Chip Amps - Anyone using or building them

[A J]

What voltage runs on 6dj8 B+?

 

I'm not certain - here's a copy of the schematic..

 

[Full Range]

My Sonic Art chip amp uses the 3876T chip not the 3886T.I agree the chip amps sound great but mine has always sounded best when used with my Supratek valve preamp which fleshes out the tonal balance nicely.Used like this it sounds very much like a good modern SET.My preamp uses 300Bs so to me this indicates the chip amp is very tranparent.More so than the vast majority of transistor amps I have tried.You need reasonably efficient speakers with an 8 ohm load.Mine drives an old pair of B&W DM2As very well.

I was thinking along the same lines

Connect a source to my combo DAC/tube pre amp then to the chip amp

[Full Range]

Research has progressed on to Chip Amp of the mono-block variety

Not sure how good this US brand is - http://www.dalaudio.com/Studio-3875-Mono-Block-Chip-Amps-p/dals3875mob-r2.htm

Again just, I am new to the world of chip amps, I have never used mono-block amps before - so I thought why not

If I'm going to change a piece of equipment I may as well go all the way as I have speakers sensitive enough to entertain such thoughts

[oceangreen17]

Hi FR, 

 

Did you have a chance to listen to a chip amp in the last few days?  

 

I am not familiar with the Dalaudio monos you mention above but suspect some SNAers would know about them.

 

I personally are still impressed with my Gainclone despite what others have said about them.

 

As I mentioned, with the right speakers they certainly compare well to some of my amps costing $3-5K  - Audion, Counterpoint, Musical Fidelity, ME, Bel Canto, and Valvet

 

Cheers Steve 

[Full Range]

Hi FR,

Did you have a chance to listen to a chip amp in the last few days?

I am not familiar with the Dalaudio monos you mention above but suspect some SNAers would know about them.

I personally are still impressed with my Gainclone despite what others have said about them.

As I mentioned, with the right speakers they certainly compare well to some of my amps costing $3-5K - Audion, Counterpoint, Musical Fidelity, ME, Bel Canto, and Valvet

Cheers Steve

The unit arrived on the weekend but I haven't tried it fully yet

It's possible that it's a DIY Gainclone chip amp but I'm not certain as I forgot to ask

It's quite a heavy and bulky unit

I was really looking forward to it too

The amp was connected via the preamp, but the test was stopped

Reason I haven't fully tried it is that it that it makes a huge pop sound through the speakers when turned on - and I thought better to be safe than sorry and not proceed with it

Edit

Just went onto the Dalaudio site and they don't make a 240 Volt version

Some photos

Edited November 14, 2013 by Full Range

[Newman]

Goodness knows what that is you have there, fullrange. The label on the back sports an Audio Note UK logo. (!)

 

Was the preamp powered up and wired to the power amp before you turned on the power amp and got the 'pop'?

[Full Range]

Goodness knows what that is you have there, fullrange. The label on the back sports an Audio Note UK logo. (!)

 

Was the preamp powered up and wired to the power amp before you turned on the power amp and got the 'pop'?

I think the case/cabinet has been repurposed Newman

I think the preamp was turned on but volume was on zero

I always connect all wiring prior to turning on

[Full Range]

I am assuming it's got no soft ON/OFF

As I have permission to check that everything is connected inside I just opened it up and took a couple of photos

[Newman]

Can you read which chip it is?

[ArthurDent]

Looks like a standard AudioSector LM3875 except for the large outboard filter caps. Which is probably causing the turn on thump. How big are they?

[Full Range]

Can you read which chip it is?

  

Here is a photo

Looks like a standard AudioSector LM3875 except for the large outboard filter caps. Which is probably causing the turn on thump. How big are they?

The noise is enough to say WTF Ken

[georgehifi]

Wrong thread

Edited November 14, 2013 by georgehifi

[ArthurDent]

The noise is enough to say WTF Ken

 

And the value of the caps?

 

Whilst we're at it.

 

No input coupling caps. But the pre has them on the outputs?

 

Without the optional DC unity gain cap in the feedback ground leg these things (LM3875's) will amplify DC just fine.

 

Have you measured the steady state DC offset on the outputs.

 

Tried powering them up with the inputs shorted.

Edited November 14, 2013 by KenTripp

[A J]

I don't like the way that those filter caps are wired directly by long flyleads to the amp PCB - better off having onbord local decoupling caps and maybe high qulaity bypass caps, at least that's what I've done, those filter caps should just be wired up to the +/- Vin. My LM3875 does not give a noticable pop on turnon, I see this in the application sheet:

 

"Under-Voltage Protection: Upon system power-up the under-voltage Protection Circuitry allows the power
supplies and their corresponding caps to come up close to their full values before turning on the LM3875 such
that no DC output spikes occur. Upon turn-off, the output of the LM3875 is brought to ground before the power
supplies such that no transients occur at power-down."

