Prototypers wanted

[CYoung234]

well, vinyl release isn't cheap so I suppose I'll go for one of the little silver discs. In fact, I might get the entire Bernstein / Concertgebouw / Mahler collection, despite it being "DG Digital"

Actually, I am listening to the Tennstedt / CSO recording right now, and still go back to this one as my favorite. I really like the Concertgebouw / Bernstein recording as well, and do prefer their tempi in some spots, but hey, I live in Chicago and know a lot of these guys personally, so stylistically I have to recommend the CSO recording. The last time I performed Mahler 1, we used a lot of ideas that Herseth had in the 3rd movement for the trumpet parts. Sam Magad, the Music Director for the orchestra I was playing in, and the Concertmaster for the CSO at the time, was a pretty hard guy to please. His usual comments to the orchestra would be along the lines of "that was NEARLY good", meaning it would never actually be good. At any rate, at the next rehearsal following performances he spoke to me and made the simple comment "just like downtown" in reference to our trumpet playing - high praise indeed from him.

At any rate, I would suggest that if you can, check out a bunch of recordings from your library to find out what you like best before you buy it. Finally, sorry for the thread hijacking; well, not REALLY sorry. At least I am using the Torpedo to listen to this stuff!

[TomB]

Hmm ... Doug's really got something with this tube bias thing. More later ... I don't want to jump to conclusions, but - well, more later ...

[luvdunhill]

3.25V == 2 x 630-HLMP-6000 ==

[TomB]

3.25V == 2 x 630-HLMP-6000 ==

OK - I'm totally clueless on that.

Meanwhile ...

I tried the new CCS awhile back with a 221R resistor in parallel. First thing I noticed was really punchy bass. Impressive, but the honeymoon was soon over - highs rolled off and the bass was obviously mid-bass exagerration. I preferred the original configuration, to tell the truth.

So ... I was ready for a change. Reading back to Doug's recent post about changing the bias point, he stated that if you had installed the resistor for the new CCS current suggestion, all you needed to do to try the new bias point was to switch the jumpers. Sounded easy enough - so, I did that last night.

Lo and behold, more detail and better highs than with the original configuration, IMHO. With Concrete Blonde's Mexican Moon (a favorite test of mine for highs), the tamborine bells were strong and detailed. That's the thing that this change has seemingly accomplished - it's brought back the smooth and clear highs that I heard with the original CCS, but now there's an obvious increase in detail and transient response that seems even better than before.

To pursue this further, I took the amp and several tubes to work today with the premise that I'd report back after extended listening determined that this wasn't any fluke. I can't tell you with specific measurements - the M-Audio Transit I have has had no working drivers since before Vista. Unfortunately, my plan didn't turn out very well - I never even had the chance to flip the power switch.

So, I listened some more at home tonight. My setup right now is a simple GrubDAC for the source running FLAC files. I'm running two Sylvania 6J6A's with halo top getters. They're not matched - I just grabbed a couple with identical construction and plugged them in. I'm using Foobar 2000 and run several music selections from different genre that I typically use to test things with my ears (terrible test device, but it's all I have at the moment). These include passages that highlight transients, midrange, bass response, and highs. For instance to me, the cymbals on Porcupine Tree's Deadwing, In Absentia, and Stupid Dream are among the best in modern music. So, I listen for whether those cymbals are clear - is there a clear swish without breakup, is there a metallic component, and can you hear the drumsticks tap as they make contact with the metal? The answers are all yes. Similar for Diana Krall - can you hear the midrance in her voice overwhelming all the other sounds? Does Rihanna's Rude Boy (Rated R) come through with impressive bass slam? There are other selections I can mention, but I'm probably beyond Head-Fi lingo by now. ;-)

I've tried the Senheiser HD600 with Cardas cables, an HD580 with 650 cable, the HD 25 II, Sony V6's, AKG K701's and the Grado SR225, HF-1, and HF-2 - even the KSC-75. With every headphone save the Grado's, the upper switch position sounded the most forward and most dynamic. Even KSC-75's sound best with the switch up. That tells me that anything higher than 32 ohms should use the high switch setting. There's plenty of bass punch, too - except for the K701's. Admittedly, the amp may not be a powerhouse. With the K701's, the bass sort of futzes out and never manifests itself. Detail, midrange and highs are all there, but the bass just loses it before it starts. Not so with lighter loads - the HD 25's sound detailed and bass-punchy; the KSC-75's are ready to jump off of your head.

The real payoff is with Grado's, however. I've said it before so will say it again (perhaps with a bit more authority now that I've been to CanJam) - there's no other amp I've heard - except for Doug's higher level offerings - that sounds as good with Grado's than this amp, especially at this new setting. Bass is strong and punchy, midrange is strong, detailed, and lush, while the highs are as smooth as silk with no breakup and no harshness. That's something I've never experienced with any other amp using the Grado SR225's, for instance. I've never had a headphone as hot and harsh as those things. They're unlistenable (IMHO) with a lot of equipment, and usually end up giving me a huge headache with any extended listening. With the Torpedo and this new bias setting, the detail and highs are exquisite. Bass is sufficiently punchy, while the midrange is lush - simply wonderful with Grado's.

