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 veryhotthread  Author  Topic: SLO Too Bright? Fizzy? PROBLEM SOLVED!!  (Read 10672 times)
MHProd
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xx SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Thread started on: May 5th, 2013, 5:47pm »

For a few months now, I've been thinking about selling my SLO. The amp was built in '93 and has the DeYoung transformers.

I've owned it for a few years but never really played it since the amp has so much high end. Then a few weeks ago, I went to a friend's place to jam. He also owns a SLO, circa '92.

His amp was plugged in one of those older Mesa vertical 2x12 with the open back on the top speaker. Speakers were a Vintage 30 at the bottom and an Alnico Blue at the top. I couldn't believe my ears when he played. Smooth, silky top end! Not a hint of harshness. I really couldn't believe it, especially with these particular speakers. My friend ran the amp with 2 tubes (KT66s) only to tame the output a bit.

At this point, I had tried several varieties of tubes to get rid of the problem. I even tried a quad of NOS grey glass KT66s which helped a bit but the amp still sounded shrill. Tried a bunch of different speakers too.

I promptly borrowed my friend's amp and brought it home to compare. The experiment went as expected: his amp sounded warm and full, mine had a very thin OD, fizzy and harsh. Tested the bias in his amp and mine was almost identical (around 70%). I tried to swap the preamp and power tubes from his amp to mine. Nope, no magic tube, my amp still sounded as usual.

I took a closer look at the guts of his amp when I noticed something around the power tubes that my amp didn't have. It looked like a resistor and a cap in series attached to the tube sockets. Then it dawned on me... CONJUNCTIVE FILTER !!! Apparently, the guy who sold the SLO to my friend is also a tech and did the mod before he sold it to him. I built several amps in the past and used a conjunctive filter on a few builds. Don't know why I didn't think of it before...

DISCLAIMER: This mod isn't approved or affiliated in any way with Soldano and if you decide to experiment with the following, you are doing so at your own risk!! Use google to find more technical information on what a conjunctive filter is.

I dug out a 2k2 5W resistor and a 4700pF/1KV cap and soldered them in series across the OT primary (Pin 3 of the power tubes). These were the values used in my friends amp (except the R was 10W).

Tried my amp: Tada !! All the top end harshness is GONE !! Even with the volume between 2 and 3, the amp sounds great on both channels. That's right, the lead channel sounds fat and thick, even at lower volume. I am rediscovering the Soldano sound again and can't stop playing with it.

Note that the values of the R and Cap are not set in stone. As a rule of thumb, the R value can be determined by multiplying the OT primary impedance by 1.3 (this is from Dr Z)
. I believe the SLO OT has a 2K2 primary imedance which would give a R of about 3K. Dropping the value a bit will shave some more high end. For the cap, the common values are between 2200pF and 4700pF, the bigger the cap, the more high end you shave off (frequency shift). Anyway, since then, I replaced the R with a 10W to be safe. Cap shouldn't be rated below 1000V.

I can't believe how much money I spent on tubes and different speakers to make this amp sound good (and failed) when all I needed was $2 worth of parts and a soldering iron... Oh well.


UPDATE!! (May 23rd, 2013)

So I just spent the last 4 days trying the SLO with as many speakers as I could gather.
My 'usual' set up is a mid 60's Fender 2x12 cab loaded with Tone Tubby Ceramic 40W speakers. I really like this cab as it has a very rich low end, especially for a 2x12, and the Tubbies sound great in this one. After calculating a few things, I changed the conjunctive filter values to a 10W 680Ohms R + a .01uF 2KV cap. This tamed the highs a bit more than the previous values, but nothing crazy. I'm running the amp with 2 Shuguang KT66s.

The test included the following speakers:
V30s, late 60's Greenbacks with 003 cone, EVM12L, Tone Tubby Ceramic 40W, Tone Tubby Alnico 40W, mid 60's Silver Alnicos with 1777 cone.

