Slow Blow pre?

[Kingston]

Well, relatively cheap anyway, since they're of very high quality. I don't have too much choice when it comes to transformers around here so I'm glad they supply at least these. :grin:

 

[sismofyt]

[quote author="FotisGR"]... with 230V or 110V primary. The price for 80VA toroid multivaltage (230VAC , 48VAC and 12VAC) will be 35Euros and the shipping cost for europe is about 10-15 euros.
The chokes are 10H/150mA - 65Ohm toroid and the price is 25 Euros each. I think that are good news[/quote]

great fotis. these are really good prices. shipping too. i don't think it's neccesary to look anywhere else

 

[sismofyt]

[quote author="Kingston"]If I may suggest,

Welter makes cheap but very high quality transformers for us europeans at least.

Have a look at this site. I'm sure there are others as well.

http://rpm.fi/[/quote]

looks nice, but too expensive. i can get toroids custom done in denmark, ship them to you and they'll still be cheaper than what rpm.fi can offer

 

[Kingston]

haha. ok, quite expensive then. :razz:

 

[Flatpicker]

[quote author="sismofyt"]...great fotis. these are really good prices. shipping too. i don't think it's neccesary to look anywhere else[/quote]
For us in the US that's roughly $130 for a two channel version, which is very do-able. This is cool! :thumb:

 

[Flatpicker]

[quote author="FotisGR"]...These are what i use on the pictures of my project except the power trannie that is 150VA version (45Euros)...[/quote]
Speaking of layouts, what is the PCB in that photo? PSU? (I may have missed this in a previous post, so sorry if I did.)

 

[DaxLiniere]

I really like the idea of a PCB for the PSU. PtP seems perfect for the rest though.

 

[Bluzzi]

fotis,

80va is ok for 2 channel preamp?
Also in the picture we see 3 transformers. Is this another build?

The transformer and choke prices are good. I think we should also encourage your cousin (maybe he'll start to make nice audio transformers too, hint..hint).


Maybe we could start to gather some orders for fotis to get them done in one shot. I'll be first to commit to 1 with 110 primary now.


jim

 

[DaxLiniere]

Aren't the other two toroids the chokes?

 

[Bluzzi]

Really? I didn't imagine the chokes being that huge! I figured 1 was the 230v, the other 2 for the 12v and the 48v. (hey I don't even know what chokes do yet).

What about VU meters? I have quite a few of those and would love to put 2 on my pre. We would need a buffer stage right?

jim

 

[DaxLiniere]

Not essential, but VERY highly recommended.
Do a little search of the forum for a post that I contributed to that had VU somewhere in the title.

NB: The 3k6 series resistor is IMPERATIVE!

 

[flaheu]

Hi there,

It's now a while that i follow the progress of the slowblow, and i will build it for sure.
I would like to know what's the difference of gain between the 5687 and 12sn7 version, because i need 72 dB for my ribbon mics.
I'ts not excluded to put a 150:600 Ohm 1:2 transformer at the output.

Is the 12sn7 version OK for a marvellous general purpose preamp ?

Thanxs
[/list]

 

[sismofyt]

[quote author="DaxLiniere"]I really like the idea of a PCB for the PSU. PtP seems perfect for the rest though.[/quote]

i don't. usually, people have used huge caps with screw terminals for the B+. those don't like pcbs. for the P48 maybe... i think there are several TLC783 layouts floating around here. the heater psu is nicely done with P2P too. currents are high(ish) and the Vreg needs a nice big heatsink

 

[sismofyt]

[quote author="Bluzzi"]fotis,

80va is ok for 2 channel preamp?
Also in the picture we see 3 transformers. Is this another build?

The transformer and choke prices are good. I think we should also encourage your cousin (maybe he'll start to make nice audio transformers too, hint..hint).


