[2359glenn]

 

If the low-Z headphones are efficient, such as the TH-X00, the Glenn OTL will work well. If you wish to use inefficient low-Z headphones, such as HE-6, then a transformer-coupled amp, such as the Glenn EL3N or 300B would be preferable.

As Glenn voices his OTL with Senns, that is a match made in heaven.

OTL it is then, my Senns are my main headphones and will likely remain that way for some number of years.

Any recommendations for the upgrades? I was thinking of getting the Lundahl transformer upgrade, trying to look up impressions for it now.

If you want to use low-Z headphones the best upgrade is the 5998 mod when used with 6336 output tubes it lowers the output impedance.

 

[gibosi]

OTL it is then, my Senns are my main headphones and will likely remain that way for some number of years.

Any recommendations for the upgrades? I was thinking of getting the Lundahl transformer upgrade, trying to look up impressions for it now.

 
The Lundahl upgrade will provide you with a quieter amp. And in my opinion, if you decide to get the 5998 mod with the intention of running low-z headphones, I consider the Lundahl upgrade mandatory. The higher gain provided with the 5998 mod picks up more background noise. The only trade-off is you can no longer roll rectifiers. All the PY500A / 42EC4 types sound essentially the same.

 

[mysticstryk]

The Lundahl upgrade will provide you with a quieter amp. And in my opinion, if you decide to get the 5998 mod with the intention of running low-z headphones, I consider the Lundahl upgrade mandatory. The higher gain provided with the 5998 mod picks up more background noise. The only trade-off is you can no longer roll rectifiers. All the PY500A / 42EC4 types sound essentially the same.

I'm mainly running high Z Senns. Would the Lundahl upgrade be detrimental to pairing with the Senns? Would like the extra versatility, but not at the expense of the main headphones I will be using.

 

[gibosi]

I'm mainly running high Z Senns. Would the Lundahl upgrade be detrimental to pairing with the Senns? Would like the extra versatility, but not at the expense of the main headphones I will be using.

 
Absolutely not! Again, the Lundahl gives you a significantly quieter amp and quiet is always good.
 
I do not have the Lundahl upgrade. I have the original transformer. And with my modded HD700, I find the 5998 mod to be too noisy. Fortunately, I don't much care for the sound of the 5998, so it isn't a problem for me.
 
But based on my experience, I believe that the 5998 mod and the Lundahl transformer should go hand-in-hand. If you are going to get the 5998 mod, you should definitely get the Lundahl, no matter what headphones you expect to use.

 

[mysticstryk]

Absolutely not! Again, the Lundahl gives you a significantly quieter amp and quiet is always good.

I do not have the Lundahl upgrade. I have the original transformer. And with my modded HD700, I find the 5998 mod to be too noisy. Fortunately, I don't much care for the sound of the 5998, so it isn't a problem for me.

But based on my experience, I believe that the 5998 mod and the Lundahl transformer should go hand-in-hand. If you are going to get the 5998 mod, you should definitely get the Lundahl, no matter what headphones you expect to use.

What didn't you like about the 5998 sound? Do you know what benefits the gold stepped attenuator would give me?

 

[lukeap69]

What didn't you like about the 5998 sound? Do you know what benefits the gold stepped attenuator would give me?

Channel balance.

If your main use of this amp is to power HD800 and HD6XX, then sixtet 6BL7/6BX7 would be the best power tubes IME. My OTL amp that Glenn built has this option and also it can use a pir or 2 pairs of 6AS7. What my amp does not have is the 5998 switch and option to use 6SN7 as driver tubes.

Please note that my amp with C3g as drivers and 6BL7 as powers has very high gain. I mean at 2nd click at the Goldpoint volume pot (24 steps), my ears are almost bleeding already so I am using a passive preamp to counter this. You may want to speak with Glenn about that.

 

[whirlwind]

You guys have any recommendations on which amp with what upgrades pairs well with Senns? Mostly use my 580/650/800 these days, though I wouldn't object to being able to power some efficient orthos and low Z headphones in addition to the Senns.

My Dac will either be the Bimby or gumby.

 
Glenns OTL with the HD650/HD800  is pretty special....
 
I am using it with a ZMF Omni and it does very well with it also as well as my Grado RS1.
 
You should be very happy.
 
