Another 'group' Melissa intended was run by the Police for young offenders, which they opened up to non-offenders - she met some interesting characters there
While she went mostly to learn to drum, she also played bass while there (only a limited number of drum kits and rooms) - and one day the bass combo she was playing through poured out loads of smoke!!. As a result, I was asked to look at it - and I was assured that the amp was still working while smoking, which I didn't believe
It was a Carlsbro 60W combo - and true enough, it was working and smoking.
I toook it to pieces, and found the Zobel resistor was smoking - something I'd never seen before - but the capacitor in series with it was an electrolytic, again something I'd never seen before.
Usually for an 8 ohm amp the zobel network would be 8.2 ohms and 0.1uF in series, so I fitted those, and it worked perfectly, and was stable as far as I could tell on a scope.
However, as Carlsbro are (were!) a local company I rang them - and spoke to the service manager - he asked me the serial number, as apparently they used different values on different production. He then told me the modification for it was to fit 8.2 ohms and 0.1uF - which I had already done.
So be aware, amps CAN smoke and work!.
Nigel, before it's death, mine smelt for over an hour during rehearsals.
On my multi-effects, low turned all the way up. Then on the amplifier, bass turned all the way up. Feeding a 4ohm set of speakers, volume at 8 or 9 out of 10.
As we moved things from the side room to the stage, during practice on-stage, volume was suddenly lost (maybe 6dB). As I was playing with distortion, I hadn't realised the bias had shot off in one direction, putting a severe amount of DC on the output (output transformer stopped this getting through). So, I turned the mid control up on my amp and the volume came back. Notice it's still smelling pretty bad at this point.
So, after another 5-10 minutes of one output transistor being stuck to supply voltage, it desoldered the wire connecting the speaker to the board. Despite all this, the 2A fuse on the output didn't bother to blow. Fixed it when I got it home, turned it all the way up and the fuse went pop on the first chord. Grrrr....
Chris
PS - in a moment of temporary insanity, I bought a battered old bass guitar for £50. Sounds lovely, but those strings are a nightmare compared to the super-easy-to-press guitar strings I love so very much.
On my multi-effects, low turned all the way up. Then on the amplifier, bass turned all the way up. Feeding a 4ohm set of speakers, volume at 8 or 9 out of 10.
As we moved things from the side room to the stage, during practice on-stage, volume was suddenly lost (maybe 6dB). As I was playing with distortion, I hadn't realised the bias had shot off in one direction, putting a severe amount of DC on the output (output transformer stopped this getting through). So, I turned the mid control up on my amp and the volume came back. Notice it's still smelling pretty bad at this point.
So, after another 5-10 minutes of one output transistor being stuck to supply voltage, it desoldered the wire connecting the speaker to the board. Despite all this, the 2A fuse on the output didn't bother to blow. Fixed it when I got it home, turned it all the way up and the fuse went pop on the first chord. Grrrr....
Chris
PS - in a moment of temporary insanity, I bought a battered old bass guitar for £50. Sounds lovely, but those strings are a nightmare compared to the super-easy-to-press guitar strings I love so very much.
What sort of transistor amp has an output transformer?.
The only ones I've ever seen are 100V line output types, for announcement type PA - not really very suitable for musical use.
Back in the sixties you could encounter transformer-coupled transistor amps every now and then. Some radio receivers for instance had two tiny little audio transfomers in them. They were actually using old-fashioned PP circuits like the ones used with tubes.
Back to topic: SS amps by Peavey for instance use output transformers IIRC when they are of the tube-sound-emulating type. Or do they just emulate the transformer behaviour ? Maybe I'll have to check back.
Regards
Charles
Back to topic: SS amps by Peavey for instance use output transformers IIRC when they are of the tube-sound-emulating type. Or do they just emulate the transformer behaviour ? Maybe I'll have to check back.
Regards
Charles
Yes, low quality, low power, hardly PA amps
One of the transformer types was an LT44 if I remember correctly?.
Seems a LOT of expense for little 'gain'? - but I can't say I've ever heard of one?.
A quick google finds a Peavy amplifier series called 'transformer', but they don't appear to use an output transformer, it refers to the tube/valve emulation.
