leadbreath
Well-known member
ian arent u using the eq with the 2 mid (hi/low) settings?
EZ Tube Mixer
- Thread starter ruffrecords
- Start date
Help Support GroupDIY Audio Forum:
Did you ever consider having onboard heater regulation?
Your prototype pic has a heatsink, but the layout doesn't seem to use one.
I think it would be handy to have local heater regulation where each pcb might use around 1A at 6.3V
Even a smaller footprint with thicker fins heatsink could be used and still allow for up to 5W or so dissipation, seeing as there is some vertical space available due to the height of the tubes.
Otherwise its a high dissipating centralised regulator per bucket ? or maybe just unregulated dc.
(Or AC ?, maybe elevated?). Could be 8A at 6.3V or so heater current for 6xchns + 2 sum chns
Your prototype pic has a heatsink, but the layout doesn't seem to use one.
I think it would be handy to have local heater regulation where each pcb might use around 1A at 6.3V
Even a smaller footprint with thicker fins heatsink could be used and still allow for up to 5W or so dissipation, seeing as there is some vertical space available due to the height of the tubes.
Otherwise its a high dissipating centralised regulator per bucket ? or maybe just unregulated dc.
(Or AC ?, maybe elevated?). Could be 8A at 6.3V or so heater current for 6xchns + 2 sum chns
ruffrecords
Well-known member
leadbreath said:
You mean the Poshmam? You can fit any passive EQ you like since it is separate from the amplifier PCB. You could do a poor man's EQP1 or the poshman if you wish. For this project though I am developing a version of the Helios Type 69 EQ which will be on a separate PCB. I am doing this because a) a prospective client has asked for it, b) it gives people a choice of EQ and c) I have already got the basis of the design from the Helios/Pultec demo rack I built.
Cheers
Ian
ruffrecords
Well-known member
alexc said:
Yes, I did and I have now decided against it as there is not really enough room on the PCB and the amount of heat to dissipate is too much. A heat sink that will fit will be no better than 10 degrees C per watt so a 5watt dissipation would cause a 50 degree rise, and it would be right close to a tube and one of the output capacitors. Incidentally, the heaters are wired for 12.6V (2 x 6922 in series plus a 12AX7). The nominal current draw is 0.45 amps and since 7 of these will fit is a sub rack that makes just over 3 amps per sub rack. I do plan to have a small per sub rack regulator based on a 5amp regulator chip fitted to a decent heatsink.
Cheers
Ian
ruffrecords
Well-known member
I am still waiting for the prototype channel amp PCBs to arrive - but that's another story. In the meantime I think I have completed the Helios type 69 EQ PCB design. The PCB is 125mm high and 74mm deep. It fits to the front panel below the channel amp. The frequencies chosen closely follow the original with an additional 400Hz and 16KHz on the mid boost/cut and 30Hz on the bass boost. I have used PCB mounting Grayhill Series 71 switches for the hi, mid and lo frequency selection. Of course you don't have to use these - you could use a regular panel mount switch and wire flying leads to the pads. Between them are two PCB mounted pots. If you do mount these pots on the PCB this means the legend becomes a little cramped unless you use very small knobs so it is probably better to mount them to the front panel a little further away on short flying leads (which is what the rough front panel layout I posted earlier assumes). The bass pot really needs to have an integral on off switch else you cannot reduce the bass boost to zero (this is in the original Helios design and is there for much the same reason the on/off switch is needed in the poor man's Pultec mid EQ). There's also pads for connection of the two switches required - one for EQ in/out and the other to select mid boost or cut (or peaks and trough as Helios called it). Again you can use any type you like attached by flying leads. As usual it uses a couple of readily available Carnhill inductors and I am sure Chrion will be happy to supply alternatives.
I will double check the layout over the next few days before sending off for prototypes. Pic of the PCB layout attached.
Cheers
Ian
I will double check the layout over the next few days before sending off for prototypes. Pic of the PCB layout attached.
