REDD EQ, Helios 69 and Dick Swettenham

[ruffrecords]

Thanks Ian! Yes, I did see that, but I wasn’t sure what to make of it. So I should add a 10k resistor to ground — RL on the schematic above — off of the yellow lead between the transformer and the eq input? (Understanding that the zobel network is then unnecessary).

Apologies if this should be implicit and obvious from your answer.

No you are right it is not implicit. What it means is that if you can arrange for the load attached the the transformer secondary to be 10K then you do not need the Zobel network. So if your load is 20K for example then you could add 20K across the transformer to make its load equal to 10K.

Cheers

Ian

 

[JMan]

Thanks, Ian!

I still don't fully understand how I will approach this from a practical perspective, but it seems like I need to go do some research about understanding load impedance. I've been googling a bit and so far everything I've found on transformer loading is way over my head (and not audio related, though I imagine many concepts remain constant). I'll try and wrap my mind around this before coming back with more questions!

 

[ruffrecords]

Thanks Ian! Yes, I did see that, but I wasn’t sure what to make of it. So I should add a 10k resistor to ground — RL on the schematic above — off of the yellow lead between the transformer and the eq input? (Understanding that the zobel network is then unnecessary).

Apologies if this should be implicit and obvious from your answer.

It is difficult to answer questions helpfully when you don't know how knowledgeable is the person asking. You have to make assumptions and often they are wrong. This is not your fault it is just life. So first things first. Do you understand ohms law?

Cheers

Ian

 

[JMan]

It is difficult to answer questions helpfully when you don't know how knowledgeable is the person asking. You have to make assumptions and often they are wrong. This is not your fault it is just life. So first things first. Do you understand ohms law?

Cheers

Ian

Hey Ian,

I totally get it! You're nothing but helpful, and it's truly appreciated. I sure hope I haven't given you any other impression. I'm a hobbyist with no background whatsoever in science and engineering, so "explain it like I'm five" is probably where I am with things. But I can promise that I do my absolute best to try and understand what people tell me.

Yes, I understand ohms law as a principle and as an equation (I like the triangle that folks use to visualize it, that was very helpful to me when I learned about it). However, I lack experience with actually using it in the practical mathematics of a real circuit, and specifically I find that I am unsure of how to derive usable numbers for the variables in practice. Most examples I have seen assume that you already know two of the three and go from there.

 

[ruffrecords]

OK, so next question, do you know how to work out the combined resistance of two resistors in parallel?

Cheers

Ian

 

[JMan]

Yes, that one I understand!

 

[ruffrecords]

Yes, that one I understand!

OK so if you looks at the schematic in post #419 you will see there is a string of series resistors from the input to 0V. If you add those all up (because they are in series) you get about 27K. If you recall from earlier I said the EQ is designed to be driven from a source impedance of 2K5 so we add a 2K4 resistor in series with the input (I will explain why later) so this gives us a total of 29K4. The transformer we know prefers a load of 10K so we need to work out what resistor to put in parallel with 29K4 so that together they make 10K. The answer is 15K (to make the numbers easy call 29K4 as 30K. So 30 x 15 is 450 and 450 divided by 30 + 15 is 450/45 which is 10K).

So now the transformer is happy but what about the 2K4 source impedance for the EQ. Transformers do what they say on the tin - they transformer voltages, currents and impedances. They have no intrinsic impedance of their own. So, although the Jensen transformer is labelled 10K:10K that only means that, due to the practical limitations of making real world transformers, it works best at that impedance over the audio band. However, you will probably drive it from an interface of some sort which will have a relatively low output impedance - maybe 100 to 200 ohms or maybe even less.. The transformer will transformer this so the source impedance of the secondary will appear to be that of the interface i.e 100 ohms or so. But we want the EQ to be fed from about 2K5 which is why we added a series resistor of 2K4.

