Bogner Ecstasy Blue channel to JCM800 Mod

[maxkracht]

I'm not an engineer, I've never majored in electricity, and I'm just doing DIY as a hobby, so there may be some immaturity in using the correct conceptual words. I ask for your understanding.
You can think of me as used the word "Gain" to mean the role that "Gain Knob" plays.

Apologies if I sounded rude, just trying to make sure we are all on the same page. I don't have formal education related to electronics either, and we are all here to learn. The word gain is often used to mean volume or simply distortion. You were correct in describing a more technical meaning of the word, how much voltage comes out of a tube vs how much came into the tube, being largely related to how it is biased.

The signal is connected to the next stage while changing the tone shape with a coupling capacitor or RC filter. By changing this, there can be a concept of how much the signal is "dropped less", but even if the amount of signal passing increases, the size of the signal I said that the amount of distortion doesn't seem to increase dramatically.

This "Unboost" function is working normally, but I wonder why the 500K Grid Leak at the same location did not change the signal even after changing or removing the value.
I checked the switch but it was normal.
Why was there no change at all when the Grid Leak value was changed?

You can think of your gain knob all the way up as a single 500k resistor to ground. This is the maximum output possible with that pot. Making that larger, say 1M, will give you more output, but more resistance in parallel to it later in the circuit makes it effectively smaller again.

Changing the ratio of the two resistors after the gain knob should be very noticeable, it is another fixed volume control after your variable volume control, but If you have the "unboost" set with the 100k/1n to ground, changing the 500k resistor to 1M doesn't make a difference, because the 500k was effectively not there to begin with. 100k is the path of least resistance. Remove the 100k from circuit, and try changing the voltage divider again and you should hear the difference. If you don't, I'm guessing there is something else in circuit that you aren't seeing.

[psychepool]

Apologies if I sounded rude, just trying to make sure we are all on the same page. I don't have formal education related to electronics either, and we are all here to learn. The word gain is often used to mean volume or simply distortion. You were correct in describing a more technical meaning of the word, how much voltage comes out of a tube vs how much came into the tube, being largely related to how it is biased.

You don't have to worry about my answer anymore.
You asked what gain means to me, and since I don't think I can give you a good answer, so I was tell you my level of electrical knowledge.

Changing the ratio of the two resistors after the gain knob should be very noticeable, it is another fixed volume control after your variable volume control, but If you have the "unboost" set with the 100k/1n to ground, changing the 500k resistor to 1M doesn't make a difference, because the 500k was effectively not there to begin with. 100k is the path of least resistance. Remove the 100k from circuit, and try changing the voltage divider again and you should hear the difference. If you don't, I'm guessing there is something else in circuit that you aren't seeing.

I installed it because there was no reason not to install a boost circuit, but in fact, this circuit is considered to be in a default state when the boost circuit is not engaged, and the tone when the boost circuit is engaged is not very satisfactory. So to be honest, I do not use this because I did not like this well.

Therefore, even when the test of switching the 500K grid leak was attempted, this "unboost" was not set.
But still, nothing changed. I also thought that it was not normal that there was no change, but maybe there was a build error that I didn't know about, so I'll have to take a look again and put the switch back on and test it.

In fact, the 500K Grid Leak resistor of the second stage of Ecstasy is expected to be installed for switching I think.
If you look at the overall circuit diagram of the amplifier in the first post of this thread I posted, you can see that the corresponding position is switched for Plexi mode.
When viewed as a single channel, the gain pot already plays the role of Grid Leak, but when switching channels or modes, DC flow is blocked with the switch disconnected, which can cause serious popping noise or switching delay. To prevent this, signal It seems to have additionally attached a grid leak that is always connected even in a disconnected state.

I don't use the plexi mode as a foot-switchable "channel" like the original amp, but as a "mode" of the dirty channel, so I think it's okay to omit the 500K despite a little inconvenience.
When considering only the sound aspect without considering convenience factors such as switching, it is considered that the gain pot is already playing the role of grid leak, and the grid leak is doubled(parallel).



I would like to ask a question for a moment here.
The configuration of the road to the second stage after passing the first coupling cap is like this,

voltage_div.jpg

In the case of most amplifiers, additional Grid Leak is rarely installed with the gain pot installed.
In the case of the ecstasy circuit, assuming that the gain pot is set to the maximum, it seems to be the same form as applying a grid leak of about 330K in parallel with a 500K pot +500K gird stopper resistor and a 500K grid leak.
Is this guess of mine correct?
If this is correct, when the gain pot is changed to 1M, a 1000K pot +500K grid stopper and a 500K grid leak are installed in parallel, eventually resulting in a grid leak of about 375K.
If so, I think that changing the gain pot from 500K to 1M actually doesn't make a big difference.
So, if you are not going to remove 500K Grid Leak, if you change the gain pot to 1M, I think that changing the Grid Leak to about 1M will have an appropriate effect.