Cheers
Ian
Attachments
leadbreath
Well-known member
shhwweeett....!
ruffrecords
Well-known member
mic pre PCBS arrived in the post today so guess what I'll be doing over the next few days!
Cheers
Ian
Cheers
Ian
djn111
Well-known member
Hi,
Looking forward to the results.
DJN
Looking forward to the results.
DJN
ruffrecords
Well-known member
Just a quick update to let you know the first prototype channel is built and so far seems to be working as intended. The phantom, phase, pad and mic line switches all appear to work as does the 12 position gain switch. I have finished the companion Helios Type 69 EQ PCB and sent off for some prototypes. When I placed this order I took the opportunity of ordering some more poor man's Pultec PCBs and some of the HT power supply PCBs because I still get occasional request for these.
I have also finished checking the 3 band Pultec EQ PCB (it is the same size and has switches in the same positions as the Helios) and found a couple of errors. As soon as I fix these I'll send that off for some prototypes too. This PCB basically holds a poor man's EQP1A plus the mid boost/cut mod on a single PCB so it should be a lot easier to build. It also allows you to build the hi boost as in the poor man's version or with an extra inductor as in the original.
Cheers
Ian
I have also finished checking the 3 band Pultec EQ PCB (it is the same size and has switches in the same positions as the Helios) and found a couple of errors. As soon as I fix these I'll send that off for some prototypes too. This PCB basically holds a poor man's EQP1A plus the mid boost/cut mod on a single PCB so it should be a lot easier to build. It also allows you to build the hi boost as in the poor man's version or with an extra inductor as in the original.
Cheers
Ian
djn111
Well-known member
Hi,
Excellent, looking forward to the results, any pictures of the test/progress ?
DJN
Excellent, looking forward to the results, any pictures of the test/progress ?
DJN
ruffrecords
Well-known member
rmaier
Well-known member
Yummy. I'd love to build a few of these as simple mic preamps. Looking forward to how this all comes together.
Ralph
Ralph
ruffrecords
Well-known member
rmaier said:
Yes, they would be ideal for that. The first amp and transformer together provide up to 60dB gain. You could then go to a fader and use the second amp with 10dB gain make up giving you up to 70dB total gain. I have also tested this amp with an external Carnhill output transformer VTB2291 wired as 2K4:600 and it will happily output +20dBu into a 600 ohm load. So you could just set the second amp gain to 16dB to drive this transformer and still have up to 70dB again overall.
Cheers
Ian
ruffrecords
Well-known member
I just wanted to ask a question about mic input transformers. At present the PCB is laid out for a Sowter mic transformer but I know these can be expensive by the time they reach distant parts. So I was thinking of maybe altering the layout so two different transformers could be used, say a Sowter or a Cinemag. I know the latter are popular and also reasonably priced. I would suggest a Lundahl as an alternative but their PCB versions have so many pins I think it would be impossible to track sensibly.
What do you think?
Cheers
Ian
What do you think?
Cheers
Ian
rmaier
Well-known member
It's a great idea. I ended up going with the Sowters for my Poshman build and they are a significant chunk of change, even before they cross the Atlantic. Cinemags would be a welcome option.
I feel a lightness in my pocketbook coming on...
Ralph
I feel a lightness in my pocketbook coming on...
Ralph
gemini86
Well-known member
ruffrecords said:
You might just give it a try with lundahls as well, my g951x layout includes the oep, cinemag and lundahl layouts and the traces are short, if you orient the transformers right.
ruffrecords
Well-known member
gemini86 said:
Can you send me a pic of how you track these?
Cheers
Ian
gemini86
Well-known member
If you need to, just swap polarity so the pins are where you want them, and routing makes more sense. Transformers don't really care if hot is cold so long as both primary and secondary are wired in correct phase to each other. (I know you're aware of that, just helping others that are lurking the forum)
