JET CITY JCA100HDM - Status Report

[IUnknown]

So, I had a few hours to run the amp through it's paces.... at
rehearsal.

Build Quality / Components:

1 - The power tube spring retainers are rather cheesy. I swapped in a
set of LV 6L6 glass.... and was able to detach the spring from the
clip accidentally (and easily).... resulting in one of the retainers
just hanging there for the rehearsal. I know they dont dampen
vibrations, but putting a stronger clip/spring would have prevented
this.

2 - The stock glass sucks. Waaaaaay to much upper mid and treble
content. Swapped in the ruby power tubes, a tung-sol in P1, mullard
reissues in P2/V3 and some JJ's in P4/P5. It fattened up a LOT.

3 - It is a 'fixed' bias but is internally adjustable..... <sigh>. I
haven't measured to see how cold they are running (yet). Seriously,
why not just expose a bias trim pot? Lame.

Sound:

1. Initially, the amp was VERY bright sounding - swapping in some
better pre's tamed that a bit. The overdrive channel is FANTASTIC-
lots of harmonic content. The crunch channel is OK. I am not a 'clean'
kinda guy, so this will take some getting used to on my part. I will
say that when playing some of the heavier parts in 'sweet home
alabama' last night - the crunch channel cut through nicely ... good
classic rock sound. But the overdrive channel is really the shining
part of this amp.

2. the EQ section is VERY useful ... good sweep ranges and all the
knobs have a noticable impact when turning. this is a stark contrast
to my 6505+ where the eq didn't help to shape the tone THAT much. the
depth control is subtle.... i was expecting a bit more effect, but it
helps for rounding out the bottom end of the tonal spectrum.

2. The effects loop is *strange*. I am not sure what to make of
it.... With ANY other amp I have used over the years, my SKB
pedalboard (with buffered ins/outs) has an absolute minimal effect on
the tone. What I have found is that when I run the pedalboard into the
effects return on the amp - there is a **noticable** drop in volume
and it is like someone put a blanket in front of the cabinet. There is
a MASSIVE upper frequency rolloff.

If I go directly into one of the pedals in the chain - the rolloff is
not present at all. I am going to experiment a little more tonight and
see if there a pedal in the chain that is causing the issue - but this
may be a deal breaker for me..... I really do not like running
delay, chorus and reverb effects into the front end of an amp.

[Flying V]

Hey, thanks for your post! I don't know what to make of your effects
loop problem....very strange! But then, I'll admit I'm no expert on
effects loops. I have only one amp that has that feature and I seldom
use it.

Maybe someone else will have some idea what's going on there.

Regarding the stock tubes, I found the same thing to be true with my
Soldano amp. I didn't care for the glass in there--the amp was
purchased brand new. First thing I did, was swap out all the tubes
and adjust the bias to my liking. That made a world of difference!
But then....that's pretty much my SOP for any new tube amp. Unless
you buy a boutique amp, the stock glass usually sucks.

Thanks again for your post! I may take a chance on one of the small
Jet City amps, yet.....haven't made up my mind.

Mike

[IUnknown]

> Mike- Hide quoted text -
>
> - Show quoted text -

I have some answers re: the effects loop.

Apparently, the loop runs @ line level. Most guitar pedalboards are
intended to be ran at instrument level, and the active buffers on the
board are having a hard time dealing with the difference..... i don't
understand electricity enough to qualify this, but the gist of this is
that the output of the pedals expects to drive one load, and the input
(effects return) on the amp is an entirely different impedance...

In other words, there is a massive impedance mismatch - hence the
issues.

Unfortunately, the response I have seen so far indicates that I need
to insert a buffer in place that will send the signal back to the amp
at line level - OR I need to purchase line-level effects gear
(rack??). Neither option is particularly palatable to me. I dont need
more gear these days - I need less :)

The other choice for me is to go old-school and just break the chorus/
flange/delay out of the loop chain, and run them as a single chain
into the guitar input....

guitar -> wah -> boost pedals -> chorus -> flange -> delay -> amp
input

This might save me a bit of noise, because I wont need an extra 50 ft
of cable (2x25ft) running the loop from the head to the pedalboard...

This is the way they used to do it before effects loops were
common.... maybe I should try it :)

decisions....decisions....

[Jim]

Your biggest problem is the level itself. The signal is at a higher
voltage. Some amps (like my Peavey XXX for example) have a level
controls on both the send and return to allow you to run the loop itself
at different voltages, without overloading effects, and still driving
the power amp.

[Flying V]

Ah yes...my Egnater loop is like that. The manual says the loop
operates at line level, which is higher than most "stomp boxes" can
handle. I have an Alesis reverb unit I've used with my Egnater, which
worked fine--but then, it can handle line level signals. I'll bet if
I tossed my little Boss phase pedal in the mix, I'd encounter the same
problem as you're having.

Good Luck,

Mike

[pvau...@gmail.com]

In pretty much full agreement with what is posted here...

I just re-tubed my HDM... Mesa Boogie 6L6's in the power section (Unknown manufacturer, but they were all matched. Guessing Sov-Tek??)

Pre-amp:
V1 - GrooveTubes 12AX7
V2 - Mullard 12AX7
v3 - GrooveTubes 12AX7
V4 - Mesa Boogie 12AX7
V5 - Mesa Boogie 12AX7

Completely new beast now, and I'm going to have to dial it in once more!

I run Reverb and Delay from a Lexicon into the FX loop
the remainder of pedals run into the front.

[Army of 7]

What about a Digitech Rp250 or 350 floor processor. They are cheap used and the reverb and modulation effects are stunning. They also allow you to tailor the input and output level for use in an effects loop. It's like having a rack sound on the floor. Neither option is particularly palatable to me. I dont need

[Army of 7]

Sorry but I just read up on the 350, you can't turn off the preamp for effects loop operation, you need a new p500. I love the RP350, I've never used it like that.

[Pt]

Stupid question but why would you expect solid state/digital effects to sound good through your loop?
Some loops are series and some are parallel.

Pt