It is currently Wed Oct 01, 2014 5:13 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 54 posts ]  Go to page 1, 2, 3, 4  Next
Author Message
 Post subject: Supersonic 112 mods
PostPosted: Tue Sep 11, 2012 1:56 pm 
Offline
Hobbyist
Hobbyist

Joined: Tue Sep 11, 2012 1:01 pm
Posts: 23
Hi

I've been lurking here for awhile, read a lot of interesting stuff, found lots of great advice, thank you all.

So I bought a used SS112, it's one of the earlier models from 2006 I believe, and obviously ran across a certain amount of known issues. Although I'm quite aware that many issues like "hiss" are very relative (I mean, yes this IS a stage amp, not a bedroom rehearsal amp, it's GREAT when played LOUD), I still would like to get some of them solved or worked around, because it's simply a great amp, I love the tone I get out it, there are many possibilities when we take the time to work on it.

Most of my issues are known, I read many threads but unfortunately I couldn't come across one SOLVED! post. Some guys here are real tube amp gurus, give great advice, then the OP doesn't follow up with a "tried your advice, it worked!!" post.... so I decided to revive this topic before 1: plug in the soldering iron 2: shell out lots of euros for tube replacement.

My issues are:
1: yes, the amp is hissy overall. The reverb is hissier than the amp itself
2: I've got hum on the effects loop
3: the vintage channel is more hissy than the burn channel, and there's some more hum in the bassman mode

I checked the bias and set it to factory specs: 32mA. All tube are original Fender parts, I don't know if they've been changed, or how many hours they have.

The power amp section is NOT hissy at all, it's dead silent. I plugged in a Morley PVO volume pedal between the preamp out and the power amp in: great! no more hiss, totally silent. This allows to have vintage channel settings at 4 instead of 1, so the overall internal gain structure is somewhat optimized, and the PVO acts as a master volume. There's a drawback: there are OP-amps in the preamp out circuitry, and they distort. That's why I said "somewhat" optimized: there's something wrong in the overall design, at least that's the impression I have. But well, we can play at bedroom levels without having this hiss in the background, it's an improvement, and its show us nothing is wrong with the power amp.

I dowloaded the original SS 112 combo schematics, and the SS60 schematics. I compared and annotated the schema, there are some mods that have been made in october 2009, someone posted somewhere that he had applied those mods, and that it gave an overall improvement like better balance between vibrolux and bassman, better low end, better reverb balance. From what I know about electronics (some basic stuff) this seems reasonable, but it doesn't solve my issues. I read that some have great sounding quiet amps, and some have noisy ones, but noone really states what his " acceptable noise floor" is, and this is the internetz, not a scientific lab so well....
I mean, the hiss when I'm on stage if perfectly normal and inaudible, but quite annoying in the rehearsal room when I'm not actually playing, and certainly much louder than any other tube amp I've owned. With all volumes down, the SS112 is very much hissier than my old MusicMan HD130 on hi-power mode (that's a full 130 watts) and volumes at stage level.

I tried all sorts of tests. I noted a drop in the hiss when I reseated some tubes. This needs exploring, maybe. But I really think, that there is a problem with the gain structure in this amp around V5b. I have the impression that there is an unneccessary gain boost here, just after a severe attenuation from R75. The signal is lowered a lot, then boosted again, thus raising the noise floor. Maybe I'm wrong, I'm not an electronics guy, just some basic knowledge and willing to learn....

So before getting out the soldering iron and apply the SS112-to-SS60 transform I'd like to discuss this some more. In fact, I think I need to solve the hiss and gain issues first, and tackle the tonestack mods only afterwards. After all, I quite like the tone as it is now, so that's not a priority.

Did anyone ever think of adding a "real" global master volume? Could we change V5 and put a lower gain 12AT7 (or a 5751) in there (we'd have some loss at the insert return, but that's not much of an issue because we can compensate with the pot), then either leave it that way so we can crank it up at the input stages a bit more, or perhaps change R75's value as well? Or anything like this?

Any thoughts?
Thanks many
Dirk


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Tue Sep 11, 2012 10:01 pm 
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8614
Location: Centreville, Virginia
I assume this is the schematic of the original 112 combo that you are looking at?

http://support.fender.com/schematics/gu ... ematic.pdf

First of all, given that you know nothing about the age or condition of the tubes, I would suggest changing them for a new set. Unless you want to spend the money on NOS tubes, I would suggest a set of JJs from Eurotubes.

https://ssl.eurotubes.com/cart/index.ph ... ory_id=153

Specifically these:

"Fender Supersonic Combo Standard Retube
Price: $124.00
Description: If you simply want to improve the sound of your Supersonic Combo amp and maintain the power and the amount of distortion in the Burn channel then this kit will do it. It uses a matched pair of the JJ 6L6GC's for power and six standard ECC83S's to replace the 12AX7's along with one standard gold pin ECC81 and a balanced ECC81 for the phase inverter. More warmth and a sweeter sound!"

