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General Discussions => Drawing Board => Topic started by: CJ on November 27, 2015, 06:18:49 AM

Title: 6N1P Bass DI - Revisited
Post by: CJ on November 27, 2015, 06:18:49 AM
there is an older thread that got kind of cluttered so we are starting a new one for purposes of clarity,

here is a schematic for a Bass DI box that uses the Russian 6N1P dual triode.

these DC voltages were taken from an actual 6N1P running at 170 V-dc plate supply,

using one cathode resistor instead of two gave the measured results from the actual unit,
so we are simplfying the possibly erroneous schematic shown in the other thread,

a DIY  OPT was used,

here ya go>
Title: Re: 6N1P Bass DI - Revisited
Post by: mrclunk on November 21, 2016, 10:10:00 AM
Is there an 'off the shelf' transformer that would work? Its gapped right?

thank you btw..
Edit:
So i need a big ole SE transformer that can handle alot of DC on the primary.  Not the cheap and simple bass di as I first envisioned!
Title: Re: 6N1P Bass DI - Revisited
Post by: My3gger on November 24, 2016, 09:04:24 AM
Is there an 'off the shelf' transformer that would work? Its gapped right?

thank you btw..
Edit:
So i need a big ole SE transformer that can handle alot of DC on the primary.  Not the cheap and simple bass di as I first envisioned!

You could try Carnhill 2290 which has very close "impedances" as original. Proper datasheet will tell more about max current, although i think this is not a problem here because 8,36mA of REDDI is pretty low for saturating such core. Another model was used in SRPP version from Ian Bell.
Title: Re: 6N1P Bass DI - Revisited
Post by: Michael Tibes on November 24, 2016, 11:12:21 AM
The original transformer is from Cinemag, but I don't know the model or whether it is a custom item.

Michael
Title: Re: 6N1P Bass DI - Revisited
Post by: mrclunk on November 24, 2016, 11:50:43 AM
Thanks chaps,
I'll have a look at the data for the Carnhill 2290. It seems too good to be true tho.
My understanding is it needs high primary inductance to maintain low frequency response . I was under the impression thats why SE transformers are big and expensive?
Title: Re: 6N1P Bass DI - Revisited
Post by: ruffrecords on November 24, 2016, 12:16:06 PM
Thanks chaps,
I'll have a look at the data for the Carnhill 2290. It seems too good to be true tho.
My understanding is it needs high primary inductance to maintain low frequency response . I was under the impression thats why SE transformers are big and expensive?

I would be interested to see the data you have for the 2290. Carnhill data seems to be very sparse.

Cheers

ian
Title: Re: 6N1P Bass DI - Revisited
Post by: mrclunk on November 25, 2016, 09:19:47 AM
I would be interested to see the data you have for the 2290. Carnhill data seems to be very sparse.
Sorry i don't have any addition data to whats on the spec sheet, which is as you say sparse.
I could order one and have it sent to your lab?  If you have the time or inclination to test?
Title: Re: 6N1P Bass DI - Revisited
Post by: PRR on November 25, 2016, 08:22:59 PM
> does this not risk operating the tube close to/ beyond the dissipation limit?

No.
Title: Re: 6N1P Bass DI - Revisited
Post by: PRR on November 26, 2016, 03:56:55 PM
> I started a thread on EL34 world, simply to thank you for all your awesome input, which I noticed they deleted almost immediately

Not deleted. (That would be exceptionally odd anyway.)

"PRR shout out and +1s"
http://el34world.com/Forum/index.php?topic=19904.msg207936#msg207936
Title: Re: 6N1P Bass DI - Revisited
Post by: ruffrecords on November 28, 2016, 03:48:39 AM
Sorry i don't have any addition data to whats on the spec sheet, which is as you say sparse.
I could order one and have it sent to your lab?  If you have the time or inclination to test?
I would be happy to have a go but I am not sure if it would be very helpful. I can certainly test the primary inductance for you at 100Hz, which is as low as the meter I have goes, and it would be without dc flowing. The thing is, iron cored transformer parameters change with dc current and frequency. Inductance goes down as current goes up and inductance tends to go up as frequency goes down. Ideally it would be good to know exactly how inductance varies with both but I don't have the kit to do that. To be honest I am not even sure of the best way to do it. CJ might have some ideas.

Anyway, I am happy to measure the 100Hz inductance for you which will at least give us a starting point.

Cheers

Ian
Title: Re: 6N1P Bass DI - Revisited
Post by: ruffrecords on November 28, 2016, 03:57:28 AM
an aside question, supposing the tube DI is not connected to a circuit and the LVL is reduced, does this not risk operating the tube close to/ beyond the dissipation limit?
The quiescent current, and hence the dissipation,  is determined by the dc load line which is set by the dc  resistance of the output transformer. Since this is very low, the plate pretty much sees just the HT voltage so the dc load line is near enough a horizontal line at the HT volts. The ac load line determines the gain and it is this that is set by the reflected load.

Cheers

Ian
Title: Re: 6N1P Bass DI - Revisited
Post by: My3gger on November 28, 2016, 11:51:32 AM
"Quote from: mrclunk on November 25, 2016, 03:19:47 PM
Sorry i don't have any addition data to whats on the spec sheet, which is as you say sparse.
I could order one and have it sent to your lab?  If you have the time or inclination to test?"


I would be happy to have a go but I am not sure if it would be very helpful. I can certainly test the primary inductance for you at 100Hz, which is as low as the meter I have goes, and it would be without dc flowing. The thing is, iron cored transformer parameters change with dc current and frequency. Inductance goes down as current goes up and inductance tends to go up as frequency goes down. Ideally it would be good to know exactly how inductance varies with both but I don't have the kit to do that. To be honest I am not even sure of the best way to do it. CJ might have some ideas.

Anyway, I am happy to measure the 100Hz inductance for you which will at least give us a starting point.