Maybe we could start to gather some orders for fotis to get them done in one shot. I'll be first to commit to 1 with 110 primary now.


jim[/quote]

80VA is fine for two channels. it should be made with dual 115VAC (it's not 110 & 220VAC anymore - it's been up'ed for years) primaries, so only one transformer is needed for all of you

 

[sismofyt]

[quote author="Bluzzi"]Really? I didn't imagine the chokes being that huge! I figured 1 was the 230v, the other 2 for the 12v and the 48v. (hey I don't even know what chokes do yet).

What about VU meters? I have quite a few of those and would love to put 2 on my pre. We would need a buffer stage right?

jim[/quote]

yes, fotis used dual chokes. you can attach any _real_ VU meter at the output. if you want it buffered you need to come up with your own solution. anyway, the pre has more headroom than anything after it, so it would be much better to watch levels on your DAW/tapemachine

 

[sismofyt]

[quote author="flaheu"]Hi there,

It's now a while that i follow the progress of the slowblow, and i will build it for sure.
I would like to know what's the difference of gain between the 5687 and 12sn7 version, because i need 72 dB for my ribbon mics.
I'ts not excluded to put a 150:600 Ohm 1:2 transformer at the output.

Is the 12sn7 version OK for a marvellous general purpose preamp ?

Thanxs
[/list][/quote]

the octal version (12SN7 / 6J5) have a little higher gain, about 6dB (with a cathode bypass cap). the overall gain will depend on the input trannie of course... figure around 55dB with a 1:5-7

if you need higher gain, i'd recommend doubling the input tube section. you can use a 12SN7 for each channel. that will give you 75dB. you can use a higher ratio input trannie, like the the Altec / Peerless 4722. that is a fine piece of kit and will up the the total gain to about 80dB

you can use a 1:2 or even 1:4 output trannie _if_ you're connecting the pre to a high (10k minimum) input impedance. such a high quality / high level output trannie is expensive though. much more than using a dual input tube. will sound different as well ..

the octal version have a little higher 2nd order distortion and sounds a bit more 'euphonic'

 

[DaxLiniere]

Sismofyt,
I know I've asked this question once already on this thread, but I didn't get a decisive response.
I restate: I know nothing about trafo suitability, hence my question.

What can you tell me about the suitability of this transformer? I have 4 of them and know where more might be available if anyone else is interested.
It's very heavy, another PP member suggested it probably has "a lot of lovely, expensive mu-metal inside."

How would I hook up the secondaries? Series? Parallel? Which way delivers 600r? Maybe do something crazy like hook one of the secondaries to a variable resistor (closed loop)? Or should I just smoke more crack?

Thanks.

How's the virgin-blood collection going?

 

[sismofyt]

[quote author="DaxLiniere"]Sismofyt,
I know I've asked this question once already on this thread, but I didn't get a decisive response.
I restate: I know nothing about trafo suitability, hence my question.

What can you tell me about the suitability of this transformer? I have 4 of them and know where more might be available if anyone else is interested.
It's very heavy, another PP member suggested it probably has "a lot of lovely, expensive mu-metal inside."

How would I hook up the secondaries? Series? Parallel? Which way delivers 600r? Maybe do something crazy like hook one of the secondaries to a variable resistor (closed loop)? Or should I just smoke more crack?

Thanks.

How's the virgin-blood collection going?[/quote]

transformers, virgin blood and crack. you sure got your priorities straight :wink:

pic aint working, btw

 

[sismofyt]

ok, i can see it now. you got to measure the ratio first, i wouldn't count on that 20-600 ohm. if it's in the 1:3-12 range, i'd connect a suitable resistor on the primary, most likely on 5 to 8 (connect 6 & 7) .. something in the 50kohm range .. and connect a tonegenerator (with less than 600 ohm output Z) and do a sweep. only then will you know it's usable. if it's ok, then sweep it with a scope to see if it's ringing ..

they might be cool

 

[sismofyt]

remember to connect the electrostatic shields, (pin 3) to ground / chassis

if the 20 to 600 ohm is true, then it has 1:5,5 ratio, but the "20 ohm" might just be optimal source impedance and the "600 ohm" optimal load impedance. fuck around with a multimeter, tone generator and some resistors and report back

tamura is extremely good iron