Hi all,
I have a Carlsbro Hornet 45 Lead Combo which I bought second hand in 1986. It may not be the world's greatest amp but it has served me well and been rehearsed and gigged with countless times and I rather like the sound of it as part of my set-up. It has been trouble free all this time other than the reverb tank breaking a few years ago but I replaced that and it was fine.
The amp has always been loud with plenty of headroom; historically I have run it in a band situation with both Gain and Master Volume both on around 5 (half way). My Overdrive sound comes from a pedal and when bypassed these levels have always given me a clean tone with just the slightest bit of edge.
After a period of non-use, however, I came to try it recently and found a problem. The sound is now distorting with very low gain settings (1 and above). The distortion is "raspy" (for want of a better description) and has some unpleasant harmonic overtones.
This is what I have done so far:
Carried out a visual inspection of all the components. Nothing is obviously damaged, blow, broken or burnt.
Cleaned all of the pots and sockets - the issue remained.
Tried the amp using headphones - the same issue can be heard via headphones so I am thinking it's unlikely to be the speaker.
I am now at a loss of what to try next. I know I'm lucky for the amp to have lasted this long and I could replace it but I do like the sound of it and would prefer to keep it in service if at all possible as long as it is economically viable.
I am OK with a soldering iron and mechanical repairs but not adept with electronics although I have access to someone that is, albeit they are not an amp specialist.
Any advice or recommendations as to what might be the problem / fix would be appreciated.
Just my 0.02
My first thought is that some electrolytic caps have gone bad/dried up, esp if there are any small value electros in the audio path.
I've been tinkering with older 70's / 80's SS amps lately, and found several that instantly sound "better" when I replace those small value electro cap that are in the signal path.
No doubt some better minds will chime in with ideas/experience. :)
Edit; none of those caps I replaced tested bad or "looked" bad, ie, no leaking/swelling etc, but nevertheless the amp(s) sounded better once they were replaced.
... and, I often installed non-electro caps in place of them, usually with those small box film types of 1uF or less.
Thanks - I was intending to give the capacitors another once-over anyway so I'll carry out a more thorough visual inspection and also test them properly.
Just to add a few more details: I have tried different guitars and cables to no effect so I can discount those. I am also running straight from the guitar to the amp so it's not my pedal board. As soon as I get a bit of free time I was going to try recording some clean (or what should be clean) guitar via the line out. My thinking is that if the issue is captured on the recording then it can't be the power amp and if it's not captured then it must be the power amp but my thinking (that the line out bypasses the power amp) could be way off so I'd appreciate any comments re this.
Try the speaker with another known good amplifier; fully disconnect it from Carslbro though, post results.
Post a speaker picture so we can suggest a replacement in case it´s needed, is it a 10" speaker or a 12" one?
Don´t excuse yourself for using a Carlsbro, excellent amps and very well built, yours is proof of decades good service.
FWIW I was in London that very same year, and way more Carlsbros were availble in Music Shops (Denmark Street and surroundings) than Marshalls or any other "fancy" brands, followed by SS VOX amps.
No Valvestate or Squire or other "famous brand" SS incarnations way back then.
Excellent HH which were quite popular were all SS, of course.
OK will do - I have another amp that I could test the speaker with and which could also provide a possible donor speaker. The speakers in both are 8 ohm 12 inch.
Does the fact that I can reproduce the issue via headphones not rule out the speaker? I thought it did but I'd love to be proven wrong as replacing the speaker feels like a much simpler job than other possibilities :)
Hi. I am new to this forum but was very interested to read your problem and experiences with a Carllsbro amp. These are a good old British made amp from the 70's and 80's and I myself have owned several. The best one I seem to remember was a Colt 45 model. What a great amp with a great range of sounds and bullt to withstand a nuclear strike! Why I sold it I cannot think because it was a cracker. Anyway, to get back to your problem - it sounds to me like a power supply might have gone down and you should check all the dc supplies with a meter. A schematic would certainly help but can be hard to track down for Carlsbro and more obscure amps. One thing I did note from having repaired several Carlsbro amps and that is that they are prone to problems with jack sockets and pots. The originals were maybe not of best quality and they go intermittent. Switch cleaner can help but sometimes the only cure is to replace them. Good luck with your fault finding.
A schematic would be handy but a quick Google search doesn't turn up much...
These guys have some but I don't see the Hornet...
http://www.amprepairparts.com/schematics.htm (http://www.amprepairparts.com/schematics.htm)
I don't suppose much chance there is a schem pasted inside the amp somewhere?
Thanks for all your suggestions and advice so far. There isn't a schematic inside that I am aware of but I will check again next time I have it apart. I haven't had much time this week due to work and other commitments but what I will try and do ASAP is:
- Try recording from the line out and post the results. Maybe someone could tell me what it they mean.
