Technical Assistance/Advice Thread

[congo5]

yes 3.3nf  

Safety Ceramic Disc Capacitors  VY1332M59Y5UQ63V0

I think he may be doing it different ways to show possibility's, both are valid, notice a different thermistor is used

there are other designs shown in the other amp guides, different ways to do the same thing, different ground loop breakers.. and so on.

notice how he does the secondary connections to bridges, completely different

one center taped, one normal  but really its the same result, isn't it?

Edited January 31, 2017 by congo5

[mwl168]

Thanks congo5!

[fat joey]

Don't understand the resistors in the electrostatics amps, since the PSU boards and amp boards are high voltage, when we choose resistors, is the Voltage Rating should at least be 100V? any special requirement on this?

[Craig Sawyers]

The ones specified for use in KG's SRM-T2 clone were Xicon 273 series http://www.mouser.com/ds/2/351/Xicon_10312016_MF-RC_series-1022131.pdf which are 1/2W, 350V continuous rating. But you can easily buy metal film 1/2W resistors with 500V AC/DC rating. Some builders used PRP resistors, which are 500V rated. http://prpinc.com/products/leaded-metal-film-resistors/pr9372-series-leaded-metal-film-audio

[G600]

Remember that PRPs are 500V rated but can leak through their package.

By raising them and depending on the circuit, it can be fine.

But with the T2 batteries, It was a big problem.

[spritzer]

Yup and many have issues with the epoxy coating so they could short out.  I've lost count of how many I had throw out due to that.  That's why I stick with the CMF60

[Craig Sawyers]

I've used both CFM60 and 55. I once chopped one in half to find out why they were so phsically big for their power rating - and saw the really thick epoxy coating over the resistive element. Much greater than that on "conventional" metal film resistors.

I built the T2 with Xicons thoughout, including the batteries, and fingers crossed that is still working perfectly. But my BH (original) is built with CFM60.

Edited February 5, 2017 by Craig Sawyers

[mwl168]

 

On 1/30/2017 at 3:41 PM, mwl168 said:

I have a 3A slow blow fuse and a CL60 (IIRC) thermistor on the IEC. I also have one 15ohm/3A thermistor on each of the two 325v secondaries which are controlled via a second power switch.

When I use this PSU to power the HV Carbon, I keep the second power switch in the "On" position and only use the main power switch to turn on and off the amp and the 3A mains fuse has no problem handling the power-on inrush.

I tried using this PSU to power the Blue Hawaii this past weekend. I kept the 2nd switch in the "Off" position, turned on the main switch which energizes the GRLV and the filament supply to the 4 EL34's. After 30 seconds or so, I flipped on the second power switch which controls the 325vac secondaries to the GRHV. The 3A fuse blew within a second or so.

I replaced the 3A fuse, used a variac to power on the PSU and the amp worked fine.    

I was really puzzled - why did the 3A fuse blow when I flipped on the second power switch? Shouldn't the inrush current be lower in this case?

Anyone has a theory of what happened?    

Replaced the mains fuse with a 4A slow blow and it survives the inrush current from the second power switch on the HV secondaries. Will try a 3.5A when I have them on hand. 

EDIT: replaced the 4A fuse with a 3.15A one and it's holding.

Edited February 8, 2017 by mwl168

[Tinkerer]

When checking to see if a transistor is damaged with a component tester, do you just make sure that the transistor type is correctly identified by the tester and check that the gate voltage and hFE is within specs? Nothing else special to it?

[GOON]

Hey. I am in the process of converting an old portable headphone amp with a dead battery to a desktop unit.

• Took apart the portable amp and found places to wire up anything necessary.
• Shopped around for a nice torroidal to spit out 12v DC.
• Found some adapters to let me rip off the SOIC opamps and use DIP ones instead http://www.epboard.com/eproducts/doc/e8-0130_ps.pdf

Now the reason I'm here asking questions.....

I've used Cincon CHB50-24S33 before on a build where I needed 24V. (25-50W 18-36V 3.3V 10A is the specs for that Cincon)

Being familiar with nothing else in this unit's price range I looked at Cincon's offerings that could hit 12V. I can get a CHB50 that outputs 12V for the same price. Is there anything else I should consider for very good 12V regulation anyone here has had good experiences with?

[n_maher]

I'm confused as to why you think you need a DC to DC convertor?  Why wouldn't you just build a small regulated DC power supply that runs off an AC wall wart and have it's output match the voltage that was previously supplied by the batteries?

[Pars]

5 hours ago, GOON said:

Hey. I am in the process of converting an old portable headphone amp with a dead battery to a desktop unit.

• Took apart the portable amp and found places to wire up anything necessary.
• Shopped around for a nice torroidal to spit out 12v DC.
• Found some adapters to let me rip off the SOIC opamps and use DIP ones instead http://www.epboard.com/eproducts/doc/e8-0130_ps.pdf

Now the reason I'm here asking questions.....

