Hi folks,
I have recently purchased some simple, 2.5 watt LM 380 based amp kits. They make a tidy little CBG amp but lack gain control for a bit of crunch. Does anyone know if putting a simple pre amp module in line between the guitar and the amp will, effectively, give me some gain control. Would this basically be like a little boost pedal?
Anyone have experience of this?
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Pre-amps are used for impedance matching, not for providing gain. Most preamp circuits have next to no gain. The reason they are talked about a lot on CBN is so that you can better match the high impedance of a piezo pickup with the lower impedance input of a guitar amp. In this role these pre-amp circuits are sometimes called "buffers". Unfortunately, to talk in more detail about this is beyond me, as most of what I've picked up about the subject was learned by reading other discussions on CBN. But, maybe some of the other members can speak with more detail on you specific questions.
P.S. Which pre-amp kit did you get (Maker, model number, price)? And do you have the URL to their website? I'm looking for a inexpensive preamp kit that includes the PCB as my breadboard experiments are to messy to consider selling.
Looking at the picture of the circuitboard for the LM380 amp there is a small black square with a stick attached between the two blue screw terminals on the left - when I try to increase the photo it pixilates too much to make it out clearly - is is a type of trim pot that lets you increase the gain of the amp circuit?
Preamps can be used as a buffer for impedance matching but can also be used to boost/add gain to a signal - from the literature on the weblink it says the one you have can give a gain of up to 100 and the hex slot can be used to adjust the gain.
I haven't used a LM380 chip (I like the growl you get from a LM386 and the smokey amp is the easiest one to start with) so don't know how it takes to being flogged with overdrive. There are a couple of links http://www.diystompboxes.com/smfforum/index.php?topic=61141.0;wap2
the first link isn't much help other than to confirm it can be done,but the second one using a "valvecaster" as the preamp is a valve preamp which uses a 12AU7 valve http://www.aronnelson.com/DIYFiles/up/12AU7-6111_Valve_Caster_Summa... (just for interest) and I have built one and it can overdrive my 20W mains practice amp so it would seem the chip can cope with overdrive.
That said I realise you have blown a couple of amp circuits already so unless you want to change your name to Ampsbane (good name that lol) I would start with the preamp turned down low ;O)
Both those pre-amps look interesting. Sorry about the mis-info I gave in my posting above. It's good to know that pre-amps can be used to provide gain and not just impedance matching. But, at least my reply along with yours stimulated a response from a more knowledgeable person. Let us know how your experience with these pre-amps turn out. -Rand.
You haven't mis-informed - what you describe is spot on for a MPF 102 type preamp circuit and trying to find the link I used to build one found your blog which covers it in much more detail
The ready built ebay uke or guitar preamps (or EQs) cost around £6 to £10 sent from China to the UK - they don't post to China according to the UK ebay listings???? Is there some sort of ban on sales? These tend to give +/- 12dbs so can boost a piezo and also boost magnetic pickups. They work well put in a separate box and used as a stand alone preamp and with a simple Smokey amp LM386 circuit make a nice travel amp with a nice overdrive.
The preamp in this was a "spares or repair" so had no back or clip on battery box - the new ones would be a simple plug and play type circuit.
No worries, all input is helpful I think, it gets the grey matter twitching and people talking. I'm waiting for the pre amps and the time to put it all into play. I will let you guys know what I find.
Replies
Pre-amps are used for impedance matching, not for providing gain. Most preamp circuits have next to no gain. The reason they are talked about a lot on CBN is so that you can better match the high impedance of a piezo pickup with the lower impedance input of a guitar amp. In this role these pre-amp circuits are sometimes called "buffers". Unfortunately, to talk in more detail about this is beyond me, as most of what I've picked up about the subject was learned by reading other discussions on CBN. But, maybe some of the other members can speak with more detail on you specific questions.
P.S. Which pre-amp kit did you get (Maker, model number, price)? And do you have the URL to their website? I'm looking for a inexpensive preamp kit that includes the PCB as my breadboard experiments are to messy to consider selling.
-Rand.
http://www.mindsetsonline.co.uk/product_info.php?products_id=1009713
...and the amp...
http://www.mindsetsonline.co.uk/product_info.php?products_id=1179
Hi Tom,
Looking at the picture of the circuitboard for the LM380 amp there is a small black square with a stick attached between the two blue screw terminals on the left - when I try to increase the photo it pixilates too much to make it out clearly - is is a type of trim pot that lets you increase the gain of the amp circuit?
Preamps can be used as a buffer for impedance matching but can also be used to boost/add gain to a signal - from the literature on the weblink it says the one you have can give a gain of up to 100 and the hex slot can be used to adjust the gain.
I haven't used a LM380 chip (I like the growl you get from a LM386 and the smokey amp is the easiest one to start with) so don't know how it takes to being flogged with overdrive. There are a couple of links http://www.diystompboxes.com/smfforum/index.php?topic=61141.0;wap2
http://www.offsetguitars.com/forums/viewtopic.php?f=11&t=15564&...
the first link isn't much help other than to confirm it can be done,but the second one using a "valvecaster" as the preamp is a valve preamp which uses a 12AU7 valve http://www.aronnelson.com/DIYFiles/up/12AU7-6111_Valve_Caster_Summa... (just for interest) and I have built one and it can overdrive my 20W mains practice amp so it would seem the chip can cope with overdrive.
That said I realise you have blown a couple of amp circuits already so unless you want to change your name to Ampsbane (good name that lol) I would start with the preamp turned down low ;O)
Regards,
David
Both those pre-amps look interesting. Sorry about the mis-info I gave in my posting above. It's good to know that pre-amps can be used to provide gain and not just impedance matching. But, at least my reply along with yours stimulated a response from a more knowledgeable person. Let us know how your experience with these pre-amps turn out.
-Rand.
Hi Rand,
You haven't mis-informed - what you describe is spot on for a MPF 102 type preamp circuit and trying to find the link I used to build one found your blog which covers it in much more detail
http://www.cigarboxnation.com/profiles/blogs/piezo-preamp-experiment
The ready built ebay uke or guitar preamps (or EQs) cost around £6 to £10 sent from China to the UK - they don't post to China according to the UK ebay listings???? Is there some sort of ban on sales? These tend to give +/- 12dbs so can boost a piezo and also boost magnetic pickups. They work well put in a separate box and used as a stand alone preamp and with a simple Smokey amp LM386 circuit make a nice travel amp with a nice overdrive.
The preamp in this was a "spares or repair" so had no back or clip on battery box - the new ones would be a simple plug and play type circuit.
Regards,
David