Amp settings ( +/- 2 depending on speaker):
Normal Pre (crunch): 6
OD Pre: 4
Bass: 6
Mids: 4
Treble: 5
Normal and OD volumes at 3 and then 6
Presence: 5

Guitars:
'64 SG Standard
'61 Strat slab board

First I tried the amp without the conjunctive filter on each set of speakers:
-V30s: Barely usable... Just bright and stiff. Had an ok-ish sound with the mids on 2 and treble on 1. Turning the volume up helped a bit but not much.
-Greenbacks: smoother than the V30s but really grainy and still super bright, bottom end rather thin.
-EVM12L: An OK sound when the master is on 6 or higher. The amps sounds ok, but nothing inspiring. I've had these for a number of years but I don't find them to sound any good unless played ridiculously loud.
-TT Ceramic: Interesting in this test. The tubbys are voiced very differently than all other speakers. Some of the spikey frequencies are tamed, yet one of them is still there and very unpleasant.
-TT Alnico (open back Vox 2x12): Similar to the ceramic, the open back cab changes the response though, but nothing that I would consider great.
-Silver Alnicos: I didn't bother trying them since they require a special implementation (see part 2 of the test).

The TT ceramic and EVs (when pushed) sounded 'the best' but I really had to turn the knobs, not to get a sound I liked but mostly to manage the perceived brightness of the amp.

Test with 680Ohms/.01uF filter:
-V30s: Virtually night and day. It took me so off guard I thought I installed Tubbys in the cab... There's still some hype in the mids but nothing crazy or unpleasant. Very usable. On the OD channel with the mids turned down, I get a really nice heavy crunch. Has a bit of a modern-ish vibe to it. Would be a great set up for heavier tones.
-Greenbacks: Great rock vibe. The SLO here brings about classic tones in spades with something extra. It was hard to put the guitar down.
-EV12ML: Very solid tone, but lifeless when the master is on 3. Very clean and controlled sounding. Not boring but I had more fun with the greenbacks. With the mids scooped, I get a cool heavy tone, different from the V30s.
-TT Ceramic: Reminiscent of the greenbacks on some aspects (top end) but the mids have a very different tone. Rounder? Hard to put the guitar down. Sounded great on the Strat neck pup.
-TT Alnico (open back 2x12): Very very cool tone. The OD channel sounded a little too much like Santana with this set up but the Crunch of the normal channel was very interesting.
-Silver Alnicos: These guys are rated at 15W each. Changed the tubes for a pair of TungSol 6V6 which can take 475V on the plates. I used a variac on the SLO to get the B+ at 450V. Lost quite a bit of power and used a Z Airbrake attenuator (1 notch, completely transparent) to keep it safe for my speakers. All I can say is WOW. Amazing blues/rock combo. Get this: Normal Pre on 7, Bass on 6, Mids on 9, Treble on 3, no Presence and WITH the bright switch engaged (!). I played with these settings for 2 hours straight and found a couple of really cool riffs.

And THIS my friends, is what it's all about! This is what gets me excited. When it's so hard to put the guitar down and suddenly things start to happen completely out of the blue.

Now back to the conjunctive filter:
Is there more to gain by changing speaker cabinets, tubes and/or bias than this mod? Not sure...

Prior to this mod, I tried tubes, speakers and bias changes and never got this quality of tone out of the amp, let alone the flexibility of using very different types of speakers and getting great results out of it.

So, where do the fizzies come from then? I'm relieved it doesn't come from my hearing. There are many many threads on the net addressing this issue with the SLO and even other Soldano amps... and Boogies, and some Marshalls, and Fenders... The cause? I'd vote for crossover distortion. Some amps do it, some amps don't and it's very difficult to figure out what causes it, especially when you have 2 of the same amps in front of you and one exhibits the problem while the other doesn't. One cure involves puting diodes accross the grid leaks resistors. I didn't try it on the SLO because of the PCB. Crossover distortion sounds bad in general but it sounds REALLY bad in a bright sounding amp. The conjunctive filter kills 2 birds with 1 stone: it tames the impedance rise in the OT which takes away the harshness of the top end and in the meantime, I believe it masks the crossover distortion in the amp. I could be wrong though...

