UcD Showdown

[justcallmefrank]

Hey guys,

I have been reading, but the sheer quantity of stuff on here makes it nigh on impossible to get just the info I'm after.

I plan in the nearish future to spend a day at my friends audiophile shop and do some listening comparisons between a few different amps. Basically, I plan to line up my Gainclone amp (which didn't fare so well last time), a much "better" Gainclone of my friends, a nice N.E.W. amp, a Bel Canto which is favoured by the store owner, a Zappulse 2.2, and this small Tripath-based amp they've not long had in...oh and the new UcD180 based amp I'm looking to make soon.

Last time, the Gainclone got owned convincingly by the N.E.W. lacking the detail level it could produce. I'd half expected this given that the Gainclone was my first amp, it was a tad dodgy and it cost me only about AU$350 to make.

Of course, one does not take this lying down, so I hope to surprise them with the UcD180 based amp. I bought two UcD180AD modules this morning, so we have a good base to work with and I really hope to produce something that performs a bit better, to the level, or exceeding the level of the other amplifiers mentioned.

If it could just stay on topic, and not turn into a conversation as some of the other threads have, which led me to create this thread as it was too hard to pick though. Input from Bruno in particular would be GREATLY appreciated.

-What size (VA) transformers are recommended, I'm planning to run two as per my Gainclone setup as this was what was recommended to me. That said, if anyone thinks that this is not the right path to be taking, I'm open for suggestions. Also, what output voltage transformers are required?

-What level of capacitance is recommended?

-What simple tweaks or ways of setting it up will yield the best results?

Remembering this is a UcD180, I'm just struggling to find useful stuff through the rest of it now the UcD400 is available.

Apologies for the longish thread, any assistance will be most appreciated.

Cheers,
Nathan

 

[justcallmefrank]

While I'm waiting for a response, I've been doing some more reading. Would a pair of 30V 160VA transformers be fine to use?

 

[justcallmefrank]

Still looking around. I was thinking of using 8 Nichicon KG 63V 4700uF caps for the power supply. Does this seem like overkill? Does anyone in Australia know where I can purchase these?

 

[ninjanki]

Nathan,

I think the 30VAC 160VA transformer is excelent for one UCD180. Many people would think that it would hold even two of those, but for a great amp, one-to-one VA-Watts rating is a great start.(My UCD400 monoblocks use 800VA transformers, because size and pricing was not very different from the 400-600 VA ones...) I personally favor the monoblock aproach, to be completelly sure cross-talk is almost inexistent.

About the capacitors, I guess the values are good enough, althoug I am not sure if you are considering 8 caps per UCD module. If it is, then you are certanly over-dimensioning, unless those caps have less than reasonable ripple current ratings... Not a problem though...


Look at the hotrodding topic for modifications. The one people seems to agree that have a big impact are the signal dc-coupling caps...

 

[Bruno Putzeys]

Apologies. I don't always look at the main page of diyaudio. One should contact me directly if one needs a certain reply.

160VA, 30 or 35V is OK. Use "slit foil" caps (available only as 10000uF so that answers that question). Soft-recovery rectifiers with 47nF caps across them. If your transformer has 2 separate secondaries, consider using 2 separate bridge rectifiers, so you get two single 45VDC supplies that you then place in series. If you want, this allows you to use schottky diodes for the rectifiers (half the voltage). In that case, substitute 1nF+10R for the 47nF caps.

Short the infamous input coupling electrolytics on the modules. If you expect a DC problem, use better caps that you place at the inputs of the modules (higher impedance than where the standard coupling caps are).

Let me know when you've gotten this far.

 

[justcallmefrank]

I was planning on using 4 per UcD, for 18800uF per UcD180, having two monoblocks yes. Does this sound like overkill, i.e. should I just go a pair of 4700uF caps per UcD?

 

[justcallmefrank]

Ahh, thanks will do in future

I'll do some digging around about these "slit foil" caps, I'm still kind of new to all this terminology.

"Soft-recovery rectifiers with 47nF caps across them." - This bit went kind of over my head, is it possible for you to elaborate slightly? I have part of an old Gainclone power supply that I was planning to utilise which has 8 rectifier diodes a channel which I'm assuming what you meant by two separate bridge rectifiers?

 

[justcallmefrank]

Also, when you say that the transformer is OK, is that a good thing, or would you recommend something with say a higher VA?

 

[Bruno Putzeys]

I'll do some digging around about these "slit foil" caps, I'm still kind of new to all this terminology.

