[cfcubed]

This topic has been covered here & elsewhere in bits & pieces (except for where amb's nice ε12 muting & DC offset protector is concerned).
I've posted a bit on other threads about what I used for my SOHA and have gotten comments & PMs about what I used so I thought a top-level thread was in order.
I finished my 1st tube amp (& now 2nd), the great SOHA, & realized I wouldn't rest easy till it had at least muting delay to protect my phones. My jacks were cheapo & might not last long w/constantly plugging phones in & out for every pwr up & down. Plus, I know for sure I'd probably be forgetting to unplug them often.

Not wanting to spend much on it, not having expensive phones & hearing the unlikelihood of a SOHA built w/good parts failing & passing loads of DC, I looked to build my own.

Quickly found this delay circuit and built it P2P on perfboard. You can see it as the cutout delay on the right:

In the upper-left, you can see the little NEC DPDT low signal 12v non-latch (mouser: 551-EC2-12NJ I think) relay glued to the output jack that I used to interrupt the lineouts. Only changes I made to original CircuitDB were 220uf cap (15 sec delay), omitted the 10k bleed-down resistor & I used some generic 2N390Xs from RatShack (like $3 for 15). This 2nd version of this delay is using a 168uf for 10 secs of delay. They are both working great... For both power-on & power-off line-out muting (used the 12v points in SOHA).

On the left, still on the perfboard is the delay I've put in my NAD 310 Integ Amp to stop the massive speaker thump upon power-on. I just finished it last night, but its working great so far. Changes for that one are 5A DPDT relay, 68uf cap (1-2 sec delay?) & TIP31 in place of the 2N3053. The 2N3053 didn't have the omph to operate the larger relay.

The real work for the NAD was that I 1st tried to find something like 12-18 volts on the board (found schematic online), but couldn't find reliable source. So, just grabbed two 1k 1 watt resistors (series) & a 1 watt 12v zener to bring down one side's 54v DC to 13v or so for the circuit. Again, this is working well so far (< 1 day tho), but if I was ordering stuff (instead of going to RatShack) I probably would go for higher wattage stuff incl maybe a 10a relay.... The 1ks & zener get warm - not hot like several resistors do in the NAD itself!

Hope this helps someone out. I owe Bill Bowden thanks for posting the circuit of course

Edit: Please read rest of thread to note possible problems using 2N3053. I've used TIP31 and another used 2N2222A instead w/good results. Depending on the specific relay, LED, etc. you use you may need to alter the 47k resistor value and/or the cap store to > 200uf to get proper delay & operate relay.

 

[Eokboy]

I built this delay for my SOHA. Works great to spare me from constantly plugging in headphones. Though, you'll have to becareful not to switch the amp off and back on a few seconds later, as the capacitor is not fully bled and the relay may switch too soon.

Also, when turning off, the relay follows only after half a second. This could be due to the 1000uF rail capacitance I used. I think a second 7812L regulator on the positive supply, with no power cap and 1uF tantalum output cap would work better.

Edit: Should I leave out the bleeder resistor?

 

[cfcubed]

Quote:

Originally Posted by Eokboy /img/forum/go_quote.gif I built this delay for my SOHA. Works great to spare me from constantly plugging in headphones. Though, you'll have to becareful not to switch the amp off and back on a few seconds later, as the capacitor is not fully bled and the relay may switch too soon.

Yes, I think I said something about short-cycling the power would null the delay... Good advice not to do that anyway with pretty much any complex electronic device (as tubes need a while to warm up, you're less likely to do this anyway). But as the SOHA is not completely drained either, maybe the shorter delay in these cases is enough? Not sure if the nice e22 is prone to the quick pwr-on/pwr-off/pwr-on lack of delay.


Quote:

Originally Posted by Eokboy /img/forum/go_quote.gif Also, when turning off, the relay follows only after half a second. This could be due to the 1000uF rail capacitance I used. I think a second 7812L regulator on the positive supply, with no power cap and 1uF tantalum output cap would work better. Edit: Should I leave out the bleeder resistor?

Yes, at pwr off the relay does take an instant to kick off. In my SOHA w/my phones this translates to a *very* brief, *very* slight click in the phones (much quieter than music I play

Doubt that causes any headphone trouble.

Independently powering the relay circuit (eg. extra reg or resistor/zener) might fix this minor pwr-off click, but its not really worth it IMNSHO. Also, the bleeder resistor would then be necessary & in my testing of this circuit out of the SOHA it didn't drain the circuit much (any?) faster than the SOHA in-circuit.

Bleeder is not needed if there's a load on the 12v supply that brings it down fast (at pwr-off) & thats the case using the SOHA's 12v... Bleeder is necessary for testing the delay (w/independent 12v supply) OR if powering it independently.

