Overvoltage of transistors? (TC Elec. Booster Line Driver Distortion)

[mnemosyne]

Hi, I have some questions about overvoltage of transistors, specifically related to the TC Electronic Booster + Line Driver & Distortion Pedal, from the 1980's.

here is a copy of the service manual including schematic and parts list:
https://www.dropbox.com/s/b5w2b4ny17zceuz/TC%20BLD%20Booster%20Line%20Driver%20Distortion%20service%20manual.pdf?dl=0

also here is the retail pedal manual:
https://www.dropbox.com/s/ya2fg1cqc5houk9/TC%20electronic%20Booster%20linedriver%20and%20distortion%20BLD%20manual.pdf?dl=0

When reading about people's opinions online it seems many people use higher voltage to run the pedal, and believe it sounds better at 24 volts DC (which makes sense to me as I have a TC Integrated Preamp from around the same era and the higher voltage supply I use, the better it sounds, it sounds kinda wank at 9 volts). 

The manual states 18vdc to 24vdc is fine, but later in the manual at the end in the technical specs it states 8vdc to 18vdc supply voltage. 

Further, the service manual states the following IC's are used:
HA4741 - quad op amp, maximum supply voltage +- 20 volts, so no problem there
HBF 4007 UBP - I'm unsure what this is, appears to be four transistors in a box, used for the bypass switching only I think (schematic above).  Datasheet shows absolute maximum supply voltage is just +18 volts. 

all the caps in the schematic that see full supply voltage appear to be spec'd 35v or more. 

datasheets:
https://www.dropbox.com/s/yduedq2uli4dq1g/HBF4007.pdf?dl=0
https://www.dropbox.com/s/rblkblm6hnxo27e/HEF4007UBF.pdf?dl=0

It looks like in the schematic that this chip receives full supply voltage to pin 14, shouldn't this cause issues / dead IC's when running higher than 18v supply?  I see people online saying they run 24v and have always done so, I've never seen anyone say they killed it with a higher voltage supply.  Are these just robust IC's?

I have just ordered an old TC Electronic BLD online and I will open it up and see whats going on when I get it.  Likely will need electrolytics replacing as it is probably more than 35 years old (my integrated preamp did). 



Furthermore, I have a TC Electronic 'Classic Booster + Distortion) which appears to be a reissue of the old BLD. Manual states 12v maximum supply voltage.  It contains some 16v electrolytics and one of them sees full supply voltage so I am limited by that cap. 

it uses two JRC4580's rather than a quad op amp (absolute maximum supply voltage on datasheet +-16v), and a HEF4013B for (i assume) switching.  I have checked with my multimeter and that chip receives full supply voltage on pin 14 and the datasheet shows absolute maximum supply voltage +18v.

datasheet for HEF4013B:
https://www.dropbox.com/s/glqibqm83q3c83o/HEF4013B%20%28CBD%29.pdf?dl=0

I don't dare try a higher voltage supply since this newer pedal is all SMD and there's no way I'd be able to fix it! Maybe I could tack a new cap onto the board where the 16v electrolytic is, but the 14-pin IC, no way. 

pics below of the CBD:






Thanks for any help!

[R.G.]

Quick reality check here: lots of people believe:
> carbon comp resistors add some magic to sound passing through them
> any guitar sound passing through solid state devices sound worse because of it
> the moon landings were faked
> the earth is flat

Mother Nature's reality is not a democracy. Opinions on the internet are notoriously unreliable.

So my question is - are you willing to sacrifice your pedal dying for some supposed increase in tone that you read about on the internet?

From professional experience, most integrated circuits will work >>a little bit<< above their specified maximum voltages. The manufacturers of the ICs do this to ensure that all of the devices they make will work at least up to the specification. But you simply can't rely on any one IC working to some amount over its specification. It may die catastrophically at one millivolt over the data sheet number. Or it may be fine. There is no way to tell ahead of time. Taking an opinion poll of whether it's OK to take this risk or not is just as unreliable as taking a poll on whether there really are alien abductions or not.

There is a way to resolve this: learn the skill of working with SMD devices so you can repair them.

Sorry if this seems harsh. It's just reality. Your particular pedal may be fine. It may die.

[mnemosyne]

I'm just a diy hack with no formal education in electronics, all I know about this stuff comes from picking things up on forums for the most part.

I was mainly wondering if there was anything special about the design of this pedal that I was missing, or something special about those HBF4007UBP ic's as I have never seen them before, that would make it 'no problem' to run a 24v supply.

