Listening Impressions SE vs Push Pull vs Solid State

[bracurrie]

Please excuse this lengthy attempt at a review of sorts.

I have been lucky enough to have around an ampsandsound.com SE amp Little Ben and an ampsandsound.com push pull Stereo 15. I do not have the technical experience to go into and fully understand what makes these amps different other than the basic differences. I won't go into the specifics of comparing the tube choices that Justin gave me when he sent the amps.

My system is a bi-amped active crossover two way consisting of Jubilee clone cabs with Crites drivers on the bottom and Dave Harris's Eliptrac 400 horn with an Faital HF200 on top. The crossover point is 500 Hz with 24db slopes.

I had been listening for about a week to the system with the Stereo 15 connected to the Jub cabs and the Little Ben connected to the Eliptrac horns. The arrangement was quite pleasing as my system images well and the SE treated vocals, strings and percussion with a delicacy that let the music be the star. Rock guitar and EDM didn't wow me, but was good enough to keep listening. But I kept playing classical and jazz favorites and was enjoying them a great deal.

Yesterday my tech guy came over and we played amp round robin and began to try different configurations. First we took my Audio by Van Alstine Synergy 240 and put it on the Jub cabs and kept the Little Ben on the HF horns. The AVA is a state of the art solid state amp that dampens the bass drivers better and thus the bass is tighter and cleaner when you turn up the volume. I had anticipated it would end up on the bottoms as I had them there before and was quite pleased. Impressions of the Little Ben on the HF remained the same.

We then switched out the Little Ben SE for the push pull Stereo 15 on the HF horns. This is where the comparison gets tricky as both are very pleasing. The Stereo 15 seemed to attack transients faster and reveal more detail with percussive sounds, guitar and cymbals. I then played a low definition MP3 that I know irritates my ears and while the Little Ben allowed me to enjoy that track the Stereo 15 revealed the annoyance more. My tech and I agreed that analogue classical and jazz would be quite pleasing with the Little Ben or the Stereo 15.

The acid test was when we put the Stereo 15 on the Jubs and put the Synergy 240 on the HF horns. The tech listened for 10 seconds and then said it sounds like almost any decent SS amp but that it was lifeless and thin compared to the either the Little Ben or the Stereo 15. We played rock and classical for only the next ten minutes as we both were eager to get the Stereo 15 back on the HF horns to re immerse ourselves in the warmth of tubes.

Then later Saturday night after attending a Vanderbilt men's basketball game against Arkansas where the good guys lost and then going to see my Predators lose to the Ducks I was looking for a music pick me up.

I hooked up the Stereo 15 to a pair of KEF 140 monitors that were my #1 speakers before I discovered horns. They are 2 way and very flat but not very efficient. I played a classical piece with a lot of transients and dynamic range where detail and volume are needed to reproduce the piece. The sound was warm, detailed with no irritants. Even my low res MP3 was listenable. I tried the same with my Synergy 240 and while there was nothing wrong, it wasn't as pleasing on the same classical piece and my low res MP3 was again unlistenable. Rock and roll was about the same on both with maybe a slight edge to the Synergy 240 on Led Zep's Celebration Day live concert. But again the Stereo 15 played the Led Zep with great enjoyment as well as EDM and pop.

All in all I would say the Stereo 15 plays the breadth of styles very well. And its just plain more fun anyway, I do not write reviews for a living and I didn't stay in an Holiday Inn Express so please excuse my attempt to describe what I heard. If there are any questions I would be happy to answer.

Edited February 10, 2014 by bracurrie

[oldtimer]

So you like the push-pull better than the set?

[bracurrie]

So you like the push-pull better than the set?

If I have to select one to cover all that I listen to then yes I prefer the push pull. The SET is wonderful for some music and it softens seemingly harsh content to allow for the music to be enjoyed.

As you can see its not a simple answer. Didn't mean to be unclear.