"Soft-recovery rectifiers with 47nF caps across them." - This bit went kind of over my head, is it possible for you to elaborate slightly? I have part of an old Gainclone power supply that I was planning to utilise which has 8 rectifier diodes a channel which I'm assuming what you meant by two separate bridge rectifiers?

"Slit foil" is a particular kind of electrolytic capacitor for audio, see http://www.dnm.co.uk/capacitors.html .
I don't buy the eddy current story, but I like the way they sound.

Diodes take some time to come out of conduction when they have been forward-biased for a while. They will actually pass current the wrong way round for some time. When they finally do stop conducting, this often happens very abruptly. This produces high-frequency noise. A soft-recovery rectifier is a diode optimised to come out of conduction in a more controlled manner after a shorter period of time. This greatly reduces the switching noise. Adding 47nF capacitors directly across the rectifiers reduces this further.

 

[Bruno Putzeys]

Also, when you say that the transformer is OK, is that a good thing, or would you recommend something with say a higher VA?

Normally one uses a transformer rated between 0.5 and 1 times the amplifier rating. 160VA is perfect.

 

[justcallmefrank]

Ok, here goes.

I've got the caps, RCA's and binding posts in my hot little hands. The transformers I've ordered and the case I've begun gutting and modifying for the new amp.

The caps I went for are Nichicon KG Super-throughs 50V 10000uF, a total of 4 or 2 per module. I got them stupidly cheap, and they are very good so I will see how they go. Thing is, even if I decide to change, I can always do something else with them. The only thing wrong with them is their physical size, but it's something I can accomodate.

The RCA's are Vampire ones, with some Cardas binding posts, so I just need to sort out the new back panels. The transformer I went for was a 30V 160VA as recommended

Now, I have a pair of these lying around:
http://www1.jaycar.com.au/productVi...d2=&pageNumber=&priceMin=&priceMax=&SUBCATID=
Problem is, while they do fit, it would be a lot easier if they weren't so big. My case is an old tuner one, and consists of a ventilated base, with a closed top. Given that the amp will never be enclosed in a cabinet, would it be okay to cut said heatsink in half and use half to cool each UcD180 module?

Cheers,
Nathan

 

[Bruno Putzeys]

One-sixth of this heat sink for each module is fine.

 

[justcallmefrank]

Haha I just wasn't sure with the partially enclosed case, half it is then, works out fine because half is only a little bit longer than the module itself.

Thanks for that Bruno.

 

[maxlorenz]

Two questions for Bruno:

Quote: Use "slit foil" caps (available only as 10000uF so that answers that question).
>http://www.dnm.co.uk/capacitors.html>

1) are you recommending us to use T-network caps? If so, a diagram with connections will be needed.

2) aren't all pricier BHC big can caps made with "slit foil" configuration?

I've searched at BHC's site and couldn't find the info.
I buy at RS-export and they only carry ALS30-31 ALS 40-41.

Many thanks

Mauricio

 

[Bruno Putzeys]

Re: Two questions for Bruno:

1) are you recommending us to use T-network caps? If so, a diagram with connections will be needed.

Although they are clearly technically better, I don't find the improvement of the T networks significant in listening tests.

2) aren't all pricier BHC big can caps made with "slit foil" configuration?

No. Slit-foil is only used on the caps made for DNM. It should not stop you from trying the standard ones out as well. Often different electrolytics made in the same factory sound quite similar.

 

[justcallmefrank]

Yay! Modules arrived. Two more questions.

I've always been told that a soldered connection is always going to be better than a "press fit" (?). Is it okay to solder the connections directly to the spade terminals?

Also, which ones are the input coupling caps on the new UcD180 modules?

 

[Pasi P]

Re: Re: Two questions for Bruno:

Although they are clearly technically better, I don't find the improvement of the T networks significant in listening tests.

I have ordered T-network caps to see how they perform anyway.

One minor question. Do T-network caps need any special attention to power supply. Only separate inputs and outputs as descriped in BHC documentation?

 

[Bruno Putzeys]

Re: Re: Re: Two questions for Bruno:

One minor question. Do T-network caps need any special attention to power supply. Only separate inputs and outputs as descriped in BHC documentation?

You have to use separate secondaries and separate bridge rectifiers per power supply side to get the best from them (so you only join the grounds at the "outputs" of the T caps).

 

[Pasi P]

Re: Re: Re: Re: Two questions for Bruno:

You have to use separate secondaries and separate bridge rectifiers per power supply side to get the best from them (so you only join the grounds at the "outputs" of the T caps).

Sorry, i did not exacly understand.
I thought it as in picture attached, but do i have to connect GND(IN) and GND(OUT) together?

(sorry about bad picture )

 

[Bruno Putzeys]

Almost OK. This is what I meant: