High Voltages After Headfirst Origin 50 Mod

Yargnad said:
Larry Carlton does that to add effects like reverb and chorus. He doesn't like to use pedals on the amp side of the chain and all his effects are in the FX bus on the mixer as if it were a studio session.
Click to expand...
Exactly.
The amp driven is just mud for the effects....
running the effects separate cleans the whole sound up.
That's what Brian May is doing too. He uses separate amps for the effects return.

The preamp needs to overdrive the power amp to get the ideal guitar sound.
But when the power amp is over driven, it's no good for effects return.
Using the board, PA, or another amp for the effects that problem is solved.

It goes from muddy to professional sounding huge difference.

Now on the other hand,
using the amp at a very low loudness, the power amp is not overdriven.
It's just preamp distortion.
Now the power amp is still clean, and effects return is still possible without so much muddiness.
But that only works at low loudness.

Once you get up to stage loudness, that possibility is lost.

And that is why effects loops in amps are not very ideal at stage level.
 
Amp Mad Scientist said:
Exactly.
The amp driven is just mud for the effects....
running the effects separate cleans the whole sound up.
That's what Brian May is doing too. He uses separate amps for the effects return.

The preamp needs to overdrive the power amp to get the ideal guitar sound.
But when the power amp is over driven, it's no good for effects return.
Using the board, PA, or another amp for the effects that problem is solved.

It goes from muddy to professional sounding huge difference.

Now on the other hand,
using the amp at a very low loudness, the power amp is not overdriven.
It's just preamp distortion.
Now the power amp is still clean, and effects return is still possible without so much muddiness.
But that only works at low loudness.

Once you get up to stage loudness, that possibility is lost.

And that is why effects loops in amps are not very ideal at stage level.
Click to expand...
I read that Brian May also has is "Guitar Sound" in the 3 amps, but only effects in the L/R Amps, making a W/D/W system, is that Correct ?
 
Yes he's used 3 AC30's angled like that(towards the side of the Stage forever, except the last 2 concerts he was using 3 big Fender Combos, sacrilege :), i don't know anything about using effects, but it seems like the correct way, to keep the main dry amp clean.
I proved mu uselessness with effects once & for all when i bought 2 of those Laney IRT-X units to go with my Amp & i used HXFX for the effects, it still sounded crap, so i finally gave up. :rolleyes:
 
Hi,

The post quoted above is mine, and my amp is NOT "Headfirst modded"!

I will eventually mod it into a 3 gain stages/cathode follower circuit (but not like the Headfirst mod as I'm not going for that sound/amount of gain) but right now I'm just doing tweaks to the original design.

The two tubes that failed was an EI and a really nice old Philips.
 
Polifemo said:
Hi,

The post quoted above is mine, and my amp is NOT "Headfirst modded"!

I will eventually mod it into a 3 gain stages/cathode follower circuit (but not like the Headfirst mod as I'm not going for that sound/amount of gain) but right now I'm just doing tweaks to the original design.

The two tubes that failed was an EI and a really nice old Philips.
Click to expand...

So these high voltages are present on a standard ORI50 ? & it's not necessarily a result of the HF mod ?.
 
old rocker said:
So these high voltages are present on a standard ORI50 ? & it's not necessarily a result of the HF mod ?.
Click to expand...

Good Morning @old rocker and @Polifemo.....

As far as we know, there is no "bone stock" (unmolested) voltage chart available for the Origin 50.

I do, however, have voltage readings from an unmodified Origin 20. These voltages will be different from the Origin 50, but I am posting for reference:

Readings going from "low" power mode to "high" power mode:
V1 ------- low ------ mid ------ high
pin1------175v------166v------151v
pin6------152v------145v------133v

V2 ------- low ------ mid ------ high
pin1------274v------262v------236v
pin6------151v------145v------131v

V3 ------- low ------ mid ------ high
pin1------39v-------70v -------149v
pin6------39v-------72v -------150v

V4 ------- low ------ mid ------ high
pin3------307v------293v------262v

V5 ------- low ------ mid ------ high
pin3------309v------295v------262v

Here are the voltage readings from my Origin 50 following the "Headfirst" modification recipe:

Rob's Modded Origin 50.jpg

Also, it's important to note that when following the "Headfirst Mod Recipe" that V2 is reassigned and appears to be running in a much different fashion.
 
