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Commercial Gainclone kit- building instructions

bridged?

Can someone point me to where I can find a discussion on benefits and problems associated with running the LM4780 kit in bridged mode? Seems to me like a pair of matched circuits on a single chip would be especially well suited for differential balanced operation. Is this correct, or am I missing something?
 
Ok, I have a problem with picking up radio frequency. It happens with my guitar amp too but not with my JVC amp. The JVC does not have a grounded plug but I dont think my apartment is grounded anyway. Most plugs dont have the place for a ground and I know its a very old place. I've tried it in all the plugs in my appartment, even the newest one added directly below my breaker box so Im not sure what the next step is. any ideas?

Thanks!
 
After all this reading, it seems that you have substituted the Panasonic 1500uf with 100uf blackgates? Then do you still use the 10uf on the power board?

For aussies who are having trouble finding a decent toroid (if altronics and jaycar are not enough for you), I ordered mine from Harbuch Electronics. 300VA 2x25V with epoxy centre order code is H/2/4/16/P
 
Ok, I have a problem with picking up radio frequency. It happens with my guitar amp too but not with my JVC amp. The JVC does not have a grounded plug but I dont think my apartment is grounded anyway. Most plugs dont have the place for a ground and I know its a very old place. I've tried it in all the plugs in my appartment, even the newest one added directly below my breaker box so Im not sure what the next step is. any ideas?

Thanks!

Well i used to have a similar problem. But after i put a ferrite bead on my interconnects it went away. I got no idea what happened there, but it was a cheap alternative! Hope someone has a scientific approach for you. Good luck!
 
Ok, I have a problem with picking up radio frequency. It happens with my guitar amp too but not with my JVC amp. The JVC does not have a grounded plug but I dont think my apartment is grounded anyway. Most plugs dont have the place for a ground and I know its a very old place. I've tried it in all the plugs in my appartment, even the newest one added directly below my breaker box so Im not sure what the next step is. any ideas?

Thanks!

Take the plate off of the wall and (after turning off your circuit breaker or removing the fuse) look where the two wires connect to the plug. In my old house they had the ground wire wrapped around one of the live wires. I asked an electrician friend of mine 'what the hell?' and he said they just used to do it that way 40 years ago because it was easy and not much needed a ground plug. So then you can unwrap it and put in a proper wall plug with a ground. Check to see if you have ground because you might honestly have to find the other end of that wire and attach it to ground. In my basement I was lucky enough that the wiring ran on the ceiling and I could follow most of it to make a fix. Now, no basement, everything is in the walls. A friend of mine installed a copper spike outside, ran a wire into the wall and into his listening room. Grounded.
Uriah
 
A friend of mine installed a copper spike outside, ran a wire into the wall and into his listening room
Uriah
this is a very dangerous practice.
Never install a ground spike in lieu of a direct connection from safety ground to neutral at the mains distribution board. The electric power supply company will have fitted this essential safety feature. Do NOT try to defeat it.
 
Ok, I have a problem with picking up radio frequency. It happens with my guitar amp too but not with my JVC amp. The JVC does not have a grounded plug but I dont think my apartment is grounded anyway. Most plugs dont have the place for a ground and I know its a very old place. I've tried it in all the plugs in my appartment, even the newest one added directly below my breaker box so Im not sure what the next step is. any ideas?

Thanks!

This may be silly but could the problem be not having the amp in a case?


Can you post a close up of the snubbed power supply? I'm getting ready to build my first amp and would like to understand this option. Good luck, Scott
 
Source selector questions

I am considering adding a source selector to my LM3875 Premium by installing a DPDT toggle switch ( two sources only). Would there be any point in using a 4 pole DT switch to switch the signal grounds also?

One source will be to a headphone plug to go into a laptop, so SG for both channels will be connected. Will this mess up the star ground? Lastly, would there be an advantage to shorting the signals to ground in this input when it's not in use?

Thanks in advance.
Dave
 
My gainclone amp is finished, sounds great

Hello all,

i just finished one of my gainclones using Peter Daniels kits. In total i will build two 2 channel amps, each having a bridged LM4780 per channel. I use balanced inputs.
So the first was finished this week, and i will post pictures later. After powering up, i measured the voltage over the loudspeaker outputs and had 0.02 Volts one one channel and 0.023 Volts on the other channel. Than i connected it to my speakers. Nu hum, noise or anything just quiet. Then i connected my preamp and cd-player, still quiet. Then the moment, press the play button, and then there was music. It has been playing now for some hours, and i am starting to like it more and more.
I found my Kenwood/Accuphase L-1000M power amp already very fast and detailed. But this is better. I cannot wait finishing the second amp and using my electronic crossover.

regards
 
I'm building a 4870 kit and have a few questions. I'm new to amplification DIY (and to these higher voltages) but I build low voltage audio electronics (guitar pedals, digital signal processors, synthesizers) professionally.

