Prototypers wanted

[luvdunhill]

I have my doubts that this is appropriate for orthos, though there is no reason to not turn the dial up to 70 or 100%.

My guess is that RMAA is requiring you to run this at a pretty high level, probably higher than you might listen with most common headphones, which results in the 1% THD.

I essentially got the same thing when attempting to set the volume to 100% - too much distortion for RMAA to function

"Flat out" assumes a lot - that gain is within the controllable testing parameters, for instance. With tubes, you could have gains well into the 20's, 30's, and higher that may have no realistic operating points at the maximum volume position.

Fair enough but that is clearly not the case here.

all good points and I think I've learned what I need to here

[kevin gilmore]

I use a old sound technology unit. You adjust the signal generator to make the output

come out to 0 db. So the position of the volume control is meaningless. You could set

the volume knob at 50% and then have to turn up the generator to get back to 0 db.

Correctly done, everything has to be relative to the main peak. This seems to be where

many people generate unrealisticly low thd numbers from their RMAA tests.

Without a carefully built attenuator, you cannot possibly measure an electrostatic amp.

[Pars]

I was looking the PCB over to figure out where to drill some holes to install SIP pins for putting the parallel resistors in when it dawned on me... pull the 75 ohm resistors, put SIP pins in their place, and solder the 75 ohms on the bottom between the pins

So that's what I did...

[dsavitsk]

I was looking the PCB over to figure out where to drill some holes to install SIP pins for putting the parallel resistors in when it dawned on me... pull the 75 ohm resistors, put SIP pins in their place, and solder the 75 ohms on the bottom between the pins

So that's what I did...

Just be sure they don't short to the case.

And I'll be happy to look at your pre, but probably not till fall or winter.

[TomB]

Just an FYI - but after more listening, I've decided I like the original CCS current better and will change it back.

Chris - your tubes should be on the way.

Marc - can you PM with your address and I'll send you some more tubes, too?

[Pars]

Just be sure they don't short to the case.

And I'll be happy to look at your pre, but probably not till fall or winter.

Yes, plenty of clearance on the bottom. I found out inadvertantly what shorting the CCS resistor to ground does... one BJT and and LED and a resistor later

Winter or whenever would be great Doug.

Just an FYI - but after more listening, I've decided I like the original CCS current better and will change it back.

Chris - your tubes should be on the way.

Marc - can you PM with your address and I'll send you some more tubes, too?

Thanks Tom. I'll have to do some listening with this after I get it cased up for safety. I played around with RMAA a bit last night. Nothing I could do would get the distortion level down so RMAA would not complain about it. I also took a look with Visual Analyzer, and yes, the THD drops quite a bit as you reduce the signal level (not surprising). I'm still fumbling around with VA however.

[luvdunhill]

I've made the change and found that it sounds significantly better for the headphones that are at the 80%+ mark on the volume dial.

[TomB]

I've made the change and found that it sounds significantly better for the headphones that are at the 80%+ mark on the volume dial.

I think I would agree with that, but most of my listening is with Grados further down on the dial.

Maybe we can talk Doug into making a switched CCS setting for the production version - or perhaps ganged with the impedance switch?

[luvdunhill]

I think it's time to play with the Vf of the cathode LEDs, just need to drag out the LED box and get a good jig to measure Vf at the proper current and voltage. Any I/V recommendations Doug?

[Pars]

Got the tubes today, thanks Tom. I only thought you were sending a pair

I put the two pairs marked 6J6 in. The first pair was marked 105/100 and 100/105. These measured PL of 124, PR of 114. The second pair (don't recall the tester values) seemed better at PL of 136.7 and PR of 134.2 IIRC. I measured the Vf across the 4 LEDs and all were 1.63V except for one which was 1.62V. The drop across the CCS resistors was 0.93V, so this makes sense (1.63 - 0.7 = 0.93). I didn't check the Vbe across each of the BJTs. CCS is right around 56.x ohms, so ~16.6mA right now.