 

More from the data sheet:

"SUPPLY BYPASSING
The LM3875 has excellent power supply rejection and does not require a regulated supply. However, to eliminate
possible oscillations all op amps and power op amps should have their supply leads bypassed with lowinductance
capacitors having short leads and located close to the package terminals. Inadequate power supply
bypassing will manifest itself by a low frequency oscillation known as “motorboating†or by high frequency
instabilities. These instabilities can be eliminated through multiple bypassing utilizing a large tantalum or
electrolytic capacitor (10 μF or larger) which is used to absorb low frequency variations and a small ceramic
capacitor (0.1 μF) to prevent any high frequency feedback through the power supply lines.
If adequate bypassing is not provided the current in the supply leads which is a rectified component of the load
current may be fed back into internal circuitry. This signal causes low distortion at high frequencies requiring that
the supplies be bypassed at the package terminals with an electrolytic capacitor of 470 μF or more."

Edited November 14, 2013 by A J

[ArthurDent]

Yeah I'd be removing the large caps and mounting some 1200uf-1500uf ones on the boards where they should be as well as some bypass caps on them.

 

These things shouldn't pop at turn or or off.

 

The other thing to look at is earthing etc.

[Full Range]

And the value of the caps?

 

Whilst we're at it.

 

No input coupling caps. But the pre has them on the outputs?

 

Without the optional DC unity gain cap in the feedback ground leg these things (LM3875's) will amplify DC just fine.

 

Have you measured the steady state DC offset on the outputs.

 

Tried powering them up with the inputs shorted.

A quick NOTE

I can invent or reinvent things mechanical that are unique at a drop of a hat

Give me something electronic and I'm lost, but I am very good at soldering to clear instructions

I can read a schematic as to individual positions, but have no idea of values and what they actually do

A capacitor photo Ken

[ArthurDent]

Wrong ones, but on the other side of the ones shown will be a value in uf (and a voltage rating) which might be useful.

[Full Range]

Yeah I'd be removing the large caps and mounting some 1200uf-1500uf ones on the boards where they should be as well as some bypass caps on them.

 

These things shouldn't pop at turn or or off.

 

The other thing to look at is earthing etc.

My thoughts exactly - the amp should not pop hence why I was cautious to proceed

Earthing was the main reason I opened it up to check for loose connections ect

I have tightened everything up just in case ?

[Full Range]

Wrong ones, but on the other side of the ones shown will be a value in uf (and a voltage rating) which might be useful.

Here you go

[Full Range]

Not sure what this switch does next to the inputs

This is how it's connected inside the case ( The blue one )

[ArthurDent]

Here you go

image.jpg

 

 Looks like 10000uf/63V and probably too big for an amp that will run happily on 1500uf per rail.

[A J]

 Looks like 10000uf/63V and probably too big for an amp that will run happily on 1500uf per rail.

 

 

To big and too far from the action - they could still sit between the rectifier and the Vin but there should be some high quality smaller caps right up next to the amp chip.

[Full Range]

If I was to purchase a high quality Gainclone kit, with good instructions ?

Offer all parts in the kit, including switches, connections ect and a case ( but nice looking cases can be purchased if not supplied )

Preferably low voltage via a wall wart power supply if that is a possible option ?

20 Watts per channel is more than enough on my speakers

Min of 2 inputs - Connections are - one for Tube Pre and one for SS Pre

I'm also open to fully built Gainclone amp suggestions - New or Preloved

Which Gainclone kit or fully built units would knowledgeable SNA members recommend

I do have a friend that is proficient in this stuff to call on for assistance on a kit ( but needs to make the time to help )

[Zaphod Beeblebrox]

If I was to purchase a high quality Gainclone kit, with good instructions ?

Offer all parts in the kit, including switches, connections ect and a case ( but nice looking cases can be purchased if not supplied )

Preferably low voltage via a wall wart power supply if that is a possible option ?

20 Watts per channel is more than enough on my speakers

Min of 2 inputs - Connections are - one for Tube Pre and one for SS Pre

I'm also open to fully built Gainclone amp suggestions - New or Preloved

Which Gainclone kit or fully built units would knowledgeable SNA members recommend

I do have a friend that is proficient in this stuff to call on for assistance on a kit ( but needs to make the time to help )

The best chip amps are based on TDA1514A chips. I don't know of any commercially available kits. If you only need 20 Watts, look for an NAD3120. They were an excellent integrated amplifier. Some small mods (new volume pot, caps, etc) and you have something that will do a superb job.

If you feel the need for a kit, then this may suffice (though it does use an inferior chip):

http://www.altronics.com.au/index.asp?area=item&id=K5114

I still reckon an old NAD3120 is a far better bet. They work well, can drive any load, are quiet, well engineered and decent sounding.

Edited November 14, 2013 by Zaphod Beeblebrox

[ArthurDent]

Okay I've just worked out that the one you have now is a loaner.

 

Is it for sale? How much does he want?