Next, the factory bias is way too cold. 32 mA cathode current at a plate voltage of about 480 VDC will give you an idle bias of only about 50% maximum plate dissipation. Optimum bias is in the range of 50% to 70% maximum plate dissipation and a good set of 6L6GCs lot to run hotter than stock.

There are no op amps in the signal path. The op amps in the schematic are used only for switching purposes and as buffers in the preamp out circuit. If you don't use the preamp out, you don't go through the buffers. Otherwise the signal goes directly from V5-B to the phase invertor, V6, via connector P303-6 to P203-6. I would not recommend using a volume pedal in that circuit.

R75 provides isolation between the input and output of the reverb circuit. Without analyzing the circuit further, I cannot say how R75 is affecting the input level into V5-B. However, I should note that the 65 Twin Reverb Reissue also uses a 3.3M ohm resistor for the same function in teh reverb circuit.

I see no need to replace V5 with a lower gain tube. In fact, doing so would mess up the effects loop as V5-A is used as the gain stage for the effects loop return path.

You said: "Maybe I'm wrong, I'm not an electronics guy, just some basic knowledge and willing to learn...." Based on that statement and the amp knowledge you showed in your post, I don't think you are ready to tackle more than just basic amp maintenance (tube replacement, bias adjustment) at this time. You need to put some fresh tubes in the amp, bias it properly and learn more about how the amp works before making significant mods like you are considering.

_________________
Bill

Jimi Hendrix, Eric Clapton, BB King: The Ultimate Guitar Trio

Image


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Wed Sep 12, 2012 12:20 am 
Offline
Hobbyist
Hobbyist

Joined: Tue Sep 11, 2012 1:01 pm
Posts: 23
Hi

Thank you, appreciate your advice, you're probably right. (Although I believe I am able to do these electronic mods, I have done quite some soldering/repairing and do have the basics neccessary including a thermo-regulated soldering station and I know how to work safely.) Talking about op-amps in the circuit, I just noted, like you, that these are in the pre-amp out-stage. I put a volume pedal in there for testing purposes first, it allowed me to check if I could get rid of the hiss altogether, which was true. So if even though the bias wouldn't be optimized (it was even colder before I adjusted it: 30mA, BTW what would you suggest then? 34mA? up to 37mA?)

Of course I wouldn't want to run the amp this way, but I'd appreciate to get the same sort of noise levels, and also, the vintage channel sounds quite good at 7, but that's way too loud, obviously! When I set the vintage channel volume at anything higher than 3-4, with my strat's Texas Specials, (what I believe) the preamp out op-amps distort. This is very audible, harsh distortion: I ran the output through a DI to my mixing desk, to make sure it was coming from the pre-amp outs, not from the volume pedal I inserted. This distortion doesn't appear at all in the "normal" circuit: the power amp section, pi included doesn't exhibit this behaviour.

I'll take a look at the Eurotubes site, they are in the USA, I'm in France. Local prices are way too high (around 20€/25$ per 12xx7!) so I'll look at some internet stores. 124$ sounds very cheap, are these tubes really OK compared to the stock GrooveTubes-Fender branded Sovteks?

Dirk


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Wed Sep 12, 2012 6:01 am 
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8614
Location: Centreville, Virginia
Dirk Offringa wrote:
Thank you, appreciate your advice, you're probably right. (Although I believe I am able to do these electronic mods, I have done quite some soldering/repairing and do have the basics neccessary including a thermo-regulated soldering station and I know how to work safely.) Talking about op-amps in the circuit, I just noted, like you, that these are in the pre-amp out-stage. I put a volume pedal in there for testing purposes first, it allowed me to check if I could get rid of the hiss altogether, which was true. So if even though the bias wouldn't be optimized (it was even colder before I adjusted it: 30mA, BTW what would you suggest then? 34mA? up to 37mA?)


Working on a modern printed circuit board amp requires more than just basic soldering skills. Just taking the amp apart to access the circuit board and components can be complex and time consuming. I spent several hours yesterday replacing THREE resistors in my Blues Deluxe Reissue in order to better bias the amp to my desires. I had to remove one circuit board to do so. I don't know the extent of the mods that you mentioned in your previous post, but I can imagine that they are more complex then that.