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Polifemo said:
Hi,

The post quoted above is mine, and my amp is NOT "Headfirst modded"!

I will eventually mod it into a 3 gain stages/cathode follower circuit (but not like the Headfirst mod as I'm not going for that sound/amount of gain) but right now I'm just doing tweaks to the original design.

The two tubes that failed was an EI and a really nice old Philips.
Click to expand...

I think it would be helpful if you could post a full description of your modifications.
 
Robert Herndon said:
Wonder what tubes he is running???
Click to expand...
Boogie had the same issue at first.
The first boogies in 1970s used to blow the top off the preamp tubes, the glass would crack from the repeated heating /cooling...it would exceed 325 volts.
but in reality the preamp tube should run about 225 volts.

The deal is to reduce the voltage with larger drop resistors in the power supply.

True certain tubes will take more voltage...
(it's really the current that is the issue)
You can't flag the voltage itself until you know what the plate current actually is.
this is not really a voltage problem it's a current problem.

The phase inverter will run with a 400 volt supply.
BECAUSE the current is properly limited, it keeps working no issues.

But it shows lack of experience in design limits, and disregard for reliability, lack of proper testing, irresponsible modification.
This guy gives me the impression of irresponsible and inexperienced , the lack of schematics only confirms what I have been telling you.
 
FYI
the hotter the output is biased the lower the voltage will drop.
The cooler bias = higher plate voltage.
So the first thing to do is confirm that the output is biased just right.
BEFORE doing anything else.

Use an O scope if you really want to know what bias is correct.
Bias meters are only ballpark, not accurate.
 
I believe that the PT is putting out about 460v.
Before the 100k plate resistor on V1a I measured 340v if I remember correctly (260v after the plate resistor).

Never measured V2, but as I remember there’s a 220k plate resistor there in the original design, where the Tube is used for the FX-loop.

Lowering that to 100k - which I believe is done in the Headfirst Mod, where the Tube is used for the Cathode follower - will of course increase the voltage significantly.

The stock Origin has enough gain for what I want this amp to do (Old School Rock Tones) but the sound is way too muddy...

This far I’ve done only minor tweaks, but the sound has improved a lot:

- Grid resistor/V1a lowered from 33k to 10k which adds some clarity

- Cap going into the PI lowered from 100nF (!) to 4.7nF which removes lots of the mud that is present in the original circuit

- V1a changed from 820r/1uF to standard Marshall values 2.7k/0.68uF

- V1b changed from 820r/2.2uF to 680r/1uF. (This is done in order to see if the low value resistor could simulate some “cathode follower like” crunch and compression)

- The Tilt Control is a bad joke as far as I’m concerned so I took that out of the circuit and reused the pot for a Soldano Resonance Control. I also a 120pF bright cap on the gain pot when doing this mod.

That’s about it.

Next stage is installing a LND150-loop and turn V2 into a cathode follower.

The pre amp will then probably end up close to a Dirty Shirley I would guess.
 
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Polifemo said:
I believe that the PT is putting out about 460v.
Before the 100k plate resistor on V1a I measured 340v if I remember correctly (260v after the plate resistor).

Never measured V2, but as I remember there’s a 220k plate resistor there in the original design, where the Tube is used for the FX-loop.

Lowering that to 100k - which I believe is done in the Headfirst Mod, where the Tube is used for the Cathode follower - will of course increase the voltage significantly.

The stock Origin has enough gain for what I want this amp to do (Old School Rock Tones) but the sound is way too muddy...

This far I’ve done only minor tweaks, but the sound has improved a lot:

- Grid resistor/V1a lowered from 33k to 10k which adds some clarity

- Cap going into the PI lowered from 100nF (!) to 4.7nF which removes lots of the mud that is present in the original circuit

- V1a changed from 820r/1uF to standard Marshall values 2.7k/0.68uF

- V1b changed from 820r/2.2uF to 680r/1uF. (This is done in order to see if the low value resistor could simulate some “cathode follower like” crunch and compression)

- The Tilt Control is a bad joke as far as I’m concerned so I took that out of the circuit and reused the pot for a Soldano Resonance Control. I also a 120pF bright cap on the gain pot when doing this mod.

That’s about it.

Next stage is installing a LND150-loop and turn V2 into a cathode follower.

The pre amp will then probably end up close to a Dirty Shirley I would guess.
Click to expand...

Updates????
 
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