So, please - some of you with RMAA and other tools - give it another shot with this new bias setting that Doug recommends and let us know what you think. I know some of you are going to try K1000's, Audeze's and perhaps some other esoteric Orthos. Like I said, it may not come through like a powerhouse with some of those phones, but right now, it sounds fantastic with many other mainstream phones.

[Beefy]

OK - I'm totally clueless on that.

630-HLMP-6000

Regarded as being excellent LEDs for biasing tubes.

[luvdunhill]

Hey Tom, do those heatsinks you included for the top come in an unanodized version?

also, are there any other unpopulated PCBs out there?

[luvdunhill]

some of you with RMAA and other tools

working a more sophisticated setup and will definitely run it on this amp.

Also, I might bring it around and give a few others a listen, Yaniger, Millett, Jan Didden, etc. at an upcoming geek fest. Don't have any Grados to wow them with, I don't think we allow those to cross the border into Texas.... if they were say to show up in my mailbox though in clandestine packaging...

[nikongod]

Also, I might bring it around and give a few others a listen, Yaniger, Millett, Jan Didden, etc. at an upcoming geek fest. Don't have any Grados to wow them with, I don't think we allow those to cross the border into Texas.... if they were say to show up in my mailbox though in clandestine packaging...

Do you want to maybe borrow the RS-60? They never made it to Texas on their continental tour.

[dsavitsk]

From your previous post, mu (38) * 40 ohms is 1520, added to an rp of 3500 = 5020 ohms. Two red LEDs in series, assuming 10 ohms, would be 20 * 38 = 760 + rp (3500) = 4260 ohms. Higher, but not huge?

I think that's enough of a difference to matter. But, try it and see what you think.

3.25V == 2 x 630-HLMP-6000 ==

Yeah, the impedance curve looks great on these.

The real payoff is with Grado's, however. I've said it before so will say it again (perhaps with a bit more authority now that I've been to CanJam) - there's no other amp I've heard - except for Doug's higher level offerings - that sounds as good with Grado's than this amp, especially at this new setting.

Um, not sure I'd go that far. But, I do think it compares OK at the anticipated price point.

Hey Tom, do those heatsinks you included for the top come in an unanodized version?

Don't think so. They are surplus.

also, are there any other unpopulated PCBs out there?

There are, but there aren't any more transformers. Send me an email ...

Also, I might bring it around and give a few others a listen, Yaniger, Millett, Jan Didden, etc. at an upcoming geek fest.

My anxiety level has increased. You should find some Grados.

OK, so here's the status. Tom and I are in a bit of a holding pattern trying to decide what the best next step is. Option 1 is to basically produce the amp as is. We would make some changes in the board and case designs, etc., but the circuit would be about the same. This wasn't really an option until playing a bit more with the bias and current, but with the improvements there, it might be viable. Option 2 is to basically leave the amp as is, but switch to a different tube -- probably a 6DJ8 with both side in parallel. These are obviously more expensive, though a pair of JJs is only $25 which isn't too bad. It would probably make a nicer amp, though the high Gm could lead to issues if builders are not careful, and it leads to the whole tube rolling nonsense, and I am not sure I want to be responsible for some idiot spending $400 on a pair of tubes. This is supposed to be a cheap intro to tubes. Option 3 is to make a little daughter board for different tubes, so one could build the default 6J6 version, or use a different board for 6DJ8's or whatever, etc. Again, this drives up the price for everyone, and not everyone would want it. And, option 4 is to alter the circuit using something like a Beta follower with a 6DJ8 again (6J6 won't work well). Upside is that it is a neat circuit that performs very well and it has a pretty low Z out meaning that the transformer ratio can be lower which translates to more power/volume. Downside is that it is a lot more complicated to get right for newbies requiring some adjustment of the HV section, and the parafeed cap would need to be a lot bigger.

So, that's what our thinking is, and any comments from prototypers would be quite helpful in sorting it out.

[Nebby]

working a more sophisticated setup and will definitely run it on this amp.

What setup do you have? I'm trying to figure out a workable PC Based measurement setup. So far, I'm looking at building Pete Millett's soundcard interface and Cordell's distortion magnifier for starters....

[dsavitsk]

What setup do you have? I'm trying to figure out a workable PC Based measurement setup. So far, I'm looking at building Pete Millett's soundcard interface and Cordell's distortion magnifier for starters....

I think Pete's box is really only necessary for power amp testing as a way to protect your sound card.

