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Post subject: Re: Supersonic 112 mods
Posted: Sat Sep 15, 2012 2:30 pm
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Yes, apologies. As I said in my 2nd post: you're probably right.

I will certainly try the advice I can, some I cannot.


Dirk


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Post subject: Re: Supersonic 112 mods
Posted: Sat Sep 29, 2012 1:39 am
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Hi

Although I still don't understand why I needed to apologize and what for (I re-read the thread and sincerely believe I wasn't disrespectful), all my posts start with" thanks", "I appreciate", etc.

I promised in my 1st post that I would follow up on the issue, so to make clear on what we where talking about originally I will quote myself:

Quote:
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).


So it happened that the hiss problem was around V5 allright, I suspected thermal noise in R75 but it was a bad connection at 7(V5b ) on the PCB (the green wire that goes from the PCB (following R75 and the reverb return) to the V5b grid).

I redid the connection and the hiss went down to a reasonable level, still more than what one would expect, especially because the Celestion V30 emphasizes that portion of the the spectrum quite a lot (a beam blocker/diffusor helps a bit), but managable on stage and in rehearsals. For "bedroom" levels, I insert my volume pedal between FX out and Power amp in, that's perfect (no reverb, but no hiss at all).

Newer SuperSonics have all wires secured by a dot of hot glue on the PCB, mine was not secured that way, probably got stressed and the connection went bad.

Dirk

PS I had also ordered, following advice here, a complete set of JJ's (matched 6L6GC's, hand-selected ECC83S in V1, gold plated balanced ECC83S for PI, and normal, sorted, ECC83S for the others (except V9, ECC81 of course). Re-biased, of course.
I found it to be no improvement, I didn't like the sound that much, very different, I found it quite ordinary and lifeless, too fat, way less bright, not as dynamic as the original set which I put back in. I don't mind brightness, on the contrary, I like to play a lot with the tone controls on the guitar, mostly I start with tone controls at 6/7 on the guitar and play around with it. With the JJ's, I need the tone controls full up all the time, and it doesn't suit my playing. I prefer my low strings to go "zinggg" if I want them to, not being stuck with "booom" however I attack them, and appreciated that sort of clarity in the SuperSonic. It's a question of personal taste, most certainly. I'll keep them as emergency spares.


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Post subject: Re: Supersonic 112 mods
Posted: Sat Sep 29, 2012 9:43 am
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Post subject: Re: Supersonic 112 mods
Posted: Sat Sep 29, 2012 10:06 am
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Just looking at the last post, have you tried a lower gain tube in V1? Say a Sovtek 5751, just to see if this drops the overall noise gain that your amp is displaying. These aren't the best sounding 5751 tubes, but it's a good experiement to check if the gain in the input section is causing the noise. Versus other issues.

In my opinion only, best to try and go section by section --- to find the one which responds to "fixes" the best. The input (or V1) tend to have the highest overall gain of all the sections in the pre-amp (EFX, tone control, phase inverter). Therefore, the input may tend to magnify its circuit noise, the most.

If the sub of the 5751 doesn't drop the noise issue... then you can move onto solder points and nosiy resistors/caps in the input section. I'd use a WOODEN chopsticks and GENTLY tap each component --- listening to the results. If tapping one resistor, say, increasing the noise ... one prolly found your culprit (either the solder points or the resistor, or both).

If after all this the noise is still the same, move onto the next stage. Follow the schematic. I call it "rinse-&-wash and move to the right."

You can also try a 12AT7/ECC81 or 12AY7/6072 in V1 and listen to the results. All of the suggestions are compatible with the 12AX7 socket.

I don't think that it's a good idea to replace all the tubes at once. At, least, not until the original problem is resolved. Easier to keep track of things that way.

Good luck!