Howt do you think about it? Please let me know if there are any problems with my guesses.

From the same point of view, I think that the reason why no change was felt when switching the 500K grid leak was because of the small difference between 500K + 500K and 500K in parallel = 330K vs 500K + 500K and 1M in parallel = 500K .
It was not even tested with the gain pot set to the maximum, so the difference may have been felt less. How do you think about it?

Actually, there are only a few parts to try, and I think it's a situation where I can try and feel it myself, but I feel sorry that I can't try it freely because of the complicated build structure.

[Lynxtrap]

In the case of most amplifiers, additional Grid Leak is rarely installed with the gain pot installed.
In the case of the ecstasy circuit, assuming that the gain pot is set to the maximum, it seems to be the same form as applying a grid leak of about 330K in parallel with a 500K pot +500K gird stopper resistor and a 500K grid leak.
Is this guess of mine correct?
If this is correct, when the gain pot is changed to 1M, a 1000K pot +500K grid stopper and a 500K grid leak are installed in parallel, eventually resulting in a grid leak of about 375K.
If so, I think that changing the gain pot from 500K to 1M actually doesn't make a big difference.
So, if you are not going to remove 500K Grid Leak, if you change the gain pot to 1M, I think that changing the Grid Leak to about 1M will have an appropriate effect.

If you had read up on voltage dividers, you would not have to guess

Assuming that the "unboost" is out of the circuit, the 500K grid leak has an effective value of 500K. Your grid stopper prevents it from interacting with the gain pot.

The grid stopper and the grid leak form a voltage divider that cuts the signal by 50%. This has been said a few times in the thread.
A 1M leak with a 500K stopper cuts 33% of the signal.

The Marshall has no such voltage divider. But it does have a 470K resistor before and in series with the gain pot.

So there are all the clues to making the circuit similar to the Marshall. I suggested using the 500K gain pot straight into the next stage (no grid resistors).

[psychepool]

If you had read up on voltage dividers, you would not have to guess

Assuming that the "unboost" is out of the circuit, the 500K grid leak has an effective value of 500K. Your grid stopper prevents it from interacting with the gain pot.

The grid stopper and the grid leak form a voltage divider that cuts the signal by 50%. This has been said a few times in the thread.
A 1M leak with a 500K stopper cuts 33% of the signal.

The Marshall has no such voltage divider. But it does have a 470K resistor before and in series with the gain pot.

So there are all the clues to making the circuit similar to the Marshall. I suggested using the 500K gain pot straight into the next stage (no grid resistors).

Thank you for your reply. As you said, it is correct to interpret it as a structure in which the voltage divider is connected in series, rather than a structure in which the grid leaks run in parallel.

To sum up what you said, do you mean that the current Bogner circuit should be changed like this to JCM800?

xtc_to_800_VD.jpg

This actually makes it exactly the same as the JCM800 except for the cathode resistance of the first stage. It seems impossible not to hear the sound of the JCM800.
However, as I said, this amplifier was made with the goal of Bogner Ecstasy, and I wanted to make the JCM800 as a side function of a kind of "mode" concept, so I am a little reluctant to change the structure like this. This is because switching cannot roll back to an intact Bogner's circuit.

Anyway, thanks a lot for your help.
In fact, except for the slightly insufficient amount of gain, I have already achieved the goal I wanted in terms of sound, so I will think about it and apply it.
The change in the value of the coupling cap and the application of the treble peak were very effective.
Compared to Bogner, the loose and wild nuance, which is not rigid, expands the expressive range of this amp so much that I feel like I got another new amp.
Insufficient gain can be solved through gain boost, or even if Bogner Red Mode is engaged in the JCM800 setting, more distortion can be obtained while maintaining the characteristics.

I learned a lot from what you told me. Thank you so much.

[Lynxtrap]

Doing it exactly like the Marshall would get you the closest of course, but here are 3 other alternatives. They should all give you more gain (less attenuation). They all assume the "unboost" 100K resistor is out of the circuit.

01.jpg

02.jpg

03.jpg

[psychepool]

Your references are very helpful. thank you

Looking at the images you suggested, I was curious.
I understand that the 500K resistor in parallel with the 470pF in the voltage divider works as a voltage divider but also as a high cut. Are the facts I know correct?

If so, does lowering the resistance result in a different tone shape?
If the tone shape is changed by the resistance value, I wondered if it would be better to leave the grid stopper value as it is and increase only the grid leak (resistor connected to the ground) value for the desired amount of gain, so I asked a question. Only a 500K resistor connected to the ground I think there will be a significant difference if changed to about 2M. Does the value of the grid leak affect not only the gain amount but also the tone shape?

