260v dc to 160v dc

[Randy Bassinga]

Power supply

Is there a way to drop the 260v output to 160v on the above linked power supply?

Thanks and regards
Randy

 

[MorbidFractal]

How brave do you feel? On the pictures there is a component sleeved in blue at one side of the transformer. It looks like two diodes in series. Note the silk screen shows a 200V/260V tap so refitting that will get you down to 200V. The supplier suggests 10% adjustment but on the other side of the transformer ther is a 4 pin DIP which will be a feedback opto-coupler. There is likely to be a bunch of surface mount components on the bottom of the board so trace from the opto on the secondary side to what is likely to be a TL431 and look at the components around that. If it is done right then you will likely see a series string of resistors, could be one big one, from the HV output into that feedback loop. Reduce its value and you will reduce the output voltage. It is likely that when you go 260-> 200 that you will not impact the 6.3V output but when you drop it further via feedback the 6.3V output will drop in proportion.

 

[Randy Bassinga]

Is there a way to step it down easily from the 200v tap? Can these types of devices be cascaded into another e.g dc step down board?

Can a regulated 12v dc output be fed into a dc boost converter?

Or is this bad practice?

 

[MorbidFractal]

Not easily if you want to maintain the same output current rating. With suitable adjustment of the secondary feedback components you should be able to get it to regulate down to 160V but as I suggest your 6.3V filament will drop to 5V. If you are not using it then not a problem. Otherwise I don't know how valves get on with having their heater run low. Tagging things on to other things might be a recipe for pain.

I'm sure AliExpress will sell you a 12V to 160V boost convertor. You just have to find one.

 

[JMFahey]

I very much doubt different secondaries are independent regulated,
Suspect there is only one voltage reference, and only one voltage is monitored and regulated, others are just in a fixed ratio to it.
So if you modify the reference resistor string, both HV and filament will change at the same time, by the same percentage.

Now 10% variation is acceptable for both .... but 40% down? ... not that much.
IF HV current consumption is low, a few mA for a preamp, just doit the old way, with dropping resistors.
Forget "it´s an SMPS", just think "DC power supply".

 

[MorbidFractal]

Using the 200V tap it would be 20% down. As I have implied and as you suggest only one output is regulated. It should be the case that it is the heaviest loaded output which may turn out to be the heater supply. Whilst the description babbles on about synchronous stuff I doubt the words are being used correctly so just to float a different idea. The device on the heatsink would appear to be the one that performs the 'soft' start'. It might be possible to use the 200V tap and then the hack the circuit that controls it rather than the main feedback to perform the soft start and at the same time use it to regulate, in a linear way, the final output down at the required 160V. If your wet finger thinks the device along with its heatsink is good for 5W dissipation then it would be good for 125mA. If you assume that in the attachment the left represents what is already present on the board then adding what is on the right might do something.

 

[Randy Bassinga]

IF HV current consumption is low, a few mA for a preamp, just doit the old way, with dropping resistors.
Forget "it´s an SMPS", just think "DC power supply".

I like this idea. Seems simple. Its just a SE tube headphone amp that needs 160v and 6n3 tube tone board that needs 150v

I also have a dc boost converter and a dc step down converter coming in to experiment with. I have two independent 24v fan connectors on my amp board. I am hoping to use these two DC converter boards to get my 160v and 6.3v for both tube devices

Problem is that I just don't know enough to be confident of my choices

 

[JMFahey]

Ok, do you know (or can reasonably estimate) the consumption both of your Headphone amp and matching preamp?
If in doubt, post schematics.