[luvdunhill]

What setup do you have? I'm trying to figure out a workable PC Based measurement setup. So far, I'm looking at building Pete Millett's soundcard interface and Cordell's distortion magnifier for starters....

It involves a Millett design, but not the soundcard interface (though I have it, and Doug is correct)

[Nebby]

I think Pete's box is really only necessary for power amp testing as a way to protect your sound card.

True enough, I'm just hoping to get a setup where I can measure more than headphone amps

It involves a Millett design, but not the soundcard interface (though I have it, and Doug is correct)

No details?

[Beefy]

OK, so here's the status......

So, that's what our thinking is, and any comments from prototypers would be quite helpful in sorting it out.

Well I'm not a prototyper and am a relative toob noob...... but as a prospective builder and tinkerer I like the idea of option two or four. 6DJ8/ECC88/6922 are ubiquitous are there seems to be plenty of inexpensive options for tube rolling. If people want to go stupid with NOS tubes, let them. 6J6 doesn't seem as widely available, with fewer rolling options. Lower heater current of the 6DJ8 might cool things down a tad?

For option 3, futzing round with daughter boards seems like a lot of unnecessary effort.

Between 2 and 4, I'd vote for the option that gives smaller parafeed caps. So 2 would get my vote - if I even have one.

[Pars]

Regarding the options for the production version, I like 6DJ8s/6922s, but had to LMAO when you posted the $400 pair of tubes link. I had a pair of those (actually 2) and liked them a lot. I sold one pair, the other was returned as one tube was microphonic... but I digress.

For Option 3, would it be possible to place the tube socket patterns for both the 6DJ8 and 6J6 coincidental and let the bulider decide by which sockets they populated. I will confess to not looking at the socket patterns before asking this, and also not seeing what pin differences there are.

Option 4 sounds interesting as well.

[Beefy]

For Option 3, would it be possible to place the tube socket patterns for both the 6DJ8 and 6J6 coincidental and let the bulider decide by which sockets they populated. I will confess to not looking at the socket patterns before asking this, and also not seeing what pin differences there are.

6J6 is a 7-pin jobbie, compared to the 9-pin 6DJ8. Might be pretty tough to allow both without an external board/converter.

[TomB]

Personally, I'd rather see some of you try this new bias option before you start voting. About the 6J6 tubes - they are as plentiful as just about any tube, but dead cheap, to boot. They're just not marketed very much: high heater current and apparently some idiosyncrasies that Doug is quickly becoming expert in solving. Most vendors I've dealt with talk about having thousands of these things. There's also quite a list of tube equivalents, although admiitedly, most are variations on the same tube rather than different tube types.

I listened more to it today just using KSC75's at work and will not back off of my previous post. I've got a bit of a mid-bass hump, but that's because I used the smaller 3.9uf Clarity Cap I think. Actually, with the mid-bass hump, it sounds very much like these esoteric CD players that everyone seems to crave at Head-Fi meets (Meridian?). I am very happy with this amp again and it's much better at powering other mainstream phones (other than Grado's) than before.

Maybe a combination of Options - two amps?

[luvdunhill]

I'd vote Option 1.

[Pars]

I put two of the red LEDs in series, and am getting 3.5Vdc in circuit. I'm guessing this may be a bit high up the curve? I will also try some blue LEDs I have. The red LEDs measured ~1.6Vdc on my meter's diode test each. I'll do both listening and RMAA on both the 2x Red and 1x Blue. The 3.5Vdc is on the LED stack or the cathode. I'll see what the grid is at.

Edited October 4, 2010 by Pars

[guzziguy]

Have you tried milspec LEDs? You can probably get some from a local amp manufacturer.

[Pars]

^ Good idea! I'll be sure to check into it, though I'm not sure I could afford them. Then again, can I afford not to?

BTW, the grid is only connected to the input (audio) and is at 0Vdc.

Edited October 4, 2010 by Pars

[digger945]

BTW, the grid is only connected to the input (audio) and is at 0Vdc.

wrt the cathode?

have you(or anyone) tried the series parallel led bias?

[Pars]

Measurements were relative to ground. The schematic shows no direct connection to the cathode, but I suppose if the cathode is at +3.5Vdc and the grid floats? I would think the 1M resistor to gnd on the grid might have something to say about that but I dunno. If I measured relative to the cathode, it would show -3.5Vdc I would guess. The grid is connected to input jack->pot->resistor to gnd->series resistor->grid (pins 5 & 6).

[dsavitsk]

The grid is at ground, and is referenced via the pot. The 1M is a backup reference in case the pot has a flaw. The cathode is biased at somewhere between 1.5V and 3.5V with higher being better but also needing to be balanced against plate voltage.

[Pars]

So is the 3.5V I am seeing too high? This is with the original 75 ohm CCS. I'll have to measure the plate voltage. I also tossed in a blue LED I have a bunch of and it was at ~3.2Vdc. And was it ever bright; made the mistake of putting my head right over it