At the end of the day, I don't really care. The amp sounds awesome and the mod is cheap and completely reversible.









« Last Edit: Jan 3rd, 2015, 10:41pm by MHProd » User IP Logged

1999Hotrod50
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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #1 on: May 5th, 2013, 7:01pm »

any chance you can post some good detailed pics of the mod? or email them to me.....fadedbluejeans05@yahoo.com

Thank you,
Tom
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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #2 on: May 5th, 2013, 8:42pm »

on May 5th, 2013, 7:01pm, 1999Hotrod50 wrote:
any chance you can post some good detailed pics of the mod? or email them to me.....fadedbluejeans05@yahoo.com

Thank you,
Tom


http://www.guitarplayer.com/article/smooth-your-sonic-ride/5505

This is essentially what I did except I simplified it by just adding 1 R and 1 Cap in series. So on my SLO:

V6 Pin3 (Brown wire primary) > R > C > V8 Pin3 (Black wire primary).
« Last Edit: May 5th, 2013, 8:43pm by MHProd » User IP Logged

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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #3 on: May 6th, 2013, 03:19am »

That's a darn interesting read, thanks !

Giga
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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #4 on: May 6th, 2013, 11:47am »

Interesting read, but honestly, in all my years of playing soldano amps, I have never found them to be overly bright, fizzy, too much high end, etc. They have always been pleasing to the ears and fit nicely into the band mix, but everyone has their own idea of tone and its always fun to read about other folks experiences and ideas. Thanks!!!
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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #5 on: May 6th, 2013, 7:58pm »

The article states "low quality transformers" can cause ringing causing high frequency shrill and fizziness. What am I missing here .... I thought the SLO has high quality proprietary DeYoung transformers ??


on May 5th, 2013, 8:42pm, MHProd wrote:
http://www.guitarplayer.com/article/smooth-your-sonic-ride/5505

This is essentially what I did except I simplified it by just adding 1 R and 1 Cap in series. So on my SLO:

V6 Pin3 (Brown wire primary) > R > C > V8 Pin3 (Black wire primary).
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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #6 on: May 6th, 2013, 10:24pm »

Yes, however, I don't think the OT is at fault here. It's either the design of the amp, or just some HF oscillation that is tough to get rid off.

The conjunctive filter is just a trick to get rid of HF bad behavior and can also be used as a tool to shape the sound. The good old Watkins amps had this and I believe several Dr Z amps have this done at the factory. A Zobel filter could do the same thing. It doesn't change the voicing of the amp, it just seems to solve the most common issue people have with the SLO: too bright, bee's nest kind of OD.

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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #7 on: May 7th, 2013, 12:11am »

Also, I find it helps with getting rid of crossover distortion which sounds very unpleasant in the higher frequencies.
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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #8 on: May 9th, 2013, 12:02am »

Master on 7-8, preamp on 5, presence on 3, treble on 2, mid on 3, bass on 4-5 is pretty fizz free and sweet sounding to my ears. There is a natural cranked sound there that no other amp can reproduce effectively IMHO. Albeit I admit it can be somewhat unforgiving and every little nuance is audible.
« Last Edit: May 9th, 2013, 12:15am by JRW » User IP Logged

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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #9 on: May 9th, 2013, 04:45am »

JRW,

Which setting are you referring to? Clean, crunch or overdrive?
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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #10 on: May 9th, 2013, 6:56pm »

on May 9th, 2013, 12:02am, JRW wrote:
Master on 7-8, preamp on 5, presence on 3, treble on 2, mid on 3, bass on 4-5 is pretty fizz free and sweet sounding to my ears. There is a natural cranked sound there that no other amp can reproduce effectively IMHO. Albeit I admit it can be somewhat unforgiving and every little nuance is audible.