According to the owner's manual

http://support.fender.com/manuals/guita ... manual.pdf

the pre out/power amp in is to be used for feeding a DI box or PA system (pre out) or using another preamp to drive the 112's power amp (power in). You should not be setting the volume controls so high as to induce distortion in the op amps. You should be using he volume pedal in the effects loop as it is tube buffered and designed to handle higher levels. Of course, there could be a problem with the op amp stages as they should be able to be driven at preamp levels without distortion.

As far as bias goes, you need to measure BOTH cathode current AND plate voltage of the power tubes. To do so safely requires a bias probe and DVM. The cathode current and plate voltage are then multiplied together to get the idle power dissipation. That value should be between 50% and 70% of the tubes rated maximum plate dissipation, 30 watts in the case of a 6L6GC. You can adjust the bias within that range to where it sounds good to you. A colder bias will sound cleaner but somewhat sterile. A hotter bias will break up a little earlier but sound fuller and richer. I run my 5F6A Bassman clone right at 70% and my BDRI at about 67% of maximum plate dissipation.

Dirk Offringa wrote:
Of course I wouldn't want to run the amp this way, but I'd appreciate to get the same sort of noise levels, and also, the vintage channel sounds quite good at 7, but that's way too loud, obviously! When I set the vintage channel volume at anything higher than 3-4, with my strat's Texas Specials, (what I believe) the preamp out op-amps distort. This is very audible, harsh distortion: I ran the output through a DI to my mixing desk, to make sure it was coming from the pre-amp outs, not from the volume pedal I inserted. This distortion doesn't appear at all in the "normal" circuit: the power amp section, pi included doesn't exhibit this behaviour.


Like I said earlier, you should not be using a volume pedal in the pre out/power in loop. That is not what it was designed for. There may in fact be a problem in that loop that should be checked out.

Dirk Offringa wrote:
I'll take a look at the Eurotubes site, they are in the USA, I'm in France. Local prices are way too high (around 20€/25$ per 12xx7!) so I'll look at some internet stores. 124$ sounds very cheap, are these tubes really OK compared to the stock GrooveTubes-Fender branded Sovteks?


In my opinion, almost any tube is better than the Groove Tube/Sovteks that Fender installs stock in their amps. Others may disagree. I use JJs in all my tube amps and like the sound.

_________________
Bill

Jimi Hendrix, Eric Clapton, BB King: The Ultimate Guitar Trio

Image


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Wed Sep 12, 2012 7:25 am 
Offline
Hobbyist
Hobbyist

Joined: Tue Sep 11, 2012 1:01 pm
Posts: 23
Hi

Thank you for caring.

For clarity, let's assume I can take an amp apart, have the neccesary skills to do some mods on modern circuit boards, (and have read the operating manual.)

Of course we can use this amp with the clean channnel around 4, which is loud, indeed, but shouldn't overdrive the op-amps in the preamp output stage. And of course I can put a volume pedal in there if I'd want to: there's no risk of damage, no overheating, high voltages or whatever: it's supposed to be a line level output. It works perfectly as such, BTW, except for this distortion, which makes the whole pre-amp out close to useless, and I wouldn't use it to drive a PA. I needed to set a -40dB pad on the DI to prevent overloading the desk line input playing at normal levels (I'm a 55 year old audio professional, dividing my time 40/60 between a job a FOH engineer and my band I play guitar in, I have quite some experience...). My goal is not to use the pre-amp out/amp in as fx loop: as I pointed out, I was checking out stuff in an attempt to zoom in on the problem.

The real problem is the hiss I (and many others, from what I read) as well as that hum from both the effects loop and the reverb circuit.

I believe there's too much gain applied by V5b, so 1: the amp is LOUD 2: background hiss and hum from preamp stages is amplified to very audible levels 3: the op-amps can be overdriven too easily 4: the reverb hum an hiss is permanently amplified to audible levels as well.

I am looking for a solution to get this down, around 6dB would be fine, and believe it can be done by modifying the gain structure of the amp around V5b, even if this involves a change in the effects return buffer because of V5a. (For example, if a 12AX7 has an amplification factor of 100, with a gain of 40dB, then what if I put a 12AY7 in there, with an amplification factor of 45, which would result in 33dB of gain, that would be just fine)

Unless someone came up with another solution... or maybe it's the result of a component failure. (I don't believe this would be because of wrong BIAS). I swapped some tubes with V5 to no avail. Because of the price, and the place I live in (I don't have tube suppliers or amp gurus next door) I didn't try with new tubes (yet).