In practice it is even more complicated than this because the transformer is not perfect and it windings will also have resistance and in a 10K:10K transformer these often amount to a few thousand ohms. So if we connected the EQ to this transformer we probably do not need the 2K4 series resistor. This means our original calculation for the parallel resistor is wrong; it really needs to be about 16K but 15K is close enough.

Bottom line, stick a 15K across the transformer secondary and feed it straight into the EQ.

As you can see, audio design is not a trivial exercise.

Cheers

Ian

 

[JMan]

Wow, Ian, thank you for that explanation. This is incredibly clear. I really appreciate your patience and willingness to talk this through with me.

And for the record, if you are saying audio design is no trivial thing, imagine what it must look like to me!

 

[JMan]

I finished up my brilliance control box based on Ian's schematic and Mike's awesome build a few pages back. I don't want to clutter this thread more than I have, but if you'd like to see it, here's a link to a post I created (with pictures!).

 

[EugeneKei]

I received the 22113 amp PCBs today and put one together. Works great in the RS127 build! No need for an external amplifier now

I used a mean well external 24v wall wart type transformer (picked it as it's the same line as the Heritage Audio HA-73EQ uses) It's a cheap switching psu but it seems good and is noiseless. I used a 600:600 output transformer as it's what I had on hand and I don't have any headroom issues that I can tell with the limited testing I've done so far.

I also opted for a panel mount trimmer since I had a few laying around (the PEC screw ones, the style like on an LA2A) That will make matching a pair easier especially as the amp pcb is pretty difficult to get to.

Here's the guts, the amp card is sandwiched under the turret board. I just have to clean up the wiring a bit, drill the holes for the power entry and the volume trimmer and it will be done.

Hello Mike. And if we are talking about dual mono device? what power trafo should be? Primary for Europe 230v, and what Secondary should be? 2x24v?
Do we need two line amps for dual mono device or one should be enough?
And another question, did you use just Input transformer for your project?
Thank you in advance

 

[EugeneKei]

@ruffrecords Hello Sir. Maybe you can help me.
If we are talking about dual mono RS-127 Brilliance control device, what power transformer will I need? Primary for Europe 230v, and what Secondary should be? 2x24v? I saw that 24v walmart power supply works, but I'm interested in suply/ trafo for dual mono device
Do we need two line amps for dual mono device or one should be enough?
Thank you in advance

 

[JMan]

Hey Eugene, the EQ itself is passive and does not require any power, regardless of whether you are doing the full EQ that Ian has designed or just the brilliance section.

So the real question is, will you build it as EQ-only and then run the output to an external amp, or (more likely) will you add a line amp in the unit after the eq? If the latter, your power supply needs are determined by the requirements of the amplifier that you choose.

If you plan to build a two-channel unit, then yes, you'll need two amplifier channels as well.

 

[EugeneKei]

Hey Eugene, the EQ itself is passive and does not require any power, regardless of whether you are doing the full EQ that Ian has designed or just the brilliance section.

So the real question is, will you build it as EQ-only and then run the output to an external amp, or (more likely) will you add a line amp in the unit after the eq? If the latter, your power supply needs are determined by the requirements of the amplifier that you choose.

If you plan to build a two-channel unit, then yes, you'll need two amplifier channels as well.

I was thinking of building just a dual mono Brilliance control box without eq. Mainly as Mick did, but I don't have DI or preamp to use it with, so was thinking about power trafo.

 

[TimG]

i think Ian’s Twin Line Amp has been used for similar passive eqs. I’m planning on using it behind his passive EMI eq for dual mono.

 

[JMan]

I was thinking of building just a dual mono Brilliance control box without eq. Mainly as Mick did, but I don't have DI or preamp to use it with, so was thinking about power trafo.

Cool. I was also inspired by Mike’s work and built a pair of RS127s as well (there’s a link in one of my earlier posts above).

