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Batman  HeadWizer Joined: May 12, 2003 |  Message [#280] posted on: 12-13-2005 01:31 PM CST (US).   |  |  We'll all be waiting for the comparison between your Millett and the SOHA.  |
Blooze HeadWizer Joined: Jun. 28, 2005 | Message [#281] posted on: 12-13-2005 01:45 PM CST (US). | | I can't wait to hear the difference, too! I don't have, nor or planning to, add the diamond buffers into the Millett. It seems to me that if I wanted an amp to sound \"as good as an M3\", I would have built a completely solid state amp to begin with. I like the different sound with the tubes and that seems to be the point of a tube amp to begin with IMO. I guess I just don't get it. Edit: But I think I will order a couple of boards in case they end up working in other designs. [Edited by Blooze on 12-13-2005 at 05:21 PM.] |
| Steve Culton HeadWizer Joined: N/A | Message [#282] posted on: 12-13-2005 03:11 PM CST (US). | | Having heard the Millet a few times, I'll be interested in the impressions as well. |
mains_hum HeadWize Fanatic Joined: Aug. 19, 2003 | Message [#283] posted on: 12-13-2005 03:17 PM CST (US). | | The original "Stoopid" uses resistors to derive the heater volts. It works fine, but it's not very efficient. We realised that we can halve the loss by changing the circuit slightly. However, this didn't address the issue that each valve is unique so the dropper resistors have to be chosen to suit. So the power resistors have been discarded and replaced by a LM337 with heatsink. Does this idea work ? Watch this space. |
| Guitarsenal HeadWize Fanatic Joined: N/A | Message [#284] posted on: 12-13-2005 04:01 PM CST (US). | | Can't wait to see how you implement that! I was thinking about just slapping on a bridge rectifier and a large cap before the filiment, but that makes it even more ineffecient than it already is, and probably drops the voltage to the filiment too much - requiring re-selection of the dropping resistors. |
runeight Headphone Council Joined: Mar. 8, 2002 | Message [#285] posted on: 12-13-2005 04:29 PM CST (US). | | OK. Here are schematics with the new heater arrangement. One for the diode ccs and one for the jfet ccs. If you look carefully at the schematic you'll see that the heater supply is a full wave rectified supply so it only makes half the full secondary voltage. The full wave diodes are in parallel with the lower half of the primary bridge rectifier. We set them in parallel with the lower half so that when the heaters pull down on the input to the regulators, this will only affect the negative regulator and, hence, won't affect the B+ for the tube. PAY ATTENTION TO THE ORIENTATION OF THE NEW DIODES AND THE CAPACITORS IN THE HEATER SUPPLY. It is a negative supply. [Edited by runeight on 12-13-2005 at 04:47 PM.] |
| Blooze HeadWizer Joined: Jun. 28, 2005 | Message [#286] posted on: 12-13-2005 04:37 PM CST (US). | | Thanks guys! I'll go through and revise my parts list. |
| Blooze HeadWizer Joined: Jun. 28, 2005 | Message [#287] posted on: 12-13-2005 08:15 PM CST (US). | | Ok, check my changes/additions please. 2ea 100V/1A rectifiers instead of 100V/100ma |
| runeight Headphone Council Joined: Mar. 8, 2002 | Message [#288] posted on: 12-13-2005 08:25 PM CST (US). | | If these are deltas from the original parts list, it looks correct to me. BTW, which CCS version are you using? |
| Blooze HeadWizer Joined: Jun. 28, 2005 | Message [#289] posted on: 12-13-2005 08:35 PM CST (US). | | Yes, the only changes I saw were the bridge rectifiers and the plate resistors, everything else was to replace the filament supply. I haven't decided which CCS I want to use yet and may order both JFETs (cheap) and the J505 (which isn't nearly as expensive as the 1N5297, but looks to be much easier to build and mess up). My only concern using the J505 is its 50V rating. |
