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Commercial Gainclone kit- building instructions

Hi Peter,

I am planning to buy two LM3875 kits to build together with a friend. Before we order we have some questions.

Let me start to describe my system:
* WEISS DAC2 Firewire DAC. It has 50 Ohm output impedance and an attenuator in the digital domain. So I will not be needing the pot and the low output impedance is good for low DC offset right?
* Floor standing loudspeakers Klipsch Synergy F2. They have 96dB efficiency and 8 Ohm and from reviews I believe they are easy to drive.

So here are my questions:
1) What configuration would you recommend for my system? In forums you mention that you like to use BG N 100uF with AC PS. But I also read that BG are not available any more.
a) Why are you supplying Panasonic FC 1500uF 50V with the kit? Are they intended for more difficult speakers and bigger bass?
b) Are those caps the best alternative or do you still recommend BG if available?
c) Where would the caps have to be placed, on the PS board or near the chips at amplifier board. Sorry, from the forums it is not clear to me.
d) Considering my high efficiency speakers, would you still recommend 100uF? What brand? I have found some BG N 100uF 50V on the internet but if they were produced a long time ago they must have altered right?

2) You recommend a 300VA transformer. In some of your Forums you mentioned 400VA transformer. In the Netherlands I found the transformers of Amplimo with good reputation. The 500VA are just a bit more expensive that 300VA. Bigger is better for more readily available current to improve dynamics and bass right?
For 8 Ohms the 2 x 22V is the optimum as I understood?

3) From your instructions I understand that you recommend the following:
a) No R1 resistance but wire instead.
b) R2, R3 and Rf are required on the amp boards
c) No „snubber” components on PS board, but do you recommend to install the Panny FC 10uF or not? What would be their purpose?
d) On the amplifier board, do you recommend 100u or 1500u FC Panny?

3) Do you have some dimensions on the PCB set so I can start looking for suitable amplifier casing?

Any help would be appreciated.

Thanks!

Frank
the Netherlands
 
Hi again,

I need someone to confirm my assumptions regarding placement of the PSU boards.

I will use as Peter recommended by email; two Torodiy Audio Transformers with 230V primary and 2x25V secondaries for my 16 ohm speakers.


See attached JPEG files.

I will need to place the PSU boards inside the same chassis of the Torodiy Transformers - right?

I will need two XLR cables between the PSU chassis and Amplifier chassis ( one cable for each channel ) - right ?

Endre
using two boxes as a two channel arrangement ends up with the same grounding problems as any other two channel amplifier.

For the same cost as your two box proposal you can build two monoblocks and AVOID the problems that need solutions in a two channel amplifier.
I reckon a monoblock for each channel will give better performance than a split supply two channel amplifier.
 
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Will Ground Issues still be there - using one transformer?

Hi again,


More questions:

1. I will connect the ground cable from the Power Entry Module to the chassis of the power supply module mechanically - this is the most secure method to do it ( non soldered connection ) - right?

2. What kind of separate heat sinks do you recommend for the amplifier chassis ( the chassis where I install the LM3875 boards? ( see attached jpeg file for my current sketch of layout )

3. I can place the speaker terminals in the front-panel of the amplifier chassis?
There is no problem doing this since the speaker wires can be longer than the input wires - right ?

See attached jpeg files… don't bother the things that look like XLR chassis mounted connectors ...

_______________________________________________________________

I´m a bit confused about what you`re saying Andrew …

Is it then better for me to use one Transformer then + just one PSU board? - if not there will be a ground issue with my setup.


If I get you right:

If I was to build mono blocks - two separate units with separate Mains Entry Modules + both PSU and LM3875 Boards inside each one - the ground problem with using two transformers would not be there …

Then I definitely would need to build a Buffer Preamp..

Right now I´m thinking ; because of your comment; one transformer will be used in first place.
In the long run I´m aiming for a monoblock setup with a buffer preamp.

Or is there something I`m missing out on?


I also found this 41-stepped attenuator from japan ….
Acoustic Dimension Stepped Attenuator - [English]
 

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As long as you use ground scheme as proposed here: http://www.diyaudio.com/forums/audi...-kit-building-instructions-4.html#post1518369 you shouldn't be experiancing any ground problems, no matter if one or two transformers being used.

OTOH, in this particular chassis configuration, it's probably better to use one larger transformer, than two smaller ones (400VA vs 2 x 200VA)

If you aiming for monoblocks later on and plan to use components from this build, by no means use two transformers and don't worry about any grounding problems.

With amp chassis as pictured, most likely you won't be needing any additional heatsinks, make sure though that panels are tight and allow heat transfer into all surfaces.

You may also consider placing inputs on front panel and outputs at the back, this way shaft extension won't be needed.
 
Peter, I want to try some Nichicon Muse caps on the amp boards. I can get 1000uf 50V in the higher quality kz and fg model. I also have some 2200uf 50v kw's on hand. Which would you suggest? BTW I am using the snubber components. Thanks!

I'm not really familiar with any of those caps in a gainclone, either try them all or go with Panasonic FC, as supplied with the kits.
 
1) What configuration would you recommend for my system? In forums you mention that you like to use BG N 100uF with AC PS. But I also read that BG are not available any more.
a) Why are you supplying Panasonic FC 1500uF 50V with the kit? Are they intended for more difficult speakers and bigger bass?
b) Are those caps the best alternative or do you still recommend BG if available?
c) Where would the caps have to be placed, on the PS board or near the chips at amplifier board. Sorry, from the forums it is not clear to me.
d) Considering my high efficiency speakers, would you still recommend 100uF? What brand? I have found some BG N 100uF 50V on the internet but if they were produced a long time ago they must have altered right?