I've used Cincon CHB50-24S33 before on a build where I needed 24V. (25-50W 18-36V 3.3V 10A is the specs for that Cincon)

Being familiar with nothing else in this unit's price range I looked at Cincon's offerings that could hit 12V. I can get a CHB50 that outputs 12V for the same price. Is there anything else I should consider for very good 12V regulation anyone here has had good experiences with?

A couple of things:

A torroid transformer doesn't put out DC... it is AC

Those SOIC adapters will be a nightmare if the opamps you replace the existing with are fast at all. What opamps are you replacing and why do you think they need to be replaced? FOTM?

Edited March 17, 2017 by Pars

[GOON]

@Pars , @n_maher , thank you both for the assistance. I guess it's clear I need it 

Regarding the DC to DC converter, I didn't so much think I needed it as it might be ultra overkill for voltage regulation to ensure clean power. However, maybe a regulated DC supply is a more efficient option here, both in cost and building...

If I used an AC transformer i would be sure to convert to DC, which I was considering, but now after thinking it over some more, it seems silly not to just use a DC supply.

Lastly about that SOIC adapter, many thanks for those points @Pars as I didn't even consider the speed issue. The amp has one OPA134 on board. There's nothing wrong with it at all - the desire to affix a DIP adapter where it was is entirely FOTM. I wouldn't be opposed to leaving the OPA134's on board. Seemed like a fun extra thing to do for the heck of it, but never was a priority really.

Thanks again very much to both of you for steering me in a more reasonable direction! 

[n_maher]

Depending on just how complicated a project you want to make this you could take a look at something like the AMB σ11.  

[GOON]

I have almost everything on the parts list already, i think i might just get that!  Thanks again, this is a vastly preferable route compared to whatever i would have come up with myself.

[G600]

How do you guys read the power switch ratings ?

I'm looking for a simple 2 pole mechanical switch for high voltage secondaries.

I often see 250VAC - 10Amp stuff.

Is there a rule of thumb, like more voltage possible with less current ? aka could they handle 360 VAC @ 400 mA ?

Thanks for the tip.

[kevin gilmore]

warning:   DO NOT DO THIS

Mikhail did this with his "high voltage option" and zapped a number of people

if you really must switch secondaries, use high voltage relays rated for 1kv or more isolation and even then, the inrush current might weld the contacts shut.

[G600]

I bet switching 450 VDC is not easier ?

No easy way then...

Found some useful kowledge here

Edited March 20, 2017 by G600

[spritzer]

If you follow the Mikhail line of thought then the 250Vac rating would mean 250*1.41 for DC but that isn't the case.  Most of these switches have a rating for DC and it is usually very low. 

I for one wouldn't worry about delay lines and stuff like that. 

[wink]

The trouble with DC switching is breaking the arc when the switch is opening.

With AC, the voltage drops to zero 100 times a second at 50Hz, or 120 times a second at 60Hz. so the contact gap doesn't need to be as large as a DC switch rated at the same voltage.

[spritzer]

Indeed

[UFN]

I would think that an SSR could be used for the switching here since there is no mechanical contact, but looking at the specs for some smaller models like the Sharp S202-series and that doesn't seem to be the case. They are rated for 600V peak voltage, but recommended operating voltage is still only 240VAC 

 

//UFN

[luvdunhill]

Perhaps one of the IXYS SSRs?

http://www.ixysic.com/Products/SSRFormA.htm#Dual1FormA

[Pars]

Would any of those handle enough current?


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[gepardcv]

UPDATED 2017-08-21: Thanks to hints from @Laowei and @MLA as well as suggestions to double-check the entire scheme from @mypasswordis and @Whitigir, I figured out what happened. See edits below.

I have a question about volume pots and hum. On my builds, there's a faint hum which begins when the volume pot reaches 11:30 o'clock, gets louder and tracks to the right channel until 3 o'clock, then disappears at max. This happens with all pots I tried, several TKD601s and an RK50. Any suggestions about what might cause this? I have a feeling I'm making a mistake in grounding, but (1) I tried a few variations cobbled from suggestions on various threads here without success, and (2) wouldn't a bad grounding scheme imply that there should be more consistent noise all the time? Likely related to this, I have found that there is much louder hum across more of the pot range whenever there is no source plugged in.

For example, my Carbon (split PSU) is grounded as follows:

• IEC earth to chassis (through IEC module) and star ground
• Transformer 0 to star ground
• PSU board 1 to star ground
• PSU board 2 to star ground
• Amp board 1 to PSU board 1
• Amp board 2 to PSU board 2
• EDIT: Pot output ground 1 to amp board 1 (this caused problems)
• EDIT: Pot output ground 2 to amp board 2 (this caused problems)

FWIW, I have always made one-box builds so far, and I imagine the transformer contributes to this, but I don't get why only part of the volume pot range manifests the problem. Like I said, the hum is pretty faint with nothing plugged in so doesn't matter much with music playing at reasonable levels, but I'd still like to understand what is going on.

Edited August 22, 2017 by gepardcv
Update the post to contain the answer to the question.