Cheap POS.... ya... maybe...BUT

In this age of "Digital Everything"
I find it somewhat refreshing to see a new all analog SS amp.

I'd also like to see a schematic. Curiosity ya know?

Its been quite some time....
....but I think I replaced both Q9 and Q10 on my 40XL.

Old guy memory here, but I also think I had a similar issue with the tremolo fading out.

Just went and looked, and I did indeed replace them with generic 2N3904 transistors.

Do you have a scope to check the oscillator waveform?

Quote from: Jazz P Bass on February 13, 2022, 04:36:14 PM
Nice job on that schematic, Galaxiex.
Serious work went into that.
Thanks for all of that!!

Quote from: BBailey on February 13, 2022, 04:48:31 PM
I should add that these schematics are very helpful! Thank you for creating them.

You are welcome guys. 

Kind of a labor of love to go to the trouble, but I like doing it.
If it helps someone out, so much the better.

Quote from: BBailey on February 13, 2022, 04:43:40 PM
Okay - I did replace C12 once already.  I'll try another.

If that doesn't help, monitor the voltages at "A" and V+ when the problem occurs.
May give a clue as to what's happening.

Did you replace any of the power supply decoupling caps?
Specifically C10 and C20.

Quote from: BBailey on February 13, 2022, 04:21:44 PM
I have attached the schematic I am using - I downloaded it from this string of posts.
All the resistors are new, but there could be one that is failing under load.
There are some differences in this schematic and my two 40XL amps, but none that I see within the tremolo circuit.

Replace cap C12.
My schematic from post #19

Quote from: BBailey on February 12, 2022, 10:17:11 AM
Yes, that is correct. It's just that the reverb sounds brassy and shrill rather than a good reverb.  When I put the repaired PCB from the "inop" amp into the working 40XL chassis, the reverb in that amp works fine, so I am convinced the reverb drivers on both PCBs are working well.  The only difference is in the quality of sound coming from the two reverb tanks.

See post #26. 

Trace the circuit.
Draw schematic from that.

It shouldn't be too difficult.

I've drawn quite a few schematics for old, cheap, SS amps where the schem is unobtainium.

Search my threads in "schematics and layouts".

Quote from: mattbianconi on May 20, 2021, 03:04:52 PM
I got the kit that came with the 8 ohm speaker.  All assembled and currently powered with a 9-volt battery.  It seems I have to have the volume absolutely cranked to be heard over the guitar strings themselves. Turning the gain up obviously gets past this a bit.
I tried to use a 12 volt DC wall plug but that introduced a ton of hum into the amp.
What are you using as power for this little guy? Would an A23 battery work?
Thanks

Install a 10uf cap on pins 1 & 8 to maximize the gain.
The pads are on the board so it's easy to do.

Quote from: joecool85 on January 06, 2021, 07:23:34 PM

Quote from: galaxiex on January 06, 2021, 07:02:05 PM
Hey Joe, pretty cool amp. 

I'd back the project but I'm in Canada.
Can you change the kickstarter to allow folks from Canukistan to back it?

Thanks!

I've made the adjustment! Only reason why is that you have to calculate shipping for each country. If anyone else from another country is interested, let me know and I'll add it as an option!

Thanks Joe, I'm in!

Hey Joe, pretty cool amp. 

I'd back the project but I'm in Canada.
Can you change the kickstarter to allow folks from Canukistan to back it?

Thanks!

Quote from: jon_bondy on January 06, 2021, 05:41:34 PM
I would love to hear some sound samples from the amp, demonstrating the tone control and variable distortion.  It might help your kickstarter, too.

The kickstarter page has a video demo.

I have this one...

https://www.circuittest.com/sx-500d-variable-temp-soldering-station-60w-iron-digital.html

I like it, it works quite well.

A solution looking for a problem? 

Bumping this cuz we seem to have reached the limitation of the tiny output transistors. 

The new 18VAC transformer and resulting 25VDC rail is just a bit too much for them. 
Playing the amp for more than 30 minutes at full volume causes the output transistors to go into thermal overload.

At less than full volume I have not reached the limit...
but this thing sounds so darned good at full. 

So options are...

1. Better heatsinking on the output transistors
2. Better (higher rated) transistors and better heat sinking.

I'm leaning toward option 2 but might try cobbling up a better heat sink for the originals.

I do have a couple of NOS T0-3 PNP Germanium transistors looking for a home...