What would account for the low-gain input having vastly lower volume than the high-gain input on a JCM 800?

Delicieuxz

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You would have to know the strength of each diode in the preamp tube to know if you are using an equal, higher or lower value in the low input side.
That requires a decent transconductance tester providing values for each side.
I just tried a few different tubes in the preamp sockets, and the sound level was the same, as far as I could tel..
 

mickeydg5

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Well, get all of those contact points cleaned with a good electronic lubricating contact cleaner to make sure all is good there.

The other thing I did is pay more attention to is your description in the first post.
It was mentioned clean up until 8 on the preamp control which seems normal for low-gain channel.
The problem is that "devastatingly loud" at 0.5 on the preamp control using the high-gain channel seems wrong. Some claim really loud at 2 or above or even 1.5 depending on the taper of the potentiometer in place.
Something seems odd with that first stage of high-gain channel.
That is going to require probing with a meter.
 

Pete Farrington

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The problem is that "devastatingly loud" at 0.5 on the preamp control using the high-gain channel seems wrong
But in that scenario he had the master volume full up.
Given the 1nF bright cap, I think it’s to be expected that as soon as the gain pot is rotated past the CCW track end pad, it’s going to be devastatingly loud.
The high sensitivity input engages a 35dB boost that is the V1b stage.
 

mickeydg5

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But in that scenario he had the master volume full up.
Given the 1nF bright cap, I think it’s to be expected that as soon as the gain pot is rotated past the CCW track end pad, it’s going to be devastatingly loud.
The high sensitivity input engages a 35dB boost that is the V1b stage.
The typicals like Bassman, 1987 and 1959 are master full up by default.
 

mickeydg5

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Yes, but those amps have less preamp gain than the 2203. If the 2203 didn’t have a master, I would expect it to be louder at a lower setting, because of the cascaded stages.
No.
The 2204/2203 low-gain input has less gain than all of those other amplifiers/channels.
It will have about half the preamp based volume, because of less gain / input sensitivity.
 

Dean Swindell

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The low input is SUPER low, a useless tone dog for two reasons. One, you're bypassing the cascade stage, but most importantly, you don't get a cathode capacitor using the low input. If I had one I'd try a mod I came up with for that.
 

peterplexi

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I just tried a few different tubes in the preamp sockets, and the sound level was the same, as far as I could tel..
When your amp is configured (mast high preamp as volume) and you are compairing yours to a friends, it may be as simple as pickup output level.
 

okgb

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I'm not going to read through all this [ trolling? ] Less gain stages = less gain
 

Dogs of Doom

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Well, darn, ain't no diodes inside a double triode. But again, as I got lashed for my last input in this thread, let´s say there are and let´s all go strutting around spreading alternative truths happily ever after. The guy wants a clean sounding amp, buys a high-gain amp. Then in stubbornness is uncivil to anyone suggesting he´s either made a less successful choice, or in all friendliness ask if he has understood that amplifier-stage gain and therefore perceptual volume is one and the same are met with unfriendly insinuations even insults when we techs try our best to bring the good and bad news alike and with the same friendly tone.

Enough. You can swap tubes until the moon leaves for Venus, China becomes a democracy or Norway the worlds largest population.
The amp WAS built like that and all others on this planet knows it´s meant to behave just like that and IF IT DOES NOT, THEN IT HAS BEEN MODIFIED.
Period.

Accept all good answers you have been given and accept what amp you have bought. It CAN of course be modified but I strongly recommend you let someone else do anything involving anything inside that and all other amplifiers you may possess now or later in life. You do not seem to have the mental capacity to work inside lethal high-voltage environments on your own. That said in an brutally honest way, yes, but most of all, for the future, if you want help, lower your own attack Blabbering Self a nice 6-8dB.

And please, choose another forum.
reading through the thread, this post seems devoid of reality & is not helpful. Your 1st post wasn't very helpful either.

Ironically, many people do not see 2203 as a high gain amp...

the tone of your postings are not very civil & it comes across as an unhinged rant. Maybe you need to revisit the forum rules, about demeanor towards other members on here.


The guy was asking for help, if you don't want to help, move on...
 

Jethro Rocker

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I think without recordings etc we can only go on descriptive analogies.

There shouldn't be a vast difference in volume with both controls full up whether using hi or lo.
If there is something is amiss.
Gain level, yes, volume no
 

Dirty-D

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Good call on converting from EL34's may l suggest KT88 over 6550. They seem a little bit more musical and not quite as stiff. l think there's only like 3 resistors to swap out to bring the bias controll into range.
 

Delicieuxz

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The real question is: Why do people even bother using the low input???
This is a question that I think is worth answering.

Despite its deserved reputation for its high-gain sound, the JCM 800 is an awesome pedal platform and does a gorgeous and very-chimey clean sound, if set right (master cranked, and use the preamp control for volume and thickness adjustment - opposite of how it's used for its high-gain sound), which is probably also my favourite clean sound. However, I should add that comment applies firstly to the horizontal-input model which, it turns out, actually has a bit of a different sound to it than the vertical-input model. The added airyness of the vertical-input model might detract from what makes the horizontal-input model excel at those things, and I indeed find that my horizontal-input 1985 2203 is giving me the tone I chased after for so long while my previous, 1982 2203, although being a really good 1982 JCM 800, didn't quite get there for me.