Dirk


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Wed Sep 12, 2012 11:22 am 
Offline
Hobbyist
Hobbyist

Joined: Tue Sep 11, 2012 1:01 pm
Posts: 23
Hi

I'd like to add, just for the record, for all those that like me are looking to use their (stage(!)) amp at bedroom(!) levels WITHOUT the hiss, that inserting a volume pedal between the pre-amp out and the power -amp in WILL get your hiss down while allowing you to up the volumes on the amp a bit (clear channel not beyond 4 but that's plenty).

I tried this extensively. So until I find a more permanent solution, you can always try this. The amp will be totally silent.

Dirk


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Wed Sep 12, 2012 1:53 pm 
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8614
Location: Centreville, Virginia
Good luck.

_________________
Bill

Jimi Hendrix, Eric Clapton, BB King: The Ultimate Guitar Trio

Image


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Wed Sep 12, 2012 2:11 pm 
Offline
Hobbyist
Hobbyist

Joined: Tue Sep 11, 2012 1:01 pm
Posts: 23
Thanks for your input.

Dirk


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Wed Sep 12, 2012 6:27 pm 
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Thu Feb 19, 2009 8:33 pm
Posts: 350
Location: Lake Panasoffkee, FL
Before diving in with a soldering iron , make sure all your tube pins and sockets are clean and seated. This makes a difference. I own the SS 60W. I am always rolling old stock tubes that I find in my journeys. Some tubes will hum until pins are cleaned. Most good clean ones are quiet. Hum from reverb can also be dirty plugs and sockets. Use contact cleaner. My amp with most tubes is quiet enough for recording.

_________________
Charlie P
Fend HSS Am DLX LSR S1 Strat 08
Fend MIM Telebot Deluxe 2011 Tronical Tuner
Fender SuperSonic 60 2010
Gibson Robot 08, Gib. Faded Ch LP 07
Gret. G5120 07, Peavey VK112 08


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Thu Sep 13, 2012 12:35 am 
Offline
Hobbyist
Hobbyist

Joined: Tue Sep 11, 2012 1:01 pm
Posts: 23
Hi,

Yes that's a good idea. Although the inside looks absolutely clean, like new, it might me that some pins have corroded somewhat.... I'll go out and get a can of contact cleaner today. BTW I did record with this amp, but I had to play it fairly loud (I enjoyed it.. great sound, great results, it is a good recording amp, very precise!). The problem is when I'm not playing. In a quiet evironment, like studios, or my rehearsal room where I work all day, you just can't leave the amp on, I'm continuously flipping the standby switch.

Dirk


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Thu Sep 13, 2012 1:47 am 
Offline
Hobbyist
Hobbyist

Joined: Tue Sep 11, 2012 1:01 pm
Posts: 23
I found another way to get the amp dead-silent: put a jumper between the fx-send output and the power-amp in, and a dummy jack in the fx-return to enable the fx-send output. The send-level full clockwise.

Perfect sound, no hiss at all, just the normal, faint hiss we get when dialing the channle volumes up to stage levels and even then we're talking about very faint levels . The only drawback is that we don't have the reverb with this routing.

So really, everything that's before the fx-send output is perfectly OK. And the power amp is OK too. Hiss and hum comes from the part I just eliminated. Basically, there's only one tube involved in that part: V5. And the reverb section.

EDIT: I've read here and there that although many people complain about the hiss and the hum, some people report their amp to be very quiet. (I'm talking about the earler SS112 here). So it might be that somewhere a critical component is out of specs, maybe a whole batch was. Or just wrongly spec'd. This can be R75. Before going wild on the circuitry, I'll try to find a low-noise metal film resistor (of the same specs) in my neighbourhood and replace R75 with that one (as well as R167).

2nd EDIT: I bough two ElectroHarmonix 12AX7 and a 12AT7. Replaced V5: 1 EH gave a loud hum, the other a light hum, both were worse than the old stock GT-Fender Sovtek, noise-wise. They had more gain (quite a lot more, really: the amp was significantly louder). In V10, there was more hum as well. I replaced V9, doesn't make much of a difference here. I tried a 12AT7 in V5, it went microphonic and gave a loud feedback squeal. Seems this is a no-go. So I put back the old tubes in. Didn't find a contact cleaner yet.

Dirk


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Thu Sep 13, 2012 3:23 pm 
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8614
Location: Centreville, Virginia
Do you have any understanding of the circuits you are altering or are you just shotgunning random changes?

