Feeler: Classic Solo

I got the boards and I'm placing the mouser order but there are a few parts I'm doubtful on because of XY reasons.

1. The manual didn't make it very clear although the schematic did but trying to make sure. The switches for the daughter board are DPDT ON-NONE-ON (ON-ON) 2.54mm PCB switches like these?
http://www.mouser.com/Search/ProductDetail.aspx?R=108-2MD1T2B3M2QE-EVXvirtualkey12040000virtualkey108-2MD1T2B3M2QE-EVX

2. The manual made it clear that the HPF was a SPST switch but not the variety. It seems like it should be an ON-OFF-ON but just to be sure. Like the following?
http://www.mouser.com/Search/ProductDetail.aspx?R=2M1-SP3-T1-B1-M1QEvirtualkey69100000virtualkey691-2M1-SP3-T1B1M1QE

3. I will be building a dual unit but I will be building out all the parts on each of the boards (HT and phantom). The manual suggests I should install the CHT cap. Is this correct?

4. Mouser didn't carry the 1000PIV rectifier specified in the manual. Is this one a good replacement?
http://www.mouser.com/Search/ProductDetail.aspx?R=DB107-BPvirtualkey54720000virtualkey833-DB107-BP

Thanks,
Alain

ding said:

I got the boards and I'm placing the mouser order but there are a few parts I'm doubtful on because of XY reasons.

1. The manual didn't make it very clear although the schematic did but trying to make sure. The switches for the daughter board are DPDT ON-NONE-ON (ON-ON) 2.54mm PCB switches like these?
http://www.mouser.com/Search/ProductDetail.aspx?R=108-2MD1T2B3M2QE-EVXvirtualkey12040000virtualkey108-2MD1T2B3M2QE-EVX

Click to expand...

It is definitely a DPDT type. It is important to get the right model as the pins fit right onto the PCB. It is easy to get the wrong sized ones. You are right, the 4toggle documentation is a little lacking. I will fix that starting with finding the Farnell number for the actual switches I use.

2. The manual made it clear that the HPF was a SPST switch but not the variety. It seems like it should be an ON-OFF-ON but just to be sure. Like the following?
http://www.mouser.com/Search/ProductDetail.aspx?R=2M1-SP3-T1-B1-M1QEvirtualkey69100000virtualkey691-2M1-SP3-T1B1M1QE

Click to expand...

Yes, it needs to be a SPST with a centre off position ON-OFF-ON

3. I will be building a dual unit but I will be building out all the parts on each of the boards (HT and phantom). The manual suggests I should install the CHT cap. Is this correct?

Click to expand...

CHT prevents instability if several amps are powered from a single HT supply. If you are powering each unit from its internal HT supply then you do not need CHT.

4. Mouser didn't carry the 1000PIV rectifier specified in the
manual. Is this one a good replacement?
http://www.mouser.com/Search/ProductDetail.aspx?R=DB107-BPvirtualkey54720000virtualkey833-DB107-BP

Thanks,
Alain

Click to expand...

That mouser bridge rectifier should be fine.

Cheers

Ian

OK, I checked my current switch stock and fortunately I had kept a pack of the 4toggles board switches in the original Farnell package. The Farnell part number is 9473068 which is a:

MULTICOMP 2MD1T1B5M2RE  Toggle Switch, 2MD Series, DPDT, On-On, Through Hole, 100 mA, 20 V

It's datasheet is here:

http://www.farnell.com/datasheets/1375607.pdf

which unfortunately appears to be inaccurate. It shows the pin size as 0.5mm by 1.52mm but  they are in fact 0.5mm by 0.8mm and the PCB hole size is designed for that latter size. The data sheet also shows the spacing between rows as 4.08mm when in fact it is 5mm.

So, looking at the datasheet of the one you linked to it seems to me to be OK:

http://www.mouser.com/Search/ProductDetail.aspx?R=108-2MD1T2B3M2QE-EVXvirtualkey12040000virtualkey108-2MD1T2B3M2QE-EVX

I will add this info to the documentation.

Cheers

Ian

and this one from Digikey:

http://www.digikey.ca/product-detail/en/200MDP1T1B1M2QEH/EG2456-ND/378925

Deepdark said:

and this one from Digikey:

http://www.digikey.ca/product-detail/en/200MDP1T1B1M2QEH/EG2456-ND/378925

Click to expand...

I can confirm that the data sheet of this one also seems to be the same as the ones I use. I will list all three in the documentation. Thanks guys.

Cheers

Ian

Hi,
Just wanted to mention that the classic solo works great. I still have to sort out the transformer wiring (I've got a telefunken 1:10) and put it into the enclosure. I did some primary tests with my bass guitar and it really sounds great. I love the smooth sound of the E88CC. It's much less gritty than 12ax7 type tubes. Thanks a lot Ian for this great preamp!!!
Cheers
Berne

I am pleased you like the sound. When the project is complete, perhaps you would send me some pics so I can get Pierre to add them to his gallery of example projects made from my designs.