[TomB]

Got the tubes today, thanks Tom. I only thought you were sending a pair

I put the two pairs marked 6J6 in. The first pair was marked 105/100 and 100/105. These measured PL of 124, PR of 114. The second pair (don't recall the tester values) seemed better at PL of 136.7 and PR of 134.2 IIRC. I measured the Vf across the 4 LEDs and all were 1.63V except for one which was 1.62V. The drop across the CCS resistors was 0.93V, so this makes sense (1.63 - 0.7 = 0.93). I didn't check the Vbe across each of the BJTs. CCS is right around 56.x ohms, so ~16.6mA right now.

Well yeah, see - anybody that measures them with that much precision, I figured I'd better increase the odds to get you a matched pair.

The non-6J6 tubes are pot-luck, though, but maybe you'll have a good time trying out the differences, anyway. I really like the 5964's - at least with the original CCS current. They're not as punchy as the 6J6's, but the highs are very nice. To be honest, I've not had much time on the 5844's, so I don't know how they do.

[n_maher]

More progress, tried to use the mill to its greatest advantage to cut a slot for the switch instead of a hole. Came out pretty good, oddly enough the ill fitting piece on the front panel was the headphone jack which sat neither square nor flat but was pretty easily adapter to even after the main hole was drilled for it.

There's the slightest lip on the slot for the switch which should come off when I apply the brushed finish to the aluminum but as is it looks fine from distances greater than 1'.

In case anyone is curious the slot is 7/32" x 1/4".

[luvdunhill]

too bad there aren't any connex 7 pin teflon sockets

like these?

[ATTACH=CONFIG]3496[/ATTACH]

[Pars]

Did some listening tonight, first with the CCS's at 56 ohm, then at 75. Same material, AKG K601s as cans as these are the closest to the 501s my brother uses. Used a Bernstein/CSO Shostakovitch recording, which my brother thinks is one of the most realistic CSO recordings he has heard. I preferred the 75 ohm setting by a pretty significant margin. The 56 ohm setting resulted in much more steeliness to the strings, etc. The 75 ohm setting tamed this for the most part (maybe all of it) and fleshed out the mids much more convincingly. I also thought the bass was better.

Not sure as to which impedance switch setting I liked better though. The 601s are 120 ohm (IIRC). Would conventional wisdom or experience tend towards one or the other setting? Time to let my brother listen to it and I'll see what he thinks.

[luvdunhill]

One man's steeliness is another man's detail

[luvdunhill]

In case anyone is curious the slot is 7/32" x 1/4".

Nate, any idea where the center of the slot is? That's the last dimension I need before starting on my front panels.

[n_maher]

I just took the dimensions shown on one of Tom's pdfs.

[kevin gilmore]

I was talking about the 7 pin socket that fit the current circuit board holes. The connex sockets can't do that.

tom has sent me some more tubes, one of my tubes definitely has a problem, as tested on my tube tester.

I did not test them before i used them however... So when they show up, i'll listen again.

[CYoung234]

Did some listening tonight, first with the CCS's at 56 ohm, then at 75. Same material, AKG K601s as cans as these are the closest to the 501s my brother uses. Used a Bernstein/CSO Shostakovitch recording, which my brother thinks is one of the most realistic CSO recordings he has heard. I preferred the 75 ohm setting by a pretty significant margin. The 56 ohm setting resulted in much more steeliness to the strings, etc. The 75 ohm setting tamed this for the most part (maybe all of it) and fleshed out the mids much more convincingly. I also thought the bass was better.

Not sure as to which impedance switch setting I liked better though. The 601s are 120 ohm (IIRC). Would conventional wisdom or experience tend towards one or the other setting? Time to let my brother listen to it and I'll see what he thinks.

