3nity
Well-known member
Good morning.
Im almost there with my single channel Solo.
I was wondering whats the rating for fuse?
Thanks.
Im almost there with my single channel Solo.
I was wondering whats the rating for fuse?
Thanks.
Feeler: Classic Solo
- Thread starter ruffrecords
- Start date
Help Support GroupDIY Audio Forum:
ruffrecords
Well-known member
The total mains power draw should be less than 20 watts so for 230V mains I would use a 100mA slow blow or for 115V mains use a 200mA slow blow.
Cheers
Ian
Cheers
Ian
3nity
Well-known member
Hello Ian.
Is there any changes to be done when running 12v heaters?
Is there any changes to be done when running 12v heaters?
ruffrecords
Well-known member
3nity
Well-known member
Hi Ian.
I have a V2 board.
Thanks
I have a V2 board.
Thanks
ruffrecords
Well-known member
OK, the V2 board allows either 6V or 12V heaters. For 12V heaters you need to link the two pads labelled 'B' and 'C' then connect your 12V supply to J9.
Cheers
Ian
Apr 6, 2023
My3gger said:
I have Edcor WSM 600:150 output transformer with the same ratio as 2400:600 used for Classic Solo, it was meant for SS project. Would inductance of 600:150 be way off compared to WSM 2400:600?
I mentioned somewhere this project was chosen for the local pro audio forum where younger members would like good tube preamp on a simple pcb. Suggested input OEP is quite cheap in the EU, output transformer is bigger problem because order from UK will almost certainly cost more than 135 pounds with customs and shipping. Before posting i would like to find something local that works well to high enough levels.
My3gger said:
I have Edcor WSM 600:150 output transformer with the same ratio as 2400:600 used for Classic Solo, it was meant for SS project. Would inductance of 600:150 be way off compared to WSM 2400:600?
Hello. As expected Edcor 600:150 didn't work well. CM9661 was wired for 3,5:1 with 10C at the input sounding great as a prototype made into some Ampex rack with lots of tube sockets on a pcb having many traces cut.
I mentioned somewhere this project was chosen for the local pro audio forum where younger members would like good tube preamp on a simple pcb. Suggested input OEP is quite cheap in the EU, output transformer is bigger problem because order from UK will almost certainly cost more than 135 pounds with customs and shipping. Before posting i would like to find something local that works well to high enough levels.
ruffrecords
Well-known member
OEP has be owned by Carnhill for quite sometime so if you can buy OEP in the EU you ought to be able to by the Carnhill VTB2291 output transformer - but the world of customs and imports is a strange one.
For the Mark 3 mixer I have been looking for smaller output transformers to fit inside a 35mm wide module but with good performance. I have worked closely with Chris at OEP back in 2020. I tried one of their K30A11C transformers which is a 2K4:600 ratio and it performed quite well. Chris offered to make a custom versions with increased turns and and various cores which I tested. The best from my point of view was an M6 cored version. I am sure if you ask chris he will be happy to help. I don't want to publish his email so PM me if you want it.
Cheers
Ian
Several months ago Farnell EU had 1:10 OEP transformers used by you, almost for sure no Carnhill models because i would see them when searching for input signal transformers. Buying locally is very important because we reduce CO2 releases by avoiding shipping small packages separately, prices are lower too. We could try UTM transformers who do custom orders at low enough prices.
Discussion we had about steel and nickel cores was very interesting. Beside Cinemag paper, Whitlock's chapter about transformers from Handbook for Sound Engineers does great job at explaining differences between steel, low nickel and high nickel. Big 50Ni or 80Ni nickel output cores do have lower distortion, our tests showed mid bass can be better in some ways even if core is smaller but not be too small. Many old transformers have also have high nickel content, i think hipermalloy used in UTC HA series is some kind of mumetal. CM-9661 can do better than 24dBu which is the limit of AP, it sounds better than most other models i tried, although cost is very very high. Here are two papers:
https://www.jensen-transformers.com/wp-content/uploads/2014/08/Audio-Transformers-Chapter.pdfhttps://cinemag.biz/application_notes/PDF/AN-104.pdfI have troubles finding usable datasheets for modern tube gear, most of them don't tell anything useful about distortion because they don't state frequency, source impedance, etc. D.W. Fearn only says 22dBm for VT1/2 without giving more data, i recall output was Ni JT-11 series 1:1.
Can you estimate distortion of Classic Solo (E88CC version) compared to other good tube designs? Thanks.
ruffrecords
Well-known member
UTM would be a good choice. From what I have seen they make good transformers and are very easy people to deal with.
