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Author Topic: Performer 1000 help  (Read 5093 times)

phatt

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Performer 1000 help
« on: December 04, 2012, 07:52:14 AM »
My mate's Performer 1000 is back. ::)
This Amp has way too much bass as well as harsh treble.
His guitar is a stock 80's strat and he is chasing a classic blues/rock tone.

OK I've tweaked the preamp but I'm still not happy (and neither is the owner).

I feel that I may have more success working from the other end but as the power stage is not straight forward I'm a little reluctant to start poking a stick at what I do not fully understand.

Anyways the detail and some Q's;
What I'm trying to get my head around is the bass roll off point for the power stage as I feel
that is going way too deep and may need some tweaks but it's kinda confusing.
This power stage obviously has fancy FB via R117 and C51 while the normal FB around U7 is via
R94 680k.
Obviously R92 and C50 will also effect the roll off, then there is R93 and C52.
As well R95 27k looks really wacky and it also connects to the output which I assume is also a form of FB.

I'm open to any suggestions,, hopefully I'll learn something lol.   

I know it's basically an opamp with a booster hung off the end but these suckers can go poof
faster than Roly can type idiot so I was wondering if the excess bass could be rolled off
without danger of a meltdown.

I'm starting to think that I should have left the preamp as it was and focused on the other
end.
A recent comment from J M Fahey prompted me to swap a few speakers but I feel after some testing it's not going to fix what maybe a deeper design issue.
PDF attch.
Cheers, Phil.

Enzo

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Re: Performer 1000 help
« Reply #1 on: December 04, 2012, 02:41:21 PM »
SO does that mean you DID try a number of speakers and cabs?

I really doubt the power amp is your tone issue, but I suppose one can never rule out anything.  Unlike a tube amp, we don;t overdrive SS power amps as a rule, this amp should be strong, loud, and more or less flat.   If your PA syste was all bassy and harh of treble, you probably wouldn;t attack thye problem with power amp swaps.   Plug a full range signal, like a CD player, into the FX return.  How's that sound?   For that matter, you can plug the guitar into that jack and see how that sounds.  You are bypassing the preamp.

If you want to roll off the bottom, do it in the preamp, this power amp should have response way past guitar on both ends.

Get your feedbacks straight.  R94 sets the gain of U7.  That is the gain setting feedback of that one stage.   SS power amps are massively fed back, and without that they wouldn;t be stable.  R117 is just one feedback path.   Note live and direct from the output bus is R95 with more feedback.

But why have we decided the power amp is the problem?

Run a cord from the preamp out to some other amp and speaker, let's listen to the preamp.  Disconnect the speaker in the performer, so we don't have to hear it during this.  Do you like the way it sounds?  If it sounds great, then I guess the power amp is your troubloe, but I am betting you won't like the preamp sound.   And if the preamp doesn;t sound good, then the power amp will have a hard time making it do so.

Too bassy and harsh treble  How about it lacks mids and also turn it down.

You have three "channels" through this preamp.  DO they ALL suffer the same way?  How does the clean sound?  Does the mid shift on the clean help at all?

There is also that whacky 12AX7 clipper in there.  Try pulling that tube, any help on the two gain channels?

And did we verify both 15v rails are clean and more or less on the proper voltage?  And for that matter are both 40v rails clean too?

Roly

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Re: Performer 1000 help
« Reply #2 on: December 05, 2012, 08:30:34 AM »
Everything @Enzo said.

First eliminate the possibility of an actual fault somewhere with the tests he suggests.


R94 is local NFB to op-amp U7 and has little to do with setting the bottom end roll off.

The bottom end voltage gain rolloff of the entire power amplifier is determined by R95 27k and C52 0.33uF and f = 1/(2 Pi Xc C) gives -6dB at 18Hz.

The path via R117 is the current gain feedback path and it has time constant R117+C51.

Both paths share another time constant, a shunt, in R92+C50.