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Post subject: Re: Supersonic 112 mods
Posted: Sat Sep 29, 2012 1:46 pm
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Hi,

Thanks for your advice, I followed it and tried a 12AT7 in V1 (the JJ Gold Pins I had initially bought for the PI). It didn't change the noise level at all, brought it up a bit in fact. I have a test setup with a measurement mic and Smaart7 (a professional real-time frequency analyser, it's part of my FOH engineering rig) and make noise profiles at each change or mod I do. This lower-gain tube in V1 didn't lower the hiss, but the hum went down by 3dB so that's interesting. Hum is not really an issue at this point, there's some, but not that much, I can live with it but it's nice to know that some of it is probably introduced at the first gain stage, and I should look a bit deeper into that later.

The overall hiss was reduced when putting a 12AT7 in V5 (fx loop off), not in a spectacular way but noticeably, and it was significantly reduced in the FX loop return. Before, I couldn't even use the FX return level pot, I needed to leave it full CCW, too much hiss and hum. With an 12AT7 in V5, no more additional hiss, but still too much hum in the FX return. Now I don't have the equipment to test tubes, maybe the original rather low gain GT-Fender-Sovtek 12AX7WC and a rather high-gain JJ 12AT7 are not that much apart, I should indeed try to lay my hands on a 12AY7 (for testing), which is not that easy where I live. I can order stuff over the internet, but for one preamp tube the shipping costs are prohibitive!

BTW, you are of course right to mention it, when I received the set of JJ's, I indeed did the replacements stage per stage, V1 first, than V2 and V3, then V4, adding V5, then V9 and V10. At last I put in V6(PI), the power tubes and biased. I made noise profiles at each stage. I can superpose these curves for comparison, it's handy for this sort of troubleshooting: I have precise references to compare with at a very precise level. When I reverted to the original set, I did it in the same order (not reversed order): as soon as put the original V1 back in the sound improved. I might keep a JJ in V3, but even then I'm not so sure of that. If I had some advice to give, it would be that in this sort of amps it's cheaper to experiment with alternative speakers than with complete sets of tubes.... it's certainly easier to resell a barely used loudspeaker than a set of tubes. Oh well, just a thought.

Thanks for your help!
Dirk


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Post subject: Re: Supersonic 112 mods
Posted: Tue Oct 02, 2012 11:57 am
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Still busy trying stuff out, and found that a 12AT7 in V10 reduced the hum and hiss of the reverb to a reasonable level as well. It doesn't change much the it works, still having the same range on the knob and the same sound, as far as I can judge. I think I'll keep it this way.

I thought keeping the JJ in V3, played and recorded all day but finally put the original back in there as well, and wow was I relieved to find the sound I liked before trying to experiment with alternative tubes. I put the whole set of JJ's up for sale. Don't like them at all, and I really tried to like them. I believe Fender just engineered the amp around these Sovtek 12AX7WC's, and did a fine job for my taste. So I go back to what I was doing initially:

1: try to get less hiss overall (by whatever means, including non-conventional experiments in an effort to zoom in on a particular area)
2: try to get the hum out of the effects loop
3: hoping someone someday will find a solution for the treble bleed issue with the effects loop. Some people report that they have spoken to Fender's rep's who confirmed this was done by design, a cap had been added as a workaround for a noise issue but we got treble bleed in the fx loop instead. If someone has some insight to share I would be very grateful!

Dirk


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Post subject: Re: Supersonic 112 mods
Posted: Sat Oct 20, 2012 1:58 pm
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Hi

Concerning the treble bleed issue in the FX loop, that has been discussed widely, (someone once posted that this was by design, so he was told by a Fender rep (a capacitor would have been added to the send circuit to work around a noise issue) and this story has been repeated ever since.) This is a big showstopper: the level of this hi-passed signal is significant and especially annoying with overdriven sounds where it superimposes a harsh edge on the sound. If we use the loop with a straight thru jack to attenuate the signal a bit, more we attenuate, more the sound gets treblier than what we intended.

