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New Conrad Echelon Amp

Dave Dog played on my new Echelon amp last night at a local jam. His response was positive. There are some interesting features on this amp and I would be interested in getting feedback from you recording guys indicating how useful these features would be in the studio.

There are three inputs on the amp. Clean (low gain), Crunch (high gain) and Lead (combines the low and high gain)

There are two preamp level controls - Gain and Drive. Each has a different flavor when driving the preamp into distortion. Next is the EQ - Bass, Middle, Treble. The reverb section has a dwell control and reverb mix control.

The output stage is unique in that there is a "Headroom" control that sets the output wattage from 28 watts down to less than 1 watt - continuously variable. In addition there is a "Trim" control which sets the drive level to the output stage. Lets say you turn the amp down to 10 watts and then drive the output stage pretty hard with the trim control turned up. The result is the amp compresses and results in a pretty heavy sustain.

So I'm curious to know how desirable these features would be in the studio?

Conrad Sundholm

Comments

Sundhy Sat, 11/28/2009 - 14:40

OK audiokid lets talk about # 5 on your list - Distributive Filtering:

In the gut shot picture attached you will notice that each filter capacitor in the power supply (blue) are located right at each tube it supplies. In the case of the single pre-amp tube notice that there is a separate power supply capacitor for each half of the dual triode. Also notice that the ground side of the capacitor is tied directly to the cathode circuit and the positive terminal of the cap is tied directly to the plate resistors. This is a very efficient way of filtering each node in the power supply. This approach also lowers hum and noise.

You will also note the filter capacitors on the right end of the board are larger and they become progressively smaller as you move down the board toward the pre-amp section. If large value capacitors are used throughout, the total capacitance is too high and the amp feels to stiff or tight. There are many factors that contribute to the feel of the amp - this is only one.

Now lets talk about the single point or star grounding scheme. Notice the green wires. They are the ground wires. As you can see, the first triode or pre-amp tube has its own ground bus (very short) and the green wire runs over to the input jack. There are a number of green wires going to the input jack - each from a separate stage on the wiring board. The result is a single ground point for all the circuit grounds - the input jack. All other jacks on the amp are lifted from the chassis and therefore are not grounded to the chassis. There is one other ground point on the chassis and that is the A.C. power cord ground which is located at the far end of the chassis - away from the single point circuit ground.

I'm not sure how to post an image here. You can see the photo at:

(Dead Link Removed)

bigtree Sat, 11/28/2009 - 15:35

Hi Conrad,

many of us are not facebook users, meaning, we can't see this image if we aren't signed up to Facebook.

To add images, its simple. bypass the quick replybox all together and hit

button.

The Quick Reply box is missing the extra option like img / bold/ youtube/ quote/ code/ list etc in post features. Its just a quick reply for text.
The official posting box has the full deal. (note) you get this in the edit mode as well)

Once there...

In the text box

copy the url of an image in the box below

highlight the full url string

like this

and click the img icon tag (above the box) and it will add the tags to make the image show on the forums. Once finished with your reply, Submit.

The image will show.

MrEase Sun, 12/06/2009 - 06:45

MrEase wrote: [quote=Sundhy]Moonbaby, you are right about core saturation in the output tranny contributing to the tone of the amp. Output transformer core saturation occurs earlier in the lower frequencies. Out of curiosity I put the Echelon amp on the bench and ran some tests at full power and about 1/4 power. Here are the results:

Core saturation of the output transformer on this amp starts at about 150Hz and increases as I went down in frequency to 40Hz. The trim control on this amp determines the signal voltage swing into the phase inverter. I was able to create core saturation at 1/4th power by advancing the Trim Control.

Therefore Output Transformer core saturation can be achieved with this amp even at the lower "Headroom" settings. Thus the tone is preserved.

Conrad

Thanks, Moodbay for the question.

Conrad

With due respect I don't think we are talking about core saturation here but a drop in anode load impedance at low frequencies caused by limited primary inductance of the output transformer and this is independent of power level. Like I said earlier, magnetic saturation of the transformer core is to be avoided like the plague. True core saturation could never be maintained at the lower power levels as lower power inherently lowers the magnetic flux in the core. I do agree though that you should be able to maintain the "sound" with the lower power levels!

First up I want to make it absolutely clear that I am not trying to decry Conrad's designs and do appreciate what he has added with this latest design. I was hoping that perhaps Conrad would acknowledge these earlier comments regarding core saturation but as he has not as yet, I felt that some further explanation would help in order to avoid any possible misunderstanding and also as some of you seem to have an interest in how these things work. I have tried to write this in a non technical fashion as much as possible - please let me know if I have failed!

