Feeler: Classic Solo

[ruffrecords]

Ian,  I have been collecting parts for my Duo build,  and I am looking at transformers and I came across this from antek.

I am just wondering if using this would allow me to power both boards and fit all components as originally intended in a solo.

If it's pointless and overkill,  then I'll wire it the way you describe in the duo build sheets,  but if this would for some reason work better then I'll use this.  It's just 7 dollars more than the antek 240. It has two separate 250 windings for both HT and two separate heater windings. 

It's 100va 250v

It is a pity it has such a high power rating because the separate windings are exactly what you need. My concern is that the heater windings are each rated for 3 amps. This means that when they are loaded with 3 amps, the voltage will be 6.3 volts. If you load it more lightly, with the 0.6 amps of the solo, then the voltage will be higher and this could reduce the life of the tubes.  To prevent this you could add a small value series resistor to drop the volts. If the regulation of the transformer is 10% (typical for its size) then the no load 6.3V output will be 10% higher or about 7V. So we need to drop abput 0.7 volts at 0.6 amps so we need a resistor of 1.16 ohms. Since we do have a load the voltage will be a bit less than this so I would try a 1 ohm resistor to start. It carries 0.6 amps so its power dissipation will be 0.6W so I would advise using a 5W rated resistor. The HT cicuit is much more tolerant of voltage variations so that will be fine despite the low loading.

Cheers

Ian

 

[ruffrecords]

Alexandru Marian has pointed out an error in the Classic Solo Lo Hum documentation. Where I talk about changing each stage from a mu follower to an SRPP stage I omitted to mention shorting out R8 and R18. I have corrected this in the new 0.2 version of the build document that I have now uploaded to my web site. It is in the Classic Solo folder of the DIY tab:

http://www.customtubeconsoles.com/diy

Cheers

Ian

 

[Johnblue]

Ian, i think i have finally received some tube pins that were holding me back from populating the board! I haven't opened the package yet, but they were delivered to my bench (took FOREVER from china) . i'm really pumped up to get started, and I'll need all the help i can get. It will be my first official GroupDIY build, so i'm going to take it easy and try to post as many pics as possible.  The next day i get to sit and solder, i'm going to lay everything out and check inventory andthen add  all the pins, jumpers and resistors and start with the smallest stuff as suggested.

i'll order the power supply now as well.

 

[ruffrecords]

Looking forward to the pics.


Cheers

Ian

 

[Tubetec]

Hi Ruff ,
That looks good . Ive done up a few tube based pre/output stages ,and Ive always had better results housing the psu in a seperate box ,and keeping it  at least a few feet away from the amp .Below you'll see my EL84(triode connected) based output stage ,I used a Sowter 9705 10k:600 ohm .gives about 15 db gain ,and coupled to a Zutt /trident 600 to 25 kohm input transformer ,gives me upto about +20 dbu from my modded Behringer B2 tube mic with vocal source .I went old school on the psu ,using an old philips radio mains transformer ,with an ez80,five stages of ht smoothing ,including two resistive and three chokes and regulated 6.3volt rail.Psu noise hardly contributes anything to overall noise ,and any noise that does remain is inductively coupled ,this can be minimised by orrientating the unit for minimum pick up of external fields. The psu is big and weighs about 14 lbs and theres a couple of thousand Uf's of capacitance in it ,but it all works to  give a very gracious overload charachteristic ,almost pure 2nd harmonic.
Keep up the good work!

 

[ruffrecords]

Hi Ruff ,
That looks good . Ive done up a few tube based pre/output stages ,and Ive always had better results housing the psu in a seperate box ,and keeping it  at least a few feet away from the amp .

I agree 110%. for ultimate performance there is no substitute for  a remote PDU and DC heaters. But people keep asking me for stand alone designs.

Cheers

Ian

 

[Tubetec]

Hi Ian,
Thanks for the reply,yeah theres no doubt for convienence the one box wonder works out alot more economical and simple, reduces the need for umbilical cords and pricey multipin connectors too .
Cheers and all the best,

 

[ruffrecords]

I was recently asked to design a 12 way switched 10K pot to replace the regular gain pot between stages in the Classic. I have done this and documented it in the Classic Solo folder of the DIY tab of my web site:

http://www.customtubeconsoles.com/diy

The file is called  12Position3dBStepped10KPot.pdf or you can just download it direct here:

https://docs.google.com/document/d/1qhxmOIv3TBSSA-CeHK_q_7YquevKr1hxia8AGCTqnc8/edit?usp=sharing

The design is a stepped attenuator of twelve 3dB steps from 0dB to 33dB of attenuation. In combination with the 20dB pad switch this gives you an overall gain range of from 17dB to 70dB in 3dB steps.

