[tangent]

Yes, that's the easiest way.

 

[spendorspain]

Hi all

I’m going to build a PPA v2 powered with a YJPS psu and I’d be grateful if you could help me regarding several doubts.

1) I have two unused Black Gate series N non-polar capacitors. I had installed them at the output of a headphone amp but now, with a FET-input opamp in it and very low dc offset, I’ve desoldered them. I think their value (1000uF/25v) and size (D 16mm x H 23mm, LS 7.5mm) are appropriate for the main cap C1 in PPA v2. I know they are too expensive, but I have no better use for them. They are very good caps for music signal and I’ve seen used in power supplies too. Mi plan is to use both in two C1 positions, in parallel, to obtain the recommended C1=2000uF capacitance in the PPA. Is their dc rating (25v) high enough for a 24v YJPS psu? Is it a problem their non-polar (bipolar) design, when used in the power section?

2) Is it possible to mount the YJPS pcb vertically to save space or perhaps will the heatsinks reach too high a temperature this way, as their fins are more effective if not horizontal? (the recommended heatsinks are from 25 to 50 mm, so perhaps the shorter one is still suitable for the expected heat)

3) I currently use a headphone amplifier with a gain of 4.3x, that is a little high for my Grado HP2 cans (I have to use a loss L-pad before the 10k stepped attenuator). Is it recommended a gain of 2x or 3x in PPA v2? I’m going to test with PPA the AD8610, AD8065, AD744 (pin 5 out) and LM49710 opamps, that I believe can be used at such low gain without problem.

Thanks in advance for your comments

Jose

 

[tangent]

Quote:

Originally Posted by spendorspain /img/forum/go_quote.gif I think their value (1000uF/25v) and size (D 16mm x H 23mm, LS 7.5mm) are appropriate for the main cap C1 in PPA v2

When the docs say you can make 16 and 18 mm diameter caps work, it's not recommending that. The way you make them work is having them span two cap positions, positive on one to negative on the other. This makes the cap hang over the board edge, so it's no good if you're using the recommended Hammond case or anything else that fits the board outline tightly. It's also less mechanically secure, so probably not a good idea for an amp that gets moved around a lot, unless you hot-glue them in place after soldering them down.

Quote:

I’ve seen used in power supplies too.

They're no good in a YJPS. 25 V main reservoir caps means you'd be configuring it for 12 Vdc out or less.

Even if they were a more appropriate voltage, I doubt they'd perform better than some nice, big, low ESR caps.

If you have to use these caps, much better to use them on the amp board, not the power supply.

Quote:

Is their dc rating (25v) high enough for a 24v YJPS psu?

Yes. D1 cuts the supply voltage down a bit, so you have about 1.7 V of margin to play with.

Quote:

Is it a problem their non-polar (bipolar) design, when used in the power section?

I don't know, but at least it seems wasteful. Why not save these caps for what they were meant for, AC signal coupling?

Quote:

Is it possible to mount the YJPS pcb vertically to save space or perhaps will the heatsinks reach too high a temperature this way, as their fins are more effective if not horizontal?

I've not tried it, and I wouldn't unless I'd configured the power supply to have lots of heat margin.

Quote:

the recommended heatsinks are from 25 to 50 mm, so perhaps the shorter one is still suitable for the expected heat

Don't guess, find out.

Quote:

Is it recommended a gain of 2x or 3x in PPA v2? I’m going to test with PPA the AD8610, AD8065, AD744 (pin 5 out) and LM49710 opamps

It should be fine. Be sure to use the lower R11 value recommended earlier in this thread. That's more important at lower gains.

 

[whitelabrat]

I've begun stuffing my PPA2 board. I'm on a very tight DIY budget these days so I have to use what I've already got, before buying parts. I've got some decent parts, but it's a bit of a hodgepodge. For example I have a combo of Panisonic FM and Nichicon KZ's on C1. I don't have any small film caps so I used ceramics.

Super cheap Nichicon PM's in C4 bypassed by 0.1uF ceramics again. I did find a pair of 1uF film box caps, but I figured I try this out before unsoldering anything. I'd post a picture but it's pretty sick.

