon as I turned the bias pot, the plate voltages dropped. I kept remeasuring and rebiasing until everything was stable:

Al knobs on 10.

Wall voltage: 240vac
B+: 360vac
Plates: 470v on pin-4
Bias: 33.5/34 mV

The heaters dropped to 2.7vac on V7-V4 and 2.5vac on V3-V1. Aren't they too low?

R

[fretwizard]

Noise tests.
These are some notes about what I've noticed when doing these tests.

When I turn on the power switch the PT is humming (probably normal).

At Volume 0 I can already hear some hiss and a low hum.

I've found about the V2-pin-2 wire and I lifted it from the chassis as much as possible. I've noticed that the most sensitive part was the solder junction between the pin-2 wire and the 470k resistors + 500pF cap. If I hover my hand on it, the hiss decreases and the hum increases.

When I turn all the knobs to 10 except the normal-channel vol, the hiss is very loud. You can still hear the hum if you listen carefully, but the hiss is definitely much louder.
Increasing normal-channel volume definitely makes the hum more obvious but still in the very low frequencies.

The presence wire is running underneath the board and it approaches the presence pot from the left and it's very far from the other pots.

The NFB wire is connected to the 8-Ohm tap. Having a smaller chassis and less space, there's very little run between the board and impedance selector. the NFB wire is far from the pre amp tubes sockets anyway, like a couple of inches from V3.

I also removed V1 to see what happens. Some how I get loud hum/buzz if I increase the volume without V1.

V1 is TAD 7025wa
V2 is TAD 7025s mullard style
V3 is JJ ECC83s

If I swap V2 with a JJ nothing changes.

With the speaker the hiss is very loud when the amp is cranked.
Obviously I cannot play that loud in my flat so I'm using a 8-Ohm dummy load with a line-out, into my soundcard and then simulating the speaker mic setup with impulse responses.

I've include a ground-lift for the line-out. When lifted, the hiss decreases but the amp sounds a bit mushier. any ideas?

Even with the amp flat out, if I keep my guitar away from noise sources (iMac screen, variac, light dimmers in the walls etc) I would say this amp came out quiet. But again I'm no expert on plexis and I need your feedback.

One more post about temperatures and I'll record some clips of my crappy playing

I also had an idea about the clips. It would be very cool if you guys suggested a micing setup.
In particular, classic setups used to get that signature plexi sound. Also if you have a riff in mind to play that setup it would be great.
I can use a free impulse response library from Red-Wirez, it's made out of a Marshall 4x12 loaded with greenbacks. There's every possible microphone in every position.

Rock -on

[fretwizard]

Temperatures

I've had bad experiences about high wall voltages and PT temperatures with my first amp. An Egnater Rebel 30 I bought last year. It had a built-in attenuator. So the first thing I did was running it flat out.

I burned it twice, in the first 2 weeks of warranty, before I realized that here in UK, voltage is 240vac.
I'm from Rome and there we still have 230vac so I didn't think about that. The Egnater says 230v behind the chassis.
So I bought a variac and I've been runnign it at 220-230v with master volume all the way up. The only way you could get some presence from it.

And then I discovered that what I really wanted was the Plexi sound.

I have a digital thermometer with K-type probe.

I've been running the Plexi almost FLAT-OUT for about 2 hours, pushed with a modded Ts-9 and 10 band eq, boosting 8dB widely around 1kHz (George Lynch territory).

Bright Vol: 8
Treble: 5
Mids: 10
Bass: 6
Presence: 10

Powertubes are biased at 62.5% of max plate dissipation (JJ E34L). Wall voltage 240Vac

The 200w resistor in the dummy load reached almost 100 °C, it has a heatsink and it's supposed to resist up to 200 °C.

The power transformer reached 70 °C on the outer steel plating (especially where the copper band is touching it). You cannot keep your fingers on it for longer than half a second... and you can smell the isolating varnish.

I've read posts from MC stating the PT should stand up to 125 °C and that normally it should work at about half of that.
I also read other posts from Novosibir saying 70-80 °C is not good...? But it was not about ClassicTone transformers.

I know that I've been pushing the amp really hard.
So If you think this kind of temperature is normal with this kind of abuse please tell me.

I know I could lower the voltages to 230vac from the wall but aren't my heaters too low already?

I think I'm going to install a lar/mar MV anyway, so I can adjust the amount of power tube distortion.

If I manage to warmup properly tonight I'll post the clips.
Cheers

R

[fretwizard]

Alright. Here's some clips. Very simple ones.
I try to stay as far as possible from the amp or the computer, or the variac to minimize noise.