H. Peavey mentions in a paper that the output transformer contributes quite a lot to the sound of tube guitar amps. He even mentions that the most expensive mistake would be to use a beefy high-quality output transformer - that is made for HiFi tube amplifiers - for a guitar amp.
Regards
Charles
Regards
Charles
I have read about using thicker strings, due to the lower string tension of short scale basses, in general
if of any use, my bridge tuning looks like this
Attachments
If it is right can only be said after checking. But the thicker stings must usually be longer for proper intonation. This is because they are a little further apart from the theoretical string model (and its behaviour) and closer to a metal rod (with its respective behaviour) due to their lenght/thickness ratio.
Intonation is the last thing that you fine tune when setting up because it has the least influence on the other parameters like relief and action.
The setting of the relief (via truss.rod) and action (via the bridge saddles) have a mutual influence. Therefore they have to be adjusted alternatively. I.e. the whole thing is an iterative task.
There is a fine ducument on how to do it on Jerzy Drozd's homepage.
On an instrument like my 8 stringed ERB this can get quite unnerving ......
Regards
Charles
Intonation is the last thing that you fine tune when setting up because it has the least influence on the other parameters like relief and action.
The setting of the relief (via truss.rod) and action (via the bridge saddles) have a mutual influence. Therefore they have to be adjusted alternatively. I.e. the whole thing is an iterative task.
There is a fine ducument on how to do it on Jerzy Drozd's homepage.
On an instrument like my 8 stringed ERB this can get quite unnerving ......
Regards
Charles
Nigel, the amp was an old one, bought faulty off eBay. Tried it after fixing it, then started playing around with mains transformers with centre-tapped secondaries on the output. It was amazing to hear the difference between transformers.
I had heard of the paper about the contributions of different components to the valve sound. Mains transformers I had, squishy high voltage power supplies I did not. It sounds pretty decent now, but it distorts when pushed. So, it remains a general messing about amp
Chris
I had heard of the paper about the contributions of different components to the valve sound. Mains transformers I had, squishy high voltage power supplies I did not. It sounds pretty decent now, but it distorts when pushed. So, it remains a general messing about amp
Chris
hey Chris
If you would like to start a thread with amp repair, I can help you to move posts over
its just a kind offer, with the best intentions
or there is also this thread with Amp Heads
http://www.diyaudio.com/forums/musi...0-amp-heads-guitar-bass-general-interest.html
If you would like to start a thread with amp repair, I can help you to move posts over
its just a kind offer, with the best intentions
or there is also this thread with Amp Heads
http://www.diyaudio.com/forums/musi...0-amp-heads-guitar-bass-general-interest.html
Tinitus,
Thanks for the kind offer, but I think the subject of my amp has died off now I've answered a couple of questions.
Having recently purchased a bass guitar, I'm reading what's been posted here with interest - the octaves (at 12th fret) aren't quite in tune with the open strings. They're close, but I've pretty much run out of adjustment at the bridge.
Thanks again,
Chris
Thanks for the kind offer, but I think the subject of my amp has died off now I've answered a couple of questions.
Having recently purchased a bass guitar, I'm reading what's been posted here with interest - the octaves (at 12th fret) aren't quite in tune with the open strings. They're close, but I've pretty much run out of adjustment at the bridge.
Thanks again,
Chris
lets hear more
I guess 12th is higher than loose string
and if you tune 12th down, it gets low and muddy on loose string
which way is your bridge run out
what kind of bridge
for the learning how to play, the best things happen around 12th, in my opinion
hey, you may be in luck
I may be able to help a bit more
I just now measured my set up
720mm scale
360mm at 12th fret
I checked a fret scale calculator
and its precisely spot on
checked another scale length
seems 12th fret is always half way
heck, I didnt know it was that simple
well, thats the rough one
fine adjust will be impossible to measure like that
but its half way there, so to speak
so lets try and measure your bass
It was never meant as a stage amp. Abuse killed it, I fixed it, abuse killed it, now it works, but it's only a practice amp.
I've been adjusting the bridge so the sliders move away from the neck. The octaves a nearly there, but they can't move much further. The bridge itself is the same design as posted at the top of the page.
Chris
I've been adjusting the bridge so the sliders move away from the neck. The octaves a nearly there, but they can't move much further. The bridge itself is the same design as posted at the top of the page.
Chris
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