Cheers

Ian

Cinemag certainly gives this kind of information, i asked them for mic input and gapped output inductance. Later at certain current and frequency for both, so why not ask Carnhill to avoid sending trafos around.
I though about having ~30mA/24V compared to ~250/5mA in core of OT. Power seems close, guess no other steps are necessary at designing them, except for lower impedances of transistors along maybe some minor things? Cores of Carnhill 2290 and custom Cinemags with iron or 50Ni/50Fe are pretty close in dimensions, as are outputs meant to be driven by transistors. 2290 expects higher impedance typical for tube output like 9600r, so it might have been requested by AML for tube projects, based on demand here.
Is my thinking correct, or expected output impedance doesn't say much about transformer quality, like those encountered from tube anodes? It seems strange Carnhill would make good low ratio and bad high ratio outputs.
Title: Re: 6N1P Bass DI - Revisited
Post by: ruffrecords on November 28, 2016, 12:27:52 PM
Cinemag certainly gives this kind of information, i asked them for mic input and gapped output inductance. Later at certain current and frequency for both, so why not ask Carnhill to avoid sending trafos around.
Good idea. We have often debayed the lack of info provided by transformer manufacturers and the best way to get it is to ask them.
Quote
I though about having ~30mA/24V compared to ~250/5mA in core of OT. Power seems close, guess no other steps are necessary at designing them, except for lower source impedances of transistors along maybe some minor things? Cores of Carnhill 2290 and custom Cinemags with iron or 50Ni/50Fe are pretty close in dimensions.
Core size is a major factor in determining power handling capability. Inductance of a gapped transformer depends a lot on dc current so higher current is likely to require a larger gap (to avoid saturation) which leads to a lower inductance. Transformer design is so cmplex it is virtually an art. I don't pretend to understand a small part of it.
Quote
2290 expects higher source impedance typical for tube output like 9600r, so it might have been requested by AML for tube projects, based on demand here.
Is my thinking correct, or expected source impedance doesn't say much about transformer quality when impedances are higher like with tubes?
A transformer does what it says on the tine; it transforms voltages, currents and impedances from one winding to another. The bandwidth over which a transformer will successfully operate is determined by the inductance, stray capacitance, leakage inductance and resistance of its windings.

For a good primer on audio transformers you should read:

http://jensen-transformers.com/wp-content/uploads/2014/09/Audio-Transformers-Chapter.pdf (http://jensen-transformers.com/wp-content/uploads/2014/09/Audio-Transformers-Chapter.pdf)

Cheers

Ian
Title: Re: 6N1P Bass DI - Revisited
Post by: My3gger on November 28, 2016, 03:37:34 PM
Good idea. We have often debayed the lack of info provided by transformer manufacturers and the best way to get it is to ask them.Core size is a major factor in determining power handling capability. Inductance of a gapped transformer depends a lot on dc current so higher current is likely to require a larger gap (to avoid saturation) which leads to a lower inductance. Transformer design is so cmplex it is virtually an art. I don't pretend to understand a small part of it.A transformer does what it says on the tine; it transforms voltages, currents and impedances from one winding to another. The bandwidth over which a transformer will successfully operate is determined by the inductance, stray capacitance, leakage inductance and resistance of its windings.

For a good primer on audio transformers you should read:

http://jensen-transformers.com/wp-content/uploads/2014/09/Audio-Transformers-Chapter.pdf (http://jensen-transformers.com/wp-content/uploads/2014/09/Audio-Transformers-Chapter.pdf)

Cheers

Ian

Yeah, i agree making transformers is an art. I remember talking to one of known transformer designers who told me to follow recommended output impedances, like not using 600:600 instead of 10:10k for line inputs. The same was for one version of Pultec where transformer with the same ratio, but not impedances didn't work as it should, it was Max from here who corrected me. So i'm left with Edcor 600:150, it will probably be used for EMRR's WE 141-A mash-up because output impedance will match well with primary and some step down will help too.
Wasn't one of guys making your mixer using ungapped Carnhill 2291 or another similar model? Iirc he did at least test it and later changed for Sowter. If this is so it probably can give some hints if they are properly designed for tube work, like i said manufacturer or AML should know it very well.

Title: Re: 6N1P Bass DI - Revisited
Post by: ruffrecords on November 29, 2016, 02:50:12 AM
Wasn't one of guys making your mixer using ungapped Carnhill 2291 or another similar model? Iirc he did at least test it and later changed for Sowter. If this is so it probably can give some hints if they are properly designed for tube work, like i said manufacturer or AML should know it very well.
Quite possible - I get so many questions there's no way I can remember them all. It is a good incentive to create documentation!!
You can use the 2281 (600:600) because it has a primary inductance of about 12H measured at 100Hz. This translates into a 1500 ohm load at 20Hz which is a bit on the low side for my tube designs BUT inductance tends to increase as frequency goes down so at 20Hz the inductance  could be twice this value which would make it OK. I have certainly used Sowter 600:600 transformers with no problems.

The 2291 primary inductance is around 48H so the gapped version will be less but as long as it is not far away from 12H at 100Hz then by the same reasoning it should be OK. Only way to be sure is to try it.

Cheers

Ian
Title: Re: 6N1P Bass DI - Revisited
Post by: CJ on November 30, 2016, 02:13:53 AM
inductance at the low end does not vary much with frequency in a gapped core as the perm becomes very stable with the air gap,

so your inductance reading at 100 Hz should be close to inductance at 20 Hz.

and if the core is big enough then the DC will not cause much decrease in inductance,
Title: Re: 6N1P Bass DI - Revisited
Post by: ruffrecords on November 30, 2016, 02:36:31 AM
inductance at the low end does not vary much with frequency in a gapped core as the perm becomes very stable with the air gap,

so your inductance reading at 100 Hz should be close to inductance at 20 Hz.

and if the core is big enough then the DC will not cause much decrease in inductance,

See, I said it was as much art as science! CJ has definitely put in his 10,000 hours.

Cheers

Ian

Edit: @MrClunk: Seems an inductance measurement at 100Hz will be valid. Drop me an email and I will give you my address so you can post it to me.

Cheers

Ian
Title: Re: 6N1P Bass DI - Revisited
Post by: EmRR on November 30, 2016, 01:02:30 PM
Polarity looks fine, unless my quick glance mixed something. 