I noticed that the bleed diminishes when the send level increases (knob turning CW). Full CW the bleed is at it's minimum level. The return level knob doesn't influence the level of the bleed (it adds significant noise though: looks like this circuit might benefit from some sort of taper-mod, it's not of much use to have a return level that adds that much noise!). Basically, there's only only one almost-usable setting here: send full CW, return full CCW.

Did anyone ever figured out a real solution for this issue? Could this be a grounding problem?

Thanks
Dirk


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Post subject: Re: Supersonic 112 mods
Posted: Sun Oct 21, 2012 7:18 am
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Hi Dirk Offringa,

It seems to me that you are very skilled at diagnosing your issues. :) BTW, I didn't see any cussing or disrespect on your part.

This amp is designed with tons of gain, and it seems that the hiss is at least partly due to this. But, could you summarize what the problem is that you have now, and what you have changed so far? And the affect on hiss level? For example, does the hiss change if you switch off the effects loop? Does the hiss change if adding a patch cable from the pre out to power in, and/or using a patch cable for effects loop? Does turning the reverb down affect the hiss level?

Firstly, the lead dressing (wire arrangement, see below picture) can affect the hiss levels. Sometimes moving the reverb cables position can have an affect, as well as the transformer leads being twisted and separated from each other. You might want to try dressing the transformer leads, doing one pair at a time to be sure of keeping the connections correct, and try various positions for the reverb cables. The picture below is my HRDlx, and dressing the transformer leads made the amp dead quiet, although the hiss wasn't terrible before, it did help. In the older Fender amps, the designer(s) used great care in the placement of the leads.

Another suggestion as far as hiss, check the preamp/PI tubes' Plate resistors. These resistors of the carbon type can be noisier than the metal film, carbon comp worse than carbon film (I doubt that you have carbon comps), and metal film resistors are quieter. Along these same lines, note that V4B has no Plate resistor, and since this is a Cathode-follower, the tube used here can make a big difference, and some tube types here can sound horrible.

Some things to consider, starting at the input, is that this amp has a much lower value grid resistor than many other amps. R1 could be increased to 34K, or even 68K to reduce the gain somewhat. You might want to compare the schematic of various amps to get an idea of some changes that might help. For example, look at coupling cap values, and preamp grid resistor values in your amp as compared to other models. Keep in mind that any changes made can have a great impact on tone, and if you get the amp to be very quiet, you might lose the sound that you like.

Image

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Post subject: Re: Supersonic 112 mods
Posted: Mon Oct 22, 2012 3:31 pm
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Hi shimmilou, thanks for caring. (and for making me feel less unconfortable, I'm not used to being misunderstood to the point of being told I had been cussing someone helpful....)

I've been doing a lot of experiments with this amp, trying to zoom into this hiss problem.

To summarize:

Problem: The amp hisses beyond a reasonable level, it's a known issue but as I said when I started this thread, many threads have been started about this but noone ever follows up just to say "it's fixed, here's what I did".

What I did until now:

-STUFF THAT DID'T HELP:

1: I checked the Bias. The first time I did this, I had followed the factory specs as per the schematics, and set the grid voltage to -54,5 vDC, and got 32mVDC voltage drop over the 1 ohms resistors which translate to 32mA idle current. I didn't find that the sound had improved, so I checked the plate voltages and found 517VDC there. I checked the mains, and found 247VAC, which is a lot (I'm in Europe, we're supposed to have 230VAC mains). I had some friends check at their places and they had their mains in the same range. So I decided to repatch the power supply and wire it for 240V. Several times per day the voltage is very near to 240, and when it's so, I measure 479VDC at the plates, but can't get the bias up to 32mA idle current, because the BIAS pot maxes out. I can get to 31mA at best, with -C at 51.5DC. When I get to that point, the hiss has increased.

I checked all the DC Test Points and with the amp wired for 240, and having actually 240VAC measured, all the TP's are perfectly in spec as per the schematics.