[mustang guy]

I haven't tried a set amp yet, but I will say that my Fisher 80AZ (KT-66 tube) monoblocks being fed by any of my tube tuners sounds more pleasing to me than my expensive pre-pro bleeding edge Integra system. In fact, I have had my entire 6.2 theater, including movie screen, off since I got the tubes dialed in. What's more, I am only listening to FM radio on my tubes. In my SS system, I have Oppo blu ray, appletv, FM/AM, and cable TV in HD. I haven't had them on in a couple months or more!

All I can say is, I like the tubes better in _my_ room with my LaScalas. Oh, and one more thing. I am not using the THT's. It's either a single Lascala with one of my mono tuners, or 2 lascalas with my only stereo tuner. They don't need a sub when using tubes, IMO. It's full sound.

[LarryC]

I haven't tried a set amp yet, but I will say that my Fisher 80AZ (KT-66 tube) monoblocks being fed by any of my tube tuners sounds more pleasing to me than my expensive pre-pro bleeding edge Integra system. I

Is the Integra an Onkyo product? The last time I was in Indy, Klipsch was using an Integra pre-pro in their Palladium HT setup in Indy, and "bleeding edge" is right!

The previous Aragon (may it RIP) units were far better.

Edited February 9, 2014 by LarryC

[mustang guy]

I haven't tried a set amp yet, but I will say that my Fisher 80AZ (KT-66 tube) monoblocks being fed by any of my tube tuners sounds more pleasing to me than my expensive pre-pro bleeding edge Integra system. I

Is the Integra an Onkyo product? The last time I was in Indy, Klipsch was using an Integra pre-pro in their Palladium HT setup in Indy, and "bleeding edge" is right!

The previous Aragon (may it RIP) units were far better.

Yes, the DHC-80.3 pre, and the DTA-70.1 multichannel amp. They are good, don't get me wrong. I like the tubes better.

[bracurrie]

active crossover two way

What brand or model of crossover is this?

I am using a MAC computer running Pure Music. Sound card that does the heavy lifting is a Apogee Quartet. Settings are 500 Hz with 24db slopes. I also have a bit of delay on the horns.

Edited February 10, 2014 by bracurrie

[Cut-Throat]

So you like the push-pull better than the set?

The amp that the OP listened to was not a SET amp but a Single- Ended Pentode amp. Far different than a SET amp, which is a Single Ended Triode Amp. I would not jump to this conclusion unless you have auditioned a 2A3 or 45 SET amp.

[Fjd]

So you like the push-pull better than the set?

The amp that the OP listened to was not a SET amp but a Single- Ended Pentode amp. Far different than a SET amp, which is a Single Ended Triode Amp. I would not jump to this conclusion unless you have auditioned a 2A3 or 45 SET amp.

I don't mean to muddy the waters, or smear the transparency and clarity of the......., but maybe one of the engineers that are more familiar with circuit design can weigh in and add clarification or more color as I’m more of a DIY builder than a circuit designer; however, while I’m aware that a portion of people believe that the only SET amp, is a SET amp with a direct-heated triode tube, I believe that a common interpretation of the term "triode" in a “single-ended triode” amplifier is used to describe how the tube in the output stage of an audio power amplifier is wired in the circuit.

I’ve got single-ended amplifiers wired with a switch for a person to listen as “triode” wired or listen as “ultra-linear” wired. I’m not entirely sure how to wire a single-ended amplifier in “pentode,” if even possible given the feedback circuit that a pentode wired circuit needs. Will Vincent (of Will Vincent Dynaco rebuild fame) makes a push-pull amplifier with two direct-heated triode 45 tubes in push-pull on each channel; however, I’m not sure if he wires those DHT 45 tubes in triode or ultra-linear. However, there are also push-pull amplifiers such as the VRDs that have a switch to choose triode wired or ultra-linear wired push-pull operation.

I believe that a basic triode wired audio power amplifier will have a driver that provides voltage gain that can be coupled to a triode tube (i.e. 1626, 10Y, 71A, 2A3, 45, or 300B, 845, etc.) or a pentode tube (i.e. 6L6 or 6550) or even a kinkless tetrode tube (i.e. EL34 or KT88) connected and wired as a triode.