Ian said some version of it already: I'd change that output control so it doesn't totally short the secondary.  There's absolutely no argument for this arrangement.  Period.  The end.  Put the rheostat on the other side of the 300R's and make it 500R instead of 1K.   Or shunt a 1K across a 1K pot if you can't find a 500R. 
Title: Re: 6N1P Bass DI - Revisited
Post by: mrclunk on December 01, 2016, 07:04:01 AM
Edit: @MrClunk: Seems an inductance measurement at 100Hz will be valid. Drop me an email and I will give you my address so you can post it to me.
Thanks Ian, have just emailed AML incase they already know all this stuff. If not i'll send one your way.
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on December 18, 2016, 08:09:48 AM
Is there anybody in EU who would make this project and wants to include CJ's transformer?
Maybe we could make group order and save on the postage… postage for up to 6 is the same as for 1.
Let me know. I would take 2.
Title: Re: 6N1P Bass DI - Revisited
Post by: rock soderstrom on December 18, 2016, 08:57:38 AM
Hi Bancho, where are you located? It makes really sense to add this to you forum account. Cheers
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on December 18, 2016, 10:02:56 AM
Heh... sorry  ::)
Title: Re: 6N1P Bass DI - Revisited
Post by: rock soderstrom on December 18, 2016, 11:14:49 AM
Thanks! :) I am interested in one. Cheers
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on February 25, 2017, 04:14:27 PM
maybe a stupid question but anyway: how much current should the PT take?
I'm thinking to order some custom toroids
Title: Re: 6N1P Bass DI - Revisited
Post by: CJ on February 26, 2017, 01:14:31 AM
that cloth wire from Antique Electronic is not easy to strip. they changed vendors, best to use a razor blade or mechanical strippers, if you use needle nose and dikes, the needle nose will slip and you will rip the leads out quicker then you can say ticonderoga,

looking for some 600 volt PVC that does not melt in the oven like the 105 C stuff, but good wire is getting pretty dang expensive, check digikey if you doubt it, evilbay not much better,

shrink pic to 600 x 800

ever hear of the Drive by Truckers? they love those transformers,  ;D
Title: Re: 6N1P Bass DI - Revisited
Post by: MRecords on February 26, 2017, 07:06:23 PM
I have some troubles with my DI. I can´t get more than 13dB of gain.

First i had two 220Ohm resistors for each cathode with 2,1V and 9,6mA across it. After increasing them to 470 Ohm i had 2,74V and 5,8mA  but the gain didn´t  changed. For a last try i tied the upper end of the 470Ohm resistors together to recreate the schematic in the first post of this thread. But still no gain change.

B+ is at 170V and plate voltage is 164V.  Can somebody help me out on this one?

thanks
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on February 27, 2017, 12:40:37 PM
So what is good B+ voltage so the gain would be in useful range? Andy you used 190V... measured on unloaded PT?
The price for custom PT is really nice but the manufacturer said the current on primary is 0.08A... is that ok?
Title: Re: 6N1P Bass DI - Revisited
Post by: CJ on February 27, 2017, 04:43:33 PM
here is the schematic again,  added transformer wire colors

anybody verify the adj regulator resistors yet?



Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on February 28, 2017, 01:20:58 AM
I'm going to make two units in separate boxes - following the sceme provided by CJ.
Yes it would be nice to include the lamp also. I will use the DC for the heaters.
As I said I will get custom PTs with 170V+8V on secondary... I'm just little concerned about 170V regarding the gain as MRecords' had... That's why.
I'm sorry to complicate but I'd like to have proper units 🙃
Title: Re: 6N1P Bass DI - Revisited
Post by: ruffrecords on February 28, 2017, 01:37:08 AM
I have some troubles with my DI. I can´t get more than 13dB of gain.

That is probably about right for this design.  There is a loss of about 11dB in the transformer. So if you measure 13dB gain then that means the tube is providing about  24dB of gain which is about right. For a bass DI you do not really need any more. Most bass guitars will output around 500mV which will give an output of over 2V which is more than enough for a regular mixer line input.

Cheers

Ian
Title: Re: 6N1P Bass DI - Revisited
Post by: MRecords on February 28, 2017, 11:14:33 AM
Thanks Ian and andyfromdenver.


MRecord's post was addressed by IAN, and he mistakenly doubled instead of halved the cathode resistor for parallel operation.

hope that clarifies it.


I always thought that the equivalent to cathodes tied togehter with one 220 Ohm resistor would be 440 Ohm on each of the cathodes.
In CJs schematic 8 mA flow through 220 Ohm which gives 1,76V. I have two resistors on each of the cathodes so 4mA of current through 440 ( i used 470) which is again 1,76V.

Am i wrong?
Title: Re: 6N1P Bass DI - Revisited
Post by: MRecords on February 28, 2017, 11:22:40 AM

anybody verify the adj regulator resistors yet?





In my calculation 390 Ohm and 1k5 gives about 6.05V. I would use 250 Ohm and 1k which should give about 6.25V. I´ll try it when i get back home.
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on February 28, 2017, 04:10:59 PM
ok, so 170-0-170VAC 40mA(center tapped, maybe obv.) or 340VAC 40mA (no center tap, bridge rectified) and 8VAC 2-3A (center tapped or not) That should work.

Sorry for my ignorance but why do I need 170-0-170 secondary?
I would make two DIs in two separate enclosures. Each would have its own supply.
I thought the tube is designed for 250V anode voltage and using 170V is kind of being on the safe side.
Another question about the 8V secondary… you said it should take 2-3A current… why if the heater current of the tube is 600 mA ± 35 mA?
And how much current should the primary take? The manufacturer said it is usually 0.08A - is that ok?
I'm sorry if these are obvious things for some of you and right now you are face palming but I'm little confused  ???
Thanks for being patient with me  :)
Title: Re: 6N1P Bass DI - Revisited
Post by: ruffrecords on February 28, 2017, 06:29:42 PM
Sorry for my ignorance but why do I need 170-0-170 secondary?
Because that creates the desired HT voltage
Quote
I would make two DIs in two separate enclosures. Each would have its own supply.
OK
Quote
I thought the tube is designed for 250V anode voltage and using 170V is kind of being on the safe side.
It can be run at up to 250V but that does not mean you have to. The typical output is 2V rms. This means the primary of the output transformer has to swing by 8Vrms which  is about 11V peak. This means the anode only has to swing down to  159V and up to 181V. Raising the HT to 250V is unnecessary and only result in more dissipation in the tube and a need for a larger mains transformer.
Quote
Another question about the 8V secondary… you said it should take 2-3A current… why if the heater current of the tube is 600 mA ± 35 mA?
As a rule, the transformer needs to be able to provide an ac current into the rectifier that is about 1.6 times the required dc output  current - so it needs to be able to provide 960mA; nearly 1 amp. If you had two in the box you would need 2A
Quote
And how much current should the primary take? The manufacturer said it is usually 0.08A - is that ok?
You need to add up the total primary VA and multiply by 1.1 to allow for the transformer efficiency. This is the VA in the primary. What current that represents depends on the mains voltage.

