My High Gain/Stock 2203 Build pics/clips page 4

[harddriver]

Hey guys, been busy these last couple of weeks finishing this High Gain/Stock 2203 build for my brother. He wanted a totally stock 2203 spec'd out to my old 79 2203 exact but also wanted a high gain 4 gain stage option. I built this amp with completely separate inputs one that feeds the all stock 2203 circuit and one that feeds the extra gain stage. Messing around with this at his house we found that we were able to switch back and forth from stock 2203 to High gain using a regular AB box that has no bleed over, which I thought would work but I wasn't 100% sure.

Anyway, the amp is running IC MPW caps 100%, the 2203 specs are 100% to marshall spec as my 79 was. The high gain side specs are borrowed from Kevin Oconner TUT1, some Soldano SLO and Arrendondo specs, running the stock pre-PI master and a Jose Master, as well as a slave out and Depth mod. Power and Output transformers are made by a company here in Chicago, they sound great, running 454DCV on the plate, exactly were my old 79 2203 plate voltage was. I'm running new Tung Sol 12ax7 in V1 and V2 and older JJ12ax7's in V3 and V4, with Winged C 6550's and .1uf's in the PI outputs because my bro like BASS!

Amp sounds awesome, very tight and aggressive, the high gain side surprised me as to how much it grinds and how much actual gain it has. My brother has a Peavey JSX and the 2203HG has as much gain as the JSX! We were running both using an AB box to switch between the two.

I would just like to thank George and Metro and all the Metrogang for all the help when I was a newbie at this.

Amp has just a tad of 60hz hum to it, I was very carefull with my lead dress and shielded wire, I only question me locating the Jose Master so close to the PI socket, not sure if I am picking up my hum there. Please look it over guys let me know if you have suggestions that I may have overlooked regarding the hum. It's not excessive but I would like it more quiet if possible.





I posted some clips of the amp on page two of this thread, give them a listen and tell me what you guys think. They are pretty much metal style clips and may not be your cup of tea but we are curious what you guys think of the gain and tone of the amp.

[xbearxau]

So just to clarify, youre running a stock 800 with an extra single gainstage infront? Care to draw a small schematic of the front end upto the 800's first gain stage? Just wondering what values you used for the extra stage. Cathode resistor and cap? Mixers, or a pot in between and finally where do you draw power for the new triode?

Ive been tossing up this idea for a while but havent had the time to put it into play.
Looking forward to your reply.

[Big Mike]

No clue.
But it looks cool!

[harddriver]

So just to clarify, youre running a stock 800 with an extra single gainstage infront? Care to draw a small schematic of the front end upto the 800's first gain stage? Just wondering what values you used for the extra stage. Cathode resistor and cap? Mixers, or a pot in between and finally where do you draw power for the new triode?

Ive been tossing up this idea for a while but havent had the time to put it into play.
Looking forward to your reply.

I do not have a scehmatic, but look for the Kevin Oconner foour gain stage layout or even the old roccaforte layout that Mark(Rockstah) had posted. PM me I think I still have it saved I can send you.

Yes the 2203 side is 100% stock except I ran the output from the original 1st gain stage direct to the preamp pot instead of throught the low input jack and I used .1uf in the PI ouputs for more bass. This amp no longer has the low input jack like a 2203 has, did anyone ever plug into that jack anyway? Just High gain and the regular high input jack as was on the 2203, also I added .1uf's in the PI outputs which helps regain some bass lost with the extra gain stage. As for the extra gain stage I used Kevin Oconners's design from TUT1 book, where he used a 680K to ground to attenuate the extra gain stage signal I used a 1M pot before feeding the input stage of the original V1 of the 2203 circuit. Look closely you can see two 68K resistors at the end of shielded wire connected to the input grid of V2(which is V1 of the regular 2203 circuit). I used a 10K for the cathode resistor on the Extra gain stage bypassed with a .22uf cap to get my RC constants close to Marshall and SLO frequencies at around 80HZ. I have seen a .1uf cap used here as well which get is around 160HZ.

I am thinking of relocating the Jose Master to the presence pot location and moving the presence pot to the back. The noise isn't much more than my old Splawn modded Marshall, I know alot of extra gain does produce some noise but I would like to get it to a low hiss if possible, when I turn the extra gain stage pot all the way down it seems to get a little louder when plugged into the regular 2203 side, I may even have to divorce the tandem inputs on V2 with a switch but we'll see, this was my first high gain build.

