Building a symmetrical PSU B1 buffer

[Salas]

Will try adding more 68R in parallel to it, once I received Alps 20k volume pot from RS. Will report back back the out come. Right now can I test DCB1 without the volume pot? connect to my system Cambridge audio C840 CDP and Mcintosh MC240 power-amp driving JBL 4310. Because Mcintosh MC240 input come with volume control.

Of course you can when there is another volume pot in the chain. How much is your voltage after rectification? Maybe its a bit low? In general use as much current as it can allow the Mosfets not to feel too hot to touch. If having sinks, more is allowed.

Also you can try this cheapo. Plays rather well.

 

[Tea-Bag]

sudgen,
sounds like a nice system.

 

[Salas]

Hi,
the 68//68 with just 1.6V across it is passing just 47mA through the CCS.
The two B1 stages may be taking Iq~8+8mA, the shunt circuit could be taking 12mA. That leaves just 19mA passing through the shunt FET.
That may be a bit low.
Experiment with adding a further 68r to make three in parallel and maybe a fourth 68r in parallel. Each 68r passes ~24mA through the CCS.

Circa 50mA per rail would leave maybe 30mA per rail to each shunt Mosfet since each side uses 20mA more or less for 2 channels half B1, & rail CCS LEDs, Vref. That is about 0.3W on each shunt one and 0.35W on each CCS one assuming 7V in-out. A 22.6R (68//68//68) for 75mA CCS in his Rset Vdrop case you recommend, will still be rather safe for 0.525W on a bare TO-247 if the ambient is average. A touch test will quickly say.

Mine definitely sounded better with about 10R in the place of the 68//68

Fran

200mA is working the Mosfets better indeed, they pick up Ygfs at that area. But it takes a fully sinked DCB1 construction...

 

[pengboon]

200mA is working the Mosfets better indeed, they pick up Ygfs at that area. But it takes a fully sinked DCB1 construction...

Heat sinked into the chassis should suffice for 200mA (~8R) right?

 

[woodturner-fran]

and the rest of the information we need for this to help us decide?

What else do you want Andrew? I did post this here but I'm sure its buried back in the thread. ..... I'll see if i can find it

Fran

 

[Salas]

Heat sinked into the chassis should suffice for 200mA (~8R) right?

Yep. I have done that with up to 36V single shunts for phono, which is more dissipation. Even in small cheap chassis. Is your chassis floor a bit thick?

 

[woodturner-fran]

Taht post is here:

http://www.diyaudio.com/forums/pass-labs/145201-building-symmetrical-psu-b1-buffer-70.html#post2010618

and from the next post by Salas:

Correct. We know from the shunt only threads that those IRFP devices pick up on their gfs curves around 200-250mA, and that subjectively it can be noticed. We knew it from the phono thread too, you confirm that the CCSed Jfet follower can benefit too. Next station is 3A, but it takes a power station too.

Fran

 

[cedricb]

just off-topic, for the IC: PCB to RCAs, volume control, etc.

Can I use this coax cable? NEXANS|RG179BU 100M|CABLE, COAX, RG179BU, PER M | Farnell United Kingdom ...it has low capacitance and it's copper with silver coated
This cable has been recommended by this site

 

[Salas]

Normal RG179 never betrayed me. That one may shine indeed. You can see some RG179 in another photo when with the HMC perf for my DL160 then.

 

[cedricb]

Normal RG179 never betrayed me. That one may shine indeed. You can see some RG179 in another photo when with the HMC perf for my DL160 then.

thanks a lot @Salas, I'll buy this one! ;-)

 

[Salas]

thanks a lot @Salas, I'll buy this one! ;-)

Buy some normal RG179 too, its very cheap, so you can compare, because sometimes silver plating can ''shine'' the wrong way.

 

[regiregi22]

just off-topic, for the IC: PCB to RCAs, volume control, etc.

Can I use this coax cable? NEXANS|RG179BU 100M|CABLE, COAX, RG179BU, PER M | Farnell United Kingdom ...it has low capacitance and it's copper with silver coated
This cable has been recommended by this site

I don't have too much experience for this, but I asked the same for a similar cable on the forum and they told me not to use it because it has STEEL in the conductor core. It gives you bad sound (at least, is what people say about steel)

If you look at the datasheet, it sais:
CONDUCTOR: S.P.C.C.S. (Silver Plated Copper Clad Steel).
What makes me think that the inner of the core conductor is made of, well, steel.

Are my suppositions right? If not, I have some similar cables wich could be able to use.

Thanks

 

[Tea-Bag]

Heat sinked into the chassis should suffice for 200mA (~8R) right?

My DCB1 with 15R resistors (what I found in basement) does not run hot attached to sheet metal of chassis.
Although not environmentally friendly, it sounds best when left on all the time.

Otherwise it doesn't really start grooving for 4-6 hrs.

 

[regiregi22]

Of course you can when there is another volume pot in the chain.

But do not forget to parallel with the input resistor (220k) another resistor ranging from 22k to 27k. This is to make the source see the end with the same input impedance as if it were with the pot soldered.

 

[Salas]

Yes it will play better that way for the short while without its own pot. But he must remember to take it out after.

 

[Salas]

I don't have too much experience for this, but I asked the same for a similar cable on the forum and they told me not to use it because it has STEEL in the conductor core. It gives you bad sound (at least, is what people say about steel)

If you look at the datasheet, it sais:
CONDUCTOR: S.P.C.C.S. (Silver Plated Copper Clad Steel).
What makes me think that the inner of the core conductor is made of, well, steel.

Are my suppositions right? If not, I have some similar cables wich could be able to use.

Thanks

He can always try a meter since that other guy in the link liked it and then compare normal RG179 or other and decide. I recommend Steely Dan's music for the comparisons then. But he must do it again sometimes because cables is a controversial issue.

 

[cedricb]

He can always try a meter since that other guy in the link liked it and then compare normal RG179 or other and decide. I recommend Steely Dan's music for the comparisons then. But he must do it again sometimes because cables is a controversial issue.

@Salas, do you have link for a pure copper RG179? I can only find S.P.C.C.S online...

 

[Salas]

I found one (looks bad copper btw), but I have never seen it in stores. Mine is copper clad and just tinned, PVC insulation. Its a smoothie sti(ee)ll. You gotta compare them as I say. They cost very normally.

 

[massimo]

The mil-spec RG179 (75 ohms) silver coated with Teflon insulator is very good for digital cable too.
The RG178 should be better for analog being 50 ohms.....

 

[sugden]

How much is your voltage after rectification? Maybe its a bit low? In general use as much current as it can allow the Mosfets not to feel too hot to touch.

After adding the third parallel 68R to my DCB1:
1. Transformer sec. output= 11.76V
2. After rectification= +14.85V and -14.91V
3. Voltage drop across 3 parallel 68R = 1.552V and 1.670V.
Any comment on all voltage above? I touch the MOSFETs after on for 15min don"t feel hot just a bit warm, i think it ok.

Edit:will add sink to MOSFETs soon i get the chassis.