Cheers

ian
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on March 02, 2017, 11:32:20 AM
OK... I did some homework and re-read some of the basics  and thigs are much more clear now  ::)
Thanks everybody!
but... I still have a question though: I there really any benefit using the PT with center tap on secondary (either for HT or heater)?
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on March 05, 2017, 06:03:10 AM
I'm sorry but there is still something that bothers me...
On the sowter page there are some basic principles about calculating the specs for power transformer.
If using two diodes for rectifying we use this formula: Vac = Vdc x 1.41
If using rectifier then we use this formula: Vac = Vdc x 0.71 which suggest that the voltage actually builds up (?). We are using rectyfier bridge here. Does the smoothing network really drops the voltage so much that  we get around 170V for HT (considering 340V secondary without center tap and the bridge)?

As this is my first tube build I would like to make things in a proper way without frying anything 🙃
Title: Re: 6N1P Bass DI - Revisited
Post by: PRR on March 05, 2017, 02:26:23 PM
> On the sowter page

Look *carefully* how they are specifying "VAC" for the center-tapped 2-diode case.
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on March 05, 2017, 03:04:49 PM
> On the sowter page

Look *carefully* how they are specifying "VAC" for the center-tapped 2-diode case.

I understand that in full wave case the secondary is just "half efficient" comparing to the bridge case...
I also believe other members made this DI with great results... I'd just like to understand where/if the drop from 340V to 170V happens (in the bridge version).
You can also post some link directing to the explanation. Thanks!

Title: Re: 6N1P Bass DI - Revisited
Post by: PRR on March 05, 2017, 03:47:49 PM
> You can also post some link

Your question. You could have posted the link to "the Sowter page" (http://www.sowter.co.uk/rectifier-transformer-calculation.php) so others would not have to re-hunt what you found.

> understand where/if the drop from 340V to 170V happens (in the bridge version).

ok, so 170-0-170VAC 40mA(center tapped, maybe obv.) or 340VAC 40mA (no center tap, bridge rectified)
This appears to be incorrect (and also un-refuted). Thank you for spotting this. The 340VAC single winding FWB will give 480V DC, which is distressingly high. You need an >450V first cap. You can drop 300V with much bigger hotter dropping resistors, but that is inelegant. If you do not *know* this will give way-high voltage, it may be trouble. (Andy should check my math; then if valid edit his post.)

170-0-170VAC 2-diode makes 240V DC.
Single 170VAC with FWB makes 240V DC.

Dropping resistors will get you into the 160V-220V range suitable for the amplifier. Ohm's Law is a friend.
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on March 10, 2017, 05:11:54 PM
Hi everybody... the more I check this and previous thread about this DI more confused I'm becoming... in the previous schematics there were two 200R and 470uF (each on its half of the tube) and now in the new one just one. Also the current was twice as big as now. Is this really ok? I know CJ said this is corrected regarding to the measurements... did anyone tried this version? Compare to the previous one?
I have to know this because depending on the current (which is now also different - half the previous one) I'll know how much voltage drop will be on the resistors - so I can choose the correct secondary voltage (the difference between 170V and 200V secondary is quite big).
Am I complicating too much? Should I just build it and see what happens?   :o


p.s.: what happened wit andy's posts?  ???
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 16, 2017, 12:24:06 PM
I pulled all my old posts so i don't confuse matters for the folks and detract from CJs scheme drawing, and to not annoy the vets.
If peeps feel inclined they can delete their now context-less responses...

In other news!  The all-enclosed version (AC heaters with hum balance and tube inside) is aaalmost done with the *patented term by me alert  ::)* "measure thrice, drill nice"
10x5x3 flimsy Hammond chassis  :P, but it will sit up-right and be a lil' DI rock.

*edit in: this chassis is a cool size, but is too flimsy for anything other than being babied at home.  Seek out a stronger chassis :-). edit in 2: DO NOT ORIENT YOUR TRANSFORMERS THUSLY IF USING PT269ex and stand-up CJ OT, see pic below for sonic perfection*
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 16, 2017, 12:32:07 PM
I did want to add this pic with info relevant to triodes in parallel, cause online info is scant.
ref: Designing Tube Preamps For Guitar and Bass- M. Blencowe
         RDH4

This is just the starting point, to chart the slope prior to -grid voltage relative to cathode. For beginners and intermediates who want to tailor the bias point and calculate V gain, Miller capacitance, valve output impedance, etc.

any corrections or additions welcome :-)

*edit in: add to my little column of parallel vs. single that gm (transconductance) doubles.  ;)*
Title: Re: 6N1P Bass DI - Revisited
Post by: dmp on March 16, 2017, 12:40:12 PM
Quote
In other news!  The, all-enclosed version (AC heaters with hum balance and tube inside) is aaalmost done with the *patented term by me alert  ::)* "measure thrice, drill nice"
10x5x3 flimsy Hammond chassis  :P, but it will sit up-right and be a lil' DI rock.

Do you get any 60 Hz hum on the output from the transformers being too close together? I built one up similar to yours - transformers were a little closer together - and I was getting hum on the output.
Title: Re: 6N1P Bass DI - Revisited
Post by: My3gger on March 16, 2017, 02:50:53 PM
Hi everybody... the more I check this and previous thread about this DI more confused I'm becoming... in the previous schematics there were two 200R and 470uF (each on its half of the tube) and now in the new one just one. Also the current was twice as big as now. Is this really ok? I know CJ said this is corrected regarding to the measurements... did anyone tried this version? Compare to the previous one?
I have to know this because depending on the current (which is now also different - half the previous one) I'll know how much voltage drop will be on the resistors - so I can choose the correct secondary voltage (the difference between 170V and 200V secondary is quite big).
Am I complicating too much? Should I just build it and see what happens?   :o


p.s.: what happened wit andy's posts?  ???

It would help us if you add links to posts, external links, maybe even post # when there are two similar schematics on same page. Quote or attachment is another option.
Iirc, there was a bit of confusion with one of DI's schematic having two cathode resistors and cathode current written very close to one triode. Compared to revisited schematic it probably contained error regarding current through each triode. Datasheet shows it at 10,5mA typical, max ~20mA (could be for pulses/transients).
Revisited schematic shows 8,36mA through both triodes, this should help you find out power transformer requirements. 30V difference in HT is not really a big problem for tube at 170V, difference between 8 and 16mA is.
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on March 16, 2017, 06:07:21 PM
It would help us if you add links to posts, external links, maybe even post # when there are two similar schematics on same page. Quote or attachment is another option.

yes it was in the other thread about REDDI but now I also see people made it with one cathode resistor/cap... so I'll stick with schematics in this thread.

So the PTs are now ordered...  thanks everybody!   ;D
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 17, 2017, 11:16:29 PM
Do you get any 60 Hz hum on the output from the transformers being too close together? I built one up similar to yours - transformers were a little closer together - and I was getting hum on the output.