I've got a pair of OPA637's DIP8 and three OPA827's SOIC's. No adapters for 827's so I'll be using the 637's with a OPA602 for the ground channel.

I've got a Blue Velvet 100k volume pot, and I'll probably just on/off switch the bass boost for now.

I'll use a TREAD for the power supply, perhaps 24v. I need to reform some old stock 2200uF 100v caps for that.

My only pinch is R12. Can I just fake the trimmer with a resistor until I get the proper part?

 

[tangent]

Yes, you can use a plain resistor in place of R12. The thing is, though, you won't know what the right resistor value is here at first: we made this a trimmer because there is no fixed resistance-to-bias-level function. It depends on the specific transistors.

You'll end up putting in something plausible, powering the amp up, measuring the effect, powering off, desoldering the R12, trying something else that moves you in the direction you want, powering up....

How's your stock of random resistor values?

 

[whitelabrat]

I rarely buy just one of anything, so I've gotten a fairly broad variety of values now. A fellow was closing up his electronics shop and sent me a large box of resistors. Thousands! Mostly carbon film along with a mess of capacitors. It pays not to be picky.

So in a pinch I can parallel or serial resistors for just about any value.

I was planning to "plug in" various resistors without soldering until I get the ideal value. Power on, test, change value, repeat.

What would be a good value to start with? I would guess something around 1k.

 

[whitelabrat]

I'm stuck. I didn't order any 2N5484's. I'd like to get all my parts from Allied Electronics, so I'm thinking that an NTE457 may serve as an alternate. Idss=1-5ma, Crss about 1.5pf, Ciss about 4.5-7.0pf. Looks good enough. Looks like I'll be getting the trim pots after all.

 

[uvacom]

I've just ordered parts for my PPAV2 and for the most part everything seems clear, but I have one nagging question - what is the black RCA signal ground input used for? I don't have any sources which have a discrete signal ground output. Why is the sleeve on the RCA jacks not sufficient for signal ground?

 

[n_maher]

Quote:

Originally Posted by uvacom /img/forum/go_quote.gif I've just ordered parts for my PPAV2 and for the most part everything seems clear, but I have one nagging question - what is the black RCA signal ground input used for? I don't have any sources which have a discrete signal ground output. Why is the sleeve on the RCA jacks not sufficient for signal ground?

I think you're going to have to clarify what exactly you're not clear about. The RCA sleeve needs to connect to the PCB at any of the IG pads. You can tie the sleeves together if you like, most do, and just run a single wire to the PPA PCB. Your statement, "black RCA signal ground input" is what is confusing me since I have no reference for whatever color coding scheme you're referring to.

 

[uvacom]

Ah, I'll take a step back. Let me ask this instead: why does the parts list at tangentsoft specify 3 rca jacks - one red, one white, and one black?

 

[MisterX]

Notice how the "QTY" colom says you only need 2?
Maybe part numbers for red, white and black jacks are
provided so people can pick the colors they prefer?
Or maybe it's because RS only stocks red and black ones.

Either way I would suggest finding better jacks then those....

 

[uvacom]

Ah! That does make *much* more sense. Silly oversight on my part.

 

[tangent]

Quote:

Originally Posted by whitelabrat /img/forum/go_quote.gif I'd like to get all my parts from Allied Electronics

A quick look suggests you can probably save enough on parts to cover shipping from Mouser. Allied's prices and selection for semiconductors is poor.

If there were just one distributor that had it all, we'd all be using them. You see people recommending so many distributors more because no one has all the best stuff, rather than primarily because of different preferences.

Quote:

I'm thinking that an NTE457 may serve as an alternate.

There are a few valid reasons to buy NTE parts, none of which apply here:

- you have more money than sense

- you need a specific part and the original manufacturer no longer makes it, but NTE carries a replacement

- you have a local NTE dealer and can't wait for a mail order

The 2N5458 and 5459 look like better bets to me. But again, I think you'd still be better off getting some cheap Fairchilds from Mouser and letting the price difference cover the extra shipping charge.

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif Maybe part numbers for red, white and black jacks are provided so people can pick the colors they prefer?

What he said. Some like white and red, others prefer black and red. I've collected all three color options so you can select the pair you like.

