Good point. It could be a cold solder on the ground pin.

I don't recall if the jrc part requires a load but it's also a good idea.

My jrc 7[8,9]15 were pumping out -/+20 v when I fed them a 24vac transformer which was labelled 18, after replacing them once already. Are these regulators toast? I wanted to double-check before I fuck up the PCB pads from desoldering

Did you test them with load? These regulators are suppose to work properly under load. See some discussions on page 175 of this thread where Kerry and others came to my rescue with my problem.

I had similar problem with the - regulator but not with the + regulator when I built my PSU. I thought the regulator was toasted too but once I tested it with load, it worked as spec'ed and has been working properly since. 

Edited August 9, 201510 yr by mwl168

yep I plugged them into the amplifier boards and I was still getting 20+ v. also checked the ground connections and those seem to be ok I'll try to measure it from the package when I get a chance. In the meantime I hooked up a power one supply for the lv section.

 

Edit: I got all the voltages to dial in properly, but for some reason all the signal outputs are stuck at +vcc. I can still adjust the balance for some reason. Maybe this is related to the problem I had with the kgsshv where the LV section might have turned on after the HV section. I wired it to manually switch on the HV after the LV and that didn't work. I wonder why I'm having so much trouble this time around

Edited August 9, 201510 yr by nopants

After swapping the 470uF/35V capacitors for 2200uF/35V (yay overkill!) on the LV section of the BH PSU I use with my KGSSHV mini stereo build, the screeching noise on turn-off went away. Thanks for the suggestion, Spritzer!

I've been readjusting the amp, and two other questions came up. One: the offset is pretty high when the amp is cold. Like 40-50V. Is it bad to have headphones plugged in with the offset that high?

Two: the servo seems to make the balance and offset somewhat less stable. I was able to get the balance to <500mV on both channels, and the offset to ~1V after an hour or so of running the amp. Both fairly stable. After placing the servos back, both balances and offsets started fluctuating between 1 and 5V. This doesn't seem right. Could I have faulty OP27s?

I've used the JRC parts for years and they don't need a load to be stable.  I've never seen them be bothered by the input voltage at all but I've never put 30VDC into them. 

If the amp is stuck at the rails then something is very wrong, blown transistors or solder bridges being the most likely issues.  Well that and flux, that can fuck up everything at these voltage levels. 

After swapping the 470uF/35V capacitors for 2200uF/35V (yay overkill!) on the LV section of the BH PSU I use with my KGSSHV mini stereo build, the screeching noise on turn-off went away. Thanks for the suggestion, Spritzer!

I've been readjusting the amp, and two other questions came up. One: the offset is pretty high when the amp is cold. Like 40-50V. Is it bad to have headphones plugged in with the offset that high?

Two: the servo seems to make the balance and offset somewhat less stable. I was able to get the balance to <500mV on both channels, and the offset to ~1V after an hour or so of running the amp. Both fairly stable. After placing the servos back, both balances and offsets started fluctuating between 1 and 5V. This doesn't seem right. Could I have faulty OP27s?

Glad it helped, took a while to figure out what the hell was going on with the circuit.   

As for the servo, the OP27 is bloody slow to work and some can be a bit off.  Personally I never use them. 

Interesting. So you don't use servos in your builds at all, or you use something other than the OP27?

Something else... 

For the new fat/split carbon PSUs, what wattage should the two 249kOhm resistors be? Would 1/2W suffice?

1/2 watt is more than enough. Just make sure the voltage rating is at least 300v.

Kevin, have you seen this company: http://jamestransformer.com/en/transformer/index.html

 

They have built a pretty good reputation with their power and output EI-core transformers for DIY tube amps. They also list building custom R-cores to order. A R-100 core size would be a physically perfect fit for a Carbon. Could add electrostatic shield,.... whatever we want.

 

There are order sheets on that site that take in all the technical specs. desired and email to them for a quote. I'm not the one to be spec'ing the transformer, maybe someone with more experience could.

 

Possibly a GB could be arranged.

 

I frequently travel to Shenzhen China for business (I'm there right now), and could take a day trip to their office/factory in Foshon to check them out if needed.

I was thinking of trying out an R-core transformer from this company too.  I'm also not sure how to completely spec out a transformer on their spec sheet.  http://jamestransformer.com/en/transformer_spec.html

I sent them 2 emails with no reply. 

Been talking with Mike at Custom Magnetics about a custom R Core. He answered back, no problem, saying customers liked their audio R Cores. Quoted $110 for 1, $95 for 10+ Based on standard R80 core.

I may have underspec'ed the transformer as similar to my KGST, not taking into account the higher current of the Carbon.

Primary: 115VAC x 2 (50-60hz)

Secondaries: 360VAC@100mA x 2; 18VAC@200mA x 2

Electrostatically shielded with ground wire

10 inch lead wires

If I can get solid spec's for the Carbon transformer, will get the quote updated and posted here. 

Edited August 23, 201510 yr by Laowei
fucking China Internet dropping out

Looking through the thread I'm seeing:

Secondaries: 360V @350mA x2  and  15V-0-15V  @500mA 

I saw that from Kerry, too. Along with several others. 

Can we confirm this the final spec? 

Also, I wanted a little more headroom on the low voltage taps for the drop out on the Golden Reference LV. 

For the Carbon with normal CCS setup I'd shoot for at least 200mA HV windings.  250mA would be better unless it is a special case where the temp rise of the transformer is tightly controlled.

I have a question concerning the use of the Goldenreference LV Supply for the KGSSHV Carbon. How much heatsinking do the transistors need? Could they be mounted to the 3mm bottom aluminum plate of the chassis?

Thanks Birgir

Any updates on potential Carbon transformer group buys?

the antek should work fine for this at normal voltages

Any updates on potential Carbon transformer group buys?

No further replies from Mike at Custom Magnetics. Maybe on summer vacation this week. Will ping him again this Monday.

the antek should work fine for this at normal voltages

Which one?

 

No further replies from Mike at Custom Magnetics. Maybe on summer vacation this week. Will ping him again this Monday.

Thank you!

Which one?

 

Thank you!

AS-3T325 - 300VA 325V should be good with 400V

No LV windings on that one. Looks like it's still worth getting a Toroidy.

it would still be significantly cheaper to pick up a separate lv transformer that only needs 100ma secondaries

Just a reminder. If you want the ability to use or to later upgrade to the Goldern Reference LV supply, get a LV transformer with split secondaries not center tapped. 

Good reminder. What are you planning on using for the GR LV? 2x18VAC?