MY H|H ic100L sounds bad lately..

[Superfuzz]

It's my main amp from years but lately it has become dull and lifeless..I also recorded some months ago thru the mixer output, and I'm pretty sure it's in the preamp.
The overall level when I play straight to the amp is much lower and lifeless, then as I put in a LOT of signal with my stompboxes the overall level is kinda right but it's very raw.
It's kinda hard to describe, it's muffled and the harmonic content is really unpleasant, plus the lows don'thave that "breathe" and fast response..

The rail voltages are fine as I get 15.7V on both

May the problem be in all the small electrolytics? I think they're still the originals, the head is from 1977..are they old enough?

[J M Fahey]

sorry but your symptoms are vague and the description may apply to 1000 different problems.
Dull, lifeless, unpleasant, are very subjective descriptions, mean different thin gs to different people.

[g1]

+/-15.7V does not sound right for the supply rails, unless you are talking about the low voltage supply.  The power amp should be running on higher voltages than that.
Without a schematic there is not much anyone can suggest.
  The schematic does not seem to be available online unless you buy it here:
http://www.majelectronic.co.uk/

[J M Fahey]

Rails for a 100W into 4 ohms amp are around +/-40V or no more than 5V away.

[tracynorton]

Hi. I'm a noob here, but have been working on HH amps for a bit. In fact, they are my fav amp now. I have a MOSFET Studio60 'PowerBaby' that rivals some SLPs in my book.

The power amp rails on the IC100L are +/-48V (given ideal mains voltage...and that can vary). These are simple PT>rectifier>cap unregulated supplies...so the wall voltage has a good deal to do w/ power rail voltage.
The preamp rails are +/-16V, simple resistor>zener>cap type...so he is prob referring to that.

Superfuzz...THE most common problem w/ these amps are the two main power supply filter caps (4700uF 50V). Every HH I've been in hasn't had these caps replaced...and either leaking electrolyte out of the plugs or the plugs are about to burst. I bought a 'not working' IC100S...and it had one cap blown out...and took one of the output transistors (2N3773 usually). I recapped and replaced both transistors....but the one thing that stood out.....when I plugged it into the wall here (120V+)...the power rails were just above 50V. I used 5600uF 100V caps, so is a non issue.
The second thing is the pots. Any time these get even a little dirty...the tone goes all to *s!!t*. You need to clean them thoroughly. Douche w/ non-residue cleaner first. If they have the 'feel grease' in them...you'll have to disassemble them and clean just the carbon track...or loose the resistive feel of the pot.

All this to say....check the big caps first.....replace if they are original. Clean the pots. Then check the outputs of all the opamps. Unfortunately...this thing uses 4739 opamps in addition to xx741 opamps. If any of the 4739s are bad....well...there are a few Raytheon RC4739s on eBay for big$.

Incidently, I just sold my IC100S to Mark Thwaite...who is Peter Murphy's guitarist. That guy can play.....

[Superfuzz]

Hey guys! I completely forgot about this post, since I spent a lot of time on recording with other gear..yeah the +/-15.7 volts are on the preamp rails, I haven't checked the voltages on the power amp rails...when I bought it 5 years ago, the seller said it was fully revisioned at MAJ electronics (the official english H|H repair center) so I suppesed the big filtering caps were good.. Now I still have to re-open it, but I recieved a bag full of electrolytics for the whole circuit.. they looked worse compared to the big ones..then I got also sockets and opamps to replace originals 741s, yeah the 4739s are too rare to replace, maybe should I make a conversion socket??

Another thing, this head has a big hiss from first time I bought it..is that normal?

[Roly]

741s, yeah the 4739s ...
, this head has a big hiss

Well bowl me over gently - who'dve thunk it?  Good ol' boys like that a hissin'?

The 741, for example, is exactly what it says it is, an operational-amplifier.  Not some fancy "audio" op-amp with low noise and distortion, and the bandwidth that the girls go wild for; no this is more your hard hat and sweaty bum crack end of the working class op-amp pecking order.  And the other one is a quad 741.

"Normal"?  It was normal then, but it ain't now.

When I referb'ed a 70's Jands 24-channel mixing desk with modern LM833's (3 or 4 per channel) instead of the old crud, the desk was utterly transformed - literally never worked better.

If "transformed" is what you want, then change the chips (keeping the old ones of course).

If it was built using such primitive op-amps then I'd be giving the signal path electros (etc) a close look too.