- Post some pictures of the amp and speaker.
- Take the amp apart again, post some pictures of the circuitry and inspect plus test the caps, pots and sockets.
- Check the DC supplies with a meter
As soon as I have time to get the soldering iron out I will also try the following and post the results:
- Disconnect the speaker in both the Carlsbro and a known good amp (I have a Park 25 watt bass amp with an 8 ohm 12" speaker)
- Connect the Carlsbro amp to the Park speaker
- Connect the Park Amp to the Carlsbro speaker
I have tried recording via the line out and can confirm that the raspy distortion is NOT present via the line out. I think this means that the problem is probably in the power amp or speaker?
Next steps will be to try the speaker with a known good amp and then maybe the amp with a known good speaker and also test the DC components, when I have time.
Here are some pictures - i can post larger ones or take specific ones if needed.
I see there is a Carlsbro company in the UK. Their logo says "since 1959".
Might be worth it to contact them and ask if they have any "legacy" product info, ie: a schematic for your amp.
http://www.carlsbro.com/ (http://www.carlsbro.com/)
I have contacted Carlsbro on the off-chance that they can provide a schematic.
I was unable to easily hook up the working Park amp to the Carlsbro Speaker, but I WAS able to hook up the Carlsbro Amp to the Park speaker and the raspy distortion persisted.
Therefore, as the sound from the line-out was distortion free and the headphone output and alternative speaker output were distorted I believe that the problem is NOT the speaker and NOT the preamp and therefore must be the power supply or the power amp. Am I correct in my thinking?
Any advice on what to check next and how to check it, bearing in mind that I am a novice?
Thanks for all the help so far.
You have done well. :)
Yes I agree the Poweramp is the obvious culprit. :trouble
Check for DC voltage on the speaker terminals, it should read very close to zero Volts.
A reading of ~100mV is normal while 10 or 20VDC means a major fault.
If high, then disconnect the speaker otherwise you may burn out the coil. Speakers don't like DC voltage. 8|
Check you have DCvoltage on both fuses and post the voltages you read.
It's not a complex circuit and I'm sure this is fixable. Wait for the tecks who will ask you to take a few voltage readings at certain places.
A picture of the reverse side of the PCB may help to work out the layout and hence how it's wired up.
Meantime you can build a lamp limiter as you will likely need it to test the power amp. Reason being, even if you replace a broken part it may instantly blow again if circuit is not stable.
https://www.ssguitar.com/index.php?board=2.0
First posting on above page will show how, what and why you need one.
Phil.
If the amp has a line out, does it follow that it also has a line in/power amp in jack? If so, it might be a switching jack, and it might be that its "switch terminals" are corroded. I've had low output/raspy distortion from older SS Peaveys before that went away if I put a patch cable from the line out jack to the power amp in jack, thus breaking that switching connection and replacing it with the patch cable's conductors.
Hi,
It doesn't have a line in/power amp in jack. I had posted pictures of both the front and rear of the combo showing all inputs and outputs but unfortunately the photos I posted seem to be half showing when enlarged so you can't see them all.
The amp has:
- Front: low gain input, high gain input, footswitch jack for reverb on / off.
- Rear: line out, headphone out.
The issue is the same when using both high and low gain inputs.
One thing I haven't tried is is using a switch plugged into the footswitch jack and I will do this for the sake of completeness; I'm not going to make any assumptions without evidence. As soon as I have reconnected the speaker I'll give it a go just in case.
Ok so now I have experimented with the reverb footswitch socket and ruled that out for now. I didn't expect it would be significant but didn't want to assume anything.
On the basis of assuming nothing, please could someone explain in idiot's terms how I should do the following? I just want to make sure I am doing everything the correct way and not making any guesses. I will get around to building a lightbulb limiter as soon as time allows too.
In the mean time, what is the correct way to:
Check for DC voltage on the speaker terminals?
Check I have DC voltage on both fuses? And for completeness are the glass fuses shown in the attachment the ones I should be checking?
You have a basic differential power amp setup which looks complex for the novice.
OK,, These are DC Amps, (Direct Coupled circuit) with no capacitors between each part so there is no isolation from input to output and any fault is often Fatal for more than just one part of a DC circuit.
When they fault you often find the output (which should be very close to zero VDC) goes off balance.
The supply is bipolar meaning you have both positive and negative voltage supplies (often called supply Rails),, Hence the 2 big Capacitors.
The center of those 2 Rails is obviously zero VDC which is what you should read on the speaker output terminals.
So take your DMM and set it to VDC and post what it reads on the spk terminals.