Core saturation refers, unambiguously, to magnetic flux saturation in the output transformer magnetic core. It is this flux that transfers the energy between the primary and secondary circuits and saturation refers to the point when the magnetic flux in the core cannot increase any further. The transition between normal transformer action and saturation depends on the transformer construction and the consistency of the magnetic circuit. For a toroidal transformer the transition is much sharper than for the "conventional" output transformer using E and I cores. This is because the toroid has a completely consistent magnetic path with no right angles or changes in cross sectional area. It is inconsistencies in the magnetic path that slightly soften the transition as some of the magnetic flux leaks in to the air (just like a permanent bar magnet) and as the core approaches saturation these "leaks" increase thus softening the transition to saturation. This is why I doubt you would ever see a toroid in an output stage - conventional construction allows a small amount of leeway in terms of aggression on the valves and also other possibilities (see the side note below).

As I said before, saturation is to be avoided, but I will now try to explain why. When the primary winding current (i.e. output level) exceeds the point where saturation occurs two key things happen. Firstly the link between primary and secondary is lost. This is because any further increase in current does not cause increased magnetism and it is that magnetism that produces the secondary current - no more magnetism = no more secondary current - so the output no longer follows the input. Secondly and more dangerously for the valves is that the primary inductance drops alarmingly (almost to zero) as there is no longer an effective magnetic core for the primary inductance. This has a double impact for the valve, the first is that current will increase rapidly to the maximum the valve can provide and secondly, due to the lack of anode impedance, the anode voltage will track rapidly up to the supply voltage. These two simultaneous events on the anode are what leads to "stripping" of the cathode, which is where the coatings on the indirectly heated cathode literally get "sucked" off, leaving the valve with progressively lower emission and premature failure. So core saturation is generally not good all round either from the sonic point of view or reliability.

(Side note: At high frequencies (not necessarily in the audio band) another coupling mechanism (i.e. capacitance) also comes into play. That is not important for this explanation but can contribute significantly to the different "sound" of various transformers.)

What this also means is that when core saturation occurs the output will always be at the same level (for any particular frequency) - as it is only the magnetism that creates the output. This is why Conrads assertion in the last paragraph of the quoted post is simply wrong. If the output is running at 1/4 power there must be a consequent drop in the core magnetisation (otherwise the power level has not changed) and therefore the core cannot possibly be in saturation.

What I am convinced of is that Conrad has actually measured the "output stage saturation" which is indicated in his comments about frequency. As frequency lowers, the impedance of the primary circuit drops. The amount of this drop will depend on the primary inductance, the transformer ratio, and the load (speaker) impedance. At lower frequencies it is perfectly possible (and very common) for the valve and its drive level to "saturate" and be unable to provide further current, thus limiting the voltage swing at the anode and thus clipping the output. This is the classic valve overdrive sound of yesteryear where it was only the output stage that would distort as no-one had ever thought of deliberately overdriving earlier stages. It in no way implies that the transformer core is ever saturated.

This is exactly the sound that it seems to me that Conrad has achieved but at lower power levels. His circuit goes further than that in that he also allows you to vary the drive to the output stage which to me is a clear clue as to what is really happening. I'm sure it will sound great but really it has nothing at all to do with "core saturation".

I hope this helps those who may have been interested and stuck it through to the end!

Davedog Sun, 12/06/2009 - 10:19

A very interesting point from the engineers POV.

So your main 'gripe' is the use of language out of context.??

Hopefully this will clear the air. I'm sure that Conrad has not intended to misrepresent his designs in any way. He has been designing tube amps for a very very long time and has been successful at it. Not just as a boutique design/build shop either. There were a lot of highly successful bands in Britain that used his designs for many years. Lots of Sunn Bass and Guitar amps floating about.

Its very exciting for those of us who have wanted something that operates like this latest one. The very point of the 'old skool' overdrive in the output section rather than the thin reedy sound of preamp distortion AND at levels that are controllable down to a whisper, is something that has been virtually unavailable for those that like that sound.

Its a question that gets asked on here a lot, referring to "How do they get that guitar sound??" and using a recording where the obvious answer is a large amp in a controlled space turned up to get that output tube warmth and speaker distortion. Much like the Marshalls of yesteryear JTM's, Bluesbreakers and the like. Also the Fenders of old, Bassman, Supers, Vibrolux, etc. They all sound great but not till you get them in that 'sag' situation where there is no more gain to be had, only powersection sag and distortion.