My wife and I are debating about getting my son one for his birthday...he is just getting into headphones and is going to be getting an HD650.  He has been listening to my amp quite a lot lately.
 
It is pretty tough deciding what options to get.......I always seem to want them all  

 

 

[mysticstryk]

Glenns OTL with the HD650/HD800  is pretty special....

I am using it with a ZMF Omni and it does very well with it also as well as my Grado RS1.

You should be very happy.

My wife and I are debating about getting my son one for his birthday...he is just getting into headphones and is going to be getting an HD650.  He has been listening to my amp quite a lot lately.

It is pretty tough deciding what options to get.......I always seem to want them all    

Yea, I CAN get them all, but I don't want to if I don't really need too. Digging through this thread to find out more.

 

[2359glenn]

There is also the EL3N amp that is a transformer coupled amp that can drive most phones
The cost is more but about the same price as the OTL with all the mods.
And I think the EL3N amp sounds better.

 

[gibosi]

What didn't you like about the 5998 sound?

 
It is not that the 5998 sounds bad. But when I was rolling 6AS7G-type output tubes, I preferred the sound of the GEC 6AS7G. And currently, I prefer the sound of four 6BL7GT or 6BX7GT. So the 5998s are not my favorite output tubes, and as a result, I haven't listened to them in a long time. Further, as I noted above, I find the 5998s with the mod-switch to be too noisy with the stock transformer.
 
Knowing what I know now, and given that I have no interest in using low-Z cans, if I was going to order an OTL today, I would skip the 5998 mod and go for the larger chassis with six 6BL7 sockets. Further, I would forego the Lundahl transformer as I enjoy rolling rectifiers far too much. lol
 
That said, if you are going to listen to 5998s the mod is a good thing. The correct bias for the 6AS7 is different than it is for the 5998. With a simple toggle switch, you can provide the 5998 with the proper bias to get the best sound. But in order to really enjoy and appreciate the 5998 sound you need a quiet amp. So again, if you decide to get the 5998 mod, I encourage you to also get the Lundahl transformer.
 
But as always, my ears and my gear. YMMV.

 

[jekjek]

Preparing myself for glenn OTL
I dig out my rectifier and I didnt know that i have National rebranded 5931

 

[gibosi]

Preparing myself for glenn OTL
I dig out my rectifier and I didnt know that i have National rebranded 5931

 
It is my understanding that the 5931 is a "ruggedized" 5U4G intended for use in severe industrial and military environments. According to the datasheet, it was designed to provide 225ma. And again, as I understand, the GOTL needs about 220ma to run the amp (with 6AS7) and a bit more to recharge the capacitors. If so, the 5931 will certainly work, but it will be operating at its maximum limit and may not last all that long. Glenn?

 

[2359glenn]

The 5931 has a max of 250ma so it should be OK to use in the OTL

 

[jekjek]

Next rectifier I have, a gz32


And the famous gz34


And some pv200/600 and pv200/1000 not in the picture

 

[gibosi]

Next rectifier I have, a gz32

And the famous gz34

And some pv200/600 and pv200/1000 not in the picture

 
The GZ32 and GZ34 are both fine in the OTL.
 
However, with GZ32 you have to be a little careful. There was and is considerable confusion regarding the 5V4G and GZ32. They are not the same. The 5V4G can put out only 175ma whereas the GZ32 can put out 250ma. Since the Glenn with 6AS7/6080 requires 250ma, a 5V4G will rather quickly burn out. And unfortunately, some 5V4G are incorrectly labeled as GZ32. But the good news is that they are usually easy to tell apart. If you see a tube labeled as a GZ32 which has 8 holes in the plates, it is actually a Brimar 5V4G.
 
For example:
 
http://www.ebay.com/itm/GZ32-EDISWAN-2pcs-/142135482545
 
The PV200/600 and PV200/1000 are rated at 200ma at 600 volts and 1000 volts, respectively. However, for the PV200/600, I have found one document which suggests that at lower voltages, it can provide more current, specifically, 260ma at 500 volts. So it may well be OK in the OTL.
 
http://www.mif.pg.gda.pl/homepages/frank/short/054/0/027.pdf
 
This may also be true for the PV200/1000, but I haven't been able to find much of anything about this rectifier.