Anderton '64 reissue JTM145 - any info?

[arjepsen]

Arjepsen

Every time the signal leaves the motherboard, and goes to toneboard, all DC component is filtered. It would not be the case this first stage, but got anyway. As there Littlewyan said other filter formed of such C15 / R36, and JCM1 plus one, formed by C16 / R24.
I suppose that the signals with DC components,, not combine with these connectors, and cause noise, maybe ...

About these "floating" circuit.

They are a type of connection, the circuit ground with the chassis ground. I do not know exactly what the advantage of this way of making that connection. But it was common in Malhalls 90s and 2000s.

Matec

Ok, you're probably right about that resistor
The reason I mentioned to floating circuits, are that they can be confusing.
I had to read through this thread when I first built the amp, to figure out what it was. With the recent development I came back to edit my amp, and looked at the new schematics, and couldn't remember what those were.
My suggestion is to make the schematic less confusing to someone like me, seeing it for the first time

Btw, I wonder if they might be some sort of hum reduction effort?

[Littlewyan]

Probably are Arjepsen as they are building their amp onto a PCB with everything close together so they need all of these extra components to lower hum and keep the amp stable. Turret board all the way for me

Edit: I wonder if the RC Filter before the tonestack is there due to the output impedance of V1B. As that tonestack will have a different frequency response coming off a Anode Gain Stage rather than a cathode follower. I have simulated this circuit in LTSpice alongside my circuit which used the standard JTM45 Pre Amp (originally, its the JMP Pre Amp now ) and found that the JTM1 Pre Amp has more bass than the standard JTM45 Pre amp in my amp. Hope that makes sense.

[arjepsen]

personally I tend to end up with ptp. I did a few turret layouts on earlier amps, but oddly enough found it a bother to have wires running underneath.
Not that the ptp approacu isn't a bother.... I guess it's just more my kind of bother....

[Matec]

Arjepsen

Your idea is good, and I'm bypassing the problem of "floating circuits". See if it is less complicated to understand the schema.

Cheers


Corrected, 03/09/2014.

Revision "R31" on July 2, 2015

[img631]http://s26.postimg.cc/yxk7lyxhl/Jtm1_01_07_2015.png[/img]

(To see the full size image, click on the link above, and open in new tab)

[arjepsen]

That looks great Matec, thanks

A few notes on the schematic:

C301 is now 47pf - earlier it was 100pf, I can't find any note of this change in the thread??

C21,102 and 103 are noted as 100V. Is this enough? I'm not sure how much voltage "wiggle" there can be across them, but usually I see people advicing 400V on signal caps.

[Matec]

New voltage values ​​are in the list of Jazzkramer, as well as some component values​​. Others I've reviewed the photos and "translated" the value of the blurred image, as in the case of C301. If you can verify that the value is correct or not, I thank you.

In my early schemes was not the C15 / R36 DC filter, so it was logical to place the capacitors tonestack with 400v insulation.

Cheers
Matec

[jazzkramer]

Hey guys I forgot to put here but I have it written in a paper: int he JTM1:

C301: is written: 4 (than a space) 7 all this has a line under it.


Bye

[Matec]

Jazzkramer

Thanks again.

That is: C301 = 47pF (100V)

[AJW]

Heaters is misspelled in the schematic ("Heathers").

I already built an early version of this design in a Valve Junior combo, and have some components on order to match what you have updated. Thanks to you all for putting this information out there! I was using Google translate for a while until I saw Matec was working here too.

I'm also glad you modified the 2 floating circuits into the schematic. I haven't incorporated those yet, but at least now I know where they are to be inserted into the circuit.

[Matec]

Sorry for the several mistakes in my English, and a few sentences with a strange sense,, that many already have noticed in my texts. I have to fight all the time with the Google translator, which often "choose" a different direction that I want to inform the phrase. All this, because my knowledge of the language is deficient.

"Heathers" is going to be corrected, and will "Heaters".

The already famous "floating circuits" as I've mentioned before, are not extremely important. In circuits like the CSJTM1, they were not implemented.

But of course, they have to appear in the schemes of JTM1, JCM1, JMP1 .....

Thank you all.

Matec

[AJW]

I know how the translation isn't always correct, but it has helped me a great deal at times. I had discovered the JTM1 schematic you created, and employed it to read the forum in Portuguese. When I saw the Amp Garage link I was happy because I knew this was a great source of amp builders, and because it was in my native language! Thank you for working with this community despite the language barrier Matec!

[electrochimp]

on the cap and resistor across the 12au7 plates, is the .0022 brighter than the .022?

[Littlewyan]

It is but I think you get less fizz with the .022uf. Anyway the amp in it's current state is bright enough trust me

[electrochimp]

Thanks LW, I don't need a bright amp, so what would the range be for this cap for a neutral effect, if that is correct term? Or is it more for oscillation and keeping it in check?

[Littlewyan]

Its to smooth out the sound. Basically with the 12AU7 you tend to get a very fizzy sound when you overdrive it and the Resistor and Capacitor absorb that. Its called a conjunctive filter or some call it a corrective filter. Its usually only required when you have a cheap Output Transformer but with the 12AU7 its a different case.