| Batman HeadWizer Joined: May 12, 2003 | Message [#290] posted on: 12-13-2005 08:38 PM CST (US). | | Hang on, I'm updating the parts list as we speak. You might also consider the original LND150 CCS, they're cheap and can take the voltage. I'm leaving those parts in the parts list too. |
| Blooze HeadWizer Joined: Jun. 28, 2005 | Message [#291] posted on: 12-13-2005 08:52 PM CST (US). | |
Would there be any advantage you think to using more expensive caps in the signal path? It would be interesting when comparing the Millett to the SOHA if I used the generic parts in the SOHA. My Millett uses regular Nichicon caps except for Cerafines in the output position and Kiwames for all the resistors. I'm just gonna beat myself if a ~$50 amp kicks my ~$200 one! (a lot of that cost is in casing by the way). |
| runeight Headphone Council Joined: Mar. 8, 2002 | Message [#292] posted on: 12-13-2005 09:23 PM CST (US). | | Blooze, don't forget a heatsink for the lm337. I don't think you'll see any benefit to special caps. Just use good metal film caps. [Edited by runeight on 12-13-2005 at 09:24 PM.] |
| Batman HeadWizer Joined: May 12, 2003 | Message [#293] posted on: 12-13-2005 09:43 PM CST (US). | | Here's the updated parts list that includes all three options for the CCS and the new regulated filament supply 1/6/06 We found out that the ST TSH22IN OPAMP produces a DC offset at its outputs and is NOT suitable for this amp. I've removed it from the parts list. 11/11/2006 I've added a PCB tube socket to the parts list for those who may be using the PCB. 
[Edited by Batman on 01-11-2006 at 03:02 PM.] Attachment: C1329.gif,C1330.xls |
| runeight Headphone Council Joined: Mar. 8, 2002 | Message [#294] posted on: 12-14-2005 12:26 AM CST (US). | | I'd like to emphasize Batman's comment a few posts back. The LND150 CCS is actually the best CCS for this amplifier because it is indestructible at these low voltages, it is an excellent CCS, and it has a very good PSRR (almost as good as cascoded jfets). Here is a diagram with all the new stuff and an LND150 mosfet CCS. Blooze, if you haven't already ordered parts, this is a good option to consider. |
| Blooze HeadWizer Joined: Jun. 28, 2005 | Message [#295] posted on: 12-14-2005 01:10 PM CST (US). | | Ordered all the parts from Mouser this morning. Got the JFETs and the LND150 for the CCS. I'm going to try the 2134 opamp replacement they had as well as I've used the 2132 replacements in CMOY's with no issues. So I basically got everything but the tube socket from Mouser. |
| Batman HeadWizer Joined: May 12, 2003 | Message [#296] posted on: 12-14-2005 02:14 PM CST (US). | | Are you referring to the TSH22IN opamp from STM? Let us know how it performs and we can add it to the parts list, it costs less than half of what the OPA2134 does. |
| Blooze HeadWizer Joined: Jun. 28, 2005 | Message [#297] posted on: 12-14-2005 02:37 PM CST (US). | |
Yep, that's the one. I hate ordering just one thing from Digi-key and having to pay all the fees. I wish Mouser would carry the OPA chips. |
| guitarsenal HeadWizer Joined: N/A | Message [#298] posted on: 12-14-2005 02:44 PM CST (US). | | I picked up a couple LM337s and heatsinks at lunch time. I'm retrofitting the DC heater supply after work tonight. |
| Batman HeadWizer Joined: May 12, 2003 | Message [#299] posted on: 12-14-2005 02:49 PM CST (US). | | Guitarsenal, shall we wait up for your report tonight?  |
| mains_hum HeadWize Fanatic Joined: Aug. 19, 2003 | Message [#300] posted on: 12-14-2005 02:51 PM CST (US). | | I think this might be a RoHS compliancy issue. ?? I see many "common" parts being sold really cheap because the supplier wants to get rid of them before restocking with the RoHS version. RoHS parts cost the same as non RoHS parts except during the changeover period. Even so, the TSH22IN spec. does look good ... and so cheap too !! |
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