[whirlwind]

Fantastic little review with some awesome pics.

Good lord I bet the LCD-4 bass about knock you out of your chair when using 6 Tung Sol 5998 and the ECC31/32

Good stuff! I love the tube layout.

 

[rosgr63]

Beautiful amp, congratulations!

I hope it gives you lots of listening pleasure.

Thanks for the detailed info and photos, a work of art.

Enjoy, Happy Listening!

 

[leftside]

For those who have asked, you can PM Mischa on here:
https://www.head-fi.org/members/a2029.68207/

 

[Xcalibur255]

Congrats on the new amp! It certainly looks like the ultimate tube rolling machine.

Does Mischa laser these front panels, or is it sent out to some place like Front Panel Express? Being able to laser the control labels onto the chassis really takes the professionalism and look to the next level on these custom builds.

 

[A2029]

Congrats on the new amp! It certainly looks like the ultimate tube rolling machine.

Does Mischa laser these front panels, or is it sent out to some place like Front Panel Express? Being able to laser the control labels onto the chassis really takes the professionalism and look to the next level on these custom builds.

I have access to an Epilog Mini Laser Cutter to do the engraving

 

[A2029]

- Using 6SN7, 12SN7 or 6J5 as driver approx. 4.5 watts into 100 ohm, and 3.05 watts into 200 ohm. (Mischa to confirm)
- With C3G as driver it gives slightly more power output: up to 5-6 watts into 200 ohm. (Mischa to confirm)

Some more specs on the amp:

Power output when running with 6 power tubes:
6AS7 & C3G Driver:
4.5W into 100 Ohm
5W into 200 Ohm
2.7W into 300 Ohm

6AS7 & 6SN7/12SN7/6J5 Driver:
4.5W into 100 Ohm
3W into 200 Ohm
2.3W into 300 Ohm

5998 & C3G Driver:
4.25W into 100 Ohm
2.7W into 200 Ohm
1.6W into 300 Ohm

5998 & 6SN7/12SN7/6J5 Driver:
4.25W into 100 Ohm
2.7W into 200 Ohm
1.6W into 300 Ohm

Damping factor:
6AS7:
>10 into 300 Ohm
>8.5 into 200 Ohm
>4 into 100 Ohm
5998:
>25 into 300 Ohm
>16.5 into 200 Ohm
>8 into 100 Ohm

-3dB Point: 2.5 Hz

Power consumption:
500W at max loading

Here are some other features of the amp:
-Zero feedback, pure class A
-Acoustic Dimensions 41-step attenuator
-Input impedance: 100Kohm
-Balanced and unbalanced headphones can be plugged in simultaneously. Can run up to three headphones at a time (Imagine running 3 HD650/HD800 from the amp at the same time)!
-510uF of oil filled polypropylene capacitance in the high voltage supply
-Over 356000uF of capacitance in 6.3V heater supply!
-ZERO electrolytic capacitors in the signal path (and the signal path includes the high voltage power supply)

 

[A2029]

.

 

[whirlwind]

Some more specs on the amp:

Power output when running with 6 power tubes:
6AS7 & C3G Driver:
4.5W into 100 Ohm
5W into 200 Ohm
2.7W into 300 Ohm

6AS7 & 6SN7/12SN7/6J5 Driver:
4.5W into 100 Ohm
3W into 200 Ohm
2.3W into 300 Ohm

5998 & C3G Driver:
4.25W into 100 Ohm
2.7W into 200 Ohm
1.6W into 300 Ohm

5998 & 6SN7/12SN7/6J5 Driver:
4.25W into 100 Ohm
2.7W into 200 Ohm
1.6W into 300 Ohm

Damping factor:
6AS7:
>10 into 300 Ohm
>8.5 into 200 Ohm
>4 into 100 Ohm
5998:
>25 into 300 Ohm
>16.5 into 200 Ohm
>8 into 100 Ohm

-3dB Point: 2.5 Hz

Power consumption:
500W at max loading

Here are some other features of the amp:
-Zero feedback, pure class A
-Acoustic Dimensions 41-step attenuator
-Input impedance: 100Kohm
-Balanced and unbalanced headphones can be plugged in simultaneously. Can run up to three headphones at a time (Imagine running 3 HD650/HD800 from the amp at the same time)!
-510uF of oil filled polypropylene capacitance in the high voltage supply
-Over 356000uF of capacitance in 6.3V heater supply!
-ZERO electrolytic capacitors in the signal path (and the signal path includes the high voltage power supply)

Very cool....thanks for posting.

 

[leftside]

@A2029 does the amp have similar power specs with 2 or 4 power tubes? Is it just the output impedance that changes with more power tubes?