You’ll need to decide what line amp you want to use, and then you’ll need to base your choice of psu circuit on that (this will include, but is not limited to, choosing the appropriate power transformer). Mike and I each did our own layout of a Helios-style line amp, but there are many options. In his documents, Ian shows a nice little IC-based amplifier that can be used, which is simple enough that you could surely build it on perfboard, and the power requirements are easy to deal with.

I might suggest that you consider using a wall wart supply for this. There are plenty of off-the-shelf models that will work perfectly.

@TimG I also think Ian’s TLA is a great option, but I think a tube circuit might not be the right choice in this case (I’m making some inferences about his level of experience in this arena based on various posts I’ve seen of his asking about power transformers).

 

[EugeneKei]

Cool. I was also inspired by Mike’s work and built a pair of RS127s as well (there’s a link in one of my earlier posts above).

You’ll need to decide what line amp you want to use, and then you’ll need to base your choice of psu circuit on that (this will include, but is not limited to, choosing the appropriate power transformer). Mike and I each did our own layout of a Helios-style line amp, but there are many options. In his documents, Ian shows a nice little IC-based amplifier that can be used, which is simple enough that you could surely build it on perfboard, and the power requirements are easy to deal with.

I might suggest that you consider using a wall wart supply for this. There are plenty of off-the-shelf models that will work perfectly.

@TimG I also think Ian’s TLA is a great option, but I think a tube circuit might not be the right choice in this case (I’m making some inferences about his level of experience in this arena based on various posts I’ve seen of his asking about power transformers).

Regarding line amp, I believe will try to use 22113. So correct me please if I'm wrong, for dual mono RS127 I'll need two 22113 line amp boards, for each rs127. And it should be good with a pair of 600:600 input transformer. But will this really works ok with just 24v laptop power supply ?

 

[JMan]

Regarding line amp, I believe will try to use 22113. So correct me please if I'm wrong, for dual mono RS127 I'll need two 22113 line amp boards, for each rs127. And it should be good with a pair of 600:600 input transformer. But will this really works ok with just 24v laptop power supply ?

Well, first, bear in mind that “wall wart” and “laptop power supply” are not necessarily synonymous.

With that said, the 22113 works great in this build. Yes, you need one amplifier per channel of EQ, so for a dual mono EQ, that’s two.

My units both use this same amp, and they are running off of this power supply. It should be plenty to power two channels in a single unit.

For your input transformer, read through the last few pages of this thread where Ian is answering the exact same questions for me. The short version is that if you use a transformer on the input, go with 10k:10k.

 

[ruffrecords]

Regarding line amp, I believe will try to use 22113. So correct me please if I'm wrong, for dual mono RS127 I'll need two 22113 line amp boards, for each rs127. And it should be good with a pair of 600:600 input transformer. But will this really works ok with just 24v laptop power supply ?

The Helios 22113 line amp should be OK as a gain make up for the brilliance section of my REDD EQ design. You will need one for each EQ so two for dual mono. You can use a 600:600 input transformer provided you load it correctly (with 600 ohms) and provided the device you feed it from can drive a 600 ohm load. it would be more normal to use a 10K:10K input transformer. I would not use a laptop 24V power supply for this. The power supply rejection ratio (PSRR) of the 22113 will not be as good as a modern op amp and the output from a laptop power supply is likely to be noisy. The power supply mentioned in the post above should be fine.

Cheers

Ian

 

[mike]

EugeneKei

The walwart PSU that JMAN used is also the one that I used. As long as your internal wiring is good/shielded there will be little to no noise. I built 2 units, each mono so you could call it dual mono, but I would say it is 2 seperate mono units Each has their own 22113 line amp card and their own PSU - I used Jensen 10:10k input transformer and jensen 600:600 output transformer on each unit. You could build it dual mono in one unit and use one PSU with no issues most likely, but you still need 2 amp cards and 2 transformer sets for each side if you are going to build it like I did.

 

[EugeneKei]

Thank you gents for you answers, appreciate this