Conrad has achieved this without the loss of the clarity. Or the 'feel' of the preamps sensitivity. The amp remains 'quick' even though it has the sound of the sag and the subsequent compressed feeling that comes with that.

My suggestion to you, MrEase, is simply email Conrad. His contact information is readily available and I'm sure he would talk shop with you about anything you desire to discuss. What I dont want is to have it appear to be running down of something that is simply a difference in terminology.

Your explanation of transformer logic was spot on and very interesting. Addressing Conrad in an email will net better results than doing so publically. He is certainly not an beginner and will see your points.

MrEase Sun, 12/06/2009 - 15:31

Well Dave, I thought I made it quite clear in my very first sentence that there is no "gripe" with Conrad or anyone here.

As far as contacting Conrad direct, I do not really see the point. I saw something I knew to be incorrect on a public forum so I don't see the point in correcting it privately and leaving the error in the public domain. That does not mean I am having a go at anyone nor making any comment on their experience however we all make mistakes and I do not like to see misleading information in what I regard as a quality forum.

What I commented on is neither ambiguous nor anything to do with language or semantics. Core saturation is VERY specific and was directly questioned by Moonbaby. What I believe Conrad responded to was output stage saturation which is a very different beast. At that stage I had already responded to Moonbaby's question so I was quite surprised to see Conrad's later response which was at odd's with what I had already posted and which I found to be referring to another phenomenum altogether.

Of course if you prefer me to respond privately and see errors stand on the forum then please let me know and I will not bother in the future! This is not trying to be awkward but is a direct response to the points you have raised.

I personally don't think that would do anything positive for the quality of this forum though. You are the mod here, you decide!

bigtree Mon, 12/07/2009 - 10:38

wow, Interesting topic.

I don't understand much on the theory side of this but I do know things don't have to make sense to sound good. I think at this point we might be suggesting Conrad disclose his design secrets. I really think we should ease and move on.

I look forward to hearing what the users are hearing, and hearing more on the different amps, designs, speakers, and how he builds these gems.

moonbaby Mon, 12/07/2009 - 12:51

Good idea, BT. Besides, my comment ws probably mis-spoken in that I never intended it to be CORE saturation of the tranny, but simply saturation of the output stage (with the tranny acting as a LP filter). At least that is how things were explained to me by the engineers at Yamaha many years ago when they were developing their line of "transistorized-but-we-make-them-sound-like-tube-amps" in the late 70's. Guess what...they didn't !!!

MrEase Mon, 12/07/2009 - 14:55

Can I just explain that is certainly not my intention for Conrad to reveal any of his design secrets. All I have been trying to clarify is that when running a transformer at reduced power, saturation of the core is never going to happen. He was very specific in his earlier conclusion and I am confident that on reflection he would agree with the points I raised.

This is not intended in any way to be a comment on the performance of his Echelon design. This is something I thought I had made clear in my first post on this thread. Having heard and used a different amp that also reduces available power I can confirm that the overdrive at lower levels is equally lush and powerful as that at full power. This characteristic sound that we all seem to love arises from output stage saturation though and certainly not from output transformer core saturation.

I only took this up as I far too often see such simple mistakes bloom into urban myth! I think it is unfortunate that Conrad has not been back here lately as I'm sure that this could have been acknowledged and nippped in the bud very easily. Sadly instead of this Dave seemed to think I was having a gripe and decrying Conrad's design (which I had taken care to point out was not the case) and he also made a false assumption that it was a case of alternative terminologies -which it definitely isn't.

Davedog Mon, 12/07/2009 - 16:45

I have explained my position very carefully and clearly in PM's to you, Mr.Ease.

My take is not an assumption as much as a suggestion of misinterpretation of technical forms as was laid out by Moon in his last post.

I appreciate your willingness to keep the airwaves clear of assumptions and half-truths. It is something we strive for here and have done a good job with over the years. Its good that someone also cares deeply about these things.

Sundhy Wed, 02/24/2010 - 15:34

MrEase, you are right concerning core saturation of the output transformer. I have been able to create it on the bench and have observed it on the scope. I believe it is possible that some players get into this region with their hot pickups and running an amp beyond its limits.

MrEase Tue, 03/23/2010 - 12:51

Sundhy, post: 300667 wrote: MrEase, you are right concerning core saturation of the output transformer. I have been able to create it on the bench and have observed it on the scope. I believe it is possible that some players get into this region with their hot pickups and running an amp beyond its limits.

Hi Conrad,

Thanks for responding - I haven't looked here for a while!

From that I presume you agree that core saturation cannot be achieved when the power level is backed off and all that lovely sound comes from saturating the output stage rather than the transformer! :<)

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