When I first contacted you, I seem to remember you saying 6 power tubes was overkill, but I said I'd still like an amp with 6 power tubes If I understand correctly, I think an amp with 2 or 4 power tubes will be less complex and therefore cheaper, but should sound very similar to the one with 6 power tubes?

 

[A2029]

@A2029 does the amp have similar power specs with 2 or 4 power tubes? Is it just the output impedance that changes with more power tubes?

Output impedance goes down the more power tubes per side:
1 tube per side -> ~70 ohm output impedance
2 tubes per side -> ~35 ohm output impedance
3 tubes per side -> ~23 ohm output impedance

Power generally goes down the less power tubes running, here is an example with the 6AS7 and C3G:

6 power tube 6AS7 & C3G Driver:
4.5W into 100 Ohm
5W into 200 Ohm
2.7W into 300 Ohm

4 power tube 6AS7 & C3G Driver:
2.1W into 100 Ohm
4.7W into 200 Ohm
2.7W into 300 Ohm

2 power tube 6AS7 & C3G Driver:
0.5W into 100 Ohm
1.05W into 200 Ohm
2.55W into 300 Ohm

When I first contacted you, I seem to remember you saying 6 power tubes was overkill, but I said I'd still like an amp with 6 power tubes :) If I understand correctly, I think an amp with 2 or 4 power tubes will be less complex and therefore cheaper, but should sound very similar to the one with 6 power tubes?

An amp with 6 power tubes definitely has more than enough power for the most challenging high impedance loads!

An amp with 2 or 4 power tubes would be less complex, smaller, cheaper, and overall have similar distortion profiles (i.e. quite similar clarity, bass, tone, and other qualities). There is some slight effect of output impedance on the tone/frequency response of certain high impedance headphones such as the Sennheiser HD650/HD800. Here is a good reference to understand this effect more: https://www.innerfidelity.com/content/musings-headphone-amplifier-output-impedance


The optimal number of tubes for a 200 Ohm headphone such as the LCD-4's is four or six. For 300 Ohm headphones such as Sennheiser HD650/HD800, 4 power tubes (2 power tube per channel) is definitely good and gives a damping factor of >8 which is ideal. 2 power tubes (1 per channel) gives a damping factor of over 4, which is still good enough for most 300 ohm headphones (Senn HD650/800 and ZMF Verite).

 

[mordy]

Hi A2029,
Is there a change in the aggregate multiplifaction factor when using 2, 4 or 6 power tubes?
If you use pairs of tubes with different mu, is there a way of knowing what the total mu is?

 

[A2029]

Hi A2029,
Is there a change in the aggregate multiplifaction factor when using 2, 4 or 6 power tubes?
If you use pairs of tubes with different mu, is there a way of knowing what the total mu is?

Hi mordy,
Not sure what you mean by aggregate multiplication factor. The output swing from the cathode of power tubes on a cathode coupled OTL amp will always have an amplification factor of less than 1. If using only 6AS7 tubes, more tubes brings the amplification factor slightly closer to 1. E.g. for an input signal of 20V at the power tube grids, One 6AS7 will have an amplification factor of 0.499 into 300 ohms whereas two in parallel will have an amplification factor of 0.555 into 300 ohms.

If you were to try to use a 5998 and 6AS7 tube at the same time on @leftside's amp, then the 5998 would hog most of the current and the overall amplification factor for the power tubes would be higher (i.e. closer to 1 on the power tubes) with the 5998+6AS7 than with two 6AS7.

For two 6AS7 per channel without balancing resistors (4 power tubes total) the 6AS7 with the highest transconductance will hog slightly more of the current and it's amplification factor will dominate. Balancing resistors help to balance the current between tubes when tubes aren't precisely matched (i.e. slightly different mu, transconductance, rp).

 

[leftside]

Picture of the amp section with the Clarity caps showing, I almost decided to keep the caps exposed, but once the tubes have been inserted I think it looks better with the enclosures on:

 

[leftside]

The amp is sounding great. Currently going through the 6N7 tubes at the moment as I've never been able to use those before without adapters. Things that really stand out are bass, depth and separation with a hint of warmth.

Nice and quiet even with vinyl last night.

 

[leftside]

It's a metal base kinda evening. Super smooth sounding. Textures are amazing. Was running a pair of Fivre 6N7G from 1940 in there the last couple of nights, and they have a bit more punch/impact with slightly more bass, but I think I prefer these 6J5/L63 and B36/12SN7 drivers. The amp already packs a punch in the bass department anyway.

Vocals are gorgeous - especially female vocals.

Will compare to 6J5 coke bottle and B65 at the weekend.