 

[Randy Bassinga]

SIngle ended tube triode amplifier for hifi 6N5P 6N5C Headphone amplifier class A

I cannot locate a schematic for this. This is the 160v one

6N3 Preamplifier Circuit Board
I cannot locate a schematic for this. This is the 150v one. I also would like to find out how to increase gain on this one

6n3 tone board
The schematic below. This is the 250v one. I also would like to find out how to increase gain on this one

The amplifier chassis will have the headphone amp, 2x tone boards acting as live channel pres if they have enough gain or preamp into tone into headphone. Objective is enough gain for a bass guitar and mic with overload possibilities. I have a thread about these boards under tubes

 

[kodabmx]

This is one of those places where linear would be so easy: A 120V secondary makes ~150V after filtering and loading. Good for the 6N5S amp.
As far as "enough gain for a bass guitar and mic": trying to use hi-fi boards for instruments usually doesn't work well.
That said, you could use this 6N1/6N2 version with 6N2 tubes to get ~3x the gain as the 6N3 version. https://www.aliexpress.com/item/1005001814294297.html
Also, the tone stack should not have any gain overall - it should just have enough gain to match the insertion loses IMHO. There's a version of the above that uses the second triode as a buffer instead.
FWIW I've tried the tone board and found it to be quite bad. 500k pots are great at adding lots of hiss and picking up hum if you don't shield the board well.

 

[Randy Bassinga]

This is one of those places where linear would be so easy: A 120V secondary makes ~150V after filtering and loading. Good for the 6N5S amp.
As far as "enough gain for a bass guitar and mic": trying to use hi-fi boards for instruments usually doesn't work well.
That said, you could use this 6N1/6N2 version with 6N2 tubes to get ~3x the gain as the 6N3 version. https://www.aliexpress.com/item/1005001814294297.html
Also, the tone stack should not have any gain overall - it should just have enough gain to match the insertion loses IMHO. There's a version of the above that uses the second triode as a buffer instead.
FWIW I've tried the tone board and found it to be quite bad. 500k pots are great at adding lots of hiss and picking up hum if you don't shield the board well.

Hey man, thanks for the interest. I have a bit of an aversion to "ring cows". I am trying to stay away from traditional supplies if possible

I think those tone boards are all using the same schematic. That should allow me to check out some different tubes like the 6n2. I have a bunch of golden russion nos 5670s so thot to play with the 6n3 board first

The listing says 20x magnification for the 6n3 tone board. I want to try an experiment with cascading left channel into right with a pot and if some kind soul would identify which resistor to change for gain increase then I would be very grateful

Are the alps blue pots better at hiss?

Re using hi-fi boards, I have tried to play the bass through all sorts of amps, including tube amps and various effects units. Just doesn't blend in with a song playing back through the Hi-fi system. My experiments with removing the passive circuitry in the bass and feeding the pickups directly to solid state pres and eq then mixing into the stereo playback track live gives that perfect blend. The bass and mics fit right in. Only thing missing is a need I feel to round off the peaks on my thumb playing that only the big Ampegs can do. I want to experiment with a hi-fi tube pre to see if I can get that soft clipping thing happening straight from the pickups, then mixed back through the headphone amp into the stereo channel. The sub filter is going to be after the headphone amp. Does this make sense?

 

[Rick PA Stadel]

The tone board (the schematic in post #11) gain can be nominally bumped up by 6 to 10 dB by partially bypassing R7. It is not, according to that schematic, providing "20x magnification", whatever that is, unless you only count the extremes of the audio spectrum with tone pots maxed.

I think you're blurring the 'pre-amp' term -- a 'modern' hi-fi pre-amp may have as little as 4 to 10 dB of gain, DAC's, CD players, other line sources don't need more, A passive bass guitar may easily need 25 or 30 dB to drive a power amp to performance level; more if you want compression. A mic needs considerably more still. Cascading line-level amps will almost surely disappoint.

Maybe try looking up schematics for some of the more popular bass amps and check out what they're doing in the first 2 and 3 stages. It won't look ANYthing like what you're used to seeing in a 'Hi Fi preamp', whether there are tubes, FET's, MOSFET's, bipolar transistors, or op-amps.

The pot's manufacture has nothing to do with the hiss the circuit produces, no matter what 'they say'.

I have no idea what this means: ". . bit of an aversion to "ring cows". But I am old . . 😉

Cheers

 

[Randy Bassinga]

The tone board (the schematic in post #11) gain can be nominally bumped up by 6 to 10 dB by partially bypassing R7. It is not, according to that schematic, providing "20x magnification", whatever that is, unless you only count the extremes of the audio spectrum with tone pots maxed.