 

[whitelabrat]

Quote:

Originally Posted by tangent /img/forum/go_quote.gif A quick look suggests you can probably save enough on parts to cover shipping from Mouser. Allied's prices and selection for semiconductors is poor. If there were just one distributor that had it all, we'd all be using them. You see people recommending so many distributors more because no one has all the best stuff, rather than primarily because of different preferences. There are a few valid reasons to buy NTE parts, none of which apply here: - you have more money than sense - you need a specific part and the original manufacturer no longer makes it, but NTE carries a replacement - you have a local NTE dealer and can't wait for a mail order The 2N5458 and 5459 look like better bets to me. But again, I think you'd still be better off getting some cheap Fairchilds from Mouser and letting the price difference cover the extra shipping charge.

I agree their selection is less impressive and I wouldn't recommend them for PPA2 parts. It's all the other parts that I buy from their overstock selection that make it cheaper than Mouser by a long shot. The $0.94 cent 2k trimmers (not perfect fit) are a nice thing. The NTE parts are more expensive but my order is much cheaper overall.

I took a long hard look at the 2N5458, but it didn't fit the bill where Idss is 2-9ma and I need 1-5ma for Q1. I've got 2N5486 in for Q2.

 

[tsaavik]

Just wanted to add this comment after proof reading the below, I really have no idea what I am talking about, I'm still a beginner in the world of electronics, so i may be missing something totally obvious or misstating facts as I see them from the schematics. It does seem like I'm actually learning some stuff though!!

I built a wonderful ppaV2 with 3 ad8610 running 30ma bias with 1ma class A. Power is normally 24v provided from a steps running around .16amps. It has been running pretty well the last 3 years, except for a minor probe slip during biasing tweaking that resulted in me replacing the Ground TLE a few years back.

A few months ago i was playing around with my e12 trying to get it to function reliably while at work and managed to short something out on my PPAv2

I finally had a chance to look at my PPA tonight. My Left/Right opamps show ~23v between their VH/VL pins but my Ground opamp was only showing 5.5v

I assumed I blew my TLE (again), so i quickly soldered in a replacement. Unfortunately this had no effect.

I pulled the opamp (smd on browndogs) and the voltage measured ~23v. I swapped opamps with another channel and the problem stayed with Ground (still 5.5v). Assumption: 2 opamps are not failing to run in unity mode

I plugged 2 wires into the VH/VL pins and ran them over to my otherwise unplugged Ground opamp. When i attach them to the opamp the voltage on VH/VL falls from 22v to 5.5v. Big Assumption: You can power an opamp this way as a test and oscillation won't be an issue

A rising or falling voltage seems to take about 8seconds to complete (fast at first then ramps off) so I'm guessing this is some cap charging/discharging somewhere. I don't think its the large bulk C1s, and am guessing its the C4 + and - 100UFs. Assumption: There is current limiting going on (Q3?) that causes the 100UF C4s to charge slowly (maybe not see below)

During all of this the consumed current from the amp's (bench) power supply never changes.

This leads me to suspect Q3G + and/or Q3G-. I measured between audio source input ground and pin 1 on the Ground channel and got the expected ~11v + and - respectively. However when i measured between audio source input ground and pin3 I got 2.8 + and -. I disconnected the opamp and measured again, I got the expected +-11volts. I checked Left and Right channels Q3s and they read the expected +-11volts on pins 1 and 3.

It seems like I have a large current draw, which is odd since my bench supply didn't show a current increase. I decided to monitor the Bulk C1 capacitors and sure enough voltage drops from from 11.53 to 11.38 when i connect the ground channel opamp.

Should my next step be swapping out both Q3 parts? Or is running the opamp without the other pins causing some sort of oscillation that is invalidating this type of test. I'm guessing i shorted the Ground output to something, so maybe i should be focusing on the output buffers instead, or perhaps that push/pull circuit between them and the opamp? Can i "jumper" over either as a test? Btw, my ground channel transistors feel about the same temperature as my Left/Right channel ones.

I do have access to an old scope (analog 60mhz circa 1982) as well so if there is any testing that would be useful with that let me know, I'm still trying to learn how to use it AND trust my measured results.

Here are some old pics of it during construction, since people like pictures
DIY Audio Projects

Thanks for reading this!!