Almost all of the electric guitar parts on the Smashing Pumpkins album Siamese Dream are recorded using pedals through the low-gain input of a 1984, horizontal-input JCM 800 2203, with Chinese KT88s in it.





Likely also the JCM 800:



And not just the electric guitar parts for that album by SP, but also Pisces Iscariot. Between those two, fuzz-laden albums, and also their Mellon Collie album (which used the same 2203 for leads, and a complex rack setup for most of the other stuff) are my favourite guitar sounds. Their first album, Gish, is also recorded using the low-gain input of the same 1984 2203, but has an ADA MP-1 preamp going into it, creating that album's high-gain sound.

So, my favourite guitar sounds are generally through the low-gain input of a 5-can, horizontal-input 2203 with Chinese KT88s in it. Therefore, that's what I want to have. And it's what I now do have.

Good call on converting from EL34's may l suggest KT88 over 6550. They seem a little bit more musical and not quite as stiff. l think there's only like 3 resistors to swap out to bring the bias controll into range.
I've just finished doing a lot of work on my 1985 2203, which is detailed in another thread here. As part of that work, I've converted the amp from EL34 to 6550, and , yes, there were only 3 resistors to change. I've got Chinese KT88-98s in it now. They sound great. I would like to try the old Beijing KT88s, but they're pretty expensive. I might get a set, eventually.

But I will say that the EL34s have some charm to them, too. I'm half-tempted to get some more NOS resistors so that I can swap back and forth between the EL34 and KT88 setups some more. I wouldn't lift the PCB next time, but would just clip the resistors from the top and make them easily swappable, until I firmly decided I want only one sound from now on. Though, I could install inline sockets for the three resistors, and then change between EL34 and 6550 / KT88 at my leisure.

After doing the work, which included replacing the filter cans, I probably do have some more volume from the amp now. But still not like what my friend claims he gets from his. However, as I'm getting the sound I want, and still have plenty of volume on tap, I'm not worried about it. I'm thinking my amp is performing as it's meant to, and it's doing for me what I want.
 
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Delicieuxz

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Having thought about this a bit now, the part about installing inline sockets for the three resistors that configure a JCM 800 for either EL34s or 6550s, to make the amp easily switchable between them, I'm thinking this would be brilliant and very usable. Is there any reason to not do this - like, would the sockets be unreliable for an amp that experiences vibrations and cause damage if a resistor popped out from vibrations (if that would even plausibly happen)?

But I will say that the EL34s have some charm to them, too. I'm half-tempted to get some more NOS resistors so that I can swap back and forth between the EL34 and KT88 setups some more. I wouldn't lift the PCB next time, but would just clip the resistors from the top and make them easily swappable, until I firmly decided I want only one sound from now on. Though, I could install inline sockets for the three resistors, and then change between EL34 and 6550 / KT88 at my leisure.
 

Delicieuxz

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While far from everybody said the amp sounds like it's behaving as it should, when you and some others did say you think the amp is behaving as it should, I replied with:

Thanks for all the feedback, it's helping to know how the amp isn't performing outside of theoretical expectations.

Your narrative that I was uncivil and unfriendly to people, or to anybody at all, and that I stubbornly rejected their feedback and insinuated insults of them, is completely invented and false. And you attacking me over your invented narrative that has nothing to do with how I actually responded to people is bizarre and irrational.

When you attacked me, amongst many other accusatory things, you said to me:

You do not seem to have the mental capacity to work inside lethal high-voltage environments on your own. That said in an brutally honest way, yes, but most of all, for the future, if you want help, lower your own attack Blabbering Self a nice 6-8dB.

And please, choose another forum.

Now you say you didn't mean to insult me and were trying to help, when you quite literally went out of your way to insult me and told me to leave the forum - which isn't helping or expressing a desire to help. And that isn't you just saying something about the amp. And you're now calling me Mr Sensitives Intelligence when it's you who is having a fit of hysteria over having the uncomfortable reality of what's happened in this thread pointed out to you in a calm manner. You also suggested that the moderator is a racist and are now calling people faggots. As with your previous tirade of accusations made against me, your sensitivity comment actually describes yourself.

I'm sorry that whatever happened here happened. It doesn't make any sense, whatsoever. But if there was any doubt about whether there might actually be something to your previous comments and upsetness, I'm sure it's now gone. You behaviour has been inexplicable.
 

Tatzmann

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Onto topic.

I read on the board somewhere that a guy
changed the low input on a 4010combo
to a switchable plexi-input.

I think it was Johan.B or some such.

It involved using a stereo-jack that replaces
the low input jack.

He showed a video and to my ears the lowinput
sounded much better and fuller than the cascaded high-input, it's maybe even louder.

Maybe that would be a good mod to do if you are not happy with the stock circuit configuration.
 


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