The Classic Solo was derived from my very first tube mic pre which used a 6CG7 tube arranged as a mu follower. This gave the lowest distortion but its drive capability was limited. Typical THD was about 0.3% at +26dBu into a 10K load. The distortion was primarily second harmonic with the 3rd harmonic being about 20dB lower. So the Classic Solo changed the tube to a 6922 which raised the output drive capability but also increased the distortion. To reduce the distortion to levels comparable to the orignal 6CG7 the 6922 idle current was increased. From memory the Classic solo will output +20dBu into a 600 ohm load with 0.3% distortion or less.
In both the 6CG7 and 6922, the distortion is directly proportional to output level so at 0dBu the Classic Solo distortion should be around 0.03% into a 600 ohm load at any frequency in the audio range.
Cheers
Ian
The Classic Solo was derived from my very first tube mic pre which used a 6CG7 tube arranged as a mu follower. This gave the lowest distortion but its drive capability was limited. Typical THD was about 0.3% at +26dBu into a 10K load. The distortion was primarily second harmonic with the 3rd harmonic being about 20dB lower. So the Classic Solo changed the tube to a 6922 which raised the output drive capability but also increased the distortion. To reduce the distortion to levels comparable to the orignal 6CG7 the 6922 idle current was increased. From memory the Classic solo will output +20dBu into a 600 ohm load with 0.3% distortion or less.
In both the 6CG7 and 6922, the distortion is directly proportional to output level so at 0dBu the Classic Solo distortion should be around 0.03% into a 600 ohm load at any frequency in the audio range.
Cheers
Ian
3nity
Well-known member
Afternoon. So I turned the pre ON today and no sound at all just hum. I bought the PCB already stuffed. My question is the Sowter 9148c has 3 pins in the primarys or 2.. ?
3nity
Well-known member
Tested DI and it sounds great.
Definitely something wrong with transformer.
The way is soldered to board is 2 pins on primary and 3 at secondary.
Definitely something wrong with transformer.
The way is soldered to board is 2 pins on primary and 3 at secondary.
ruffrecords
Well-known member
I am not familiar with the Sowter 9148. Do you have data for it? It does not appear on Sowter's website.
Cheers
Ian
Cheers
Ian
3nity
Well-known member
Sorry Ian typo 1948c
ruffrecords
Well-known member
OK, if memory serves the 1948C is the custom version of the the old Helios 1:10 microphone transformer without the 1:1 tap that Brian Sowter designed for me.
This transformer has only two connections to the primary and two to the secondary. The transformer should have 6 pins in total.
Pin 1 is primary cold
Pin 2 is not connected
Pin 3 is primary hot
Pin 4 is secondary cold (connect to 0V)
Pin 5 is internal screens (connect to 0V)
Pin 6 is secondary hot.
Pin 1 is usually denoted by a dot on the can.
Cheers
Ian
3nity
Well-known member
Thanks for the answer Ian. The one I have only has 5 pins. 2 pins were soldered to primary and 3 to secondary..not sure if it's the correct way to do it.
3nity
Well-known member
This is what i calculated by the voltage drop across HT filters. Does 300V HT drop further 20V because of 30mA at 240VAC power tx? I'm asking this because my typical toroid for ~20mA/300V HT would be 50mA at 240V or so with almost no drop. Maybe i'm using stabilized or regulated supplies for too long to remember drops with passive supply.
Classic Solo project at the local forum is going well, we will have a lot of fun testing quite big collection of signal transformers, E88CC's, SRPP on the output, etc. Thanks
ruffrecords
Well-known member
There are three things that determine the voltage drop in a simple RC smoothed supply. First there is the regulation of the transformer, which is essentially the dc resistance of its secondary winding. Then there are the series resistors in the RC filter and lastly there is the load.. Variations in any of these will affect the actual voltage drop and hence the actual HT voltage seen by the amplifier. Fortunately, simple class A tube amplifiers like the Classic Solo are very tolerant of HT supply. Anything from 250V to about 340V will be fine.
Cheers
ian
Cheers
ian
3nity
Well-known member
So I'm finally done with my single channel preamp..
I used decor output transformer and a chinese case I found on eBay Wich is not a 19" but more like 17".
Front panel I use letter punch, Wich works ok if you know how to use it right..then I filled with white paint.
I need to thank Pucho812 who gently offered me the tubes out of a good heart..once again thank you my friend!
Ian thanks for this great project.
I used decor output transformer and a chinese case I found on eBay Wich is not a 19" but more like 17".
Front panel I use letter punch, Wich works ok if you know how to use it right..then I filled with white paint.
I need to thank Pucho812 who gently offered me the tubes out of a good heart..once again thank you my friend!
Ian thanks for this great project.