Technically, I believe that a portion of the people would think of the 2A3, 45, 300B, or 845 tubes in SET amplifiers as Direct Heated Triode (DHT) SET amplifiers. Of course, while experimenting with various DIY builds, I probably lean more toward the camp of looking how the tube is wired, but I’ve also heard the triode wired pentode or tetrode tube called a “fake” SET or "psuedo" SET by people from time to time.

Given the above, should the question be expanded more along the line of “what's the difference between a "real" triode like the DHT 45 and a pentode such as the EL84 that's wired in triode?” The EL84 and EL34 can sound pretty good wired in single ended triode.

From the various threads over the last several weeks, I’ve learned that the quality of the source, the type of music listened to, the circuit design, the choice of driver tube, the power supply design, the types of capacitors in key areas, speakers, cross-over networks, room acoustics, acuity of a person’s hearing, and of course, let’s not forget cables, in addition to, subjective personal preference are all variables that can impact a person's conclusion of "which is better."

It even gets better if a person works from the premise "that all tubes can sound a little different." I suspect that there are differences in sound between wiring a pentode as a ‘fake’ triode and wiring a true triode as a triode. However, you also will find differences between brands of the same triode or can find differences between types of triodes of the same brand (i.e. 1626, 10Y, 71A, 45, 2A3, 300B, 845, etc.).

It seems that there are just so many variables involved no matter which way a person turns.

[bracurrie]

It seems that there are just so many variables involved no matter which way a person turns.

And the fun is when we all learn through the discussion. I knew I was going to get something wrong when I started this thread.

[mike stehr]

I’m not entirely sure how to wire a single-ended amplifier in “pentode,” if even possible given the feedback circuit that a pentode wired circuit needs.

You just make another filtering stage in the PS for the screen grids with the pentode, you want to make sure the screen voltage doesn't exceed the plate voltage and have it somewhat regulated.

You can bring feedback back from the output transformer and apply it at the cathode of the driver tube. Using square waves and a scope, you can noodle with the feedback R and adjust, along with a feedback compensation cap, and monitor for best square wave response. One way to go about it.

Tons of variables...

[Fjd]

It seems that there are just so many variables involved no matter which way a person turns.

And the fun is when we all learn through the discussion. I knew I was going to get something wrong when I started this thread.

I don’t think you necessarily have anything wrong. Since I’ve been doing some apartment living for longer-term work travel, I’ve been focusing more and more on near-field listening and it has given me the opportunity to experiment with much higher sensitivity speakers and shorter signal paths (i.e. SET amps).

While I really enjoy the emotional aspect conveyed in the music using my SET amps, both the DHT variety and the non-DHT variety, and use them often, I find that they are not for every situation.

In many situations I would rather bi-amp or tri-amp (depending on the speaker in use and music played) with the SET on the high frequencies or the smaller push-pull on the high frequencies and have a more powerful amp for the low frequencies. In my view the small SET amps just cannot drive those 15 inch woofers with enough authority and the music ends up sounding somewhat soft and dull.

Now I suspect that a larger SET amp with the 845, 211 or GM70 tube on those 15s may be a different story? I think those Welborne Apollos that I've read Dean talk about may have been SET amps with the KR 300BXLS tube and pushed about 20 watts per channel or so.

[Fjd]

I’m not entirely sure how to wire a single-ended amplifier in “pentode,” if even possible given the feedback circuit that a pentode wired circuit needs.

You just make another filtering stage in the PS for the screen grids with the pentode, you want to make sure the screen voltage doesn't exceed the plate voltage and have it somewhat regulated.

You can bring feedback back from the output transformer and apply it at the cathode of the driver tube. Using square waves and a scope, you can noodle with the feedback R and adjust, along with a feedback compensation cap, and monitor for best square wave response. One way to go about it.

Tons of variables...

Thanks, it seems like wiring for pentode would be more difficult to get right.

[bracurrie]

In many situations I would rather bi-amp or tri-amp (depending on the speaker in use and music played) with the SET on the high frequencies or the smaller push-pull on the high frequencies and have a more powerful amp for the low frequencies. In my view the small SET amps just cannot drive those 15 inch woofers with enough authority and the music ends up sounding somewhat soft and dull.

