Can I Swap out some parts on a PCB board to improve sound??

[TerryD]

OH How the Mighty Have fallen!

I went from a 1966 Vibrolux that I sold to buy some drums to a Bugera V55 head (2 by 12 Jensens).  What a difference.  Makes me long for the point to point.

But hey, I'll jerk around with this while I got it.  It could be a little thicker.  It's now a little thin with brittle highs.

The insides and board are really user friendly. I switched out the rectifier diodes for FREDS which I always like for a smoother musical voice.  It's not helped as much here as with a Bassman head I had.
Would swapping out the other IN4007s help?  (FREDS enthusiast only need reply on that one)

What if I swapped out some of the plate resister or some capacitors with real life size carbon comp resisters and 25 mfd spragues?  Or some other ideas while I'm in there?


http://bmamps.com/Schematics/Bugera/V55-Schematic.pdf

Thanks,Terry

[jjasilli]

I my experience the best improvement in tone will come from replacing caps in the signal path, swapping-in quality caps of your preference, and starting with the tonestack.  I would do one circuit section at a time.  That way, if there's a problem it will be easy to trace.


For pF caps use silver mica.  (Alternatively, vintage ceramic caps are reputed to sound better than modern production.)  For larger caps the usual choices are either Orange Drops or Mallories, with more exotic alternatives available. 


This should make an objectively obvious tone improvement. 

[TerryD]

Let me be a pain and ask you for more specifics. The tone stack=bass, treble and midrange right?  And what else?  Resisters, not so much?  Thanks, Terry

[PRR]

If the new amp has real problem, I don't think dusting it with FREDs is a big enough hammer.

To the *average* player in the store, a really fine tube amp sounds a lot like a really fine transistor amp, and the tranny amp is a lot cheaper. So the tube-amp pushers have resorted to extreme tone-shaping (frequency response) and extreme overload behavior (choking intermediate stages so it can be overloaded without getting you thrown out of the store). Un-doing these hacks may help a lot. Undoing them on PCB jammed in a chassis may take heroic bench-work.

[jjasilli]

Let me be a pain and ask you for more specifics. The tone stack=bass, treble and midrange right?  And what else?  Resisters, not so much?  Thanks, Terry

I stick to my 1st reply above.  Quality caps in the signal path, especially the tonestack, is the best way to improve a mass production amp. 


PRR has a point.  There is junk in there.  E.g., the input circuit off the bright jack seems to have way too many components.  But, 1st things 1st.  You should see how things stand after you recap the tonestack and signal path, before getting more aggressive with mods.

[TerryD]

What else is the signal path besides the tone stack is my question?  Thanks, Terry

Anything to do to reduce the input circuit?

[shooter]

the signal path

typically the signal path, in the grid, out the plate....repeat.
exceptions, CF, some PI

[Fresh_Start]

Respectfully, swapping in quality NOS or ANOS preamp tubes might yield better results without the risks involved in modifying PCB components. V1 almost always has the biggest impact, so only one tube might do it. Experiment with output tube bias too - that can affect tone a lot. How about a set of Svetlana "winged C" power tubes?

As far as resistors go, changing values will have a much bigger effect than swapping in noisier carbon comp resistors. I noticed that 3 of the preamp stages have 150K plate resistors with the "standard" 1.5K cathode resistors.  You might try the "standard" 100K plate resistor(s) - one triode at a time - to listen for any improvements. The fourth preamp stage already has a 100K plate resistor but only 470 ohms on the cathode. You could try increasing the value of that resistor.


The problem with this approach is that the circuit is designed as a whole. There are a lot of voltage dividers to knock the signal back down throughout the signal path. Changing the bias points of the preamp tubes may reduce the signal too much without tweaking the voltage dividers too.  Unfortunately, at that point you're re-designing the preamp circuit.


There also are several high-pass filters. C54, C56, C32.  You might try a jumper across each of them, one by one, to listen for changes. But again, they work together with the rest of the circuit design.


I agree with JJ that the first place to replace components is the tone stack caps:  C46-C49.