2: I got a whole new set of JJ tubes. The JJ 6L6GC's do behave exactly the same way as the original tubes as far as the idle current draw is concerned. (EDIT: I don't know what's going on here, I just can't get those power tubes to draw 32mA with -54.5VDC bias voltage and 479VDC on the plates, as per the specs. Both set of tubes I have draw way less with those voltages) I decided to set Bias back just as cold as it was when I received the amp, near 26mA. I liked the sound better and it was a bit less hissy.

3: changing all the other tubes made stuff worse. More hiss, furthermore I didn't like the sound of the amp, nor the feel of the dynamics.

4: pulling all the preamp tubes except V5, all at once or one by one doesn't make any difference

5. totally isolating the reverb circuit doesn't make any difference (there was a separate hiss and hum issue with the reverb which I had already solved by trying out several 12AT7's in V9, one of them fixed the hum, then I put a 12AT7 in V10, that solved the reverb hiss issue. V9 seems particularly sensitive to the quality of the tube, btw)

6: Using a patch cable in the fx loop and lower the send level doesn't make any difference. (And adds a treble bleed problem). Any position of the return level but full CCW adds considerable hiss and hum.

7: Using a patch cable between preamp out and power amp in doesn't make any difference BUT the opamp in the preamp out section is overloaded giving harsh clipping (any setting of the vintage channel/vibrolux mode over 2 will overload the opamp).

-STUFF THAT DOES HELP:

8: A patch cable from fx send to power amp in makes the amp dead quiet (but we don't have the reverb circuit anymore)

9: a 12AT7 in V5 reduces the hiss considerably. But it changes the dynamics in an unpleasant way especially with clean sounds. (Note: I should definitely try a 5751 here)

-STUFF I CONTEMPLATED BUT POSTPONED:

10: lead dressing. That is a good suggestion, but it's a HUGE job: the build quality is not top-notch. The wires going from the PC to the valve sockets are tiny gauges, not secured by hot glue or otherwise. The PT wiring is all dense and we can hardly do anything about it. (pic attached..... )

Image


Image

That's all for now. I have spend many many hours on it, trying out different tubes in different positions trying to get a nice sound and managable hiss. I always end up reverting to the stock Fender Sovtek 12AX7WC, any other brand seems to have to much gain, or otherwise doesn't sound that good to my ears. The only valves I changed and kept as of today, is a ElectroHarmonix in V3, which does sound good in that position, and V9 and V10 (both EH as well).

I write this at my desk in my office. It's late, past midnight, everyone's asleep, it's dead quiet over here. Under my desk, I have a MusicMan 212HD130. It's on, used it last evening and forgot it. It's not on standby, it's on full 130Watt setting. I don't hear it! Nothing! No hiss at all. Zero. Quieter than my laptop. And boy, can this amp get loud. I bought the SS partly because the MusicMan is way too loud (and heavy too). Now I understand that the SS has a part of the circuit dedicated to high gain, but the vintage channel is not a high gain preamp, and should be quiet. But instead, it's the vintage channel/Bassman setting that really is the most noisy (I'm not the only one who find this). I'm sure this can be fixed! I have the impression, that V5 just has too much gain. It overloads the opamps in the preamp-output circuit. It amplifies the background hum/hiss from the preamp channels. Something around V5 could be changed to make this managable in my opinion. Even if it's not "like it was meant to be". If everything had been done "like it was meant to be" there wouldn't be any rock 'n roll anyway, let alone Fender amps.

If we could come up with some sort of a master volume, that would reduce the gain of the V5b stage somewhat I would be perfectly happy! But for now I'm still trying to figure out if this is just normal, or if it's a faulty component or cold solder joint or whatever.

This is a great amp, very versatile, I could be very happy with it but I need the dynamics: my playing is dynamic, I mean I go from very very light touch to heavey pulling, that's part of what I do and the amp I use must be quiet. Not DEAD quiet, but reasonably quiet.

Thanks again
Dirk


Last edited by Dirk Offringa on Tue Oct 23, 2012 4:27 am, edited 1 time in total.