I'm playing a 2011 Charvel SanDimas, JB in the bridge, 59 in the neck. Gotoh 1996 floyd tremolo.

I just play 3 chords in the 3 pickup positions and let ring. on the higher volume setting you can hear some computer interference.
I'm using an impulse response for a SM57 on the cap edge position, 3 inches from grill cloth.

Bright Vol at 1
Tone controls at noon
presence at noon
https://soundcloud.com/overtone85/gdc-b ... on/s-JAKGi" onclick="window.open(this.href);return false;

Bright Vol at 3
Tone controls at noon
presence at noon
https://soundcloud.com/overtone85/gdc-b ... on/s-JAKGi" onclick="window.open(this.href);return false;

Bright Vol at 5
Tone controls at noon
presence at noon
https://soundcloud.com/overtone85/gdc-b ... on/s-JAKGi" onclick="window.open(this.href);return false;

Bright Vol at 10
Tone controls at noon
presence at noon
https://soundcloud.com/overtone85/gdc-b ... ck/s-JAKGi" onclick="window.open(this.href);return false;

Bright Vol at 10
Tone controls at 10
presence at 10
https://soundcloud.com/overtone85/gdc-b ... 10/s-sJ5Mt" onclick="window.open(this.href);return false;

My sloppy blues solo
https://soundcloud.com/overtone85/solo- ... -8/s-HMsO3" onclick="window.open(this.href);return false;


Here I've changed setup. I'm playing some sloppy george Lynch riffs

Guitar into Boss GE-10, boosting around 1kHz 8dB.
Bright Volume 8
Treble 5
Middle 10
Bass 6
Presence 9
SM57 in cap off axis position, 2 inches from cloth.

https://soundcloud.com/overtone85/lynch ... axis-2-0in" onclick="window.open(this.href);return false;

I hope it sound good. Any comments are welcome!

Cheers

R

[julkke]

The hiss is caused by carbon comp resistors throughout the board. Swap them for carbon films and you will have quieter amp.

[fretwizard]

The hiss is caused by carbon comp resistors throughout the board. Swap them for carbon films and you will have quieter amp.

Yeah i guess this board is only carbon comp apart from a couple of components... right?
According to this article:
http://www.geofex.com/article_folders/c ... oncomp.htm" onclick="window.open(this.href);return false;

In which position would you start replacing with metal film? I mean those positions where the voltages are two low to benefit from carbon comp distortion?

Also do you have anything to say about the heaters voltages and temperatures? About the clips? Any flabbiness? Harshness? Any particular settings you would wanna hear the amp at?

Thanks for the feedback so far dude.

R

[julkke]

The hiss is caused by carbon comp resistors throughout the board. Swap them for carbon films and you will have quieter amp.

Yeah i guess this board is only carbon comp apart from a couple of components... right?
According to this article:
http://www.geofex.com/article_folders/c ... oncomp.htm" onclick="window.open(this.href);return false;

In which position would you start replacing with metal film? I mean those positions where the voltages are two low to benefit from carbon comp distortion?

Also do you have anything to say about the heaters voltages and temperatures? About the clips? Any flabbiness? Harshness? Any particular settings you would wanna hear the amp at?

Thanks for the feedback so far dude.

R

Hey, your heater voltages do seem low. What primary tap on the pt secondary are you at? 240v? Moving to 220v tap might bring your heaters back to spec. I'm mostly posting on my phone here and can't get soundcloud to run so I can't listen to your clips right now. About the PT heating: It should be normal for it to heat up. I read post from Larry on this subject somewhere and he said "as long as you can't literally fry an egg on it it's all good."

For the carbon comps, I'd just replace them all with 1w carbon film or 2w metal film for reliability and lowest noise.

I hope someone who knows more than me will chime in here and help you too.

[Haze13]

The best place for metal films is the plate resistors (because of the good tolerance and low noise) and the every thing that goes in B+, and the chatodes (just beacuse of the good tolerance). Plate and cathode resistor it's a "bias" for the tube, the gain stage.
Then don't forget that JB-4 pickup is very noisy. I have 2 guitars, one with EMG's and other with JB in the bridge position. JB gives more noise, but I like it more than EMG's.
To reduce the noise you can put shielded wire before V1 and V2, I did so for V1 and it solved the problem that I had (There is my topic "JCM 800 2204 on JTM45 Chassis" pic included ).
On youtube, on Rob Chappers channel there are some video clips with the name "How loud is...". He turns the volume at max and shoots the video. They all noisy!
There is no "realy clean" amp on DIRTY channel, exeption is if you have a nosie gate in FX loop. Like Kranks and jcm 800 2203 Kerry King.