Hope,this helps,


Chip

[HotBluePlates]

There is junk in there.  E.g., the input circuit off the bright jack seems to have way too many components.

Maybe compared to classic guitar amps. However, what I see is an attempt to preserve treble for the Bright input, regardless of cable capacitance.

The circuit reduces to a voltage divider made of resistors R59 & R53, in parallel with a capacitive voltage divider made of C31 & C24 (plus cable capacitance). This arrangement was/is used a lot in test equipment which needed to operate over wide frequency range. The resistive divider which was intended to have a fixed signal reduction at all frequencies actually has drooping response at high enough frequencies because of stray wiring capacitance, as well as the Miller capacitance of the tube and the capacitance of the cable connecting the signal source to the first tube grid.

For a fixed signal reduction at all frequencies, the ratio of resistance in R59 & R53 is inverse to the ratio of capacitance of C31 & C24 (but same as the ratio of reactance of C31 & C24). That would be a 2nF cap for C24, less the value of expected stray/cable capacitance. That's because R59 & R53 are in a 1:5 ratio, so the caps would be a 5:1 ratio.

Except the designers wanted this input to have lifted treble, made C24 smaller to boost highs.


There's stuff like this throughout the amp. It's not that there are too many parts, or that what's added is bad. The designers obviously had a larger palette of experience they drew from compared to those who just copy a 50's amp.

Dave Funk wrote in his book words to the effect of, "Others copy amps based on 1930's technology. I build amps based on 1960's technology, which seem very modern by comparison." The Bugera has a lot of clever design to shape the sound and frequency balance. That can be changed, but we don't have enough info on what Terry thinks is "brittle-sounding" (Clean channel? Distortion? Both? Bright input? Normal input? etc) to know what to sensibly hack.

You could go in ripping out the various compensating caps to darken things up, but some also serve to keep the distorted sound from being bloated-sounding and/or noisy. I believe a parts-value change will have a bigger impact than just swapping for a different component type, but would need a lot more info on what change is desired to get there.


We also don't know what speakers Terry is using with the Bugera (the original post was a little ambiguous)... I have a Valve Jr combo that sounds ho-hum through the stock internal speaker, but remarkably good (stock) through a 2x12 cab with good speakers. So if your ear is attuned to darker sounds from 60's ceramic Jensens with decades of break-in and something newer is being used, it may not give the amp a fair shake.

[jjasilli]

Yes, though Terry asked specifically about internal circuit changes, a better speaker often yields significant tonal improvement.  Which speaker to use is a subjective, personal choice.  And it can be expensive, though worthwhile.


Hotblue's  analysis of the input circuitry is informative, though the circuit design still violates the KISS principle.  FMV amps sound fabulous.  An optional bypass cap across the vol pot, possibly switchable, can get the job done.  But, try a humbucker pickup through the stock bright input jack and see if you like it.

[HotBluePlates]

... the circuit design still violates the KISS principle.  FMV amps sound fabulous.  ...

Yeah, I was thinking about that, too. Might be wise to use the KISS principle in the selection of the amp; meaning "sell the Bugera, buy the Fender reissue". 

An optional bypass cap across the vol pot, possibly switchable, can get the job done.

One issue with a bright cap at a volume control is that its effect changes with the volume setting. Near the bottom, things can be unusably-bright (which is why I rarely like bright caps/switches). At the top of volume rotation, they have no effect.

The complicated circuit does have the advantage that it has a non-changing impact on the sound.

[Fresh_Start]

+1 on speaker choice.

There are tons of proposed mods for a Blues Junior, but swapping a Weber Blue Dog in place of the stock speaker made a BIG improvement. (So did experimenting with different power and preamp tubes.)

HBP is far more knowledgeable than I.  He said what I was trying to say only better. The Bugera designers made deliberate choices for specific reasons. Random changes in component values are not a good approach.

Respectfully,
Chip

[jjasilli]

It can be fun to get a bargain amp & improve it; and a good learning experience -- especially if it's easy to work on.  Tube rolling and speakers swaps are non-invasive alternatives, but can be expensive.  Improving signal cap quality gives lots of bang for the buck.


