Wonderland/JM100 build

[Krinkle]

my only thought is it's not that loud for a 100w amp, going to check voltages now.

I built an Express for my friend a few months back and I had the same thing, sounded good, just lower volume than I expected. I had heard about the old 470k/470R swap in the phase inverter of some amps. Double checked and sure enough I had the wrong value in there. Changed it out and everything was good. I know the values aren't the same here but maybe double check the phase inverter resistor values? Or other values for that matter. You never know.

[martin manning]

it's been a journey this one so far, but a great learning experience again.
I'm hoping this 'mature USA Iron' will be worth all this faffing around to get it to work.

No too bad really, the power supply mods are more-or-less standard fare for reusing transformers, so good to know.

Good suggestion by krinkle above to look for a wrong part value. Disconnecting NFB as I suggested is just to prove to yourself that you don't have the primaries switched, and you should expect some volume boost without NFB even if things are wired correctly.

[norburybrook]

martin,

I've just taken the send from my 102 into the return on the wonderland and it's fine, what i'd expect, so I can rule out the OT primaries then. At least I've broken my record with wiring them wrong this time.

I reversed the two amps then by taking the send form the wonderland into the return of the 102 and it's weak.

So it' something in the pre amp section.

Does the return signal come in before or after the PI? what i'm getting at, if the send from the 102 into the wonderland is OK does that mean the P.I. section and output is all OK and I need to only check v1 -4?

I presume I can't check resistances in place I'll need to lift a leg at a time.

I's there a quick and dirty way to bypass certain section to see where the loss is?


Marcus

[martin manning]

Ok good, the power section is fine then. The return goes into the PI input.

You could plug a cable into the return jack (which disconnects the preamp output) that has no plug on the other end, just a very short bit of the center conductor exposed. You could touch that the the output side of the coupling caps stage-by-stage to look for signal loss. This might give a clue. Notice there is a cap to block DC at the PI input, but be careful to probe the low voltage end of the coupling caps.

[norburybrook]

Martin,

just been having a fiddle around and disconnected the reverb pan and played around with the send return knobs. They're acting like a tone control, is that normal? there's no level changes but if the return is up full then the send acts like a treble tone control.

I'm not 100% sure of what you meant about where and where not to probe

I'll attach a pic of the board

Wonderland board.jpg

I presume I can add an alligator clip cable to the tip and use the other end to probe.

marcus

[ToneMerc]

yep 12 AT7


the tone is superb it's just quiet for a 100w amp. It's quieter than my 50w 102 I've just built. the donor Peavey was LOUD..even running at 60w with two valves when I bought it.

Is it possible the OT primaries are the wrong way round and it's phase cancelling rather than squeeling? just thinking outside the box here.
Something seems to be sucking power.

As I said everything in the pre amp/tone section, switches ,contour etc works as expected sonically.


I'm home for the night now so will try any suggestions in the morning.

I'm going to take the output form the send on the Dumble into the return on the wonderland and see how that is. and vice versa maybe.


Marcus

That particular reverb circuit really loads down the signal down.

TM

[norburybrook]

ah, It's hard to know though unless you've got something to check against if that's the issue or something else.

I was expecting a LOUD clean amp here and it's just not very loud.

I can have the gain fully up and the master at 12 o clock and it's just starting to break if I hit hard with a strat.

feels to me like there's not enough gain at the front end. I presume it should be like a fender where you start to break up around 5.

anyone any experience with this circuit/amp?

Marcus

[ToneMerc]

anyone any experience with this circuit/amp?

Marcus

Look early in Taylor's thread when he posted this JM/AN layout, he mentions it being low in volume. I made a few changes in my build to compensate but I can't say that it definitely will work because I paused on my build to build a bass amp.

TM

[norburybrook]

funny I was hoping for a big loud clean amp, I really can't imagine John Mayer being happy with the volume I'm getting from this at the moment on a big stage!

My 100w BM through the EV cab could part your hair at 10 paces on the clean channel. I sold that amp and was hoping this would give me that level of clean but with spring reverb which I'd missed.


M

[erwin_ve]

Maybe by adding a cap before going into the reverb part of the circuit or a bigger resistor?

[dhudson]

Hello again, take a look at v1b plate cap there is a 1m/68k to ground thats like a master on 2? mabe increase that 68k to 100k and see if that gives you more output.

hope that helps,
dave

[norburybrook]

Hello again, take a look at v1b plate cap there is a 1m/68k to ground thats like a master on 2? mabe increase that 68k to 100k and see if that gives you more output.

hope that helps,
dave

thanks Dave. Not sure what you mean exactly by 'like a master on 2' but swapping that 68K for a 100K is an easy experiment tomorrow.


M

[ToneMerc]

Hello again, take a look at v1b plate cap there is a 1m/68k to ground thats like a master on 2? mabe increase that 68k to 100k and see if that gives you more output.

hope that helps,
dave

Yes, that's one of my tweaks...decrease the amount of signal that's dumped at the voltage divider.


TM

[norburybrook]

Hello again, take a look at v1b plate cap there is a 1m/68k to ground thats like a master on 2? mabe increase that 68k to 100k and see if that gives you more output.

hope that helps,
dave

Yes, that's one of my tweaks...decrease the amount of signal that's dumped at the voltage divider.


TM

so the larger the resistor the less signal is dumped? how large can you go?

while we're active on this thread, can anyone show me on my board layout above where/how I can jumper the gain stage after the tone stack straight to the PI so I can remove the whole reverb from the equation.

actually if some one would be so kind it would be very helpful to me in general if someone could draw on the signal path with gain stages.

I'm a bit lost still with the language/terms used and some of the basics.

Marcus

[dhudson]

yes a resistor to ground , closer you go to zero ohms the more signal is taken from the path, that is a simplification of what's happening there of course.

also 1 megohm trim pot at that location would allow you to adjust it to your taste.