Anderton '64 reissue JTM145 - any info?

[Smokebreak]

Thanks guys. Don't get me wrong, I'm really diggin the amp, it's just one of those that if I can tweak that last 5%, I'll be extremely happy with it. I'm may be being overly picky..
I'm gonna take a break till Sunday, as I'll be away all day tomorrow .
The only thing I tried was increasing R10 stopper to 1M, and also tried a 1M directly on the grid pin, after the R9/R10 junction. The latter may have smoothed things out a bit, but no big change.
Matec I'll try the OT primary swap. Seems I read somewhere recently that can remedy some weirdness other than the usual piercing ear-splitting whistle at startup.
Talk soon-J

[Smokebreak]

Well of course I just couldn't let it be.
Matec, you were right! I swapped the grid wires at the board(instead of at the plates) and all the buzzy sounds went away. Great suggestion
This thing is rippin now.

[Matec]

Great!

Can I ask you to record another sampler? I would like to show in my topic that the amp works. Do you allow?

The layout that you created, I thought it was great. I will create a layout with turrets, like him. It is a good option for those who do not like PCBs.

Thank you.

Matec

[Smokebreak]

Yes, that is no problem at all . I have to go out of town today, so I will record another clip after the weekend.
Feel free to use the layout as well. I'll check it again and update it next week.
I'll give a full report with the details of my build, too. I was thinking maybe put the 820r / 330u cathode on a switch for "fat", as well.
Cheers-J

[roberto]

Thank you Roberto!

Foi um prazer! Graças a você Matec!

[Smokebreak]

Here's an updated clip : https://soundcloud.com/jeremyslemenda/jtm1-5-6
I started with gain on 4, then 7, then 10. My favorite sounds are right around 7.
This is on the ".1W" setting. When I get the place to myself, I'll do a clip with the roaring 1W

[Matec]

Hello Smokebreak

The sound sample, it was perfect. I have already created a link for people to listen to them.

Thank you!

[Matec]

Hello
The news are: The inside of CSJTM145

[img1016]http://s26.postimg.org/xboirhert/JTM145_01_A.jpg[/img]

[img666]http://s26.postimg.org/wnfo8jg21/JTM145_02_A.jpg[/img]

(Photos Forum Marshall Roadhouse)

Matec

[Smokebreak]

Very nice, Matec. Interesting placement of the conjunctive filter resistor

So, from the description..: http://www.andertons.co.uk/guitar-amp-h ... w-head.asp... I wonder how they are running the jumpered "gain stages", with 2 gain controls. This implies some sort of parallel input stages, but there are still only 3 tubes in this amp, like the JTM1. Hmmmm...

[jazbo8]

The JTM145 is using the same PCB as the JTM1, so it already has the "internal jumper" emulation circuit, I speculate Marshall simply added another volume control or more likely a variable "brightness" control and call it Loudness 2, as well as discrete TMB controls - so Anderson can charge a few hundred more quids - pure marketing genius! The most expensive parts were probably the white plexi panel and custom knobs...

[Matec]

Hello Smokebreack

How is your little monster?

" My " speculation . = > ON

The basic circuit JTM1 not changed much.

The tone controls are the same that I already drew posted in the above scheme , based on the description of James Marchant .

Inputs . I suppose there is the greatest " creativity " . The HI and LO inputs that go into the JTM 45 independent valves . In JTM145, become hi impedance and lo impedance it because they go to a single stage valve ( equal to JTM1 ) .

The LOUDNESS controls 1 and 2 . They are volume controls in parallel. One with brightness, and a normal one.

The rest of the circuit with some news .

The power has some components JCM1 . Bypass capacitor on the cathode of the 12AU7 .
The attenuator 1W - 0.1W . Has the capacitor attenuation of high frequencies, mode 0.1 W.
Just as in the JTM1. Keeps the feedback capacitor 22nF, and RC filter on the plates of the 12AU7 .
It is a mix of powers

The power source circuit with a capacitor filter more .

The motherboard has some differences , is not exactly the same as the models JTM1/JCM1

Speculation = > OFF

Agree with jazbo8 , marketing is much more than development.

Matec

[Littlewyan]

I've put a schematic together for the JTM145 based on what I've been reading and based on an assumption I made with the volume controls. I'll post it later.

I'm actually going to build a JTM1 myself and have made a few changes to the schematic. I have removed C301, C15, C17, C19, C22, R29 and R34 as I believe these are not necessary on a turret board build. With proper layout and lead dress the amp should stabilize without these parts. What do you think Matec?

[Matec]

Hello Littlewyan

You have freedom to make these changes, that's for sure.

But most of the components you want to remove the circuit, designed to improve stability and prevent noise.
If you can keep them in your circuit, it may work better.

I was interested in your interpretation of the CS JTM1 circuit. I await your posting.

Matec

[Smokebreak]

Hey Matec, the little monster is doing well, meeting new people, and bought a house today!
A parallel pot w/o the bright cap is exactly what I was thinking, though that could mess with the loading, compared to the JTM1.

Littlewyan, all the components you want to remove can easily be placed on existing components(caps on caps, resistors on pots), so they don't take up any board space, if that's your concern. As Matec said, I believe the caps were built in the design to cut highs and keep things stable, regardless of board material.
The resistors across the gain pot, and from wiper to ground play a role, too.
Hopefully someone can explain this better, but if you remove the 1M resistor across the pot, and go with a 500K pot, the coupler still sees 500K, but the bright cap also sees 500K, as opposed to the designed 1M, changing the response. You may be able to get away with upping the bright cap if you're set on a 500K.
The wiper to ground resistor will change the high pass , keeping things tighter at higher settings. I think.
I'm interested to see your ideas. This might be the only amp I never really tweaked, but I thought about separating the "jumpered" cathode network and run it like a plexi, or JTM45 dark, or both.

[Littlewyan]

Here is the schematic I have come up with for the JTM145, sorry its not very clear I made it in LTSpice. With the two volume controls I can only assume that is how they have done it. I've simulated this in LTSpice and the controls work as they should so it is possible that they've done it this way.

Smokebreak - Your right the components I've removed are very easy to put back into the circuit so I should be able to easily install them if I run into any issues. It'll be good to see if I don't need them though. Don't forget the board which Marshall use for this amp is very small, especially for the amount of parts they use. I was actually quite shocked when I saw the size of it! I suspect if you removed C15, C17 and C19 from your amp you wouldn't notice any difference. C301 could be a keeper though as this will/should dump all RF Interference from the input to ground, which in a way enables them to keep the grid stopper R28 small. As for the Volume Pot I'm going to stick in a 500K and keep one of the 1Meg resistors. Really can't see the point of C18 though as it makes near enough no difference taking it out. Attached the schematic of the amp I'm going to build.

Liked the audio clip of your's by the way, was that an Airbourne song you were playing?

Edit: Actually I see what you mean about the bright cap. I might just put back the 1Meg Resistor that I took out as I can easily mount it on the volume pot like you said. Now with your amp would you miss the Bass and Middle Controls if you removed them or do you use them? Also did you use a 470pF Cap for your Tone Stack or 250pF?