[Olaf]

Looks cool. Congrats.

To get rid of hiss when the amp is idle, reduce the 68k input Rs to something like 4k7 - you'll be surprised

[HTH]

hiss: try metal film plate resistors and you might get a little improvement over 1w carbon films.

hum: reference the heater winding's center tap to around 40v via a voltage divider off the HT rail.

[Roe]

larry style grounding also helps with hum

[HTH]

I see that you also have the extra tube's unused triode unconnected - try hooking the unused plate, grid and cathode to ground.

You might also try rectifying the 6.3vac heater supply and running DC heaters on the extra tube stage.

[harddriver]

I see that you also have the extra tube's unused triode unconnected - try hooking the unused plate, grid and cathode to ground.

You might also try rectifying the 6.3vac heater supply and running DC heaters on the extra tube stage.

Roe, I did use an alternate non-marshall grounding scheme, I'm sure Larry's is top notch I will look into it.


HTH, will wiring the unused, plate, grid and cathode to ground help reduce hum? That won't screw anything up with the live 12ax7 will it even though that side is unused?

I am very interested in trying that! Is it just as easy as running a wire through all those pins to ground?

[harddriver]

Looks cool. Congrats.

To get rid of hiss when the amp is idle, reduce the 68k input Rs to something like 4k7 - you'll be surprised

I will explore the 4k7 suggestion, thanks! But is seems to be more of a 60Hz hum,

Do you think the Pre-tonestack 1M master pot is picking up 60Hz hum from the PI socket/circuit, I used all shielded wire for it's connections but the pot is still exposed?

Thanks alot Olaf, the compliment means alot coming from you, I have seen the High gain and channel switching amps you have built, very amazing work!

It was a fun build, most of all my brother loves the amp as it has met all of his expectations, it was alot of pressure.

[harddriver]

I was reading that some people were having hum issues with the new Tung Sol 12ax7 tubes, so I am going to swap them out of V1 and V2 to see it that gets rid of or lessens the hum I am hearing at idle.

[harddriver]

I pulled the V1 and V2 Tung Sol 12ax7's and replaced them with tested JJ 12ax7's. The hum was reduced slightly but the tone of the amp suffered badly. With the JJ's in V1 and V2 the amp lost it's clarity, bite, definition and became muddy no matter how we Eq'd the amp.

Mostly the reason I didn't run JJ's in V1 and V2 in the first place. The amp's owner (my Brother) stated he would rather live with a little hum over the drastic bad tone changes the JJ made. He promptly ordered me to remove the JJ's and replace the Tung Sol's immediately.

So I guess I could try the 9th generation Shuguang 12ax7 as these are venerable high gainer tubes with a good reputation.

I still need to try grounding the unused grid, plate and cathode of V1 as HTH suggested and maybe mess with DC heaters.

[darkbluemurder]

Yeah, that's a bit of a dilemma. The JJs are functionally good tubes but do not have the tone, especially in high gain circuits. The Tungsol RIs blow them away tonally (IMHO) but they have functional issues. If it's only the hum then I would try to elevate the filament center tap or the connection of the 100R resistors (DC stand-off heater connection).

As regards other preamp tubes, I would agree that Shuguang 9th gen (I believe the TT12AX7 belongs to that group) is an adequate choice.

Good luck
Stephan

[Olaf]

Looks cool. Congrats.

To get rid of hiss when the amp is idle, reduce the 68k input Rs to something like 4k7 - you'll be surprised

I will explore the 4k7 suggestion, thanks! But is seems to be more of a 60Hz hum,

Do you think the Pre-tonestack 1M master pot is picking up 60Hz hum from the PI socket/circuit, I used all shielded wire for it's connections but the pot is still exposed?

Thanks alot Olaf, the compliment means alot coming from you, I have seen the High gain and channel switching amps you have built, very amazing work!

It was a fun build, most of all my brother loves the amp as it has met all of his expectations, it was alot of pressure.

Thanks for the kind words.
How much hum do you (still) have when you pull V1 and V2?

[thousandshirts]

Looks like a fantastic amplifier!