Universal PCB for Purifi 1ET400A amps

[Carl_Huff]

This weekend build a new tube buffer for driving the 1et400a amp.
It uses the 6N6P tube but also can adapt the ECC99 ...

Koifarm,

It is great to see that you are working on this again! Please keep us posted as to your progress.

 

[_henry_]

i would love to try the tube buffer. looking forward for your updates.

 

[Koifarm]

Today, did some testing with the 6n6p mu-follower in to a 2k2 load(as et400a). It had a frequency response from 10hz to 100khz within +/- 0,5db. Gain 16x.
Because of the high gain i will apply some feedback to get 3x gain for balanced and 10x gain for unbalanced operation.
Further do not use the lundahl transformeer because of high cost. I use neutrik XLR/6.3 jack input chassis part.
Schematic and PCB design will follow soon.

Henry and Carl do you like PCB with 36pin,10pin and 6pin connector to connect to 1et400a or without?

 

[Carl_Huff]

"... Henry and Carl do you like PCB with 36pin,10pin and 6pin connector to connect to 1et400a or without?"

Koifarm,

You've made some impressive progress! How was noise on this circuit?

Did you listen to your invention? I am curious as to your impressions

As to connectors ...
I am flexible. But since you asked, how about a row of PCB mounted connectors like this one?

But that's just my two cents worth. I invite others to make comment. Thank you for the update.

 

[_henry_]

Today, did some testing with the 6n6p mu-follower in to a 2k2 load(as et400a). It had a frequency response from 10hz to 100khz within +/- 0,5db. Gain 16x.
Because of the high gain i will apply some feedback to get 3x gain for balanced and 10x gain for unbalanced operation.
Further do not use the lundahl transformeer because of high cost. I use neutrik XLR/6.3 jack input chassis part.
Schematic and PCB design will follow soon.

Henry and Carl do you like PCB with 36pin,10pin and 6pin connector to connect to 1et400a or without?

i actually would like to use the buffer with NC500. yes please for the connector like any other buffer on the market.

regards
Henry

 

[Carl_Huff]

"i actually would like to use the buffer with NC500. yes please for the connector like any other buffer on the market."

Henry your request sounds very reasonable. I 2nd the vote and agree with you.

 

[Carl_Huff]

Koifarm, anything new to report?

 

[Koifarm]

Because of the nice weather a have a lot of work outside my home. I have got me a behringer umc404hd to make THD measurements the tube circuit measures 0.0086% THD. I am still working at the power supply and PCB.

 

[Koifarm]

Today completed the new design. Shall order PCB this week.

 

[Carl_Huff]

Looks very good Koifarm. I for one am eager to see how well it works! Please keep us posted as to your progress.

 

[Koifarm]

Last week received the PCB and tested it today. Best result until yet with a tubebuffer. No noise or hum. 0.0043% THD.

Next i shall build second channel and do some listening. And compare with no buffer version.

I make some optimalitions to the PCB. Publish also schematic and gerber files as build.

 

[Carl_Huff]

That looks really good! Are you still using ECC99 tubes? If so, what voltage are you running them at?

I am looking forward to your listening tests. This looks to be a fun project.

 

[Koifarm]

I am using 6n6p with 260V anode supply.. I =2 x 13,2mA. Ecc99 with same 260V runs at I = 2 x 12,5mA. ECC99 has a all over smooth sound. 6n6p is more clear with a little more punch.

PCB has universal connectors also for standanlone preamp. 1 PCB for L+R unbalanced preamp or 2 PCB for balanced preamp.

 

[Carl_Huff]

Great! I am looking forward to your final results

 

[Koifarm]

Below schematic and gerber files as-build.

Features:

• For Purifi 1ET400A or Hypex NC500 or universal use.
• Balanced 6n6p/Ecc99 tube preamp.
• Ecc99 or 6n6p heater supply jumper selectable.
• Gain 3x or 9x jumper selectable.
• Unbalanced input possible with RCA/Jack adapter.
• Connectors for Hypex SMPS1200A400 supply.
• Connectors for universal supply.
• Amp ON detection with LED in tube socket.
• Tube preamp ON delay.
• Low THD = 0,0043%(just 2nd harmonic).

Tube preamps need 265V/54mA and 6V3/3A2 power supply(2 boards).
I used 265V/6.3V SMPS from aliexpress.

Total cost for 2 channels(boards) is about € 150,- inclusive PCB's, Power supply and all parts.

 

[Koifarm]

Below schematic for a universal unbalanced(2 channel) tube preamp.
You can use the above PCB(only one), but you do not need the fancy headers.

 

[Carl_Huff]

Well that was quick! Thank you for this I will be studying what you have posted.

Have you had a chance to do some serious listening? I am curious as to your impressions

 

[cab]

Can't help but wonder why?

 

[Koifarm]

Well that was quick! Thank you for this I will be studying what you have posted.

Have you had a chance to do some serious listening? I am curious as to your impressions

I still have to build the second channel. Listen experience is very personal and subjective. Freq. curve is straight, distortion is low. No hum and no noise. There is a little more wider(spatial) soundstage. I already have and used the same tubebuffer together with the 1et400a. I am building the tube preamp for a friend. So we have two amps with 1et400a. One with no preamp and one with tube preamp.

 

[Brijac]

Can't help but wonder why?

Why lamps in anything then? Class D ain't just for low distorsion, it heats way less, takes way less space, and with tubes you get that nice well known sound signature.