JCM800 not sounding as good as it should

John_A

Recently got a JCM800 4010 combo and not sure it's sounding as it should, with the gain on 10 the low end is a bit farty/fuzzy/flubby.  Had one years ago and I'm sure it wasn't like this.


So far I've changed the filter caps and bias caps, fitted a new pair of JJ EL34's, biased to 33 mA and a new set of JJ pre amp valves and it sounds exactly the same.


prior to my tinkerings the amp is un-modified


Any ideas?

ICBM

Fit good preamp valves...

John_A

ICBM said:

Fit good preamp valves...

What would you suggest?

ICBM

Standard cheap Shuguangs are fine - nice bright tone with no muddiness or fuzziness - and equally important, don't fail in V2 like Russian-made and JJs can do... JJs a bit less so but I've still come across a few.

If you want to spend a bit more there's nothing as good as old-production RFTs in any 70s or 80s Marshall in my opinion.

John_A

Thanks @ICBM any need to put anything special in the PI?

ICBM

John_A said:

Thanks @ICBM any need to put anything special in the PI?

No - in fact one of the JJs would be OK there. It's V1 which is the most important for tone and V2 for reliability, although I think it does make a difference to the sound as well.

photek

Doesn’t have a G12M-70 in it does it?

John_A

ICBM said:

John_A said:

Thanks @ICBM any need to put anything special in the PI?

No - in fact one of the JJs would be OK there. It's V1 which is the most important for tone and V2 for reliability, although I think it does make a difference to the sound as well.


Thanks again, i'll grab a few and give them a whirl.  Actually found a 'ruby tubes' I had lying around and popped that in V1, still doesn't sounds how I'd like, but it's better

photek said:

Doesn’t have a G12M-70 in it does it?

Not any more, has a creamback 65 in there now, but mostly playing through a reactive load & IR's at home

tekbow

Split the difference and stick an RFT In V1, and some shuguangs in the rest.

I've got a stash of nice NOS tubes and I really like shuguangs that have been properly tested, which any decent re-seller will do.

Plus they're generally inexpensive and abundant.

I honestly dont understand the aversion to them, which granted noone has expressed here.

WiresDreamDisasters

JJ's can sometimes make a Marshall sound flubby and fizzy in the lows as I recall. I put a bunch in my JVM once and didn't like it, which was unusual at the time because JJ's in my Fryette sounded monster.

As I recall I got some Gold Lion's from @karltone at the time, and those were a bit better.

I've noticed in tests that the Electro Harmonix 12AX7 is fairly bright and cutting too. 

(these are all subtle differences when measuring a single tube, but a block of 5 of them and it starts to add up!)

John_A

Thanks everyone, got a few ecc83s incoming, will report back

Modulus_Amps

I normally stick a JJ in V1 as out the box they are the most consistent for low noise/hum ( I have spent way to much on expensive pre-tested valves trying to find alternatives that deliver the same performance for the buck), typically go Shuguang after that

Modulus_Amps

John_A said:

Recently got a JCM800 4010 combo and not sure it's sounding as it should, with the gain on 10 the low end is a bit farty/fuzzy/flubby.  Had one years ago and I'm sure it wasn't like this.


So far I've changed the filter caps and bias caps, fitted a new pair of JJ EL34's, biased to 33 mA and a new set of JJ pre amp valves and it sounds exactly the same.


prior to my tinkerings the amp is un-modified


Any ideas?

Why have you biased at 33mA  (approx 60% plate dissipation??)

John_A

@Modulus_Amps   ‘Internet wisdom’ seems to be hotter isn’t necessarily better for JCM800’s but if you’d advise otherwise I’m open to suggestions 

John_A

My JJ in v2 went microphonic after a day in there

Modulus_Amps

John_A said:

@Modulus_Amps   ‘Internet wisdom’ seems to be hotter isn’t necessarily better for JCM800’s but if you’d advise otherwise I’m open to suggestions 

Guess it depends what you want from the amp, but since you are playing into a load box you are likely distorting the power section too and cross over distortion becomes a thing, I need to re bias my 800 for a video series I am about to do, will see where it lands.

John_A

Modulus_Amps said:

John_A said:

@Modulus_Amps   ‘Internet wisdom’ seems to be hotter isn’t necessarily better for JCM800’s but if you’d advise otherwise I’m open to suggestions 

Guess it depends what you want from the amp, but since you are playing into a load box you are likely distorting the power section too and cross over distortion becomes a thing, I need to re bias my 800 for a video series I am about to do, will see where it lands.

Thanks Michael.  I’m not running it really hard, master on about 3

John_A

Well, got 3 Shuguangs. Just tried one in v1, and then both v1 &2, as expected v1 made the most difference, and definitely prefer it to the JJ, didn’t actually expect it to make as much difference as it has.  Tonight was a quick test with load box and headphones, will give it a better try tomorrow.  Thanks everyone 

arayadis

Do you playing the amp in the same room you used to? Room acoustics can change everything drastically.

John_A

arayadis said:

Do you playing the amp in the same room you used to? Room acoustics can change everything drastically.

Yes, it always been in the same room

brooom

One thing is for sure, my 4010 sounds quite flat (it's a nice sound but lacks dynamic range), if the master is below 5 or 6. The whole amp sounds much more interesting and dynamic if I run the master quite high and control volume from the pre amp or guitar. But of course if you're looking for some breakup, pedals or an attenuator will help get there if you open the master. No surprises here.

This is probably also why I think my plexi sounds more complex. There's no master option there. It's always flat out.