Okay, time to venture out of "lurker mode" for a first post. I am the "brother" that Pars refers to, and he delivered the "Torpedo" yesterday. I spent about 3 hours listening to it yesterday afternoon, although not under critical listening circumstances, as I was (supposed to be) working at the same time. I used my laptop (Thinkpad T61) as the source with ITunes, and listened to a number of recordings I use to evaluate sound. I was using whatever tubes Chris had installed, and was using the 75 ohm setting on the CCS's. I found that with my K501's (3rd generation - the supposed "bass-heavy" ones), that the 300 ohm switch setting worked best. I did find that with the Thinkpad's volume all the way up that I had to turn the volume on the Torpedo up to about the 1:30 position. Incidently, this Thinkpad does a decent job of driving these headphones, but the addition of a decent amplifier solidifies the soundstage and improves the low end stability.

In listening to the amp, I noticed a bit of distortion at first, but I think I needed to mess with the settings a little more. My general first impressions were good. The system was quite detailed, instrument separation was good, and I only noticed a little steeliness or harshness in the 3rd movement of Shostakovich 7 that I use to gauge that. I will try to get some time to listen under more critical circumstances to post further. I could hear the cooling fans on my desktop computer through my headphones, so things were not ideal by any means. I will hook up my CD player and external DAC (borrowed from Chris) to get a better front end for doing further listening. In the 3 hours, the Torpedo did not get too warm - the hottest spot seems to be the heat sinks near the tubes. The transformer did not get too warm at all.

[luvdunhill]

I just took the dimensions shown on one of Tom's pdfs.

ah, I assumed that the center of the switches would be different on the two models... guess not! thanks!

[Pars]

Okay, time to venture out of "lurker mode" for a first post. I am the "brother" that Pars refers to, and he delivered the "Torpedo" yesterday. I spent about 3 hours listening to it yesterday afternoon, although not under critical listening circumstances, as I was (supposed to be) working at the same time. I used my laptop (Thinkpad T61) as the source with ITunes, and listened to a number of recordings I use to evaluate sound. I was using whatever tubes Chris had installed, and was using the 75 ohm setting on the CCS's. I found that with my K501's (3rd generation - the supposed "bass-heavy" ones), that the 300 ohm switch setting worked best. I did find that with the Thinkpad's volume all the way up that I had to turn the volume on the Torpedo up to about the 1:30 position. Incidently, this Thinkpad does a decent job of driving these headphones, but the addition of a decent amplifier solidifies the soundstage and improves the low end stability.

In listening to the amp, I noticed a bit of distortion at first, but I think I needed to mess with the settings a little more. My general first impressions were good. The system was quite detailed, instrument separation was good, and I only noticed a little steeliness or harshness in the 3rd movement of Shostakovich 7 that I use to gauge that. I will try to get some time to listen under more critical circumstances to post further. I could hear the cooling fans on my desktop computer through my headphones, so things were not ideal by any means. I will hook up my CD player and external DAC (borrowed from Chris) to get a better front end for doing further listening. In the 3 hours, the Torpedo did not get too warm - the hottest spot seems to be the heat sinks near the tubes. The transformer did not get too warm at all.

Good first post

[digger945]

Okay, time to venture out of "lurker mode" for a first post. I am the "brother" that Pars refers to,

Welcome, Chris' brother.

Good first post

Indeed.

[CYoung234]

Time for another listening update, after having this amp to try out for about one week. I am currently using a modified Adcom GCD-575 as the transport with an outboard DAC that Chris made. I spent a fair amount of time A/Bing this setup with my RE0’s driven by my iPod Nano, as well as both the K501’s and IEMs driven from my laptop and desktop. Music included:

Shostakovich Symphony Nos. 1 & 7 – CSO / Bernstein – DGG 1987. I used all of the 1st Symphony because it is a gorgeous recording. I also used the 2nd movement of the 7th Symphony. I like this particular recording because I know probably 25% of the musicians on this recording personally, having played with many of them. I have a decent idea of how they sound live, having heard the CSO perform on numerous occasions. Great brass playing. I even have a couple of funny stories about this recording, but I digress…

Shostakovich Symphony No. 15 – CSO / Solti – Decca 1998. Another very well recorded and performed work that I am very familiar with. Adolph Herseth is amazing on this recording, as he is very close to retirement, but still sounds great here.