But the simplest way to reduce the amount of bass getting to the power stage would be to reduce the input capacitor C48 2.2uF, if that is really what needs to be done(?).
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

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Re: Performer 1000 help
« Reply #3 on: December 05, 2012, 01:45:07 PM »
Quote
and he is chasing a classic blues/rock tone.
Well, that ain't easy !!!
I mean, if the amp is broke, fine, it can be restored to as-new spec, but making a regular, mid priced standard SS amp do what usually means buying (or building) some 50 years old design still built around 40's technology tubes, is nothing short of a miracle.
And many *tube* amps can't give you that sound either.
I'd repair the amp as-new and experiment with pedals, I think it's the most practical approach.
Many say thet the Marshall Bluesbreaker pedal makes a very convincing imitation of an overdriven late 60's JTM45 ; I'd start experimenting with that.
As of SRV tone and such , the road is not easy.
The Tube Screamer is a part, but on its own, far from it, it stills rounds off by overdriving some tube Fender amp later in the audio path. 
That said, our own Phatt has gotten incredibly good sounds by overdriving a small tube amp into a passive load, then further EQing that signal and amplifying it with, of all amps, a Laney SS *keyboard* amp, so definitely it can be done.
Or experiment with one of KMG's incredible preamps, and inject it straight into the Performer Power Amp, fully bypassing its internal preamp.
Unfortunately your friend wants the hardest to get sound :( .
PS: not even the "Tube Fender in a box" Roland/Boss pedal does it, if not plugged into a tube amp.
So try one of SSGuitar's own solutions suggested above :)

phatt

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Re: Performer 1000 help
« Reply #4 on: December 08, 2012, 04:03:22 AM »
Wow, 3 of the best advisers around, Thanks heaps. :tu:

@ Enzo,
          Yep good point about running the preamp out into another amp. ( I completely missed that one.)
I think I've looked at this for far too many hours and I'm getting lost in my own head space.
 :duh

I've run through at least 4 speakers and nothing works right,, except the rather dark *NoName* speaker which is just magic if chasing the older blues rock sound.
Sadly no names, no numbers,, ziltch.
Just a big fat sound that is balanced for rock sound. My guess is it produces a lot of energy around the 200hZ area, probably as close to those greenback drivers which from my understanding hit a brick wall at around 3~4khZ.
That driver (whatever it is) is the only improvement worth a mention but I can't sell him my best speaker. xP

I did wonder about removing the Valve,, heck the red and yellow channel signal is already slammed with diode limiting anyway (via CR6,7,8,9)
I notice the DC Offset (if that is the right term?) on the Valve is switched to different levels for Red and Yellow selection. via Select 1 and 3.

No, the mid shift is just a useless annoying switch. Either way it misses something.
The only knob worth turning is the body when on Yellow drive channel.
Also works on Red but by then the gain is too much and the dreaded diode fizz is made even worse.

I doubt there is anything wrong with the Amp as all voltages read as per schematic.
The whole Amp is just plain wrong, Made for the kids with tin ears me thinks.  ::)

The Amp is back with the owner but I'll likely hear from Him soon so I'll run some more testing and see how it goes.

I've gigged with this chap many times and He mainly used the Power Amp part to drive my (not so famous) Anywatt setup, that being a small valve rig soaked into a line out > passing through a graphic EQ and then sent to the Performer efx return. The EFX Mix knob was then used as master volume control.  Even then it still lacked something.

Now he plays in a very small venue and He does not want to lug around the extra complexity so He is stuck between a rock and hard place.
I feel the circuit has potential it's just a matter of finding the right part to tweak or the right combinations of tweaks and speakers.

@ Roly,
Durh! I completely missed C48 2u2. I'll certainly find that sucker and try a smaller value.

Ok you say the Roll off point is about 18hZ,,, WTF? Holy crap man surely that is way too low for guitar and no wonder this thing has trouble with the bottom end.

OK I know many roads may lead to the same basic outcome but here is what I've come to understand.
I don't know if it will hold water for You but some (ok many) simulations revealed to me that a lot of those famous Valve rigs had massive bottom end in the first stages but big cuts (below ~100hZ) at the output. There is also the roll off effect of low frequency content on almost all stages as well, via delicate selection of cap coupling to name one.

But it seems to me that a lot of SS design is the exact opposite. (Headscratch)

Some might say the end result is the same (give or take a diode fizz or a speaker flab) but I do wonder if this is worthy of investigation.

In a recent rebuild of a Jade Quattro 4 input mixer amp (Long story) which was to now drive my Guitar preamp as well as my old JV 80 keyboard and I found that just a little extra low cut before the power stage allowed a much bigger keyboard output before the signal flubbed out on lower notes. As I'm sure you know, Digital keyboards have huge bass on some patches which at bedroom level might sound rich and big but it all goes belly up at gig levels).