Does not matter if the voltage is Pos or Neg,, as long as it is close to Zero,, if not then something is wrong.
Disconnect the speaker if the voltage is like say 20 volts otherwise you could burn out the speaker. :'(
The DC supply Voltage will be on the terminals of those 2 large caps,, Where those 2 caps meet will be the Common which is often case ground as well (but not always). Black probe on the Center Tap join of those 2 caps then read voltage on the positive and negative rails. They should be very close to the same.
The fuses will be the AC Voltage supply from transformer and the black square blob between the caps and fuses will be the Bridge rectifier diodes.
Set DMM to ACV and read the AC voltage from the Transformer on those 2 fuses.
Just probe across each fuse will tell you the full AC voltage the amp runs from.
by the picture it looks like you have clear access to the track side of the PCB so should be easy to find the test points for the DC voltage.
hope it helps,, Phil.
DCV across the speaker terminals is 0.167
I'll post the other results when I take them (when I have time to take the board out again).
All good,That is a normal reading :tu:
Good chance the power is working ok ,,maybe somewhere between the line out and poweramp input is a failing component, Without a schemo it's hard to know.
Maybe some close up pictures of both sides of the PCB might help folks here work out the problem.
Phil.
Thanks :)
OK I'll get on to that after work. Given that the speaker terminal reading is OK do you still need me to take the other readings (DCV on the power rails, ACV on the fuses)?
Yes! as that is what powers the whole amplifier.
When I work on gear I first find the **Mains** input which is the Deadly end and if I see bare terminals with mains wires I cover them as it's all to easy to slip up. Even a small sheet of plastic will save you from a wandering finger. :trouble Also Check the Earth pin is attached to the case. I've found a couple of cheap far east rigs that have never been opened with No Earth pin connected,,Factory stuff ups.
I then establish the AC secondary windings and check the AC voltage (jot it down). Most common is 3 AC secondary wires being 2 actives and one common which is the CT center tap and that will be circuit common or Zero and often Case ground.
These wires might be 2 reds and 1 black but other colors are used but format tends to be the same.
This tells you that black is CT and the 2 reds are the Hot wires.
Voltage from black to either Red will be close to the same AC reading. Obviously Red to Red will read twice the value.
Then I read the DC voltages at the main filter caps.
Your supply is a Full wave bridge supply so the DC Voltage will be 1.4 times the secondary AC Voltage.
i.e. With a secondary of say 20/0/20VAC the resulting DCV after the Recto and filter caps will be close to 28/0/28VDC, give or take a volt for diode drop.
That is the DC the Amp runs on.
As the output is zero then I'd say the supply is working fine but you may get asked to cross check some voltages so wise to have the DC voltage that powers the circuit.
Meantime with the amp powered up get a small chop stick (Wood or plastic Not metal) and gently probe around the components on the pcb while running an mp3 player or some other audio signal see if you can find a cold solder join.
Often pcbs crack at the solder points and a wiggle of a component can find the offending break. As the rig is older it is a prime candidate for cracks on the solder pads.
Often you can't see them easily you need good light and a magnifying glass to see them.
Phil.
This is just to let you know that I haven't forgotten about this - circumstances have just got in the way and I have't been able to progress. As soon as I am able I'll take the readings and photos and post the results.
OK so here are some photos of each side of the circuit board - DMM readings to follow ASAP.
One thing I have noticed is hopefully shown in the close up photo of the two large black capacitors. Is the substance at the base of the capacitors glue or is it (as I suspect) evidence that one or both of the capacitors is leaking and if so is this a possible cause of the fault (the raspy distortion at low gain settings)?
Yes the caps could be leaky but maybe Don't replace caps just yet.
Check and post the voltages and also note the transistor part numbers as that will give the better minds here an idea of how the power stage works ,, and how to fix it. :tu:
Looks like the power stage has only 5 active parts so it is a very simple circuit and my hunch is it's just bad Xover distortion due to an aging circuit.
With the part numbers of those 5 transistor and the pictures you have taken it would not be too hard to draw a schematic.
In fact that is how i got started years back,, simply back engineering simple circuit like this one. I wasted a lot of paper at first but it did not take too long before I got legible drawings that looked a lot like the professional ones.
Here is a simple power amp circuit that is not much more complex than your unit except it has 7 transistors;
http://sound.whsites.net/project03.htm
Your unit might have Darlington power transistors hence only 5 transistors,,, the 3 or 4 bias diodes strapped to the heat sink are a clue.
Phil.
I see 5 transistors , please read what they have printed on the case and label them in the pictures.
You also have 3 2 leg thingies touching the heat sink, might be 3 diodes or 2 diodes and 1 resistor, please label them in the pictures.