Hi DMP, no hum.
it's not as easy as with spkr matching OTs (4,8,16, etc.), but I always check with headphones on the secondary to ensure it is in a flux dead-zone with the PT.
Are you going in line level with the LVL knob at max? 
If I crank the following stage (ex: mixer) I can get to the noise floor, but that is way too hot for normal use.

I've done three varieties now, ac and dc heaters, one with PT outside enclosure too, as long as the transformers are oriented right, they are all super quiet.

hope you get it where you want it :-)

Andy

Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 20, 2017, 07:42:02 AM
On the subject of inputs, if one is forgoing the xlr/ 1/4" combo-jack.
Here is a (large  :P)  pic of my cliff jack wiring, one switched and one not (for the "thru").

aaaand on this subject, my heart wants to use 1M..., but I have settled for 560-680k... the Russian datasheet sez 1M and another sheet too, aaaand the *red object* lists 1M inpt imp on their specs. However the Svetlana brief datasheet that I used above lists 500k as the max....
Title: Re: 6N1P Bass DI - Revisited
Post by: ruffrecords on March 20, 2017, 09:51:51 AM
On the subject of inputs, if one is forgoing the xlr/ 1/4" combo-jack.
Here is a (large  :P)  pic of my cliff jack wiring, one switched and one not (for the "thru").

aaaand on this subject, my heart wants to use 1M..., but I have settled for 560-680k... the Russian datasheet sez 1M and another sheet too, aaaand the *red object* lists 1M inpt imp on their specs. However the Svetlana brief datasheet that I used above lists 500k as the max....

Usually the grid resistance spec is for use with grid leak biasing. This circuit does not use grid leak biasing, it uses cathode biasing so you can safely use 1M.

Cheers

Ian
Title: Re: 6N1P Bass DI - Revisited
Post by: dmp on March 20, 2017, 09:58:23 AM
Quote
I totally take it at face value if you say your PT is inducing a hum in the OT, and if so, I imagine you might be thinking about rebuilding?  Or, if you have a stand-up PT, and can possibly try a 90 degree turn.
I did some tests that made me think it was the transformer orientation but I haven't looked at it since. 
Thanks for your observations  -  I will have to revist this project to try to figure out a solution.
Since I already did the metal work in the compact box, I REALLY hope I can get it to work with the close transformers. 
I have an edcor PT, but since it is the same style I don't think that would make a difference. 
Title: Re: 6N1P Bass DI - Revisited
Post by: PRR on March 21, 2017, 12:51:56 AM
> Usually the grid resistance spec is for use with grid leak biasing.

That is not how I understand it.

6N1P data does not say. Some US sheets show 1meg max grid resistor, then 10Meg in the amplifier table for Rk=0 (gridleak bias).
Title: Re: 6N1P Bass DI - Revisited
Post by: CJ on March 22, 2017, 04:16:16 AM
note that there is an internal shield that should probably be grounded,

there are a lot of 6N1P tubes out there, some better than others as far as noise is concerned,

Svetlana might be he way to go,
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 23, 2017, 05:15:13 PM
Huge update guys!  CJ, dmp, et al eager builders or refiners.

dmp, you got me really obsessed with the noise floor. I was able to borrow one of my other builds back when CJ was finishing the OT with horizontal feet.

I realized that those builds were, in fact, quieter with the Hammond PT 269ex.

Look at this orientation everyone. This is the absolute, super-duper-est, hifi studio fanatically quietest way to orient these two transformers. Ka-PERIOD! lol (I like to add Ka like KAPOW!!)

look back at my work in progress pic a few posts up (reply #41) when I had the OT standing. That is not the ideal orientation. The new way is much much quieter as far as flux induced hum.

So dmp! can you swing your OT this direction and re-attach?  I think you will be very pleased :-)



Title: Re: 6N1P Bass DI - Revisited
Post by: dmp on March 23, 2017, 05:50:59 PM
dmp, you got me really obsessed with the noise floor. I was able to borrow one of my other builds back when CJ was winding the OT with horizontal feet.
I realized that those builds were, in fact, quieter with the Hammond PT 269ex.
Look at this orientation everyone. This is the absolute, super-duper-est, hifi studio fanatically quietest way to orient these two transformers. Ka-PERIOD! lol (I like to add Ka like KAPOW!!)
look back at my work in progress pic a few posts up (reply #41) when I had the OT standing. That is not the ideal orientation. The new way is much much quieter as far as flux induced hum.
So dmp! can you swing your OT this direction and re-attach?  I think you will be very pleased :-)
I remember at one point reading about it and seeing something about that. if you look at Fender guitar amps, that's how they orient the transformers.
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 23, 2017, 06:53:09 PM
I remember at one point reading about it and seeing something about that. if you look at Fender guitar amps, that's how they orient the transformers.

Well, the stand up way is how Marshall did the 2204s, so really it just depends in my experience! :-) and listening tests rule all. 
As I was saying before (may have deleted it) the headphone trick is great for guitar amps, but it's much harder to hear the hum levels with headphones and this OT.

Solution: For experimenters with other PTs, with the OT secondary output circuit built up and leaving the primary disconnected, it is much easier to plug into a mixer and listen to the hum change as you move the OT around.

Here's a little glory shot if it inspires anybody (cept it really really needs a new paint job now that i drilled the front...). if one is going to put a new exit hole in CJs OT, please use a grommet :-)

Take care!

Andy


Title: Re: 6N1P Bass DI - Revisited
Post by: yosh on March 27, 2017, 11:19:01 PM
I just finished a build of one of a pair that I'm making and it sounds great! Though voltages aren't quite where they should be. I'm getting 6.7 VAC on my PT heater winding and 7 DC out of the rectifier. This is going into an LM317 which is obviously not enough voltage to get me my 1.25V drop needed for regulation. Then while I'm getting 250 volts AC out of my high voltage PT winding, after rectification I'm getting 350V! More increase than I expected. After the 3 2k resistors, I'm getting about 250V. For the B+ I can just order different resistor values to get me closer to 170 there, but I'm not exactly sure what to do about the heater voltage. I'm thinking about just trying AC? Any suggestions? Thanks!
Title: Re: 6N1P Bass DI - Revisited
Post by: dmp on March 28, 2017, 12:23:41 PM
I just finished a build of one of a pair that I'm making and it sounds great! Though voltages aren't quite where they should be. I'm getting 6.7 VAC on my PT heater winding and 7 DC out of the rectifier. This is going into an LM317 which is obviously not enough voltage to get me my 1.25V drop needed for regulation. Then while I'm getting 250 volts AC out of my high voltage PT winding, after rectification I'm getting 350V! More increase than I expected. After the 3 2k resistors, I'm getting about 250V. For the B+ I can just order different resistor values to get me closer to 170 there, but I'm not exactly sure what to do about the heater voltage. I'm thinking about just trying AC? Any suggestions? Thanks!
I am using a 9v heater winding before rectification. AC heaters should work well if they are twisted and oriented properly.