I agree as my solid state really punches out the bass. What are you listening with now?

Edited February 10, 2014 by bracurrie

[justinsweber]

To add one more wrinkle. It’s a SET or a different flavor… Single ended tetrode wired as a triode with ultra linear operation and 6db of feedback. The Stereo 15 is push pull pentode.

[Fjd]

If I may. A pentode wired as a triode is NOT fake in any substantive circuit way. For what counts in all this is the TRANSFER FUNCTION. When the tube has the TF of a triode, it is a triode.

All the topologies do spund different characteristically. SET and SEP sound different because the triode TF is very different than the pentode TF. And of course PP is very different in all respects from single ended which by definition Class A. PP can be Class A, AB, or C. Ultralinear is a special TF which lies between triode and pentode and presumes to take the best from each. This is all to say tha the topology and the TF, are the more important idea than the tube type. Each is a compromise, none perfect.

I think the amps being reviewed here are SEP, not SET.

To add one more wrinkle. It’s a SET or a different flavor… Single ended tetrode wired as a triode with ultra linear operation and 6db of feedback. The Stereo 15 is push pull pentode.

Thanks guys, I didn't want to over-simplify or take the thread into too much detail, but there seemed more to a single-ended design that a single-ended amplifier using a pentode tube wasn't locked into being wired into a pentode circuit, but still can be wired into a triode circuit as I've tried to understand the circuts. Hopfully, this helps Brad too. So it does seem that the overall reference to "SET" is related to "single-ended" and the type of "tube" (i.e. triode or tetrode) or SEP for "single-ended" and "pentode" tube? However, it seems like it may be just as important, to then work down from there one level to the various transfer functions used in a circuit such as wiring the tube as triode or wiring the tube as pentode since the tube using the triode transfer function will sound different than the sound using a pentode transfer function?

Edited February 10, 2014 by Fjd

[tube fanatic]

You just make another filtering stage in the PS for the screen grids with the pentode, you want to make sure the screen voltage doesn't exceed the plate voltage and have it somewhat regulated.

You can bring feedback back from the output transformer and apply it at the cathode of the driver tube. Using square waves and a scope, you can noodle with the feedback R and adjust, along with a feedback compensation cap, and monitor for best square wave response. One way to go about it.

Tons of variables...

True pentode operation puts the screen supply at the "bottom" of the output transformer primary. The DC resistance of the latter will always keep the plate voltage somewhat below that of the screen. This is considered insignificant unless the screen is powered before the plate. And since the relatively small DC current variations from zero to maximum signal will drop both voltages in proportion, it's not of consequence (a few volts of line voltage variation can cause a similar effect.) Depending on the power supply design, the screen and plate supply can be taken from the same point. For example, in a typical CLC or CRC filter, the screen and opt primary can be fed from the same output filter cap. The goal here is to keep the ripple as low as is feasible. I'd be more concerned about providing additional filtering for the voltage amp stage by using a CLCRC or CRCRC arrangement. The feedback arrangement you outlined is popular in 2 stage amplifiers, but can get a bit dicey if applied to more stages than that. It's often expedient to use local feedback at each stage, the goal being to drop distortion to the desired level. This is particularly useful in SEPs which usually have acceptable distortion figures only up to around 1/4 of maximum output. And, to stir the pot a bit more, I can truly say that I don't like the sound of Ultralinear, and that using a regulated screen supply with small pentodes (6V6, EL84, etc.) is not necessary!!! Let the "hate mail" begin........

Maynard

[bracurrie]

And, to stir the pot a bit more, I can truly say that I don't like the sound of Ultralinear, and that using a regulated screen supply with small pentodes (6V6, EL84, etc.) is not necessary!!!

After listening to the three close together and reading all this I still maintain that the speakers and their placement with room treatments are still way more impactful to the resulting sound. Some of this amp design detail is over the top for us non-technical guys. Yes I understand I got it wrong when I used SET instead of SEP. Is the SE part more impactful to the outcome the T or P?