Having experimented with this power stage roll of trick more than once I'm wondering if the same idea might work with the Performer. One value change in the right place certainly beats messing with each preamp stage.  :tu:

@ Jaun,
          Yes yes,, :lmao: I know I've made a rod for my own back as these guys hear my setup and they ask How do you do that? Expecting and hoping for a one line answer, with a brand name heading to make life easy. yeah right!  $%^&&
I reply by saying if you have got 30 years spare I'll explain it all. :o
And My knowledge is only the tip of the iceberg compared to some of the amazing stuff I read from you blokes. :dbtu:
My really big fear is the relay setup, if I blow that up I may not have the brains to fix it. :-[
I hate relays, partly because I don't fully understand them and also because more often than not I end up trying to fix Amps where the Signal works fine but the relay has farted out. :grr
My latest floor preamp is all mechanical switches and although there are issues with those cheap foot switches at least It's a simple fix job when they break.
Unlike most fancy pants electronic switching setups mechanical foot switches often give a hint that they are starting to fail. ;)

The more I've fiddled with Amplifier stuff the more I've come to understand that bandwidth and tone shaping are key to success of any sound one is trying to achieve.
To add to the complexity measuring/plotting a shape at one point in the signal path my not give a true representation of the final sonic signature.

The Performer has the mandatory high pass filter right at the input, (common in a lot of fender gear) which drops sharp just below 100hZ. (30 dB drop from 100hz down to 10hZ on my sim)
 
Sure Ok a good start but this tone shaping thing is cumulative (as noted above) and that 30dB drop at the input may become redundant at the output without further bass cut along the way through.
( please fill me in if I'm completely off the rails with this thought :duh)


The Laney Amp sounds effectively flat but the power Amp is not capable of extremely low freq.
Yet with the right speaker the bottom end is still big and round. (even without my preamps in front)

This point was driven home to me while tweaking that Jade Amp I mentioned above.

Of course I could have gone back and changed the 4 tone control circuits at the preamps but just one Cap swap at the poweramp input and bingo. :tu:
Or I could waste a lot of money buying speakers. :grr

I'd love to have a crack at some of KMG's ideas but I've come this far and had reasonable results with basically diodes and tone tweaks.
The other point; If His ideas where using real easy off the shelf components then heck I'd jump on it.
Truth is,,, AX7's and diodes are *everywhere* and there is plenty of advice for those type of circuits.

Re the bandwidth issue;
I noted a while back after acquiring a very good transistor radio I could once again listen to AM radio broadcasting. It struck me that the AM sound was much more pleasing above my work bench.
FM radio has a much wider bandwidth. Hum,, same songs but they sound sweeter on AM with less bandwidth. (Signal was driving the same speakers)

A long time back I saw a documentary on Pipe Organs.
They lined up 20 students from some Uni and blind folded them all and asked them to identify the Real Pipe Organ from the digital reproduction.

13 out of 20 got it wrong.

Long before they gave the answer, I instantly stated in front of my wife which sound was real.
She asked how did you Know so fast?
I sad that one was dead simple,,, the digital reproduction had way too much hi freq content.

So call me a bragget but it shows my ears are reasonable at picking up the finer points of tone. 8|

Thanks to All of you, it has helped to reset my train of thought.
I'll update this when I've had time to revisit the amp.
Phil.

J M Fahey

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Re: Performer 1000 help
« Reply #5 on: December 08, 2012, 08:20:00 AM »
Cool.
If you have the time, slap together a simple "Twin" type preamp, such as 1 channel of Alembic F2-B

There even is a PCB layout if you wish, although it's easily built PTP or on eyelet board.
http://www.lorcan.me/projects/tube-bass-preamp/
And then plug it straight into the Fender power amp, fully bypassing that preamp.
Only "mod" I'd suggest is wire two series back to back 6 to 10V Zeners across the output jack; this preamp can and will kill SS stuff, it can supply around 200V PP (70 V RMS) if driven hard.
Even used "clean", it will add some "tube taste" .
You can even add 2 clipping LEDs and a 100K to 250K Master volume at the output, it sounds reasonably good, I have already tried this and it works.
You may fit everything into a compact size cabinet which lives on top of the Performer, easy to carry in a gig bag.
« Last Edit: December 08, 2012, 08:21:37 AM by J M Fahey »

phatt

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Re: Performer 1000 help
« Reply #6 on: December 10, 2012, 08:10:11 AM »
Thanks Jaun,
                  Yes my new preamp has a triode inside (Think the clean channel of the Mesa Vtwin idea) but He has only the performer and a couple of pedals.
Anyway,, played with him on Sunday Arvo and having had time to get used to the dials (which now work differently because of mods,, He is now quite happy with the sound.
So if the player is happy then all is well.  :tu:
Phil.