It doesn't sound like your tube is pulling the right amount of current. Unloaded, the B+ will be much higher. Maybe you don't have the tube hooked up to the power supply yet?  What is the cathode (pin 3 / 8) voltage of the tube? Compare to the voltages posted by CJ on the first post.
Title: Re: 6N1P Bass DI - Revisited
Post by: yosh on March 28, 2017, 01:19:38 PM
I am using a 9v heater winding before rectification. AC heaters should work well if they are twisted and oriented properly.

It doesn't sound like your tube is pulling the right amount of current. Unloaded, the B+ will be much higher. Maybe you don't have the tube hooked up to the power supply yet?  What is the cathode (pin 3 / 8) voltage of the tube? Compare to the voltages posted by CJ on the first post.

Yes, I have the tube installed  :)  The cathode voltage is 3.45 VDC or so, which looks like about double what it should be. Is this because my B+ is too high? I'll try those AC heaters, thanks!
Title: Re: 6N1P Bass DI - Revisited
Post by: dmp on March 28, 2017, 01:31:42 PM
Yes, I have the tube installed  :)  The cathode voltage is 3.45 VDC or so, which looks like about double what it should be. Is this because my B+ is too high? I'll try those AC heaters, thanks!

The higher the cathode voltage the more turned off the tube is. With the bias low, the tube draws less mAs, and you have less voltage drop across the power supply resistors (and higher B+). So it's all related. Instead of changing the power supply to get a lower B+, you need to figure out why the tube is biasing so low. What is your cathode resistor (s)?
If you have more cathode resistance, the cathode voltage is higher, the grid is more negative, and the tube is biased colder.  The B+ doesn't set the bias - the grid to cathode voltage sets the bias.
If your tube isn't properly heated, it won't operate correctly either - so maybe you need to get the heaters hooked up properly before the B+
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 28, 2017, 03:39:01 PM
yosh, +1 with dmp on going AC heaters. just keep the wiring tight and twised and wedged in a corner.

what is the plate voltage (pins 1 & 6)?

and did you use 220ohm on the cathode.

sounds like your build is in the zone to me.
though you can alter the dropping string like you stated. just the last 2k ohm will do.

If you want to experiment and leave nothing on the table, you can make a rheostat with a 500-1k ohm linear pot in series with a 100ohm resistor (so you don't ground the cathode) and vary your bias (cathode resistor) in real time, to find where you are happiest. can observe/measure change in V and I too for educational purposes :-)



Title: Re: 6N1P Bass DI - Revisited
Post by: yosh on March 28, 2017, 07:58:57 PM
Thanks for the advice! If I lower the cathode resistor to 80 ohms then I get 1.84 VDC on the cathode. B+ is then down to 198 VDC or so. That all seems much more along the lines of what to expect, but I'm not sure why the big difference between 80 ohms and 220 as designed. Any ideas?

Heaters are much noisier when I use AC so I might try using some schottky diodes and a low dropout regulator then perhaps I'll have enough room to get 6.3 V regulated DC.

Thanks again!
Title: Re: 6N1P Bass DI - Revisited
Post by: dmp on March 29, 2017, 09:48:31 AM
Yosh,
Are you following the schematic on the first post? With a shared cathode resistor, it is strange you need to go down to 80 ohms to get the right bias. Doublecheck your circuit to the schematic or post a picture.
Did you connect the AC Heaters to ground with 100 ohm resistors or a center tap? If your heaters were floating they will be noisier.
Title: Re: 6N1P Bass DI - Revisited
Post by: dmp on March 29, 2017, 09:54:22 AM
Getting close...
I had both the transformers standing before, but with one laying down it is very quiet. Andy, thanks for getting me going on this project again. Just need to tidy up the wiring and it's ready for the studio.
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 29, 2017, 12:55:18 PM
Getting close...
I had both the transformers standing before, but with one laying down it is very quiet. Andy, thanks for getting me going on this project again. Just need to tidy up the wiring and it's ready for the studio.

yes! *hi 5* you got it really tiny! nice  ;D


and @ yosh. 

it's time to look for my post on the grid curves and graph for biasing your particular amp.

This could get really deep and technical really quick and I defer to the ninja masters of the electronics world, but I'll hopefully help ya out. 
The important considerations are
1. staying below max dissipation.
2. centering (or hey! not) your bias for max swing before grid current limiting or cut off.
3. The DCR (resistance) that the OT primary presents to the circuit.

THEORETICALLY! with an ideal transformer and no regard for running your paralleled tube to it's new max dissipation (probably not good...) you would simply determine the slope of the load line given a particular supply voltage and primary impedance. Then, you simply draw a straight line up from the supply voltage to the point of max dissipation and use the graph and ohm's law to determine the cathode resistor (which sets the negative grid voltage). However, the line actually will not be straight up and down due to losses in the primary, it will slant over in actual testing as the supply voltage is reduced to the plate.

so use my graph and slope since your supply voltage is 200.

mark a point where your actual plate (anode) voltage is and the voltage drop across the cathode (1.84) as the negative grid voltage.

your signal will swing from that point along the slope to the limit of the grid voltage (0) to where it hits the horizontal axis.

this is super simplified and leaves out some details and I welcome any corrections.

I hope some of the more knowledgable will agree, it is more about how it sounds to you, because the more uneven the wave clipping is, the more distortion that is introduced, and it could be just what you are looking for? 
Title: Re: 6N1P Bass DI - Revisited
Post by: dmp on March 29, 2017, 03:24:31 PM

For the 6N1P, max dissipation is 2.2 watts PER triode. For class A you can bias pretty close to max dissipation.
As you experiment with biasing this hotter though, keep in mind  the transformer has to handle the bias current going through it. It is a transformer coupled tube design. Most tube circuits are resistor coupled with an output transformer connected after a DC blocking capacitor. 

