miniHRM evolution

[10thTx]

Excuse my mediocre playing. This was recorded with my mini-Tweed Overdrive Special. It's about 3.5 watts.

http://www.soundclick.com/player/single ... i&newref=1

I used a 12AV7 in V1. A 5751 has better blooming and sustain.

Volume was 5.5, OD1 was 5.5, OD2 was 6.

With respect, 10thtx

[rogb]

Nice work there Jeff, good tones and playing too

What impresses me a lot is the use of a whole bunch of different tubes from the usual 12AX7 and EL84s. You are showing us there can be a real variety in tube choice. Also adapting the topology to suit what you want to achieve. Respect!

Well done buddy

[10thTx]

Thanks for the nice comments!

I drew up a 6V6 version also that uses a mosfet CF following the 5879 pentode. I have not built this version (yet).

The editable schematic and layout are here:
http://www.el34world.com/Forum/index.php?topic=11607.0

With respect, 10thtx

[layupe]

Very interesting your work and the results you've got 10thTx! I like the mosfet CF thing, its something i wanna try soon as well as working on something with the 6bm8 myself...

[layupe]

Unfortunately i am kinda frustrated right now not being able to trace where the problem came from in my build Yesterday i separated the ecc83 and the ef86 sections sending them directly to the PI alternatively, i was nicely surprised since i was not able to hear the "weird noise" through none of them by their own so i connected them again in the usual way and the noise did came back...What is worse is that then i separated those again to go back on my steps and this time the ***** noise was there on the ecc83 alone and also on the ef86 alone!!!!!! Seems pretty strange to me and makes me reach high levels of frustration but ill keep on, what else?

I noticed something "extrange" while i was there, the volume pot, when its at its zero (closed) position doesnt cut the sound completely,there is little sound still that only get silenced completely by the clean master pot...I guess this is not its normal behavior, am i wrong? Should the volume pot silence completely all the signal?

[layupe]

Well, im back This time i bring an mp3 i recorded today with my videocamera so you can hear what i was talking about when refering to "a weird noise" and yeah, the quality is low but more than enought to what is needed in this case...

http://www.soundclick.com/player/single ... D=10793617

Hopefully someone will recognize this "symptom" and/or is able to give me some ideas on where to look cause right now i dont know why this is happening...

Also some pics, as i said earlier was not meant to be beautiful, just functional funny isnt it? Well, not really much to see from the pics anyway...

[img768]http://img94.imageshack.us/img94/7817/dsc00134ef.jpg[/img]

[img768]http://img88.imageshack.us/img88/1822/dsc00128dm.jpg[/img]

[img768]http://img30.imageshack.us/img30/317/dsc00124hl.jpg[/img]

[img768]http://img11.imageshack.us/img11/5726/dsc00123zr.jpg[/img]

[img768]http://img88.imageshack.us/img88/1822/dsc00128dm.jpg[/img]

[img768]http://img96.imageshack.us/img96/9831/dsc00122qt.jpg[/img]

[Structo]

I find it difficult to trace point to point wiring from pictures.

Also finding lead dress problems in point to point is hard as well since you have less wire.

But to me it sounds like when you have wires too close together and they bleed into one another.
Sort of an intermodulation distortion.

May I ask why you chose to go with point to point wiring instead of a board?

If you have a lot of experience in PTP construction then I bow to your expertise but having seen other PTP builds where the builder was not experienced, lead to a lot of problems that were very difficult to trace.

[layupe]

Hi Tom, yes, its gonna be difficult to trace anything from this pictures also there is a lot of components in the front side where the pots are located that is no really visible here but makes sense what you say about wires too close and that sort of intermodulation distortion! Thanks for your suggestion, im really frustrated right now after check and check and check again against the schematic and not finding anything wrong, so any help is very welcome! Im wondering about "cutting" the B+ of the ecc83 to have it really out of the circuit and test the amp from the ef86, i think that doing this way, if the problem its something related to those too close wires and its happening in the preamp section it should? go away...Then i would know more or less where is the problem and work on it, if im not lucky and the problem persist maybe i could do the other way, "eliminate" the ef86 section by cutting the B+ there and if it works ok (through a "bridge" from ecc83 to PI of course) maybe those wires are located between the ef86 section and the PI? I dont know if it makes any sense, just wondering about cause i have not any better "method" to hunt the problem...FWIW before i started to build the preamp i tested the power amp section and it was everything ok there.

As per your question, good question i must say! the reason of why i gone PTP instead of doing a board is because i thought this way would be more easy to me to mod the amp...This was the idea behind my choice, at least before i started! I had a marshall type preamp in there before that i ended modding almost completely and it was ok, thats why i thought it would be ok to do it this way. Also i like specially PTP over other techniques, i find it beautiful and "exciting" to work in, but no, i have not much experience in this kind of construction other than few projects of a very much simple nature.

[Structo]

I don't see them but did you happen to install the FX loop jacks?

That is a good way to test the preamp and power amp separately.

You can plug the preamp into another amp to test and plug a different preamp into the loop to test the power amp.

[layupe]

Yes i did, on the first pic, left side, you can see or almost see 2 black jacks for the FX loop and yes i did as you say, can you believe there was the same problem when sending the signal from the preamp to another amp and also when inserting another preamp into the power amp? That's why i was thinking on cutting the voltage on some parts of the circuit to really take them apart because i think that if the problem is some sort of intermodulation due to some wires being too close, the problem will persist as long as they carry the signal, i mean, lets imagine there are 2 problematic wires there, one from ef86 and another from PI are too close, then, even i send the preamp section through the loop to another amp those wires will still be too close and the PI will be still working so the problem could/should persist also in that scenario...Not sure that i explain myself very well

On friday i will have some free time again and will test this thing of cutting the voltage of the ef86 section for example and (in my opinion) efectively leaving it apart from the circuit, if it works then i can say the ecc83 and power amp sections are ok, then connect maybe only the first triode and see what happens, if still ok then i guess i should look for something between the second triode and the ef86 but well this is just an idea, i bet its not gonna be so "easy" in the end, we will see then...

By the way, i did not mention but voltages on the preamp are very close to those that Mat noted from his own amp and voltages from the power amp are also in the range of what they should be as per ax84 November schematic (remember thats where my power amp come from)


Thanks![/b]

[Structo]

It will probably end up being a simple wiring error.
That happens to everybody occasionally.

You will have an, A Ha! moment and fix it.

[layupe]

I hope so! damn i just want to enjoy my amp!

Thanks for your support Tom, very much appreciated!

[memphis032]

Dragging this one back from the grave, a couple of questions:

First, I'm used to seeing EF86s as the first tube in the amp - I would have thought it would improve the clean channel putting it there - is it not tough enough to drive the tonestack?

Second, I am planning a SE dumblesque build at the mo, and am reluctant to build something without a driver stage before the output tube (probably a KT66). I've been tinkering with the idea of a half dumbleator, ie CF before the loop, but no recovery stage, except for the driver stage. Then I wondered about tubes with a single stage in, and wondered about the following options:

1. EF86 instead of V1a, then normal lineup, leaving half a 12AX7 for the driver
2. EF86 instead of V2a (like Mat's), but keeping the second OD stage, and using the second half of that as the driver
3. Something else that I haven't thought of yet.

Any thoughts?

[memphis032]

I've remembered option 3 now - use the EF86 as the driver stage - would it distort in a similar way to a power tube?