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Post subject: Re: Supersonic 112 mods
Posted: Mon Oct 22, 2012 5:58 pm
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Dirk Offringa wrote:
...pulling all the preamp tubes except V5, all at once or one by one doesn't make any difference...then I put a 12AT7 in V10, that solved the reverb hiss issue...A patch cable from fx send to power amp in makes the amp dead quiet (but we don't have the reverb circuit anymore)...a 12AT7 in V5 reduces the hiss considerably. But it changes the dynamics in an unpleasant way especially with clean sounds. (Note: I should definitely try a 5751 here)...lead dressing, The wires going from the PC to the valve sockets are tiny gauges...The PT wiring is all dense and we can hardly do anything about it....


So, it seems that bypassing the reverb circuit and V5 circuits with the patch cable from FX Send to Power Amp in makes the amp dead quiet? And the sound is to your liking? (other than missing reverb) This indicates the reverb circuit and/or V5 circuit as the problem area. Any change when removing only the two reverb tubes? [s]Or, any change when removing only V5? [/s] Scratch that, as pulling V5 would give no sound out at all. :lol:

Don't worry about the PCB to valve socket wires, just all of the transformer wires should be twisted pairs, being sure not to pull the wires out of the transformer. Do them one pair at a time. Tedious maybe, but do-able by disconnecting the end of each pair at the connectors to the board. I use a sharpie to mark one wire of each pair, and a corresponding mark on the board before removing, in order to insure reconnection to the same terminals.

BTW, good catch rewiring for 240 volts. This has been discussed before, and has helped others.

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Post subject: Re: Supersonic 112 mods
Posted: Tue Oct 23, 2012 1:19 am
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Yes, the patch cable from fx send to power amp makes the amp dead quiet, and I had eliminated the reverb circuit before. This was easy to do without unsoldering stuff simply by shifting the ribbon cable P100-P200 so that it only jumpers pins 1 and 2. Now the whole reverb circuit is disconnected. This doesn't make any difference.

(SIDE NOTE: There are several issues with the amp (either MY unit or by design), including reverb hiss and hum, which I found a fix for as I explaned. Then we have this main hiss issue, and last but not least the fx loop treble bleed issue. It's all centered around the same area)

(SECOND SIDE NOTE: at the start of this thread I mentioned other mods, and that had been interpreted as if I was contemplating those mods in an unreasonable attempt to fix the hiss issue, obviously not knowing what I was doing. I never have said that, the other mods simply consist of applying the very few changes Fender made to the 2nd generation SS 60, and mainly adress the issue of the Vibrolux voicing being both too trebly (C7) and to low in level compared to the Bassman voicing (it's now similar to the Twin voicing in the newer SS100) and a mod to the channel switching circuit that I didn't analyse yet). Nothing to do with the hiss issue. There was a misunderstanding here... let's skip that now)

Talking about other mods, you suggested the grid resistor at V1, I might try that one day, but well it's not a point-to-point wired amp and getting the PCB out is time consuming and risky because of all the unsecured valve socket wiring, it feel like those wires can break off anytime I don't think that's where my issue comes from, but it's a good suggestion for customising response and sound, I'll look at that later! That other observation you made, V4 being wired as a cathode follower thus important to look at, you we're very right there. I put a JJ 12AX7 in there, changed the whole dynamic response it was certainly not better, the clean sounds on the vintage channel became too dynamic: ear-shattering attacks and no sustain. Less problematic when using the already compressed burn channel.)

So: that leaves the V5 circuit. We either have a design issue, or one (or more) components that are out of spec/toasted or otherwise need to be fixed/replaced. If it's by design, other than the fact that I just can't believe that for a Fender amp in this price rang then we need to figure out a mod or a workaround; otherwise, we need to locate the offending part and fix it.

I looked at the latest SS100, and compared, this part of the circuit is nearly identical, but they changed R75 and R76, both to 1.2M. Their reverb recovery circuit is a bit different, so maybe it's impedance changed, might be related, might be not, I don't have the schematics right here.