[bracurrie]

And, to stir the pot a bit more, I can truly say that I don't like the sound of Ultralinear, and that using a regulated screen supply with small pentodes (6V6, EL84, etc.) is not necessary!!!

After listening to the three close together and reading all this I still maintain that the speakers and their placement with room treatments are still way more impactful to the resulting sound. Some of this amp design detail is over the top for us non-technical guys. Yes I understand I got it wrong when I used SET instead of SEP. Is the SE part more impactful to the outcome the T or P?

Yes, the "single ended" attribute is a large impact on the sound, probably greater than the T or P.

Yes, room and speakers are important, but amplifier differences can easily be appreciated without room treatment. I think in your setup, as I understand it, the computer and crossover is far more of a concern than anything to do with the room. You are running your source through a computer and little electronic crossover before the tube amps. That's less than ideal, compared to say, 'source--->tube amp---->speaker.'

Actually if I use a high res file my Apogee sound card is no different than a good preamp. It's very much ideal other than being unusual.

[mike stehr]

You just make another filtering stage in the PS for the screen grids with the pentode, you want to make sure the screen voltage doesn't exceed the plate voltage and have it somewhat regulated.

You can bring feedback back from the output transformer and apply it at the cathode of the driver tube. Using square waves and a scope, you can noodle with the feedback R and adjust, along with a feedback compensation cap, and monitor for best square wave response. One way to go about it.

Tons of variables...

True pentode operation puts the screen supply at the "bottom" of the output transformer primary. The DC resistance of the latter will always keep the plate voltage somewhat below that of the screen. This is considered insignificant unless the screen is powered before the plate. And since the relatively small DC current variations from zero to maximum signal will drop both voltages in proportion, it's not of consequence (a few volts of line voltage variation can cause a similar effect.) Depending on the power supply design, the screen and plate supply can be taken from the same point. For example, in a typical CLC or CRC filter, the screen and opt primary can be fed from the same output filter cap. The goal here is to keep the ripple as low as is feasible. I'd be more concerned about providing additional filtering for the voltage amp stage by using a CLCRC or CRCRC arrangement. The feedback arrangement you outlined is popular in 2 stage amplifiers, but can get a bit dicey if applied to more stages than that. It's often expedient to use local feedback at each stage, the goal being to drop distortion to the desired level. This is particularly useful in SEPs which usually have acceptable distortion figures only up to around 1/4 of maximum output. And, to stir the pot a bit more, I can truly say that I don't like the sound of Ultralinear, and that using a regulated screen supply with small pentodes (6V6, EL84, etc.) is not necessary!!! Let the "hate mail" begin........

Maynard

The guy mentioned that he didn't understand how to configure a single-ended pentode amplifier, or if it was even feasible. I'll openly admit I'm rank amateur, and just explained to the best of my knowledge.

I mentioned "somewhat regulated" because I didn't want someone coming in saying that regulated screen supplies are a must or some such. I mostly work with simple 2 stage single-ended pentode circuits, and have never used regulated supplies for the screens, and have never had screen related issues. You explain why I never have these issues in your post above.

This is why I shouldn't answer these sort of questions. I don't have enough technical knowledge to explain things in the correct manner, but I tried.

I do appreciate the points however, and am not afraid of constructive criticism. I'm always on a learning curve.

With regards to "stirring the pot", and I bring this up with no offense...but you have "tube amp designer" emblazoned above your avatar. I know you may be some sort of electrical or audio engineer just by the way you help folks out around here, and the technical prose of your posts.

But I haven't seen any images of your products or projects, unless I missed them.

I know you have your reasons, but the only reason I'm bringing it up is you called Justin Weber out basically demanding underside images of his amplifiers, which he did.

IMHO, I feel it is only fair that you return the favor and show some of your work...even a above shot of a amplifier. I'm not afraid to show my work, and I am a rank amateur.

I'm not trying to be a jerk about it, I just think fair is fair.

Edited February 10, 2014 by mike stehr