Universal tube preamp PCB, ECC99/6N6P/ECC88/ECC85/6922/6DJ8 etc. MU follower or SRPP

[Koifarm]

After 18 years challenging myself, learning from you and sharing nice projects I will leave this forum.
Also because being bullied and get physical threads without support of the moderators for the last 18 years.
See you all on the next forum.

R.I.P by mod.

 

[alain98]

Hy Koifarm,
Do you have a PDF file of your pcb to make my own pcb?
Thanks in advance
Alain

 

[ruffrecords]

I think you should include a bypass capacitor for the lower triode.


Cheers

ian

 

[Koifarm]

Alain, i can generate the pdf files after my holiday.
There are gerber to pdf converters online.

Ian, frequency respons is from 10hz to 100khz within +/-0.5db and gain is enough.
But thanks for the reply.

 

[rongon]

Local shunt NFB! Nice. That's a cool little circuit.
Do you have a link to the power supply you mentioned?

 

[rongon]

I think you should include a bypass capacitor for the lower triode.


Cheers

ian

Perhaps sub an LED for R4 and R14?

 

[Koifarm]

Link for smps:

https://nl.aliexpress.com/item/1005...216579079850164762ec166!12000029255708991!sea

https://www.aliexpress.com/item/1005001407107303.html?spm=a2g0o.detail.1000014.10.525f7cceWG2j7G&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.40050.281175.0&scm_id=1007.40050.281175.0&scm-url=1007.40050.281175.0&pvid=7b953e52-5229-49f4-9564-a3facfdebdaa&_t=gps-id😛cDetailBottomMoreOtherSeller,scm-url:1007.40050.281175.0,pvid:7b953e52-5229-49f4-9564-a3facfdebdaa,tpp_buckets:668#2846#8115#2000&pdp_ext_f={"sku_id":"12000015963231639","sceneId":"30050"}&pdp_npi=2@dis!EUR!!45.69!!!!!@211b5db316551372258983283ee191!12000015963231639!rec

https://www.aliexpress.com/item/32997695785.html?spm=a2g0o.productlist.0.0.1cad7ea2fTpgxI&algo_pvid=4a3e6604-8832-4a24-a7f6-8790a3a5400e&algo_exp_id=4a3e6604-8832-4a24-a7f6-8790a3a5400e-32&pdp_ext_f={"sku_id":"66980528735"}&pdp_npi=2@dis!EUR!!29.79!!!!!@0b0a01f816551358878617330eb7a3!66980528735!sea

https://www.aliexpress.com/item/100...b16551378287617573ee8f6!12000018192145879!sea

 

[Koifarm]

Perhaps sub an LED for R4 and R14?

As you see freq.respons is very linear and distorsion is 0.0043%
Noise floor is also -118db.

 

[ruffrecords]

Ian, frequency respons is from 10hz to 100khz within +/-0.5db and gain is enough.

But open loop gain will be improved with bypassed cathode so distortion will be lower but a LED will probably do the trick since the PCB already exists.

Cheers

Ian

 

[ruffrecords]

Noise floor is also -118db.

This is an amazingly good noise floor. . Can you show the actual measurement and the conditions under which they were made please?

Cheers

ian

 

[Koifarm]

Ian, when i am back from holiday i shall make some measurements with different output impedance and topology. I use Arta and Rew software with Behringer UMC202.

With SMPS there is no 50/100hz interference, this helps.

 

[ruffrecords]

Ian, when i am back from holiday i shall make some measurements with different output impedance and topology. I use Arta and Rew software with Behringer UMC202.

One thing to be aware of with software like ARTA and REW is that their FFT displays usually show the noise per root Hertz. To get the rms noise (which is what you hear) you have to integrate over the 20KHz bandwidth. Assuming the noise is pretty flat then this just means adding about 43dB (20 log (root(20K))to the per root Hz noise floor. Edit: REW will show you the A or C weighted rms noise.

With SMPS there is no 50/100hz interference, this helps.

I agree, I use them all the time now for heaters. I recommend MeanWell,

Cheers

ian

 

[ruffrecords]

I wish someone would come up with an HT only SMPSU. The aliexpress ones all have 6.3V outputs and you have to use them because that is the one that is regulated and the HT is just rectified and smoothed.

Cheers

Ian

 

[alain98]

Koifarm, I used the software Gerbview to convert gerbers to pdf with success.
Thanks.

 

[Koifarm]

Making your own PCB is nice. But for €7.50 you get 5 PCB incl. tax and shippingcost.

 

[dBel84]

Hi. thank you for sharing your work. I have always liked the sound of an SRPP topology and this seems like a very simple project to try out. I used your gerbers to place an order for PCBs . I have never seen these compact SMPS units before either, I have used 6.3V smps for heater supplies but never for the B+.

I will let you know how I get along..dB

 

[Koifarm]

I can recomend these smps. No problems with EMI or hiss.

 

[jean-paul]

Measured with RF capable equipment? All too often I read this but then my stuff does register other reality.

 

[Koifarm]

No measurement, just my experience with the phonostage who is nearby in wooden housing.

 

[jean-paul]

As expected, sorry. It is often assumed one can not hear RF so it is not an issue. EMI and RF are nasty in audio though and in semiconductor stuff sometimes the cause of "listening fatigue" and this intermittent or depending on the time of the day/temp etc. Even when devices look nice and have blue LEDs 🙂 Not measuring = not knowing.

BTW I do like your design so no negative criticism except a few quibbles like lacking volume control and PSU. Nice design.