Scenario 1 (CJ's schematic, first post): shared 220R cathode, V_cathode=1.84 V, V_plate=162 V, i=4.18 mA/triode
Power = 0.67 W/triode
transformer DC current = 8.36 mA

Scenario 2 (dirty1_1garry schematic): 220R per cathode, V_cathode=2.02 V, V_plate=162 V, i=9.18 mA/triode
Power = 1.48 W/triode
transformer DC current = 18.36 mA

Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 29, 2017, 04:27:01 PM
Heaters are much noisier when I use AC so I might try using some schottky diodes and a low dropout regulator then perhaps I'll have enough room to get 6.3 V regulated DC.

sorry i missed this part and i apologize to ask, but did you leave out a center tap when you went AC? 

I would be so hesitant to use the the words "much noisier" when describing the difference in my experience.

I do realize that the world of pro audio is all about chasing the super percents, and what is measurable etc.

just wanted to clarify before you pursue the DC heaters.
Title: Re: 6N1P Bass DI - Revisited
Post by: yosh on March 29, 2017, 11:50:59 PM
Thank you again for sharing your knowledge! I will spend some time with those graphs and get my head wrapped around this.

I did leave out the center tap. Oops. I'm realizing how much I don't know about tube design. I think I'll be reading up a lot in the near future. I'll put the center tap in and see where that gets me. Thanks!
Title: Re: 6N1P Bass DI - Revisited
Post by: CJ on March 30, 2017, 06:37:47 AM
that transformer should handle 18 ma no problem,

18 ma time 5000T = 90 amp turns, or 113 Gilberts :D

figure a natural air gap from the butt stack = to about 4 or 5 mil = 1 Tesla or 10 K gauss.

core is good for 18 KG, and AC flux is only about 2 KG so you still have 6 KG of core left before saturation,

can't vouch for how long the tube will last,  :o

Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 30, 2017, 07:00:33 AM
haha! great to know CJ, thank you very much for the detailed breakdown.

@ yosh, you're so welcome! I say give AC heaters another try. Does your PT already have a 6.3V winding center tap?  If not, and if you are a tube socket wiring ninja, you can fly two 1/2 W 100 ohm resistors from each of the heater pins (4 & 5) to both terminate at the shared cathode of the socket, this is safe and has convenient tie points.

But basically you'll need 100ohms from each heater end to ground, it shall be super quiet after.  If by chance you are using a 6.3V lamp, you can add the heater artificial CT off that, if there is a nearby ground. 

Time to drop some bass... j/k

Andy

To add cause I am a pics junkie: Here is a pic of my first all-enclosed, the Cobra Box *makes the devil horns gesture and headbangs for a second until i get a crick in my neck*
Sigh, I jacked up the paint job, but I etched in that cobra I have been drawing since I was a kid, probably going to sand it all and repaint.

If only Hammond made this chassis...oh...4 x thicker  :o, it would be stellar.
this one's mine so no grd lift and no polarity flip.

Title: Re: 6N1P Bass DI - Revisited
Post by: dmp on March 30, 2017, 10:28:01 AM
Looks good Andy, how does it sound?
Did you go for the 18mA bias or 8mA?
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 30, 2017, 06:12:29 PM
Looks good Andy, how does it sound?
Did you go for the 18mA bias or 8mA?

Thank you!  Mine is stock CJ scheme with higher supply/B+
~10 mA

It sounds exactly like the red object. exactly! ;-)
Also, thank you for sharing information on the circuit and biasing; very helpful!

Here is a test measurement summary (pic) and a scheme I drew up for an elevated Heater CT ref DC V.
This is for the next DIY shennanigan... A separate 6N1P EQ box so i don't exceed heater-cathode V with a cathode follower circuit.
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on March 30, 2017, 06:23:20 PM
and here is a summary I did for varying Cathode resistance. (apologies: big pic d/t small writing...) with an earlier box on, lvl max, and no connection. I interrupted the plate to primary connection with my meter, just to feel the wind in my hair  ::)

I did like the 100ohm version too.

I was thinking, what if you had like a 270ohm and another 180ohm on a spst switch for either 270ohm or 108ohm action.

I thiiiiink it would be audibly noticable?
can call it the "Hair" switch  :P
Title: Re: 6N1P Bass DI - Revisited
Post by: yosh on April 03, 2017, 12:59:54 PM
I have a finished DI and I used it all day on a tracking session yesterday. Sounded fantastic! Installing the center tap for the heater winding made it very quiet again. At the moment I'm using a 100 ohm resistor on the cathode. But I might play with that value a little more to find exactly what I like. Maybe even install a 200 ohm trimpot.

For enclosures I used Hammond P-H1441-20BK3 with cover P-H1431-20BK3. Ordered from CE Distribution. I think it was around $90 for two enclosures including shipping. They work great!

and here is a summary I did for varying Cathode resistance. (apologies: big pic d/t small writing...) with an earlier box on, lvl max, and no connection. I interrupted the plate to primary connection with my meter, just to feel the wind in my hair  ::)

I did like the 100ohm version too.

I was thinking, what if you had like a 270ohm and another 180ohm on a spst switch for either 270ohm or 108ohm action.

I thiiiiink it would be audibly noticable?
can call it the "Hair" switch  :P

I did this with a pair of tube mics that I built years ago. A switch on the power supply flips a relay inside the mic and changes the cathode resistor. The switch is labeled "Clean and Pretty / Hot and Dirty". I use them all the time  :D
Title: Re: 6N1P Bass DI - Revisited
Post by: bancho on June 11, 2017, 07:50:56 AM
Ok, so I'm at the final touch of this DI (I know it takes too long but anyway...) and there is some question/doubt about grounding the whole thing. For more complicated / advanced circuits I know it is very important how you make the power supply and signal grounding because of all the ground loops and things.
Is it here also that important? Can I make a single node for the power supply (RC network) and the signal circuit?
Title: Re: 6N1P Bass DI - Revisited
Post by: My3gger on June 11, 2017, 09:32:16 AM
Is it here also that important? Can I make a single node for the power supply (RC network) and the signal circuit?

It is very important, not only because you want to avoid noise on supplies, it has to be Safe in the first place. Judging by pics you showed there are a few things to inslulate, take decision about heater voltage and check where supplies are taken. + line from the end of power supply, never close to diode bridge because of interferences. You haven't mention ground on IEC and HT bleeding resistor, those are first two things to do imo and is good practice in general.
Title: Re: 6N1P Bass DI - Revisited
Post by: damianschwartz on July 03, 2017, 06:56:44 PM
Will give a go on this quite soon. Just gathering all the info i can, but i'm sure i will have to ask for some help, even though i did many DIY projects, 90% of them were Synthesizers, and no tube experience apart from fixing my old Bassman a couple of times.

