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 1 
 on: August 15, 2018, 03:54:40 PM 
Started by Tchock - Last post by DrGonz78
Not sure if they will support you on this specific product?? But I did call Fishman when I was fixing loudbox mini and they were very receptive to my call. In fact, they offered repair rate that seemed reasonable and they helped me out with schematics. Now that might be the result that the model I was trying to fix was far past being a warranty repair. Not sure about your product but it is worth the time to call... They have general 1-800 type number and international type too.

https://www.fishman.com/contact/

 2 
 on: August 14, 2018, 03:46:09 PM 
Started by flester - Last post by flester
Heres what I came up with. The bundle of 6x AA rechargeables to the right of the pedal box has a centre -ve  lead supplying pedals, and a centre +ve  supplying the amp in the fudge tin. The Orange is my cab.  I guess I need reverse polarity protection for the amp and maybe the pedals. Can I use an LED for that or do I need another type of diode? I know battery life may be an issue but may be a proper FX power supply mat work better?

Sent from my SM-G935F using Tapatalk


 3 
 on: August 14, 2018, 01:14:03 PM 
Started by psafloyd - Last post by psafloyd
I'd try that trick with the soldering iron if I were you, as I found it most effective.

Thanks.

If I have to, I can replace them all. For an hour's work and a few quid, it will be worth it, if I didn't have a Drive Master in fully working condition. Still, I can always get my money back on the Guvnor if I replace the pots. Assuming I can, as they're small board mounted ones. I will have to check.

 

 4 
 on: August 13, 2018, 11:41:11 PM 
Started by Tchock - Last post by Tchock
I'm looking for Fishman Loudbox amplifier model PRO-LBX-001 schematics.
Can anybody help me, please?

 5 
 on: August 13, 2018, 11:02:33 AM 
Started by psafloyd - Last post by psafloyd
Thanks, Estomagado, your idea worked a treat. After two sessions trying to get enough contact cleaner in to free them off, I only managed to get one working.

So, I got the soldering iron out with . nice fine tip and gave each a little heat, moving the point around after a few seconds. This loosened all of them off and I gave them a good dose of contact cleaner and they are now lovely and loose.

As I said to Phil below, I believe it must have been during the two weeks we were on holiday and the house was shut up as it must have been incredibly hot and completely evaporated any remaining lube.

Thanks for your help – another piece of kit resuscitated and put back to use.
 

 

Thanks.

If I have to, I can replace them all. For an hour's work and a few quid, it will be worth it, if I didn't have a Drive Master in fully working condition. Still, I can always get my money back on the Guvnor if I replace the pots. Assuming I can, as they're small board mounted ones. I will have to check.

 

 6 
 on: August 13, 2018, 10:59:02 AM 
Started by psafloyd - Last post by psafloyd
Thanks, Phil. Points all well made and I completely agree. I was simply thrown by all five pots being equally seized – each utterly immobile – and I can only assume it has been the long hot summer we have had, particularly hen I was away and the house was locked up.

Have resolved now and will be posting to above response.

 

 7 
 on: August 13, 2018, 02:10:41 AM 
Started by Aleksandar - Last post by Enzo
All WHAT DC ripple?

A zillion hifi stereos and other solid state amps and none have chokes.  Ever see a choke in a PA power amp?

Just my opinion, but it sounds like a solution looking for a problem.

 8 
 on: August 13, 2018, 01:19:16 AM 
Started by Aleksandar - Last post by Loudthud
Using chokes is no guarantee that your amp will be hum free. A bad grounding scheme can introduce hum that you can hear when there is no signal. In general you need to know how much current will pass through each choke. Once you get  up to the several Amp territory, you are looking at a 5 pound (2 kilogram) chunk of iron and for a dual rail amp, you will need two. That is the case when you pass all the current for the power supply through the chokes.

Link to data sheet: https://www.mouser.com/datasheet/2/389/tda7293-957143.pdf

The TDA7293 is a 15 pin chipamp so it may be possible to only pass the current for the driver stage through the chokes. (This allows the use of much smaller chokes.) This is uncharted territory, you'll need to experiment and you may blow up some chips before you get it right. A simple RC decoupling network might work just as well.

When a solid state power amp clips to the rails, any ripple on the rail is transferred to the speaker. Tube amps do the same thing. It's hard to hear this hum because the amp is as loud as it will go at that point. If you want to eliminate this hum, you need to lower the Voltage to the driver stage so the it "runs out of gas" before the output transistors clip to the rails. This lowers the power output by perhaps 10%.

Another way to eliminate this "slamming the rails" hum is to not let the power amp clip to the rails. You can do this with a Master Volume control, but this only works if the power amp is acting as a Voltage amplifier with no mixed mode feedback. Mixed mode feedback means current flowing in the speaker determines if the power amp needs to "Go to the rail" to make current in the speaker follow the input. (Flame On Non-believers)


 9 
 on: August 12, 2018, 05:28:34 AM 
Started by Aleksandar - Last post by GB
Yeah... agree with JM. Not worth it.
The TDA will inherently reject power supply ripple in any event.
The TL072 should be de-coupled from the PS with a couple of (say) 100 ohm resistors in series and 100uF caps behind them on each of the + and - supply rails... as OP Amps normally are.

 10 
 on: August 11, 2018, 06:15:19 AM 
Started by Koreth - Last post by GB
Attached a schematic of the preamp (only) section. It may be a little confusing at first... but to simplify...
The section immediately after the first stage is simply for switching between the normal and top-boost modes... and the section at lower right to do with the biasing of the power amplifier... not shown in this drawing. In both cases there are associated LEDs which are primarily front panel indicators

I'm thinking of starting a separate thread on this... if there is continued interest... and so as not to hi-jack the intent original thread...

... and a bonus!  :)
Attached also an MP3. It is in stereo. The left channel is simply a mike in front of the speaker cab (a bit boomy?) - and the right channel is DI from the speaker out of the amp.

GB

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* Recent Posts
Fishman Loudbox PRO-LBX-001 Schematic by DrGonz78
[August 15, 2018, 03:54:40 PM]


Centre Negative DC Jack by flester
[August 14, 2018, 03:46:09 PM]


Seized pots on a Marshall Guvnor Mk 1 by psafloyd
[August 14, 2018, 01:14:03 PM]


Using a choke for a TDA7293 amp by Enzo
[August 13, 2018, 02:10:41 AM]


Thoughts on the difference in sound between tubes and solid state by GB
[August 11, 2018, 06:15:19 AM]

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