Cheers

Ian

Yes, of course I can send you some pictures, but the frontpanel design will be a bit ghetto style  with transparency foil or stickers.  I still haven't  decided yet if it's going to be a dual DI box or a single mic preamp with DI  input. I've stuffed the 48V part as well and bought an additional 2x24V transformer. Well, let's see whether it fits into the box.
Bernd

So I'm almost done. After testing various configurations I've finally decided to make a double DI box out of it.  It sounds extremely clean with a gentle but typical tube patina. It's impossible to get some distortion from the tubes when feeding it with electric guitar or bass. I tested it with a quite hot line signal from my Synthesizer and then of cause distortion gets audible. Absolutely cool, and in stereo!
But do we want that? I don't think so,  we have the Rude Tube for that. The versatility of the preamp is really stunning.  While waiting for some transparency foil I'm working on a frontpanel design. I'm going to post pictures here soon and send them to you, Ian. Ah, almost forgot. I need to power the Jewel light somehow. It works with 5-12 VAC (LED type). Can I take it from the 6,3V heater secondary although it's elevated?
Cheers
Bernd

I am making a preamp with DI and I am thinking of putting a floating Bridged-T attenuator on the output to try and get a little more grit out of the DI but if you say the DI and fully cranked drive doesn't get that hot than maybe I shouldn't bother. I guess I will try it and report. Not to expensive to buy a lorlin and some resistors. I was planing on a 0, -5, -10, -15, -20, -30 db attenuation between the output transformer and the XLR.

bernbrue said:

I need to power the Jewel light somehow. It works with 5-12 VAC (LED type). Can I take it from the 6,3V heater secondary although it's elevated?
Cheers
Bernd

Click to expand...

Yes, that should work fine. Just make sure you don'y accidentally connect one side to 0V.

Cheers

Ian

ding said:

I am making a preamp with DI and I am thinking of putting a floating Bridged-T attenuator on the output to try and get a little more grit out of the DI but if you say the DI and fully cranked drive doesn't get that hot than maybe I shouldn't bother. I guess I will try it and report. Not to expensive to buy a lorlin and some resistors. I was planing on a 0, -5, -10, -15, -20, -30 db attenuation between the output transformer and the XLR.

Click to expand...

If you build the preamp/DI with the two stages cascaded then in DI mode there will usually be plenty of gain to drive the output stage very hard. I built a version for ribbon mics with a DI input. I fitted an attenuator on the output but even with 20dB attenuation the output was too hot for the following amplifier so I think you range of 0 to 30dB is about right.

Cheers

in

Should I then skip the -5 and -15 and do a 0, -10, -20, -25, -30, -35 instead?

ding said:

Should I then skip the -5 and -15 and do a 0, -10, -20, -25, -30, -35 instead?

Click to expand...

You can dial in different tones by varying the the 10K log gain pot and tweaking the output pot to set the right output level. I think 30dB is about the right range for these two to operate over to obtain a useful set of tones but I am not sure of the best way to split up this range. Distortion will be directly proportional to output level so a 6dB gain change will double the distortion so you could for example just split the 30dB into equal 6dB steps 0-6-12-18-24-30. Also, different instruments will have different signal levels so the control settings for the tone you want will depend on that too. I think you need to experiment to see what works best. On mine I am going to fit one of AVRs T-pad pots when they arrive.

Cheers

Ian

How much gain reduction with one of AVR's pots? That sounds much simpler than wiring up a bunch of resistors with a bit more fine control.

ding said:

How much gain reduction with one of AVR's pots? That sounds much simpler than wiring up a bunch of resistors with a bit more fine control.

Click to expand...

As designed it is just like a regular pot but designed for a balanced signal so the ultimate attenuation will be nearly infinite. The mid point of the pot should be close to 20dB. You can limit the maximum attenuation by the addition of a series resistor or two so you can set its range to 0 to 30dB if you want.

Cheers

Ian

I'm trying to figure out what fuse to get for this thing. I imagine it would be slo blo but would a .6A do it?

ding said:

I'm trying to figure out what fuse to get for this thing. I imagine it would be slo blo but would a .6A do it?

Click to expand...

The mains transformer I use is rated at 15VA wich is about  130mA at 115V. Inrush current will be at least twice this, say 300mA maximum.  so I think a 0.5A would be about right.

Cheers

Ian

Yeah, I guess I'm missing some vital info. I would be using a 50va 240v transformer for HT and a 25va 25-25 transformer for phantom.  I'm also going to have 2 boards feeding from the same toroid. Should I divide and then add. I guess I'm confused about it since I would be using 2 transformers. Speaking of that is there any news on the power transformer front from your side of the pond?

ding said:

Yeah, I guess I'm missing some vital info. I would be using a 50va 240v transformer for HT and a 25va 25-25 transformer for phantom.  I'm also going to have 2 boards feeding from the same toroid. Should I divide and then add.

Click to expand...

As a rule, you should design the fuse based on the expected load. The transformers clearly need to be able to provide this load but, even if bigger than needed transformers are used, the fuse size should be the same. For two channels the required VA is 30 which draws 260mA. Double this to allow for inrush and you reach just over 0.5A so your suggested 0.6A should be just about right.

I guess I'm confused about it since I would be using 2 transformers. Speaking of that is there any news on the power transformer front from your side of the pond?

Click to expand...

I have had the quote for 10 transformers sitting in my inbox for a few weeks. I have not done anything about it because there did not seem to be a lot of interest in it. If people are still interested in this I will get them to confirm the total pric to me incluing tax and shipping and let you all know. I am happy to pass these on at cost.

Cheers

Ian