"If it measures good and sounds bad, it is bad.
If it sounds good and measures bad, you've measured the wrong thing."


Post Reply
Forum Home > Amplification > Glenn's OTL headphone amplifier

Amine Slimani
Site Owner
Posts: 162

After some hesitation on what amplifier to get for my Beyer T1, Stavros (rosgr63) pointed me towards Glenn for getting an OTL headphone amplifier. 

From It is an OTL amplifier using a 6SN7 tube as driver and 3DG4 as a rectifier. As for the output tubes, it can use different kinds. Here is what Glenn wrote : "It uses six 6BL7s for outputs or two or four 6AS7s or two 6336."

Here is a picture of the amplifier as of 20 november (still not finished) :

Given the good results that the Beyer T1s give with even a "modest" OTL amplifier, I am eagerly awaiting for Glenn to finish building the amplifier - hopefully by december.

While waiting, I started looking for a few 6SN7 tubes.

As a starting point, I purchased :

  • One Sylvania 6SNGT VT231
  • One Sylvania 6SN7W


But there seems to be a long road to go as there are so many great / appealing tubes to choose from!


Everything in Audio is sublte and not worth it - Patrick82

November 21, 2013 at 8:08 AM Flag Quote & Reply

Amine Slimani
Site Owner
Posts: 162

I am thinking of getting some tube dampers from Herbie's (the Ultrasonic RX). I already tried some of their dampers on the "modest" Little Dot MKIII and they did improve noticeably and positively the sound. I am hoping, they can provide the same improvement on the amplifier being built by Glenn.


Provided the dampers do not degrade the sound quality, even if they offer a small improvement, that improvement shoud in theory span over all the tubes that I will roll into the amp.


There are different school of thoughts on tube dampers - so I will be interesting in hearing other members thougts on the subject.


Everything in Audio is sublte and not worth it - Patrick82

November 22, 2013 at 9:12 AM Flag Quote & Reply

Posts: 141


This is one of the very best OTL's around.

Tube rollers dream, depemding on your tube choice it can drive both low and high impedance headphones.

I have a selection of tube dampers/coolers but hardly use them.

Some people use them extensively on some noisy tubes, Ken-Rad 6SN7 even though are a wonderful tube tend to be noiosy.

Tubes are microphonic to some extend, that doesn't bother me as it's part of a tubes character, part of the tube magic!


There are few pleasures as simple, and wonderful as music - Craig Uthus

November 22, 2013 at 12:58 PM Flag Quote & Reply

Amine Slimani
Site Owner
Posts: 162

Below are some first impressions of the amplifier :


Power tubes :

- With the two RCA 6AS7s, the sound is reminiscent of a bigger more complete LD MKIII - it is very appealing, and simple to like

- With the six RCA 6BL7s, the sound was very different : much more refined, more extended in the frequency extremes, more delicate ... but it took me some time to "get it"


Driver tubes (6SN7) :

- The sound with the stock 6SN7 RCA Glenn provided with the amp was neutral and dead quiet (no noticeable noise floor with my Beyer T1s)

- The sound with Sylvania 6SN7W was very nice : more refined, richer and warmer than the "stock" RCA. However, the noise floor is higher than the stock one, though once the music is playing, it goes slightly unnoticed

- The sound with the VT231 6SN7 Sylvania was fantastic : great timber, great soundstage and excellent resolution but there is a annoying buzzing on the right channel --> I hope it can disappear with burn-in


Rectifier :

- I personally didn't like much the sound of the 3DG4 tube (Westinghouse and Zenith). The sound was very "strong"/powerful but at the expense of the soundstage layering and spaciounsness

- The 5AW4 RCA worked better, especially in the soundstage department

I wrote those impressions after listening for only a few hours. I will post some more detailed impressions/review later on.

But the more I have listened to this amp, the more I came to appreciate what Glenn has done. It is a dynamic, fast, accurate and "rich sounding" amplifier. I was fearing that a tube amp might be too warm or not enough detailed, but the resolution of Glenn's amplifier is as good or better than anything I have had the pleasure to listen to.


Everything in Audio is sublte and not worth it - Patrick82

March 4, 2014 at 11:50 AM Flag Quote & Reply

You must login to post.