They also changed the fx return level adjust circuit which looks reasonable to me because on my unit it's just not usable as is, needs to remain fully turned down otherwise it's not hiss we get but a storm! Way too much gain there!

I'll do the PT lead dressing, as you suggested, as soon as I get a free moment. I had already somewhat re-arranged the filament heater wiring so that these wires would alway cross signal wires in a 90° angle and never be parallel. Not very conclusive, but then again there's not much margin to move those around.....

Thanks!
Dirk


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Post subject: Re: Supersonic 112 mods
Posted: Tue Oct 23, 2012 4:08 am
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And just some food for thougt: there are a lot of posts about customizing the SS 112. In fact it's a quite difficult thing to do and many many posts draw wrong conclusions: for instance I just read that putting a 12AU7 in V1 mellowed the vibrolux channel because of the lower gain. This is wrong advice: the fact is that putting such a low gain valve there, will enable you to crank up the gain knob beyond 12o'clock, so that the C7 capacitor gets bypassed, hence the way more mellow sound. I myself so much disliked that capacitor that I just removed it. Now the Vibrolux doesn't have that over the top ice-pick anymore. Nothing to do with the very low gain of the 12AU7! That doesn' mean that it's not a good idea to try a 12AU7 in V1 to see what it does and one might like it. I just tried a 12AT7 in V1, and I think I like it better than a 12AX7. I definitely need to find a bunch of 5751's! Not easy where I live, there's no such thing as "my local tube supplier" over here....



Dirk


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Post subject: Re: Supersonic 112 mods
Posted: Tue Oct 23, 2012 5:06 pm
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Dirk Offringa wrote:
...So: that leaves the V5 circuit....or one (or more) components that are out of spec/toasted or otherwise need to be fixed/replaced...but they changed R75 and R76, both to 1.2M....


You seem to have zeroed in on the remaining problem as the V5 circuit, right where you first suspected, I have to agree, maybe in particular R75 and R76, and don't forget the V5 Plate resistor(s), especially R77 for V5B.

I hope that you make this one of those "problem solved" threads that you mentioned not seeing. 8)

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Post subject: Re: Supersonic 112 mods
Posted: Wed Oct 24, 2012 11:58 pm
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Hi

I made somemodifications to the lead dress but it doesn't change much for the hiss, maybe slightly less hum but that wasn't a priority issue. I took the main board out to examine it for cold solder joints (I had spotted one earlier, fixing it reduced the hiss somewhat). I notice that at least two different solder jobs have been done. The PCB is industrially soldered (wave probably) and that part looks fine. All bigger components such as the bigger electrolytic caps as well as the coax cables have been soldered, probably manually, afterwards, and that part is less clean. As on all PCB's, a coating is applied after wave soldering, but this apparently has been done before the other components and wiring was installed, and the person that did that, didn't remove the coating before soldering the stuff, so it melted and it's quite visible who did what.

I think I will leave that part of my "research" alone for now, I don't have time to redo that at all and it might be just fine as it is.

Doing some more chop-stick poking I find that R75 R76 are very microphonic, as well as the the P100-P2OO cable and the green wire from the PCB to V5B'grid. nowhere else do I notice that. Once more we're zooming in to the same area: the mixer node. I'll have to get that board out again and really unsolder and check all those resistors (including the plate resistors).

I ordered a couple of other preamp tubes, and will be on standby for the next fex days, I have a lot of work pending.... so more to come next week.

Dirk


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Post subject: Re: Supersonic 112 mods
Posted: Thu Oct 25, 2012 8:25 am
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I wonder if the coating that you see is just flux, which is normal, especially if they used rosin core solder to touch up by hand. The flux would be a dark brown crusty looking stuff when heated. Some times the flux is cleaned off afterwards, sometimes not. If it is only flux, it won't hurt anything to leave it.

Waiting anxiously for your next report.

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Fender Play Winter Sale 2020

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