[psychepool]

Doing it exactly like the Marshall would get you the closest of course, but here are 3 other alternatives. They should all give you more gain (less attenuation). They all assume the "unboost" 100K resistor is out of the circuit.

Your references are very helpful. thank you

Looking at the images you suggested, I was curious.
I understand that the 500K resistor in parallel with the 470pF in the voltage divider works as a voltage divider but also as a high cut. Are the facts I know correct?

If so, does lowering the resistance result in a different tone shape?
If the tone shape is changed by the resistance value, I wondered if it would be better to leave the grid stopper value as it is and increase only the grid leak (resistor connected to the ground) value for the desired amount of gain, so I asked a question. Only a 500K resistor connected to the ground I think there will be a significant difference if changed to about 2M. Does the value of the grid leak affect not only the gain amount but also the tone shape?

[Lynxtrap]

Your references are very helpful. thank you

Looking at the images you suggested, I was curious.
I understand that the 500K resistor in parallel with the 470pF in the voltage divider works as a voltage divider but also as a high cut. Are the facts I know correct?

If so, does lowering the resistance result in a different tone shape?
If the tone shape is changed by the resistance value, I wondered if it would be better to leave the grid stopper value as it is and increase only the grid leak (resistor connected to the ground) value for the desired amount of gain, so I asked a question. Only a 500K resistor connected to the ground I think there will be a significant difference if changed to about 2M. Does the value of the grid leak affect not only the gain amount but also the tone shape?

The cap across the resistor is more like a high boost, it lets high frequencies pass unaffected by the voltage divider, just like the cap across the gain pot. The treble peak may be less prominent with less attenuation from the voltage divider no matter which of the two resistors you change. I would let my ears be the judge.
A 2M grid leak seems a bit over the top. There may also be input impedance of the following tube to consider, but I don't think we need to go there.

[psychepool]

The cap across the resistor is more like a high boost, it lets high frequencies pass unaffected by the voltage divider, just like the cap across the gain pot. The treble peak may be less prominent with less attenuation from the voltage divider no matter which of the two resistors you change. I would let my ears be the judge.
A 2M grid leak seems a bit over the top. There may also be input impedance of the following tube to consider, but I don't think we need to go there.

With some free time, I tried to modify the 500K+470pF/500K voltage divider.
I didn't have enough time to try various things, so I only fixed the 500K grid leak.
In fact, I have already tried it, but there was no change at that time, but there was a change this time. Perhaps there was a wiring mistake in the last work.

I felt that the gain increased when 500K was changed to 1M, but I did not feel that it was significant.
When 2.2M was applied, there was a gain increase that was clearly felt.
I haven't tried higher values. It probably doesn't make much sense.

Because I tried it for a while before going to work in the morning, so I couldn't check if there were any other side effects when applying 2.2M.
Anyway, this 2.2M resistor will be applied only when in JCM800 mode through the switch, so I think it would be good to go with this if there are no other side effects in the JCM800 setting.

As you said, this 500K+470pF/500K chain after the gain pot is the same result as the 1M pot with the 470pF bright cap attached, so remove them altogether and attach the 1M pot + 470pF cap to the corresponding location to find the sweet spot before applying It seems like a way to try it.

The more I try new tests, the more points I have to switch to, but I need to choose well and summarize them.

Currently, the A250K is applied to the travel pot, but I will change it to the B250K and test it.
In fact, at first I attached a B250K pod, but I heard that a certain model of Ecstasy uses an A250K pod, and after applying it, I liked the characteristics better, so I applied it to the A250K, but I think the B250K would be more suitable for the JCM800. The JCM800 has a brighter tone than Ecstasy, but rather the treble-up sound suited the unique character better.


I bought a 4PDT on-on-on switch for mode change and am waiting for delivery.
The coupling capacitor is intended to be applied as a separate DPDT on-on switch.
I need to summarize the points to be changed so that I can finish the work right away when the switch arrives.

[Lynxtrap]

As you said, this 500K+470pF/500K chain after the gain pot is the same result as the 1M pot with the 470pF bright cap attached, so remove them altogether and attach the 1M pot + 470pF cap to the corresponding location to find the sweet spot before applying It seems like a way to try it.

I don't think I said exactly that. If you remove the voltage divider altogether, a 500K gain pot will make it closer to the Marshall because of the Marshall's 470K resistor before and in series with the gain pot.

Also, the cap across the signal half of the voltage divider is a "preset" treble boost. A bright cap across a volume pot becomes less effective as the pot is turned up, as is the case with the "preset" cap when you alter the ratio of the voltage divider.