Cheers

Ian

 

[Johnblue]

just for clarification...

one pole 12 position rotary switch ?  and can you suggest a voltage and current rating for the classic solo?

 

[ruffrecords]

just for clarification...

one pole 12 position rotary switch ?  and can you suggest a voltage and current rating for the classic solo?

Almost any rotary switch will be rated well enough. I had in mind one of the low cost Lorlin types or the more expensive Grayhill 71 series. Any switch rated at least 50V should be fine. The maximum expected current is no more than 3mA (30V rms into 10K)

Cheers

Ian

 

[DerEber]

Hey Ian,

I have the Classic Solo V2 PCB's without the low hum alteration.
I am now questioning myselfe, if I should use DC Heaters ?
I am not super sensitive for hum. So my plan was now to just go for AC.
8)

all the best,
Stephan

 

[ruffrecords]

Hey Ian,

I have the Classic Solo V2 PCB's without the low hum alteration.
I am now questioning myselfe, if I should use DC Heaters ?
I am not super sensitive for hum. So my plan was now to just go for AC.
8)

all the best,
Stephan

Under normal conditions the hum will be completely inaudible. Even in unusual situations where you need all 70dB of gain the design can offer, the hum will easily be swamped by acoustic noise from the mic (unless you are trying to record a fly fart in an anechoic chamber with a ribbon mic).

Cheers

Ian

 

[DerEber]

Thanks Ian!

 

[kambo]

what was the THD at 20dbu/600ohm out on Classic!

edit: found the docs.


edit: one down, 3 to go, but i need to order some resistors, those made up values not looking good...

 

[kambo]

hey Ian, ur Mu Followers are freaking ROCKING  ;D i forgot how good they were.
especially in ur mu follower distortion notes, 6SN7 8mA version, is the best of all to me...
edit: i think i like sound of 6SN7 compared to 6092.
600ohm load is a breeze at 20dbu, which i have anyway!

will make 12-15mAmp versions just to experiment/play!

thanks
and
cheers !

 

[ruffrecords]

HI Kambo, glad you like them. The 6922 has a lot lower plate resistance than the 6092 so I suspect that explains why the 6922 sounds better. 6SN7 definitely has the lowest intrinsic distortion of just about any tube which is why it makes a good mu stage. Just watch the plate dissipation if you raise the quiescent current.

Cheers

Ian

 

[kambo]

HI Kambo, glad you like them. The 6922 has a lot lower plate resistance than the 6092 so I suspect that explains why the 6922 sounds better. 6SN7 definitely has the lowest intrinsic distortion of just about any tube which is why it makes a good mu stage. Just watch the plate dissipation if you raise the quiescent current.

Cheers

Ian

oh, 6922 sounding very FAT, bad a$$,
slightly on the darker side compared to 6SN7, but no complaint  ;D

 

[kambo]

if i change 2*Mu to 2*SRPP to keep the part numbers down,
am i still using  10K pot for the gain ?

and also,  can i use use a 10k:10k trx as insert point, unbalanced send, balanced return,
in between the two stages?

 

[ruffrecords]

if i change 2*Mu to 2*SRPP to keep the part numbers down,
am i still using  10K pot for the gain ?

Yes, 10K is still fine. SRPP will drive just as good as Mu but at lower current. SRPP distortion is always higher than Mu Follower.

and also,  can i use use a 10k:10k trx as insert point, unbalanced send, balanced return,
in between the two stages?

Yes, 10K:10K transformer on insert return will be fine.

Cheers

Ian

 

[kambo]

nice, thank you
i love the SRPP for its simplicity, and lo part count, and sounds really good,
but, i hate the way SRPP distorts.. never liked it,  not even once! (personal choice i guess)
thinking/working on 8/16 Ian based micpre/line mixer for a project will come in later this year!