2) You recommend a 300VA transformer. In some of your Forums you mentioned 400VA transformer. In the Netherlands I found the transformers of Amplimo with good reputation. The 500VA are just a bit more expensive that 300VA. Bigger is better for more readily available current to improve dynamics and bass right?
For 8 Ohms the 2 x 22V is the optimum as I understood?

3) From your instructions I understand that you recommend the following:
a) No R1 resistance but wire instead.
b) R2, R3 and Rf are required on the amp boards
c) No „snubber” components on PS board, but do you recommend to install the Panny FC 10uF or not? What would be their purpose?
d) On the amplifier board, do you recommend 100u or 1500u FC Panny?

3) Do you have some dimensions on the PCB set so I can start looking for suitable amplifier casing?

If you can get Black Gates, I would definitely recommend them, but I didn't see those particular values available anywhere (BGN 100/50 and BG STD 1000/50)

I choose Panasonic FC 1500/50 because in my tests they sounded better then other caps I tried:

http://www.diyaudio.com/forums/digi...gate-caps-out-production-so-2.html#post574431
http://www.diyaudio.com/forums/chip...ut-any-comments-suggestions-8.html#post581230

The particular value of 1500uF is not critical here, you can use 1000uF or 2200uF and differences might not be obvious, I just use 1500 as nice in between value.

First choice is to place the caps as closed to the chip as possible. I wouldn't recommend any 100uF caps unless they would be BG N and only when used them in high pass networks when bass performance or hum is not critical.

Black Gates are made differently then other electrolytics and I don't think the age alters them much.

With regards to transformer, I don't think bigger is better. The bigger transformer ads more substance, but also slows things down and reduces immediacy and transparency. it will certainly also depend on particular manufacturer, but for two channels I wouldn't go with more than 300VA. With 4 channels (bi-amping) I'm using 400VA toroids with custom quadruple secondaries.

With 8 ohm and to achieve max power you may as well go with 2 x 25V

You are correct about above parts configurations. I presently don't even supply 10uF capacitor and don't recommend using it.

If your only cap is 1500uF, place it on amp board, if using 100uF BGN use this on amp board and addiitonal bigger caps on PS board.

The pcbs are approx 2.9 x 1.4"
 
Thanks for helping me out Peter! Now it is quite clear to me. My friend and I are going to order the kits to have a nice occupation during grey winter weekends...

Two more questions though.
1) Assuming I am going to use the small BGN on the amp and bigger on the PS boards. Then I would need to install the snubber parts as well right?
2) I have also considered building two monoblocks as discussed above. I was also charmed by the idea that I would not have to make any special arrangements for grounding. But I did not completely get your last reply to tralalalala (my english is not that good..). If I build two completely separate monoblocks with two transformers I will not have to make any special grounding arrangements right?
3) Regarding PCB dims; I guess that is pcb for one channel amp+PS?

Frederick Joan
 
All integrated amplifer.

Thanks for the replay,


So I´ve put all components within one chassis now - see attached jpeg file.

Is this setup too tight? - or will it work?

I´ve put in a single 400VA transformer into the chassis of this integrated amp.

On the Toroidy webpage they recommend a innrush current limiter for 400VA transformers or above...


Still there`s something I´m wondering about:

1. Regarding the use of a single transformer: Since Toroidy is recommending an innrush current limiter for 400VA transformers and above - should I just go for a 300VA transformer?

- with 230V input.
- with 300VA nominal power
- and 25V output. ( 25V; not 22V , since my speakers are rated at 16 ohm )


PS: the diameter for the 400VA and 300VA Audio version from Toroidy has both a diameter of 130mm - but with the 300VA version I will not need room for the innrush limiter box...


Thank you again for the help - and your patience...

Endre
 

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1) Assuming I am going to use the small BGN on the amp and bigger on the PS boards. Then I would need to install the snubber parts as well right?
2) I have also considered building two monoblocks as discussed above. I was also charmed by the idea that I would not have to make any special arrangements for grounding. But I did not completely get your last reply to tralalalala (my english is not that good..). If I build two completely separate monoblocks with two transformers I will not have to make any special grounding arrangements right?
3) Regarding PCB dims; I guess that is pcb for one channel amp+PS?

Frederick Joan

The dimensions are for single pcb: either amp or ps

The issue of grounding arrangement is greatly exaggerated by some people. Just build the amp and don't worry about it, if anything goes wrong it can be easily fixed.

No snubber parts are needed if you use reasonably sized caps (2200uF or so).

Snubbers were recommended for much larger caps (10000uF or so).
 
I leave my inbox full deliberately to avoid repeated PMs from beginners who want personal responses.

I assemble my own soft starts.
I have a selection of 3VA to 6VA transformers specially for powering auxiliaries in amplifiers.

T2A fuse allows for around 460VA transformer. That's quite high.

I find that with a close rated fuse and a soft start that T1A does for many transformers. I would only use much higher rated fuse for >=600VA and even then I would try using <T2.5A
A 625VA will soft start on a T1.6A fuse and allow a pair of ClassAB amplifiers to run at "party" loud volume.
 
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Hi to all,

Is it important to shield the toroid transformer from the pcb's by means of an (aluminum) sheet of metal inside the chassis? I mean to have separate compartments for the transformer and the pcb's?

Tim thesavage, I am in much the same phase as you, trying to collect all the parts. Trying to find suitable connectors as an alternative for the Cardas suggested by Peter. Cardas are hard to get here in Europe, only their cables and interlinks.

Regarding chassis I found very nice and reasonably priced ones from Modu in Italy. I plan to order their Galaxy Maggiorato model (80mm high inside). I figure that 230x230mm would be a nice compact enclosure for the stereo version with one transformer.

Here is their website: modu.

Dunno if they are available in Australia though.

Cheers, Frederick Joan.



Frederick Joan