I'm having trouble figuring out whether I want to build these boards as bridged or parallel amplifiers. I am building this to be a bass guitar amp. I'd like each board to have a single output to a single speaker, and will likely use 8 ohm speakers. I will be driving these with a DIY preamp that's unbalanced.

I'd like to send a single mono signal to both 4870 boards, and have each 4870 driving a single 8 ohm speaker.

Which makes more sense for this setup: bridged or parallel?
 
If you are using unbalanced preamp it's better to use the amp in parallel mode as bridged amp by itself will not perform unbalanced to balanced conversion. OTOH, with bridged setup you will get more power into 8 ohm than running amp in parallel.

I am considering adding a source selector to my LM3875 Premium by installing a DPDT toggle switch ( two sources only). Would there be any point in using a 4 pole DT switch to switch the signal grounds also?

One source will be to a headphone plug to go into a laptop, so SG for both channels will be connected. Will this mess up the star ground? Lastly, would there be an advantage to shorting the signals to ground in this input when it's not in use?

I like to use toggle switches for input selection myself : http://www.diyaudio.com/forums/audio-sector/76609-most-advanced-gainclone-amp-yet-3.html#post1069555

Originally, I was switching grounds too (with a rotary switch though) but later abandoned that and do signal switching only (besides that it's more complicated, you may also get noise when switching grounds)

It's hard to say if it messes up a star ground. If you short the other signal to ground, you should get less crosstalk, but that usually is not a problem.
 
Question on technique:

I really liked your ground star wiring in the post below. Trying to mimic the same in my own build, I had trouble with soldering the copper wire on the back side of the OG pads. The wire from the other side got in the way of a solid resting place for the copper wire. Do you have any technique you can share on this? Do you use a short output ground wire on the opposite side--so it doesn't stick through? Thanks.



The important aspect about sharing a single transformer and common rectifiers per two amp channels is power star ground.

While you could simply run PG+ and PG- (ground) wires from rectifier board to each amp board, in some setups hum problems were reported and presently I always use star (power) ground in all my amps.

I simply achieve it by connecting output grounds (OG, on the opposite side of speaker wire connection) with a 14ga solid core copper wire.

The center of that wire is my power star ground and both PG+ and PG- grounds from rectifier board connect here. In the picture below the connections are so short that I used single runs of wire, normally I use two wires for both PG+ and PG-.

Please note that power ground is also directly connected to the chassis.

I specifically refer to it as power star ground, as signal wires from RCAs are not connect directly here. They connect through separate traces on PCB to OG (output ground) pads.
 
I solder the copper wire directly to output wires on the opposite side of the pads, it's very simple. With Patek, I do it as in attached pic.


Any thoughts on using Vishay Z-Foil for R1, R2 and Rnfb and Vishay VTA55 for R3? The boards look great by the way, thanks Peter.

Z-Foil would be certainly very good choice for input series resistors. Caddock MK132 were the best resistors for input shunt and feedback, better than Vishays. As to R3 (680R), Rikens were the best. I use Kiwame now, as Rikens are discontinued. You can try Vishays for that location, but results might not be better.
 

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Peter, I just finished my LM3875 classic test assembly very similar to your build in the first pages of the thread. Only difference is there's a 1/4" chunk of copper between the chips and the bottom of the aluminum channel. And I upgraded the RF to a Caddock MK132. The amp powered up with a DC offset of .049 -.078 on one channel and .05-.036 on the other. Those seem like OK numbers to me. So far I'm very pleased with the sound. I immediately understood what people describe as "fast". I'm also hearing a smoothness in the midrange similar to my old VSP Labs Trans mos 150. Dare I say " tubesque" Thanks so much for the great Customer service.


I do have a couple questions.

1. I left the input series resistor off, using a piece of bare copper. What effect on the sound do people perceive when adding that R?


2. I'm interested in at least listening to the amp with a snubbed PS. I'm taking it that RZ and CZ on the amp board are the zobel. What are the correct values to use?
They also talk about an additional bypass C along with the series R-C snubber network. Where does this C mount and what is the correct value?

Thank you, Scott
 
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