Also, I haven't advocated changing component values, at least not yet -- but first swapping-in quality caps of the same values.

[TerryD]

Thanks a lot guys.

I got two jensens from the 60s, one ceramic and one alnico to cover my bases in a 2 by 12.  I wondered if they were too bright.

I have two RCA 6l6s (good used ones) and upgraded the 12 ax7s.  I did put in a 12AT7 phase inverter in place of the Bugera 12AX7B they had there and I wonder if that was a mistake.

I always read these post several times and more to be sure I'm understanding you guys.  Any more ideas would be greatly appreciated.

I know I'm a psychopath but the amp sounds "digitally" almost like I hear if I have a digital pedal in the signal path.  (Which I never keep there-they may be ok when they are on but when they are off the pure sound changes to thin and something rotten/sterile)  The amp is not blossomy (I didn't say distortiony) but thin and sterile.  It's clean clean and sounds like it wants to be a good boy.  I don't care about the distortion channel.  They are never salvagable.  Listening on youtube, I thought the clean channel had great promise.  When I use the normal channel it's better, but then something else is lacking.

Thanks again,
Terry

[HotBluePlates]

Also, I haven't advocated changing component values, at least not yet ...

No, I was the one to suggest changing parts values, as I think it will do more, quicker. We just don't know enough about what is/isn't liked to have a starting place.

I got two jensens from the 60s, one ceramic and one alnico to cover my bases in a 2 by 12.

Cool. Let's assume your speakers are set & good.

The amp is not blossomy (I didn't say distortiony) but thin and sterile.  It's clean clean ...

Control settings? Do include Clean Volume, Master Volume and all tone control settings.

The clean channel itself is close enough to Fender's to not quibble. The difference is the shared EQ is after the gai stages, not in-between. C54 & C56 could be removed to see if things warm up a bit.

Other than that, this amp has a higher-voltage and stiffer power supply than your old Fender. If you can't get the clean channel, using the normal input, to work for you at any tone control setting then you might just think about selling the amp & moving on to something that works better for you to start with.

That may sound harsh, but isn't intended that way. Looking at a youtube video of the innards, the p.c. board will be even more of a pain to work on that other p.c. board amps. This amp has the board inverted, which means while you can easily get at the solder joints (you'd normall have to pull the whole p.c. board out to do this), you can't ID what part you're poking without flipping the board over. So you can't know where to remove the 2 caps I mentioned earlier without removing the board, which appears to also require disassembling all the front panel pots as well.

[TerryD]

I've removed to board to put in some FREDS.  Its not that bad.  I just wish I could try these changes without having to assemble it again after each change.  The back side of the board is connected to a metal (aluminum??) piece to the chassis.  Doe that have to be connected to try the amp out after an alteration (hopefully not altercation)?

I might be able to pick up a Fender 100 PA head with reverb for 250.  I might drop this one like a hot potato or work on it.  There is a lot of good ideas here.  It's very close to a good amp.  But maybe with the Fender, I'll have a good replacement for my vibrolus, though not the same thing.

[HotBluePlates]

I might be able to pick up a Fender 100 PA head with reverb for 250.  ...  But maybe with the Fender, I'll have a good replacement for my vibrolus, though not the same thing.

You like blonde Fender girls. But you got one of them red-head German girls.

Go get your new Fender blonde (the PA 100); it's easier to give the blonde a new hairstyle than to change the red-head into something she's not.

(and the PA 100 will be much easier to work on, not to mention 90% or more of the way to where you want).

[TerryD]

That simply sounds like good advice.  Thanks

[Ritchie200]

Terry,


Just for giggles, swap your AT7 and AX7.  I've done this with a lot of "gainer" type amps.  It really opens them up musically with a little less drive on the front end, and gets rid of some of the brittleness.  Not sure how it would work here, but is a painless experiment.


Jim

[TerryD]

It might work as there was an AX7 to begin with.