I think you're blurring the 'pre-amp' term -- a 'modern' hi-fi pre-amp may have as little as 4 to 10 dB of gain, DAC's, CD players, other line sources don't need more, A passive bass guitar may easily need 25 or 30 dB to drive a power amp to performance level; more if you want compression. A mic needs considerably more still. Cascading line-level amps will almost surely disappoint.

Maybe try looking up schematics for some of the more popular bass amps and check out what they're doing in the first 2 and 3 stages. It won't look ANYthing like what you're used to seeing in a 'Hi Fi preamp', whether there are tubes, FET's, MOSFET's, bipolar transistors, or op-amps.

The pot's manufacture has nothing to do with the hiss the circuit produces, no matter what 'they say'.

I have no idea what this means: ". . bit of an aversion to "ring cows". But I am old . . 😉

Cheers

Hey man, thanks for that. I am trying to learn. I tried to make my shopping list based on this

Reading Tube Amp Schematics

The tone board schematic seemed to reflect this to my uneducated eyes. The tone filter section also seemed reasonable. The 5670 tube also seems highly recommended as having better frequency response

Below is the other schematic I have been looking at for trying to find similar things in shopping

5670 (2C51) Bass preamplifier

Again, this one seems similar to the tone board. The cathode bypass (very grateful to you for pointing them out) are fitted. There is an extra pot for midrange

I had been hoping to find similar boards online and hopefully mod them to the performance of these two examples


I thot I was onto a good thing, didn't realise how far off I was! Thing is that the pre sections of ampeg and fender seem based on the same layout and the 12Axxx tubes are being called inferior to the 5670s on the Engel page.... I am a bit lost

 

[Rick PA Stadel]

Oh, oh, and for the most part, the B+ difference from 160V to 150V -- almost no valve gear would give a hoot about. The capacitors are most likely 200V or higher, and the tubes rarely care. Check the ratings of the relevant components carefully, confirm their adequacy, then light up those filaments, and don't look back . .

Well (just cruised your post from 56 minutes ago), everybody has a favorite valve! I'm personally hard-pressed to puzzle out why anyone would want a VHF valve to amplify bass guitar! But the Robinette site is otherwise excellent . . Please keep studying it.

Cheers

 

[Rick PA Stadel]

Oh, oh, oh 🙂oops🙂, and although it is common practice in the guitar/bass world, I do not recommend depending on the wiper of a gain or tone control to provide the grid bias reference point -- an additional 1 or 2 meg shunt to ground (or whatever the grid bias point is) can spare the user a lot of objectionable behavior when the club-smoke/crud-monsters queue up to ruin the gig.

Best Regards

 

[Randy Bassinga]

Rick, I wanted to thank you again personally

I started this thread as I wanted to find out if DC-DC boost and step down boards can be run off regulated connectors, e.g. the 2x 24v fan connectors on my class D amp board. Or can the DC-DC boards be run off a nice fat 24v switch mode power supply, I have the DC-DC boards and some power supplies on order and I have some fat 12v supplies on hand

I want to stay clear of "ring cows" in this project

Also, please allow me to draw your attention to the actual project thread here
Tube flavour for 5.1 dual-purpose system

Thanks man, really appreciate your input on this

 

[dkfan9]

I am still trying to figure out what a ring cow is

 

[Randy Bassinga]

I am still trying to figure out what a ring cow is

Hahahaha as did I after browsing thousands of tube descriptions - lost in translation, finally clicked “toro” cow and ring maybe dial……. Bloody transformer!!!

All the preamp tube descriptions contain “bile”, “bile duct”, “billary” and “gall bladder”

Haven’t decoded that one yet. But from now on, power transformers are “ring cows” for me!! What better name!

 

[Rick PA Stadel]

Certainly WAY lost in translation on me . .

And you're welcome -- happy to proffer something useful.

It'll take me quite a while to sift through the other thread -- the main project, it seems -- the first post alone is a full evening's work to study! 😱

Regards

 

[kodabmx]

Transformer and cow / cattle are the same word in Chinese... A "Ring Cow" is a toroidal transformer... Bile usually means tube... Fever means voltage from what I gather.