Agreed, yet it isn't unpleasant to have the Master on 3 with the Treble on 4 and Mids on 5 or 6 and not having a bee's nest polluting the SLO's tone.
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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #11 on: May 9th, 2013, 10:27pm »

Sorry guys, I've been dealing with imbeciles all day long and I don't want to sound callous at all I promise, but I'm claiming BS on this.

A "design fault"? You have to be kidding me. The SLO is ICONIC in every way possible.

I'm glad this works for you MHProd, really I am, but this is no different than the way some guys felt in the 60's and 70's by installing PPIMV's on 4 input Marshall's, or "black facing" silver Fenders. First thing I did with my 69' Plexi was have Mike Soldano put it back to COMPLETE originality. It is perfect again.

I have a 3rd SLO shipping to me next week. It is a 2 year project, one off amp, built just like they were in 87', except I'm going with DC heaters, IEC power cord, and effects loop bypass switch.

Glad you found what you wanted.

I'm gonna run this by Mike and see what his response is.

LB
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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #12 on: May 10th, 2013, 01:20am »

on May 9th, 2013, 04:45am, Wolfgang von Bockenheim wrote:
JRW,

Which setting are you referring to? Clean, crunch or overdrive?


Wolfgang - Good point -- I was talking about the overdrive channel. I do adjust things a bit from time to time though, but that seems to be a sweet spot for my setup.

MHProd - While I remain open-minded and interested in individual tastes, the topic you are addressing, and other ideas for things that may sound better at lower volumes, I agree with JLB. At the end of the day the SLO is a 100 watt tube amp and to me it sounds best (and smoother) to me once the OPT and OP tubes kick in. Much like other great high wattage tubes amps, including those without high gain preamps IMO. I personally don't find it too buzzy or overly bright myself but I do prefer 6L6's over the 5881's and I also think a certain combo of NOS and high quality ECC83 preamp tubes do make a slight difference in warming up the tone a bit.

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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #13 on: May 10th, 2013, 1:09pm »

on May 9th, 2013, 10:27pm, JLB wrote:
Sorry guys, I've been dealing with imbeciles all day long and I don't want to sound callous at all I promise, but I'm claiming BS on this.

A "design fault"? You have to be kidding me. The SLO is ICONIC in every way possible.

I'm glad this works for you MHProd, really I am, but this is no different than the way some guys felt in the 60's and 70's by installing PPIMV's on 4 input Marshall's, or "black facing" silver Fenders. First thing I did with my 69' Plexi was have Mike Soldano put it back to COMPLETE originality. It is perfect again.

I have a 3rd SLO shipping to me next week. It is a 2 year project, one off amp, built just like they were in 87', except I'm going with DC heaters, IEC power cord, and effects loop bypass switch.

Glad you found what you wanted.

I'm gonna run this by Mike and see what his response is.

LB
BCM


Hell yes!!!! I agree!!!!!
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xx Re: SLO Too Bright? Fizzy? PROBLEM SOLVED!!
« Reply #14 on: May 10th, 2013, 3:43pm »

To JLB and JRW.

I did not say the SLO had a design fault. It IS designed to be a bright amp. Now the fizzy brightness problem I was having with my amp is similar, in sound, to HF oscillation/crossover distortion and I don't think Mike designed an amp around that. My amp is still bright (Treble doesn't really get past 6) but it doesn't have the problematic frequency spike any more.

Yes, the SLO comes alive with the master turned up (sweet spot for me is just around 7) but I still prefer it with the conjunctive filter. There is a number of threads online of people finding their SLO too bright, it's not just me. The usual route is changing tubes and/or speakers. The conjunctive filter, IMO, yields great results for a lot less cash.

I'm just really happy with the way it sounds right now. The OD channel is sick and I can't think of another amp that would come close to doing what it does. The SLO, IMO, is one of the greatest tone machine out there. It has a unique sound signature, it's not sterile like other esoteric amps that sells for 10x more and I don't think I'll ever separate from it!
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