[FraGGleR]

Quote:

Originally Posted by boomy3555 /img/forum/go_quote.gif I often end up using a resistor so I can up the source input. This helps with the low volume hiss. I use a Ultimate Ears 50 ohm inline resistor but when I made up my breifcase toolbox I put 160 ohms of resistance to one of my 4 pin mini-XLR jacks. I have only used cheap Ratshack resitors, but I hear that "Mills" resistors are excelent for making DIY attenuators.

Thanks boomy! I will I try a couple in the 50-100 range.

 

[sohels]

I just received a JAN Sylvania 6DJ8 which I purchased on Skylab's recommendation and I must say the difference over the stock tube is not subtle. The most obvious difference is that the highs have opened up and there is better clarity and definition across the spectrum. Also, the stock tube had a slight channel imbalance which has now been corrected. Very nice upgrade for $15.

 

[boomy3555]

Quote:

Originally Posted by ttan98 /img/forum/go_quote.gif I suppose many headphone users here buy this small and compact headphone amplifier is because it is well priced(cheap for what it can do) and also users can tube roll the 6N1 tube with 6DJ8 or 6922. I thought what I can do is to replace the input tube with a solid state ie FET(costs less than 50 cents each) so that [size=medium]1. there no need to tube roll[/size] and 2. listen whether there are any differences between tube and FET sound. I bought 2 units and pull one apart and the the other remains unchanged. I modified one unit in incorporate a low noise input FET and output MOSFET remains the same. I was able to compare the 2 units. What are the differences you want to ask? There are more similarities than differences. Similarities ---------- a. The sound stage remains unchanged, both can generate a large soundstage. b. Both are able to drive low load headphones and they are Class A amp. c. Only subtle differences in both units, see below d. Distortion(THD) of both units are at similar level lying between 0.2 to 0.5% @ 1V rms output. BTW most Cmoy amp cannot drive low load headphones and cannot generate large sound stage Differences ----------- a. FET sounds a little cleaner and more distinct in the sound reproduction whereas the tube sounds a little "tubey" and smoother. b. FET sounds a little more dynamic than the tube. According to my ears there are very little differences between the 2 units, I believe the reasons being both have similar distortion levels and both units belong to a same configuration/circuit topology. If those who can perform changes to this amp, I like to suggest besides changing components is put a large heatsink to the MOSFETs and current regulator. The current heatsinks are "too small" this my next project. Cheers enjoy this amp.

And what would be the fun in that?

 

[Megaclocker]

I just received mine (bravo model). It definately work very well. My grado seems smoother. I will listen to the amp a bit more before making a final judgement.

The only little problem I've found with the amp is that when it become hot (2 black heatsink) it produce a slight hiss sound. I've put the amp close to one of my computer exaust fan and now everything is fine.

The amp is very powerfull, will probably blow my grado if I put it at 100%

 

[ttan98]

Boomy3555,

Fun is fairly subjective, to you maybe tube rolling is fun but I have done this long time ago and not really interested now. Now I am more interested in whether there is a big difference in the sound reproduction between FET and tube(*) as input amplifier. I think I have achieve this. This is fun to me. To each its own. Have your own fun.

Cheers.

* The tube in the position implemented by Indeed is not optimal because the anode voltage is too low, it will work but the sound is less than optimal, it could explain why it is less dynamic than FET. Usually the anode voltage for 6922 is about 80-90Vdc not 16Vdc.

 

[Crookshank]

Whats the best imput, RCA or mini? Or its same?

 

[ashtray9]

Quote:

Originally Posted by ttan98 /img/forum/go_quote.gif ...the anode voltage is too low, it will work but the sound is less than optimal, it could explain why it is less dynamic than FET. Usually the anode voltage for 6922 is about 80-90Vdc not 16Vdc.

I was under the assumption some mini step-up transformer was being used on the board. Can tubes really operate at 16vdc?

 

[ttan98]

Quote:

Originally Posted by ashtray9 /img/forum/go_quote.gif I was under the assumption some mini step-up transformer was being used on the board. Can tubes really operate at 16vdc?

It uses a switching power supply which gives 24V output to the amp., after a voltage drop about 8V across a transistor, to reach the tube's anode of about 16V. On some units it maybe more less 1~2V. You can adjust it by turning the pot near the tube, if you are not sure better not touch it.

I have the circuit diagram if you are interested.