It sounds like the answer is 'no' and perhaps 1980's tc electronic were just playing it a little fast and loose with the specs of their pedal in the manual.

When the 1980's BLD pedal arrives I'll still take a look inside and maybe measure voltages. If I want to try higher voltages (mainly for my own entertainment) I guess I'll see what I can do to reduce supply voltage to that chip specially. It's though-hole so shouldn't be difficult to work on.

As for the SMD reissue, I wasn't intending to mess with that. Maybe I'll get into SMD soldering at some point. I have tried 9 volts and 12 volts supplies with it and 12 volts sounds a bit better, probably doesn't help that I am using high output humbuckers.

Cheers for the info RG, your posts, and geofex, are great resources.

[R.G.]

I was mainly wondering if there was anything special about the design of this pedal that I was missing, or something special about those HBF4007UBP ic's as I have never seen them before, that would make it 'no problem' to run a 24v supply.

It sounds like the answer is 'no' and perhaps 1980's tc electronic were just playing it a little fast and loose with the specs of their pedal in the manual.

Ah. That makes sense. I intended no slight to you - I just have to assume the least amount of experience to reply to someone I'm not familiar with on forums.

There is probably not something special about those HBF4007UBP ICs. It's possible that they got special, high voltage chips or pre-selected them for higher voltage tolerance, but it's much more likely that the maker simply used the stock ICs and convinced themselves that the nature of how the devices were used would make them never exceed their  specifications.

The pros can sometimes do this, making detailed calculations to prove that using a device "over spec" will always work. The pros sometimes get bitten by this too.  It's really interesting that the earlier pedals allowed higher voltages, then it was dropped back. The pessimist in me thinks that the maker had quite a few warranty returns. Or maybe they used premium, hand selected ICs at first, then cost-reduced by using the plan-vanilla ones. A designer that has not yet been hurt by optimistic reading of spec sheets usually doesn't do it again.

I really like the quote "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." It's been credited to Mark Twain, Josh Billings and others, but it is really appropriate. I've caught myself "knowing things that just ain't so" enough times that I try to avoid it.

[mnemosyne]

I was mainly wondering if there was anything special about the design of this pedal that I was missing, or something special about those HBF4007UBP ic's as I have never seen them before, that would make it 'no problem' to run a 24v supply.

It sounds like the answer is 'no' and perhaps 1980's tc electronic were just playing it a little fast and loose with the specs of their pedal in the manual.

Ah. That makes sense. I intended no slight to you - I just have to assume the least amount of experience to reply to someone I'm not familiar with on forums.

There is probably not something special about those HBF4007UBP ICs. It's possible that they got special, high voltage chips or pre-selected them for higher voltage tolerance, but it's much more likely that the maker simply used the stock ICs and convinced themselves that the nature of how the devices were used would make them never exceed their  specifications.

The pros can sometimes do this, making detailed calculations to prove that using a device "over spec" will always work. The pros sometimes get bitten by this too.  It's really interesting that the earlier pedals allowed higher voltages, then it was dropped back. The pessimist in me thinks that the maker had quite a few warranty returns. Or maybe they used premium, hand selected ICs at first, then cost-reduced by using the plan-vanilla ones. A designer that has not yet been hurt by optimistic reading of spec sheets usually doesn't do it again.

I really like the quote "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." It's been credited to Mark Twain, Josh Billings and others, but it is really appropriate. I've caught myself "knowing things that just ain't so" enough times that I try to avoid it.

Interesting, I suppose it's mostly unknowable at this point, and probably I'm best off sticking to 18 volts maximum on the 80's BLD (when it arrives). I don't fancy trying to pull a 14 pin IC off an old single sided pcb.

I recall contacting tc electronic customer support a couple years ago about my 80's integrated preamp, I forget about what exactly, but they said they don't have any documentation from the old stuff anymore.

[R.G.]

Interesting, I suppose it's mostly unknowable at this point, and probably I'm best off sticking to 18 volts maximum on the 80's BLD (when it arrives). I don't fancy trying to pull a 14 pin IC off an old single sided pcb.

