Haven't built an amp for a while ... JCM800-ish content

4114Effects

Had a rare couple of days to myself so decided to knock up an amp. I built this cab a while back so I thought it was about time I filled it with some of the parts I bought from @martinw . Martin included some of these gold faceplates in with all the other parts, so I decided to use one and build the amp around the controls available. No idea what they were originally intended for?

It's my take on a JCM800. Designed for straight forward rock it's a simple single input that's based on the high-gain input of an 800. I've made a couple of tweaks to the preamp to tame down the harsh treble, resulting in a much smoother and fuller drive but still able to cut through if you need it to. Probably closer in tone to a Friedman Dirty Shirley now, at a guess.

I've also kept the EL34 power section but decided to cathode bias, again I think this makes the drive a little less harsh and more pleasant, albeit at the expense of a few watts. 30ish seems plenty loud enough anyway, plus you can just pop whichever EL34 pair you like in there and not worry about bias. 

Master volume is now  PPIMV so you can turn down but still get phase-inverter distortion in there. Works well for playing at bedroom levels (obviously comes into it's own when cranked though!).

Lot of fun to play - just plug in and turn up, control the gain with your guitar and you're off. Old school rock goodness. 

bandmaster188

No gut shot? How rude!

4114Effects

bandmaster188 said:

No gut shot? How rude!

Fair comment. Will see if I can be bothered disassembling it tomorrow ... :-)

bandmaster188

4114Effects said:

bandmaster188 said:

No gut shot? How rude!

Fair comment. Will see if I can be bothered disassembling it tomorrow ... :-)

I'm sure it will look just as tidy on the inside as it does on the outside!

MartinB

Looks like a useful amp, and the cab is well done (I haven't quite got the knack of tolexing inside corners perfectly yet myself).  Is the missing presence control just replaced with a fixed resistor?  They can be limited in usefulness with a PPIMV, so I guess the presence knob might not be missed. 

4114Effects

MartinB said:

Looks like a useful amp, and the cab is well done (I haven't quite got the knack of tolexing inside corners perfectly yet myself).  Is the missing presence control just replaced with a fixed resistor?  They can be limited in usefulness with a PPIMV, so I guess the presence knob might not be missed. 

Yeah, presence is set at 1 out of 10. I very rarely use the control so it's no big loss for me. :-)

TTBZ

That looks great! Love that colour.

MatthewShreddery

How much?

rico

This is the amp. 

MatthewShreddery

Would u sell it?

4114Effects

MatthewShreddery said:c

Would u sell it?

I might yeah. Send me a PM :-)

RaymondLin

I swear your builds looks better with each new amp.

ICBM

I like the narrow vent grilles above the chassis - I've never seen that done before. Very neat-looking and will definitely help with cooling. Intentional, or a happy accident caused by the chassis being too small for the cutout? (No bad thing even if it did start out that way! Some of the best ideas do…)

Out of curiosity, is it common cathode bias or separate?

4114Effects

ICBM said:

I like the narrow vent grilles above the chassis - I've never seen that done before. Very neat-looking and will definitely help with cooling. Intentional, or a happy accident caused by the chassis being too small for the cutout? (No bad thing even if it did start out that way! Some of the best ideas do…)

Out of curiosity, is it common cathode bias or separate?

Happy accident! Compensated for the router collet the wrong way and ended up with the cut out too large ... seemed to make sense to add the grille and as you say it'll help with airflow. Might make it standard on my amps from now on I think. 

Shared cathode at the moment, may switch to split though as that will be more within the safety margins of the cathode resistors.

4114Effects

RaymondLin said:

I swear your builds looks better with each new amp.

That's the idea. Very happy with this one. :-)

Modulus_Amps

4114Effects said:

ICBM said:

I like the narrow vent grilles above the chassis - I've never seen that done before. Very neat-looking and will definitely help with cooling. Intentional, or a happy accident caused by the chassis being too small for the cutout? (No bad thing even if it did start out that way! Some of the best ideas do…)

Out of curiosity, is it common cathode bias or separate?

Happy accident! Compensated for the router collet the wrong way and ended up with the cut out too large ... seemed to make sense to add the grille and as you say it'll help with airflow. Might make it standard on my amps from now on I think. 

Shared cathode at the moment, may switch to split though as that will be more within the safety margins of the cathode resistors.

I built two cathode biased EL34 amps, one was shared cathode the other split, I much preferred the split cathode one.
I then converted one to fixed bias, much closer to Marshall tone/feel, but it did not have the compression and bloom that the cathode bias did.

Nice amp and a nice circuit to try ideas out on.

timmysoft

An absolute work of art!

the little grill could easily be a signature feature! 

Sassafras

What the Astoria range should've looked like.
Look out Marshall, Danplifier's coming to get you.

english_bob

4114Effects said:

Happy accident! Compensated for the router collet the wrong way and ended up with the cut out too large ... seemed to make sense to add the grille and as you say it'll help with airflow. Might make it standard on my amps from now on I think. 

Sort of like the engineering equivalent of that joke about how when you play the wrong note you should play it again on purpose and call it jazz.

Looks amazing, and probably sounds just as good.

ICBM

Even if accidental it looks so right, and it's really a great improvement over the usual cooling methods - a lot of people forget that in order for convection cooling to work really well, you need a cold air inlet at the bottom, as well as a hot air outlet at the top, to create an airflow. That will allow the cold air in at exactly the right place where it can flow over the top of the chassis and then up and out of the back grille.

It's also *far* better than the usual method of a grille in the back and one in the top - AKA the 'beer trap'. Those are always a bad idea...

4114Effects

Right, better get it registered with the patent office then :-)