Glad to hear its working pretty well for you....

 

[fortney]

Do I need one of there circuits for each stereo channel or does one relay connect to both and manage to keep the channels isolated from each other?

This is a real improvement for the Szekeres and Poorman's Zen amplifiers also.

F

 

[Pars]

If it is a dual relay (DPDT), you would just need one. If you need longer delays, or better control over the delay, I would use a 555 timer (8-pin DIP IC) to control it (and have done so on a modified e12 circuit... see the e12 thread if you want to see how to use it).

 

[fortney]

Thanks, Pars. Now I see it.

F

 

[cfcubed]

Just a little update - I'm having some trouble w/the low power 2N3053 being able to control the relay *and* certain LED/resistor combos. While trying to add a larger LED as a relay-on indicator on my 2nd SOHA, I found that I got lucky w/the 1st SOHA for this (tiny LED & larger resistor value).

From now on, I'm using the higher-power TIP29 (or equiv.) in my builds of this circuit.

 

[JakeMMX]

Has anyone done any SQ comparisons with and without a muting delay? How does this affect the ability of the power supply to maintain power during quick transients? (Sorry, but I really can't find any information on the effects of these circuits....)

 

[cfcubed]

I posted details of the circuits draw somewhere (I think it was like 12-15ma when latched, which is nothing... negligible impact for any proper tube amp PS).

The Millet Max incorporates a similar delay circuit & relay and SQ does not seem like a concern there.

 

[tomb]

Quote:

Originally Posted by cfcubed /img/forum/go_quote.gif I posted details of the circuits draw somewhere (I think it was like 12-15ma when latched, which is nothing... negligible impact for any proper tube amp PS). The Millet Max incorporates a similar delay circuit & relay and SQ does not seem like a concern there.

Yep - it's sort of like asking if a panel LED affects sound quality.

Certainly, it's one of the most convenient things going. Most tube hybrids or OTL tube amps can do real damage to a pair of headphones if they're plugged in on power-up/power-down ... without a delay circuit. It takes away a huge worry and concern, letting you focus more on enjoying the amp and having more pure fun with it.

 

[JakeMMX]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Yep - it's sort of like asking if a panel LED affects sound quality. Certainly, it's one of the most convenient things going. Most tube hybrids or OTL tube amps can do real damage to a pair of headphones if they're plugged in on power-up/power-down ... without a delay circuit. It takes away a huge worry and concern, letting you focus more on enjoying the amp and having more pure fun with it.

Is it worth is for a SS only amp? (assuming you keep the volume down while turning it off)

 

[Eokboy]

With the relay turning off half a second late, do you still leave your headphones plugged in? Since I just got a HD580, I've been extra cautious during power off.

The circuit in my SOHA:

 

[cfcubed]

I've put the circuit in 2 SOHAs & it *seems* much less than 1/2 sec to me... It's just a faint click when relay engages & disengages (turn off) for me (DT-880s). I leave them plugged in.

Not sure I can make out your relay circuit, but mine is that little perfboard thingy to the left & above the tube socket here:

and you can see the little relay itself glued on front cover (orange w/+/- on it).

My delays were 11 sec & 16 sec and IIRC, DC offset was no issue at on or off (and would especially not be when loaded w/phones).

Your SOHA is quite a bit different then my final v3 PCBs, & maybe the 12v+ collapses a lot faster in my SOHAs than in yours. You can see the 12v feed lines coming off the SOHA PCB to the relay circuit in the pic.

Edit: I think I see your rather large relay in the lower-right of your pic.. It could be the must-latch & must-release voltages of our relays are different. Mine's mouser 551-EC2-12NJ "NEC Miniature Low Signal" & in my sets it latches kinda late & releases *very* quickly at power-off.

 

[Eokboy]

The must-release V of your relay is twice the one I used. I can't find that specific model but Farnell has EA2-12NU. Could this one work? Same must-release voltage as your EC2, 1.2V. If this is a matter of expensive headphones life and death, I'm going to have to change the relay.

I use 1000uF caps for my 12V rail, and will use twice more for JISBOS version.

 

[cfcubed]

I looked at the specs for my EC2-12NJ, the EA2-12NU you mention & one mentioned in the MilletMax BOM and they look similar to me.

It'd be nice if someone familiar w/the Millet Max (or maybe muting delays in general) could provide some operating info about its release behavior (latch is not at issue since its delayed past harmful DC).
Before worrying about the way yours is performing, I'd hook up a meter to your headphone outs w/your phones connected & see what measurements you get at power-off. Maybe post them back here & someone can comment on them. Regardless, I'd take a fraction of a second of DC over the several secs of it that my cans would see w/o this muting delay (upon forgetting to unplug).