 

[ashtray9]

Quote:

Originally Posted by ttan98 /img/forum/go_quote.gif It uses a switching power supply which gives 24V output to the amp., after a voltage drop about 8V across a transistor, to reach the tube's anode of about 16V. On some units it maybe more less 1~2V. You can adjust it by turning the pot near the tube, if you are not sure better not touch it.

Thanks for the good info. So as to the point of the two pots on the board... I am guessing wildly unbalanced triodes would need to have the voltage adjusted. If running a good tube could I max those pots? What can go wrong?

I apologize for all the questions, tubes are still a new frontier on my end.

 

[ttan98]

By tweaking the pot will not damage the amp, it will make the heatsink esp the aluminium one even hotter if you make the anode voltage higher eg. 20V.

Do you have a multimeter if you do, I will guide you to measure the anode voltage.

 

[mrB]

Quote:

Originally Posted by sohels /img/forum/go_quote.gif I just received a JAN Sylvania 6DJ8 which I purchased on Skylab's recommendation and I must say the difference over the stock tube is not subtle. The most obvious difference is that the highs have opened up and there is better clarity and definition across the spectrum. Also, the stock tube had a slight channel imbalance which has now been corrected. Very nice upgrade for $15.

I have been reading this thread with a great deal of interest and have noted down a number of tubes that could be swapped for the stock 6N11. Among them are: Jan Sylvania 6DJ8 and 7308, Jan GE 5670W, Mullard CV 2492, Telefunken ECC88/E88CC, ???? 6922. It seems there is considerable advantage in trying a replacement tube. Can anyone describe the nature of the improvement for each of these tubes individually and summarize by pointing out the best value for money? Does each manufacturer have his own code number for the tube, or can many manufacturers make a 6922 for instance? I intend to use the amp with my ER-4Ps, but will consider getting a P to S adapter if warranted (another topic). Sennheiser 650s are on my Xmas shopping list. Will they be a good match with this amp? Maybe with a particular tube in it?

A lot of questions .... I'm a newbie who's just bought an Indeed on eBay. They have a "Buy It Now" listing going now for $49.99 plus shipping, for those who (like me) don't have the patience to wait out an auction. Ebay item #250530070834

I'm in Germany at the moment. I guess I'll be able to find a recommended tube here.

Happy to take guidance from those of you with experience with this amp and/or the phones I mentioned. Cheers!

 

[boomy3555]

I have run the Russian 6922/E88cc's and found them harsh and uninteresting. I got some Jan Slyvania 7308's which are now what I keep in the four indeeds I have. I was DIYing with these amps and pulling them apart and soldering them here and there so I never invested in the big names like Mullard of Telle. The best way I found is to simply type in all of the numbers I find here into the google or eBay search. Your numbers will hit regardless of the brand name and will also tag the listing with other supposedly compatable tubes.
I had HD650's when I started using these amps and the Indeeds are not really strong enough to drive them well. IMHO of course. The 650's are quite power hungry and although they love tubes, they really need some powerful amp to get the best from them.

 

[sohels]

Quote:

Originally Posted by mrB /img/forum/go_quote.gif Sennheiser 650s are on my Xmas shopping list. Will they be a good match with this amp? Maybe with a particular tube in it? A lot of questions .... I'm a newbie who's just bought an Indeed on eBay. They have a "Buy It Now" listing going now for $49.99 plus shipping, for those who (like me) don't have the patience to wait out an auction. Ebay item #250530070834

Darn! I paid $79.99 plus shipping for a Buy It Now. Looks like you got a better deal.

I am using my Indeed amp with HD650 but I suspect mine are the older version. The only tubes I've tried are the JAN Sylvania 6DJ8 and the stock Chinese tube - the former is definitely a better match for the HD650 and well worth the extra $15 I paid for it.

I haven't tried the HD650 with any other amps, but I'm quite happy with the sound of this combination. I was looking to upgrade my amp but the tube change has made a nice difference and I will probably postpone a new purchase.

 

[Megaclocker]

I will probably order some tubes next week. Sylvania and maybe an Amperex.

Stock tube seems very adequate, at least for my headphones. But I would like to try other and have at least a few backup tubes.

After a few hours of listening, the only subtle difference I can spot is an slightly improved soundstage and a bit smoother sound.

 

[mrB]

Maaaaaan! What am I getting in to here? Following Boomy's advice I started looking around and came upon this site: 6DJ8 Tubes From Brent Jessee Recording
There's a lot to digest there for a newbie, but it gives a lot of useful background for informed decision-making. The 7308s seem to be worth aiming for.

What did you pay for yours Boomy?