Tony Banks – Still and Strictly Inc. – I have listened to Genesis for years.

Sheryl Crow – Wildflower. I do not really like any of her other albums, but I like this one. Well recorded.

Okay, so now on to how things sound. I used the K501s with K601 pads for this test. Soundstage (headstage???) was excellent and stable. Instruments had body and position, and did not shift around. Tonally, I am very happy with how these phones match up with the amp and source. The high end was good and quite extended, no real trace of sibilance. Low end was actually quite impressive for these phones, given their reputation in some circles as bass light. I have never really felt they deserved that reputation, and this amp solidifies and extends very well in the lower octaves. Probably not for head bangers, but given my musical tastes they fill the bill quite nicely. Oh, and the thing the K501’s are known for, their gorgeous midrange, really shines. Great solid center channel effect. For example, Wildflower really really is centered on these phones with a wide but not unrealistic and deep soundstage. Another key is that I can listen to this setup for hours without getting fatigued. So, generally, very natural and realistic.

Okay – now for what I don’t like. The main thing that is missing for me is the sense of scale and dynamics in classical music. This is for me what makes the biggest difference between live music and what I am hearing. The amp is very quiet – maybe it is just the source, but soft is not soft enough and loud is not loud enough. I never buy that I am there. Real life world class symphony orchestras can play so soft you can hardly hear it, yet it still has body and is alive. Recorded music just doesn’t do that, and neither does this setup. And at the other end of the spectrum, in real life, loud comes from nowhere, from total silence to WHAM! Again, this combination does not make me believe that I am hearing real life. I guess in all fairness, I should note that I have NEVER heard any type of sound system that came very close to real life, at least for large symphony orchestral music. For pop / rock / jazz / even chamber, it gets somewhat closer. The other thing that may need some work is the gain. I have to turn the volume up to about the 1:30 position with these phones, so I may need to have that changed somehow.

Finally, I suppose I should introduce myself, as this is just my second post.

My name is Craig Young, and I am Pars brother – actually his identical twin brother. I currently work as an electrical engineer doing electrical systems design and project management for large commercial and industrial construction. However, my major was music, and I played the trumpet professionally part time for over 20 years in regional symphony orchestras in Iowa and Illinois. During that time, I studied briefly with trumpet players in the Chicago Symphony, New York Philharmonic and North Carolina Symphony orchestras. So, I have a love of classical music and of course, large-scale symphonic music. In connection with my comment above about recorded never matching live, I suppose my perspective is skewed, since a lot of my live music experience comes from sitting within the orchestra. But, enough about me.

[mypasswordis]

Welcome, Craig. And I think the skewedness comes from being a trumpet player, of course you're going to say it doesn't get loud enough. Just kidding, dsavitsk has a thing for low gain and the K501 is pretty inefficient. So much Shosty, but no love for the 5th?

I have a lot of experience with the K501 with K501 and with K601 pads, as that is probably the headphone I have listened to the most, but I sold it awhile back. What I found weird about the sound is the soundstage is big but oddly shaped and the midrange can seem shouty at times because it is brought to the forefront while the bass and treble seem distant. That said, I wouldn't mind owning another pair at some point.

[Pars]

Craig, I'll give you a call. How do your impressions stack up if you use the GCD-575 by itself? This is modified with a cetoole discrete I/V stage. I would think it at least has a decent chance of bettering the Pedja Rogic NOS TDA-1541a DAC that I built (and that he is listening to). Not sure about dynamics. The amp is probably going to require a decent amount of pot rotation with anything save Grados. Not sure if there is much at all that can be done about that, but I don't see anything wrong with turning it up that much.

Also, did you try the higher bias on the CCS? Interested in what your take is on that as well. I could also lend you my Gilmore Dynalo to see what your thoughts are in comparison, but I know you like your toobies.

EDIT: Also, how do the dynamics compare to your Apogees? If they are similar, then that is probably about all that you can ask for with your source, etc.

Edited September 3, 2010 by Pars