_________________
Bill

Jimi Hendrix, Eric Clapton, BB King: The Ultimate Guitar Trio

Image


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Thu Sep 13, 2012 11:57 pm 
Offline
Hobbyist
Hobbyist

Joined: Tue Sep 11, 2012 1:01 pm
Posts: 23
Sorry, it seems I was on the wrong forum. I'll start a thread elsewhere.

Apologies for having disturbed.

Dirk

PS You don't know anything about me, my situation, why I'm doing this. We don't need to pass an exam before posting here, do we? We don't live the same lives, nor do we live in the same places. Elsewhere than where you live, life can be so different you can't even imagine. We don't necessarily follow the same roads to get to the same destination.

If you believe I need more information to get me there, and you believe you have that information, why don't you share it?


Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Fri Sep 14, 2012 1:32 am 
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8614
Location: Centreville, Virginia
Dirk Offringa wrote:
If you believe I need more information to get me there, and you believe you have that information, why don't you share it?


I tried. You chose to ignore it. You are convinced that there is a problem with V5, yet you have done nothing to convince me that there is. When you did your last little experiment of jumpering from the effects out to the power amp in, you claimed that proved that V5 was the problem. Really? Did you forget about the fact that you also removed V9 AND V10 from the signal path as well as every other component in the reverb circuit? Obviously not, since you concluded that V5 was the problem. Then you tried to swap tubes in V5, V9, and V10 and every one of them apparently physically/electrically failed or failed to do what you wanted them to do. You must have very bad luck to have gotten three brand new, yet bad tubes. But you are still convinced that V5 is the problem.

Let me ask you a few questions:

1. Have you replaced ALL of the tubes like was suggested? You bought the amp used. It is several years old, and you admitted that you had no idea what condition the tubes were in. Seems like that would be a good thing to do to me.
2. Did you try and at least clean the pins and sockets of each tube and reseat them as another poster suggested?
3. Did you bias the power tubes PROPERLY as I suggested? You would be amazed as to the difference in the sound of an amp that that little adjustment can make.
4. Have you measured the power supply voltages and the voltages at each of the tubes to make sure that there isn't a problem with very low or very high voltages that is affecting a tubes performance?
5. Have you used an oscilloscope to trace the signal through the amp to see what it is actually doing in each amp stage and where any gain problems might actually be, if indeed there are any problems?
6. Have you done ANYTHING to determine what the actual gain is through the part of the circuit that you are convinced in the problem?

Somehow I doubt you have done anything that has been suggested or thought through the amp circuits and how those circuits might affect the amps performance. No, you have a marked up schematic and a list of mods to make and you are convinced that V5 is the problem. So go ahead. Make all those mods. I would be very interested in how they all turn out and if you are able to turn your amp into the fire breathing but quiet amp you think it should be by doing those mods, I will gladly apologize.

Oh, and one other question. This forum is visited regularly by several people who know more about amps than you will ever know. In fact, they know more about them then I do. Have you stopped and asked yourself why after reading your thread (notice how many people have visited your thread compared to the number that have actually posted in it) none of those people have taken the time to try and help? Could it be because it is obvious that you have ignored everything that has been suggested to you and are convinced that V5 and only V5 is the problem? Think about it.

I don't need to know anything about you, where you live, what your situation is, or anything else to help you troubleshoot your amp. But you need to have some understanding about how the amp operates and what the impacts might be of the changes you are considering making. You need to learn to LISTEN. If you are willing to do that and try and understand what you are doing, I'll be glad to try and help you. Maybe some of the others will too. But if you are going to blow off what people are saying, then by all means, go ahead and make those mods. You're on you own.

What's it going to be?

_________________
Bill

Jimi Hendrix, Eric Clapton, BB King: The Ultimate Guitar Trio

Image


Last edited by bluesky636 on Sat Sep 15, 2012 2:30 pm, edited 2 times in total.

Top
 Profile  
 
 Post subject: Re: Supersonic 112 mods
PostPosted: Fri Sep 14, 2012 10:22 am 
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Thu Feb 19, 2009 8:33 pm
Posts: 350
Location: Lake Panasoffkee, FL
:wink: :wink: :wink: Doesn't make sense to cuss out someone that is trying to help! :!: :!: :!:

_________________
Charlie P
Fend HSS Am DLX LSR S1 Strat 08
Fend MIM Telebot Deluxe 2011 Tronical Tuner
Fender SuperSonic 60 2010
Gibson Robot 08, Gib. Faded Ch LP 07
Gret. G5120 07, Peavey VK112 08


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 54 posts ]  Go to page 1, 2, 3, 4  Next

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group