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i'm on a roll... the kgsshv


kevin gilmore

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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 by mwl168
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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 by nopants
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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?

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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. 

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  • 2 weeks later...

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

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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 by Laowei
fucking China Internet dropping out
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