I did realize the DW Fearn "All tube DI" (that they have in a studio i work sometimes) is a double channel DI sporting 1 6n1p on each channels, by Mr Fearns webpage. Bet it's not a much different design, wondering which output trafo that might be using.
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on July 04, 2017, 09:53:36 AM
Will give a go on this quite soon. Just gathering all the info i can, but i'm sure i will have to ask for some help, even though i did many DIY projects, 90% of them were Synthesizers, and no tube experience apart from fixing my old Bassman a couple of times.

I did realize the DW Fearn "All tube DI" (that they have in a studio i work sometimes) is a double channel DI sporting 1 6n1p on each channels, by Mr Fearns webpage. Bet it's not a much different design, wondering which output trafo that might be using.

You can do this project, if you can work safely w/ high voltage :-). The circuit is as simple as a first tube project gets.

I checked the DW site. Their DI is a different flavor. two gain stages (well, one gain stage and one cathode follower) cap coupled between and cap coupled cf to OT (read no DC on primary and no need for gap and large size).
The CJ iron 6N1P tube DI is a single ended design with no caps in the signal path. It's a single gain stage with the valve paralleled and the signal taken from the anode with the OT serving as the anode/plate load. It has to have a huge OT to handle DC on the primary, a gap, and low freq friendly specs.

The picture on the DW site is a little funny, but perhaps conveys something meaningful to the inexperienced musician.

In conclusion, CJs iron is a must. I think there is a suitable Sowter that I mentioned before and someone else mentioned a cinemag, but CJs price is 1/3 less than Sowter, and is so custom it makes me cry/smile.

Andy
Title: Re: 6N1P Bass DI - Revisited
Post by: Hank Dussen on January 23, 2018, 05:07:43 PM
I'm having some trouble with the heaters.
Without the tube I get 6,3v DC but with the tube inserted I can not get it higher then 5,9v.
The PT has 4A on this winding so that should be enough. Is it correct to have pin 4 connected to the 6,3v and pin 5 to ground?
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on January 24, 2018, 08:12:03 AM
I'm having some trouble with the heaters.
Without the tube I get 6,3v DC but with the tube inserted I can not get it higher then 5,9v.
The PT has 4A on this winding so that should be enough. Is it correct to have pin 4 connected to the 6,3v and pin 5 to ground?
Hi Hank. your connection, as stated, is correct for DC heater operation.  Question: what is the AC voltage of the heater tap directly off the power transformer (PT)? perhaps it is not high enough or perhaps the rectified DCV is not high enough?  If you are using a PT with a 6.3VAC winding, you could perhaps just use AC heaters, however at lightly loaded and with wall voltage fluctuation/ increase you may exceed a comfortable max for the tube.


keep at it! this is a cool tool!  and to update, I am getting close to having the free time to explore the 6N1P treb mid bass eq add-on for CJs awesome iron project. tbc!
Andy

edit in: I forgot to add that 5.9VDC on the heaters is perfectly acceptable imo :-)
Title: Re: 6N1P Bass DI - Revisited
Post by: Hank Dussen on January 24, 2018, 04:47:38 PM
Hey Andy, thanks for your suggestions.
I tried 2 power transformers for this. The first had 8v on the secondary but is only rated 600mA so that's not enough after the rectifier. The second transformer I tried is rated as 6,3v (4A) on the secondary but unloaded I get 7,4v. After the rectifier that's 8,9v so that should be enough for the voltage drop of the LM317. But when I insert the tube the voltage after the rectifier drops to 7,8v and after the LM317 it drops to 5,8v.
And this is resulting in a too loud hum. Or maybe that's caused by something else. I'm trying to find out.

I'll try to run the heaters with AC. But I think I better try to drop the 7,4v a bit.

BTW, your plan for adding an EQ to this design sound great. Keep us posted!
Title: Re: 6N1P Bass DI - Revisited
Post by: andyfromdenver on January 24, 2018, 06:50:21 PM
Hey Andy, thanks for your suggestions.
I tried 2 power transformers for this. The first had 8v on the secondary but is only rated 600mA so that's not enough after the rectifier. The second transformer I tried is rated as 6,3v (4A) on the secondary but unloaded I get 7,4v. After the rectifier that's 8,9v so that should be enough for the voltage drop of the LM317. But when I insert the tube the voltage after the rectifier drops to 7,8v and after the LM317 it drops to 5,8v.
And this is resulting in a too loud hum. Or maybe that's caused by something else. I'm trying to find out.

I'll try to run the heaters with AC. But I think I better try to drop the 7,4v a bit.

BTW, your plan for adding an EQ to this design sound great. Keep us posted!
Interesting.  I did DC heaters without a Vreg, I imagine you will need to adjust it per data sheet and formula. Just to clarify, if your PT has a heater CT you cannot connect it and also chassis ground post rectifier.
I implemented DC heaters with big resistors and 10k mfd caps, as an alternative.
The hum sounds like you need to chassis ground the DC heater circuit (again, not a with PT heater center tap (CT) simultaneously).
Here is a relevant link: http://www.valvewizard.co.uk/heater.html  apologies if you have already read this.  DC heaters are discussed at the bottom.
edit: here is a thread from a while back on my dc heater circuit, I made several changes when finally finished that I didn't add and the device is gone, I think it was just another 10k mfd cap, but it shows another means and has helpful input from the super-users. Just scroll towards the end when I switched to unregulated :-) as an alternative.
https://groupdiy.com/index.php?topic=64560.0
Title: Re: 6N1P Bass DI - Revisited
Post by: yvus on November 22, 2020, 05:54:42 AM
Hello guys,

Thank you for this very useful thread. I built 2 units based on the scheme showed in the first message and they sound great. I used Carnhill transormers. Both units are in the same box and are powered by the same PSU.
When i test each unit individually, i get a B+ voltage of about 190 V with about 3 V on the cathode resistor (which is 220 Ohm as stated on the diagram). However, when the two units are feed in parallel from the PSU, the B+ voltage drops to about 150 V with a cathode voltage of 2,2 V approximatively and I can not figure out why ? The low voltage supply for heaters remains quite stable in both cases.

Do you have any idea ?

Thanks.
Title: Re: 6N1P Bass DI - Revisited
Post by: ruffrecords on November 22, 2020, 12:58:03 PM
If the HT supply uses simple RC filtering then the additional current draw of two using will drop the HT and alter the operating point which is reflected in the cathode voltage.

Cheers

Ian
Title: Re: 6N1P Bass DI - Revisited
Post by: yvus on November 22, 2020, 04:43:53 PM
Since the HT supply in the build I'm testing indeed uses simple RC filtering, it makes sense. Thank you for your answer, I will check this out.