[julkke]

I just listened to your clips, sounds good! I hear a hint of blocking distortion in the all controls dimed clip, try to put a 220k resistor on V3 pin 2 to cure that.

[fretwizard]

Just came back from Axe-Mas holidays

I think I'm gonna let the amp burn in for a few days before trying to cure anything.

One thing I didn't mention is that 1 of the power tubes is 6-7mV higher in bias. Should I still use as the 'hottest' tube?
I tried biasing the other tubes at 65%, 34mV. That one single tube stays at ~40mV but no red plating so far.
If the tubes are gonna drift, how long could that take?

As for the heaters, I will wait for the same reason as above although I've read somewhere that something might still draw too much current from the PT sometimes.

Does elevated heater supply increase voltage too? or it's just for the noise?

R

[julkke]

Bias to the hottest tube! It might take a while for the bias to settle so it's a good thing to check it now and then for some period of time.

[fretwizard]

I was talking to Nik about the low heaters.
He thinks they're too low (5vac).

So I did a little test for him I measured B+, plates bias voltage and heaters, both at 240vac and 260v from the variac.

While I keep the wall voltages at 240v, tone controls at 0:

Heaters are 2.7vac per pin. (might be lower on some tubes)
B+ is about 175/180vac at both sides of the standby switch. So I guess is about 360vac. The PT should give 350vac CT.
Maximum negative bias voltage at the grid stoppers is -45v
Plate voltage at pin 3 is 488v
When I bias the power tubes at 65%, the voltage/bias becomes stable at 468v / 34.6mA

When I increase the wall voltage using the variac to 260vac:

Heaters increase to 2.9vac
B+ is 190/195 on both sides of the standby switch.
Maximum negative bias voltage at the grid stoppers is -50v
Plate voltage at pin 3 is 533v
When I bias the power tubes at 65%, the voltage/bias becomes stable at 522v / 31mA

So far I haven't found a thread about plate voltages being too high, people seem to worry mainly about nowadays tube being not strong enough and that early Marshall had such high voltages anyway.

I've also found this thread, with exactly the same heaters problem:
http://forum.metroamp.com/viewtopic.php ... 13#p377813" onclick="window.open(this.href);return false;
Although we don't know how he fixed it...

R

[fretwizard]

I contacted Magnetic Components. They replied very quickly:

Sorry to hear that you are having some issues with our 40-18053 power transformer. First off, the 350V is measured at full load rated current and not at idle. Second, it's measured hot, after the unit has thermally stabilized under full continuous load.
Regarding the 6.3V CT, please be aware that there are TWO GRN wires.
The CT for the heater winding is the heavier GRN wire and it comes out on the opposite side of the secondary leads on the primary side). You should measure 3.36V from each BLK lead to the GRN CT lead with all windings unloaded.

Mark Sacketti
V.P. of Engineering
Magnetic Components, Inc.

I'm pretty sure my heater CT is the right one, I checked the spec diagram and looked at all the notes, and based on this reply I made another test.

I've set my variac to 240vac, unplugged all the tubes and switched the amp ON.
The heaters increased to 2.8vac for each heater pin.

Switched OFF and unsoldered the pilot light from the heaters pins on V7.
Switched ON, the heaters increase to 2.9Vac for each heater pin.

Today I don't really have the time to unsolder all the PT connections to remove the load on all the other windings.
I just tried to connect the mains ground wire directly to the heater CT to exclude the chassis and thing connected to it.

The filtering part of the circuit is still working but probably it's not loading the PT (correct me if I'm wrong).
I showed the Marshall schematics to my brother who's an electrician and he made me notice that this way the PT stays cold, proving that there's not much load.

He also told me to to measure the two halves of the heaters together instead of each half separately,
and as soon as I did, my multimeter was showing 6.2vac on the heaters, with no pilot light and no tubes.

I've rewired everything back, re-checked the 240v from the variac.

- No pilot light and no tubes: 6.2vac testing pin9 and pin4-5 together on V1.

- No pilot light, with tubes in: 5.8vac on V7 and 5.6vac on V1.

My multimeter is cheap and it's likely it's giving different readings when I measure the single pins to ground especially when I can only use the 200vac range.
I have a better multimeter but I need to replace the fuse. As soon as I have it running I'll measure again.

R

[julkke]

Get a proper multimeter and do these checks again!