Amp discovery!

[Chris mudd]

I just got my amp in the mail and can't wait to start putting it all together.
What I would like to do is put this in an enclosure with the Blackface Fender w/tonemender preamp from this site. Ths voltages for both are 18+ volts, 24 should be OK.

Is there a reason I couldn't box it all together and power it with this supply:

https://www.jameco.com/z/BLP40-1024G-Bel-Power-Solutions-24-Volt-1-1-Amp-25-Watt-Open-Frame-Switching-Power-Supply_2227575.html

from what I can tell, unless having the power supply too close to the amp is noisy, it should be a nice self-contained amp fro practice and what-not.

Will this work?

[rocket88]

that's similar to what i used. one big think you need to do. make sure the power supply is enclosed. you're going to have a 120VAC coming in and you can easily get a nice shock.

btw, for those that are curious for how these little class d amps sound with a preamp in front. here's a short clip of my build, 100watt mini model t. gain for both channels is at noon, and i through one of my distortions in front of it that's essentially a highly modded Ross Distortion.

[zoof]

Tried this with a bassman preamp at 9v and the amp at 12v. It's really nice. Only thing that bugs me is a white or pink noise coming from the amp. That setup takes dirt pedals really well. New workbench amp :) Thanks for the tip!

[Sensei Tim]

Finally got around to wiring this up tonight.

I’m getting a high pitched whine coming from my speakers when I connect things. I don’t think it changes in volume as I change the volume of the preamp.

Using an 8ohm Mesa cab.  Using a plastic isolated jack, + to tip, - to sleeve.

Using a 24v dc power supply.

[Travis]

What voltage are you reading when the amp is powered up?

Do you have a stompbox that you could test with the power supply to maybe determine if the noise is from the power supply?

[Sensei Tim]

I’ll check voltages tomorrow. I’m pretty sure it’s gling to be around 24v based on what I was measuring on the dr boogie transistors.

I don’t think that I have anything here that can supply high enough current.  I can borrow a bench supply from work on Tuesday to test with.  

I’ll also try injecting a sine wave into the amp input to see if possibly one of the preamps is causing the noise.

[Travis]

Checking the voltage with the amp powered up should let you know if current is an issue. If the voltage is dropping considerably when the amp is plugged in then you need more current

[Sensei Tim]

Don’t think current supply will be an issue. It’s a 4 or 5 amp power supply

[Travis]

Ah, I was confused by the previous post

Sensei Tim wrote

I don’t think that I have anything here that can supply high enough current.  I can borrow a bench supply from work on Tuesday to test with.

[Sensei Tim]

Ok so I did a few things earlier this evening:

Confirmed that I’m getting 24v to the amp module.

Tried the power supply with another pedal: no hum.

Disconnected power to the amp board and played the preamp into an amp. No problems.

Connected power to the amplifier module and as soon as power was connected I heard the hum thru the preamp which was still connected to an amp as a pedal.

Those of you guys who have had success:  were you using high gain preamps into your amp?  Did you do anything to isolate the amp power from power going to your preamp?

Happy new year!  ;)

[balazs.bencs]

Sounds like ground loop to me. Try to isolate the power for the preamp, that should make things better.

[Kinski]

I used a low/medium gain preamp and haven’t had any issues with noise.

[Sensei Tim]

What would you recommend?  A 46R resistor between the preamp and power supply or an opto isolator?

[kuzieem]

Any thoughts on this amp comparing to Tiny Giant? Volume level and signal/noise ratio? Also, the Tiny is class AB (probably) and this one looks like class D (economical but poorer fidelity). Anyone?

[rocket88]

Class D is not considered economical and may high end amps are class D based, look at bass amps from mesa boogie, aguilar, etc., and they're commonly used as amps for car audio. Class D amps are small and efficient, and the chip is what determines their fidelity.

Haven't build the tiny giant, but i have the parts sitting around since i was planning to years ago when the layout first appeared on the main page, just other builds got in the way. With that being said, the class D board i used sounds great. I have no more noise then the actual tube amp, and output is about 80watts at 8ohm, which is more than enough for home use, and if being used in a gig more than enough if you're being miced.

You can hear what mine sounds like in the video above, gain is at about noon, and the master volume is at about 2 o'clock. The mic is not recording, it was recorded through my iPhone which was about 8ft away from the speakers. Keep in mind, just like any other amp if the gain is lower you'll get lower output.

[BetterOffShred]

Did you use the Model T layout (yours I believe) from the forum?  It sounds really good.   I haven't built anything with mine yet, but I was planning on doing a Model T or bassman type preamp.  Thanks dawg
-Brett

[kuzieem]

Thanks. By saying economical I ment efficient. My bad (English). Low power consumption comparing to wattage was what I understood as "economical".

[rocket88]

Hey better. Yep used my layout on the main page to make the mini model t. The thing is I'm running it at 24V, just like the power amp, and removed the switch so theres a single input going to both channels at the same time.

No worries kuzieem. Most of the time when people say economical they mean cheap and not always in a good way.  just wanted to make it clear it's not cheap and really a high quality power amp.

[BetterOffShred]

Sure, that makes sense.  Use that extra gain stage :)   Yeah were the stock trimmers enough to bias the Fet's at 24V?   Worst case scenario a fella could just put a 7809 after the power socket receiving 24V and spew 9V at the preamp board.  

[rocket88]

Unfortunately they weren't, I had to up them to 50k if I remember correctly. You could do that, but the FETs like higher voltage and make them behave more tube-like dare I say, and it will sound more like the real deal. Plus you get more output.

It's not that you're using the extra gain stage, what I did is make it so you're plugging into both channels, bright and normal, just like plugging into the middle jack on the amp. So to control each stage you use the gain pots, just like the real amp. The thing is, keep in mind I've place the real thing years ago, that's where the amp shines and what 99% of people that have them do.