It's actually pretty simple to remove DIPs of any size, and probably easier on single sided. The big decision is whether you need to not damage the IC, not damage the PCB, or not damage both. If it's one of the first two, you're in for an easier time. If you think the IC is bad and want to save the PCB, use your diagonal cutters and snip off all of the leads on the DIP right next to the body. This leaves you two rows of separate pins sticking out the component side. Prop the board up so you're seeing it from the side, hold one of the pins with needle nosed pliers, and touch the solder side of the pin with a hot, well tinned soldering iron. The instant the solder flows, the pin comes right out the component side; remove the soldering iron FAST. Do this again until all the pins are gone. This often leaves the hole clear on single sided boards, generally not on double-sided with plated-through holes. To fix any that are not cleared, put the board down on the bench, solder side up. Take a pointy wooden toothpick or a whittled splinter of wood, hold it touching the solder over the hole, and touch the solder pad with the soldering iron. The instant the solder flows, the toothpick/splinter will plunge right through the hole. Remove the iron, leaving the wood in place for a second, then remove it. Hole cleared. Works on double sided, but you have to heat the hole/pad longer to get it to melt all the way through.

If you expect trouble in the future, put a socket in the now-cleared holes.

I recall contacting tc electronic customer support a couple years ago about my 80's integrated preamp, I forget about what exactly, but they said they don't have any documentation from the old stuff anymore.

Companies sometimes try to forget the oldies. I understand Fender considers every amp sold up through the 1970s as a competitor to any new sales. It's an MBA way of looking at things, I guess.

[mnemosyne]

Interesting, I suppose it's mostly unknowable at this point, and probably I'm best off sticking to 18 volts maximum on the 80's BLD (when it arrives). I don't fancy trying to pull a 14 pin IC off an old single sided pcb.

It's actually pretty simple to remove DIPs of any size, and probably easier on single sided. The big decision is whether you need to not damage the IC, not damage the PCB, or not damage both. If it's one of the first two, you're in for an easier time. If you think the IC is bad and want to save the PCB, use your diagonal cutters and snip off all of the leads on the DIP right next to the body. This leaves you two rows of separate pins sticking out the component side. Prop the board up so you're seeing it from the side, hold one of the pins with needle nosed pliers, and touch the solder side of the pin with a hot, well tinned soldering iron. The instant the solder flows, the pin comes right out the component side; remove the soldering iron FAST. Do this again until all the pins are gone. This often leaves the hole clear on single sided boards, generally not on double-sided with plated-through holes. To fix any that are not cleared, put the board down on the bench, solder side up. Take a pointy wooden toothpick or a whittled splinter of wood, hold it touching the solder over the hole, and touch the solder pad with the soldering iron. The instant the solder flows, the toothpick/splinter will plunge right through the hole. Remove the iron, leaving the wood in place for a second, then remove it. Hole cleared. Works on double sided, but you have to heat the hole/pad longer to get it to melt all the way through.

If you expect trouble in the future, put a socket in the now-cleared holes.

I recall contacting tc electronic customer support a couple years ago about my 80's integrated preamp, I forget about what exactly, but they said they don't have any documentation from the old stuff anymore.

Companies sometimes try to forget the oldies. I understand Fender considers every amp sold up through the 1970s as a competitor to any new sales. It's an MBA way of looking at things, I guess.

Ooh good tips, thanks.

I guess that is the big business way of looking at things. Tc electronic are owned by behringer now so I wouldn't be too surprised if they were only interested in the brand name, and just threw everything else away.

[duck_arse]

the HBF4007 datasheet in the OP is of interest. it bears the date 10/76 and sez "PRELIMINARY DATA" at the top. I've never heard of the HBF prefix, would have expected HEF as a Philips part. if it is a Philips part. the datasheet shows no manuf name, either.

being old and prelim still doesn't let you exceed quoted specs tho.

[mnemosyne]

I ended up just using this pedal on 18 volts and forgetting about using anything higher.

It did end up dying last week, and I measured full supply voltage on a bunch of IC pins I shouldn't be, finally opened it up and replaced all the electrolytic caps (dated to 1984) and now it's working fine again. Took some pictures while I had it open so at least now I know the specific parts in there.

These old pedals are real fun to get into since you have to desolder the power jack, external bypass jack, and xlr output on the side to lift the pcb out.

This one has a toshiba TC4007UBP (datasheet says maximum supply 20v) so 18 volts should be fine.

The op amp is Exar 4741 which the datasheet stated maximum supply +-20v so plenty of room there.

I noticed someone has been in this pedal before and they replaced a resistor at the bottom of the pcb with a massive carbon comp. it measures about the right value though so I left it.